I’m putting a new roof over my garage, and I have a fastener question.
Code for attaching roof deck sheathing to rafters is to use 8d common nails. I have a personal fetish for screws, and would like to substitute screws for common nails in as much of the work as I can (the shingles will still be nailed). Unfortunatly, I haven’t found a source that would help me determine what size and length screw would be appropriate for a given task.
The closest I’ve come was a USP Structural Connector website that said the correct screw to replace an 8d common nail was a #8 1.5″ wood screw. This seems right to me, but are there any other sources or opinions out there?
I will also be replacing some studs here and there, any ideas for screw size and length there?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Replies
the rule of thumb is that the fastener should be three times the length of the material being help so if you are using about 1/2 plywood then that sounds about right. (don't use or even suggest using sheetrock screws around here. There are several people who have a real issue with them and would likely suggest any use of them for any reason other than holding sheetrock in place is likely to lead to a fate worse than death!)
I would agree about those drywall screws! Right now I'm pretty impressed with the square drive screws from McFeelys. On second look at the web page I mentioned, I realized they were talking about use with a structural connector. Mabey I'll go with 2" just to be safe. I'm still trying to reach my local inspectors to make sure they will approve it too.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Well my home is mostly screwed together. I have a timberframe and I'm building it to European specs . They require metal fasteners hidden under false pegs. I did the structural calculations and where a normal roof will come off in a tornado by my calculations my roof will remain on in a level 5 tornado. I've got some datta here someplace that says a 3/8ths inch lag bolt has somewhere close to 10 times the pull out resistance of toe nailed nails. Since I'm using 1/2 inch stainless steel 18/8 hardened lag bolts the numbers go through the roof.
Let me caution you, a decent sized roof that is screwed down rather than nailed down will take 20 times longer to do than with a nail gun.. If like me you use predrilled holes with the head counterbored (and thus three differant size drill bits) plan on each rafter taking a couple of days!
"Let me caution you, a decent sized roof that is screwed down rather than nailed down will take 20 times longer to do than with a nail gun.. If like me you use predrilled holes with the head counterbored (and thus three differant size drill bits) plan on each rafter taking a couple of days!"Frenchy,Counterbored screw holes on roof sheathing: sounds like the removal of wood tissue during counterboring would weaken the structure by reducing the thickness of the sheathing where the screws penetrate, offsetting the added strength provided by the screws.
-Jazzdogg-
Whether you think you can, or you think you can't, you're right.
Jazzdog,
I'm sorry I should have given you more data. I'm building a timberframe home. Some of my timbers are as large as 12"x12" or even 18"x8" white oak, I seriously doubt it would be possible to weaken such timbers with counter boring..
Although techinically you have a point The counterboring does weaken the timbers a bit... (I'd love to see someone pulling the head of a 1/2 lag screw (especially since I use large 1 1/2" washers under each head through one of those timbers, anyone who could so so would most definately earn my admiration)
If you think your roof system would survive an F5 tornado, I think you should look at pictures of areas that an F5 has hit. It pretty much scours the earth---nothing is left standing in its path--your roof might hold together for a while as it is being hurled into the next county. And who would countersink their roof sheathing?? Way too much time on their hands--time that could be spent making an actual difference on their house. And why would anyone use three different drill bits to countersink?? Why not buy a countersink with a pilot bit---a tapered one at that?? I love working on my house and doing things right, but as mentioned in previous posts, using glue and ring shank nails would have to be the way to go. I doubt that in a real world situation, that there would be any difference in performance---in a monster tornado or hurricane--the house is going to come apart.
Personally, I'd relish the challenge of building an F5 proof house... yes, it can be done.
L
GardenStructure.com~Build for the Art of it!
how deep ya intend on going...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Chyannne Mountain complex might be a good starting point...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Maybe a concrete dome home could be F5 proof.And no screws vs. nails debate (no wait... tapcon's vs. paf's).
Edited 3/5/2005 3:05 pm ET by basswood
I thought we were talking a level 5 hurricane... F5 tornado.... build it into a hill... Windows to south only...metal shutters activated by a wind meter... closes the vault at 150 mph. Best to also have that same shutoff on the air exchange as well.
That... or a steel drum like the one the last guy went over the falls in... I think it was filled with expanding foam. Would be a hell of a ride though... wouldn't it?
What is a Paf?
L
GardenStructure.com~Build for the Art of it!
Edited 3/5/2005 9:59 pm ET by Lawrence
What do people think of using "structural" screws over nails? I'm thinking of the Timberlok screws or the Simpson 1/4" wood screws, which are shear rated for about 200 lbs. That's better than a 16d nail (bigger hole though).I'm putting 11ga steel plates on some joists to cover 3" notches left by carpenter (sisters notched for electric cables, cables since removed). Although 16d nails would make smaller holes, it seems to me that they're useless if they bend, so I'm better off with those big screws....
GRK makes some very good structural screws and lag screws with T30 (torx) drive. I've had mending plates made at a metal shop (they drilled the larger holes I needed in a staggered pattern to avoid too many screws in a line splitting the wood). These were for repairing notched or cracked beams, not joists. You may just want to sister the notched joist with another (unless too much plumbing or wiring is in the way).Bass
Things are too tight for another sister, I've added blocking between the joists and I have to leave room for a DWV pipe (the blocking is to spread loads because joists will have to be notched beyond specs). The original joists are notched from above by plumbers, the sisters from below by the carpenter.... All of this is to avoid tile failure like I've had in the past....I got a small plate from a metal shop, predrilled, for $60. I got 4 more plates from a steel fabricating plant for $10 total, I drill the holes myself.
PAF = Powder Actuated Fastener (a la Hilti, Ramset, Remington) vs. TapconNails vs Screws debate all over again except for fastening to concrete.
No clean arguments there... thanks for the bringing me up to speed.
L
GardenStructure.com~Build for the Art of it!
You're right, this is taking way too long but the jerk that owns the place insists that it is done that way... <G>
As for being hurled to the next county I'll bet you' ve never looked at my foundation.. Trust me, as over kill as my roof is the foundation is even more over kill.. footings twice as large as required, three times as much steel and all properly tied together. the rebar is even tied around the J bolts which are twice as many and twice as large as code calls for..
Yes I did have custom bits made up to drill the counterbore, shank and pilot hole but found that sharpening them took too much time and trying to force a dull 1 1/2 bit into dried white oak took too long.
On occasion the holes I drilled were so deep and the Oak so tough that the 1/2 shank would snap off! I shattered at least 12 custom made bits before I settled on my three bit Monty.. Actually I still use my last custom drill bit but as final clean up I drill the 1 1/2 counterbore with a forstner bit, I then drill the 1/2 inch shank hole and finally the pilot hole is drill with a ship auger. I stop everything about at 11 inches and use the final custom bit to got the last inch. That ensures that everything is aligned correctly.
No I don't wear out the chuck changing bits I actually have 4 drills,... well, I probably have a dozen but use 4 as my set-up.. If you've seen my roof trusses in the pictures I posted in the past even you'll be forced to agree that a mere F5 tornado isn't going to do more than cosmetic damage..
My walls are 20 plus inches thick with black walnut timbers on the outside lag bolted thru the SIP's to the 6 inch white oak timbers on the inside..
structurally this house is stronger than the world trade center by a factor of 20
As far as the "surviving an F5" thing, have you actually done the structural calcs for the 1100 lb/ft^2 windload that F5 winds can produce?
With the pitch of your roof, it's not hard to imagine a cross section of 1200 - 1500 ft^2. That would yield a force of 1.3 million to 1.6 million pounds, not including the negative pressure on the back side of the house.
I'm not doubting you. Just asking if you really designed to those loads.
I know this is all in good fun here, but it's prudent not to joke too much about things like F5 Tornados.
Consider that "little" F2's produce damage such as "Roofs torn off frame houses; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
F3's: "Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown."
F4's: "Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated."
F5's: "Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur."
No question that your house is of impressive design, but a telephone pole travelling at 200 mph or an "automobile-sized missile" is going to do a lot more than cosmetic damage.
Even a fortress like Casa de Frenchy could easily be reduced to debris by a "mere F5."
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
The daunting task of designing a structure that will withstand a F5 tornado isn't my original intention.. rather I started to design what I considered a sturdy structure, only after I designed it by intuition did I do the calculations and yes it should withstand a F5 tornado (although the highest recorded tornado to ever hit Minnesota) was a F2
Wind speed isn't as difficult as it seems, the Mosquito fighter of World War 2 was a mostly wood structure that was among the fastest planes of World War 2. Those wooden wings were able to handle 400 mph with flimsy little pieces of wood that was mainly glued together!
Now regarding a 200 mph telephone pole, I have no doubt that it would result in penetration of the structure. But the building would put up a good fight, That telephone pole would have to go thru a 4 to 6 inch thick stone wall, then a 6 inch foam SIP and possibly a 6 inch white oak timber.. Before you dismiss the effect of that 6 inch foam remember the soft walls they now use at Indyannapolis and daytona have only a little more foam than that between them and the car that hits it at 200 mph..
I suspect that the stone would slow down penetration sufficiently that the foam could absorb all of the rest of the impact.
Edited 3/6/2005 12:32 pm ET by frenchy
My theory on the F5-proof residence is to buy a surplus WWII submarine and bury it with only the conning tower above ground. ;-)
-- J.S.
take over space at Cheyanne Mountain or somewhere's similar..
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Edited 3/7/2005 2:17 pm ET by IMERC
Aren't they still using Cheyenne Mountain?
-- J.S.
some of it they're not...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
While googling this morning I found out the following:- Shear strength of 10d nail: 92 lbs
- Shear strength of 16d nail: 138 lbs- Shear strength of #8 McFeelys wood screw: 200 lbsNow that I've finished pounding about 400 10d nails into joist hangers, maybe someone could explain why I should not have used #8 wood screws? Perhaps the inspectors out there could explain why they would not okay it?Another data point on nails: Dropped a 10d nail into a stud bay with a hole in the fire blocking (so air coming up from basement laundry room). Retrieved it a couple of days later and it was completely covered in corrosion. Switched to HDG nails. After having about 1 in 10 nails bend during nailing, going back to ordinary nails (heard that HDG may weaken the nail).
Cost? Time? Availability? I'd think all of those factors would favor nails.
That doesn't mean that you can't use screws. Simpson makes a screw that is designed for use with joist hangers.
http://www.strongtie.com/products/connectors/screws.html
I suspect the inspector would have no problem with any screw for which you could demonstrate a shear strength equal to/greater than a 16d nail. Of course, each jurisdiction is different.
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
"I suspect the inspector would have no problem with any screw for which you could demonstrate a shear strength equal to/greater than a 16d nail."
I think you indirectly hit the nail on the head there. (pun intended)
It doesn't matter why you or I or anyone here thinks about nails vs. screws. What matters is CODE ACCEPTANCE.
Take a look at the nails and/or screws on the Simpson website. They have to test those things and come up with allowable design loads for each one. You can get code reports on ANYTHING they manufacture.
Then they have to submit those reports to code authorities to get them accepted. It's a lengthy and expensive process.
Telling your building inspector "I think these are good enough" isn't going to carry any weight. You have to have something to back you up.
Another reason is liability. Let's say a HO sues you over a disagreement - Doesn't really matter what. If their lawyer can find something you've done (Like using screws for framing) that isn't code accepted, they're gonna have a field day with you. And believe me, they're gonna find anything they can to use against you.
So as far as I'm concerned all this discussion is interesting, but meaningless.
The less hair I have, the more head I get
I think you indirectly hit the nail on the head there.
That's better than a direct hit to my thumb.... I'll take it!
No question that you're right about the inspector's opinion vs ours. Some quick Google work brought up several suggestions that screws can be code compliant if their shear strength can be shown to be comparable or better than the required nails. That's all I was trying to pass along.
I thought Taylor was suggesting that screws would never be accepted. I believe that if you do have some type of documentation that shows a certain screw has sufficient shear strength, there's reason to hope that any given inspector will approve them. No guarantee, but reason to hope.
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
Actually I was told by Simpson *not* to use their SDS8x1.25 in lieu of nails. I seem to recall last time I looked there was no shear rating, now it's a puny 50 lbs. I think these are strictly a DIY thing (ie non-critical parts of decks, shelving, etc).I suspect the real reason is economics: installing screws just takes longer. Building code sounds like an excuse, as in, if the construction industry would accept screws for framing, codes would be updated with minimum shear strengths etc. And we'd be able to get McFeelys at the orange box :-).I also wonder how great these nails are. All I can get either at the Orange Box or local bldg supply stores are Grip-Rite, now I know what happened to all that scrap shipped to China...
"Building code sounds like an excuse..."
I think you're WAY off base. You don't get to pick and chose which building codes you follow. The code acceptance has to come first.
How much more do you think the general public would pay for a house framed with screws? My guess would be a big fat ZERO. The construction industry is largely price driven. Spending a bunch of extra money to use screws would just cost you money.
One more thing to keep in mind - The shear strength of nails or screws isn't important. It's the shear value of the CONNECTION. Out a screw into soft wood, and the shear value doesn't do any good. The strength of the wood surrounding the fastener is what's important.
I considered atheism but there weren't enough holidays
I agree with you absolutely, the proliferation of POS McMansions tells us everything we need to know about what the market wants. That was actually my point. So nobody in their right mind frames with screws, so there's no demand for code changes to allow it....Fair enough on strength of connection, so it's not only the strength of the fastener, it's also how many fibers it is in contact with. That doesn't invalidate the usefulness of screws of strength at least equal to nails (as long as there are as many screws as nails of equal diameter).
On a different connector website, they had comparison tables showing the loads a subtituted fastener could carry vs. what it was designed to use - the highest number being 1.00, and a lesser fastener would be some smaller number, like .71. Substituting their #8 screw for a 10 nail gave some smaller number, but they didn't have a number for a #10 screw.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Hmm, this is interesting...
Here is an Email exxhange wit McFeelys:
Me:
I would like to use your fasteners for my reroofing project. Do you have any information on shear and pullout for the #8 and #10 (and any others if you have them) wood screws. I will be attaching 1/2" OSB to 2x6 rafters, and using Strongtie metal connectors.
Them:
Our data shows the average single shear of a # 8 deep thread wood screw to be 1200 lbs and # 10 deep thread wood screw to be 1500 lbs.Pull out values will depend on the density of the wood, diameter of screw, and penetration depth but a screw will out perform a nail in pull out strength every day of the week. Nails bend under stress, then pull out as the members separate. This is a slow process. Hardened steel screws have a greater single shear but break suddenly when stressed to their limits.As always, check with your local building code inspectors.Pull out values may be determined by the following formulap=15,700(GxG)DLwhereP= Max withdrawal load in poundsG= Specific Gravity of the woodD= Screw Shank Diameter, in inchesL= depth of penetration, in inches of the threaded portion of the screw into the member receiving the point
And to my message to SENCO
Me: I've gotten approval from my inspector to use #8 screws to attach my roof sheathing to the rafters over my garage. I plan on using the #8 2 inch Weatherex II collated screws. I'd like to have some technical information to back up my choice in case it gets questioned later. Can you provide any shear and pullout information on your fasteners?
Them:
Files attached
and the files the attached were the Nail and Staple codes, with the Code addendum ES-6068, which you can see here:
http://www.icc-es.org/reports/pdf_files/ICBO-ES/6068.pdf
The relevent text:
The Senco wood screws described in this report are alternates to the 8d common nails used in the horizontal diaphragm and vertical shear wall assemblies specified in Tables 23-II-H, 23-II-I-1 and 23-II-I-2 of the 1997 Uniform Building Code™ (UBC).
So it looks like #8 screws are good to go - and Code Approved!
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Edited 3/18/2005 10:45 pm ET by xxPaulCPxx
What is meant by "average single shear"? I've seen Fastenmaster cite similar numbers for "average ultimate shear strength" of some of their screws. I somehow doubt a #8 screw can on its own carry a load of a ton, so it would be useful to know what we're talking about here (and how to compare to nails' shear strength).
Edited 3/22/2005 1:51 pm ET by Taylor
Think of one plate laying on top of another, with a rivot tieing them together. As the plates try to slid, they put the rivot into single shear.
Now think of a stack of three plates, with the top and bottom plate trying to go one way and the center plate trying to go the other. That puts the rivot into double shear. Double shear joints are stronger and more stable.
That's probably not a very clear explanation. Maybe these pictures can express it better. "Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
John Sprung,
I'm pretty sure that most WW2 subs are melted into Toyota's by now anyway I doubt Uncle Sam would sell me one since I voted for the wrong party the last election! ;-)
I had to laugh a little. All this talk about screwing and no blondes mentioned! Also, I was curious as to the square drive screws you were referring to. I think you mean 'Robertson' screws. Phillips and Robertson feuded way back when and the Phillips head became popular in the US. Robertson only became popular here in the great white north.
As to screwing your roof decking, if you have the time go for it. We screw and glue all our floor sheathing. Metal roofs are screwed not nailed. I like to screw not nail...oh wait that's a different topic !
Budman
Walk up and ask Joel or Bob in the Building Department!
Im not in a high wind area sooooooooooo
talk about gross overkill. screw down your roof sheeting, wow
if its gonna blow that hard, yikes
we nail or staple, in worst case senerio I guess you could shoot it down with ringshanks or hand pound galvy nails, man real galvinised holds stuff a whole lot better then vinyls better then tons of stuff ( real meaning real galvys, hot dipped, not nail gun galvys or electro which, IMHO, are a joke but better then vinyls for rust resistance, by about 15 minutes, passing city inspection or _______)
one of the first guys I worked for had us caulk the roof plywood seams
wow.......... that was either overkill or he worked with a sheep for brains roofer
I love screws, esp torks. screws will stick stuff and pull stuff..........great !!
Ive screwed lots of studs in place in remodels
( actually Ive heard a "dancer" saying she screwed lots of studs in place too)
and yes drywall screws are good for drywall and hanging pictures, popping tires, light weight cabinets etc, bit nothing structural
if you have a good stand up screw gun, tons of time and a true fetish , then go for it
if it helps you sleep at night....( I over build, when asked why, I say ...sleep at night)
believe me, there are worse fetishes out there
I have no doubt it would work, but I'd imagine you'd have to provide the technical data for tension, compression, shear strength etc. to your building official. That's assuming he could make sense out of it to compare it to nailing. Happy screwing!
You know, cement coated nails are pretty darn hard to pull out. But, if screws float your boat, definitely make sure they have equivalent strength to the holding power of nails.
Paul... no, just stop it.
If it has a tapered head the sheathing will peel off in the wind. Screws are more brittle than nails... so if you are in an area prone to earth quakes you could have a bigger problem on your hands.
There's a place for screws... and a place for nails. I am always looking to improve things, but I've seen folks try to frame with screws before with dismal results.
Get a good coil nailer and have at it.
L
GardenStructure.com~Build for the Art of it!
Lawrence,
Please read the Best of Fine HomeBuilding, Framing roofs, starting on page 126 and pay particular attention to the chart on page 129. You couldn't be more wrong!
Sorry guy, that last statement came off wrong, let me apologize,...
While the information backs up my point I shouldn't be a jerk about it.
Frenchy... I don't follow Fine Homebuilding's advice on installing crown either... It's not gospel...just a magazine... a pretty good magazine at that, but their editors and authors have been known to be way off base. Typically they know what we tell them.
With Utmost respect... aside of course the moderator that muzzled Gabe and I in the political forums. Neither respectful nor funny. Both opinions should be heard-unless you want to declare this a partisan forum once and for all.
L
GardenStructure.com~Build for the Art of it!
Lawrence,
You would have a point if the opinions were simply those of the auther, but if you'd read the article I mentioned you'd know they used actual testing to determine their numbers..
Thus those weren't opinions but facts. when I used the numbers I did I didn't make them up but reported the results of labratory tests.
finally do a test yourself. Install a wood screw properly in a board and nail another board with a similar sized nail.
Now pull the boards apart and tell me how much effort each required..
No way frenchy, not buying it. I've seen hundreds of deck screws break going into wet pine. Unless I was planning on gluing it down, nada chance. There are thousands of screw manufacturers and your are playing russian roulette using screws and guaranteeing their strength and durability with one scientific test.
Furthermore much scientific testing, certainly when it comes to composite decking and that ilk, is worded to make the results more favorable than it may seem otherwise. You simply cannot duplicate the stresses involved in an actual earthquake or hurricane.
Given the rules they went by (all of them), specifications, testing methods, I guarantee I could blow a half a dozen holes in their rationalizations.
As with others here, screws in sheathing simply doesn't meet the common sense judgement for this skeptic. Besides, of all the things on a house to fail... the roof is the worst. When big trusses lay down it can mean a world of hurt for a family inside.
L
GardenStructure.com~Build for the Art of it!
"Typical construction practices for homes and schools in the United States reflect little or no emphasis on structural engineering, especially when it comes to factoring in wind resistance." From:
http://www.clemson.edu/special/hugo/wind.htm"While nails tend to be the fastener of choice in today's fast-paced construction industry, Clemson researchers found that screws do a better job of preventing roof systems from being lifted or damaged. With today's power-driven tools, using screws has never been easier. If re-roofing, have 2 1/2-inch #8 screws driven between the existing nails."From:
http://www.clemson.edu/special/hugo/wind3.htm
Ok, 4, you speak sense and that idea you quote creates the best hurricane damage prevention I have heard of. Shear strength of the nails, holding power of screws. Now, if the screws had a larger flat head (like a washer) and they mandated plywood... we would have something truly superior.
Nice Work!
Brilliant.
L
GardenStructure.com~Build for the Art of it!
Paul:
Keep in mind that one of the basic differences between nails & screws is that nails have shear strength and have very little resistance to linear forces (being withdrawn from the material that they are driven into), where-as screws have a great deal of resistance to being withdrawn but have very little shear strength. Screws are intended to pull two materials together and keep them there (as in a tile backer application) but not intended to keep the two surfaces from sliding past each other (as in a roof application). Obviously if you step the screw size up sufficiently you can compensate for that (remember, screws are not an acceptable substitute for the use of hurricane clips etc.) but I would have to ask why. If you follow the correct nailing schedule for your geographical area and application, nails will do the job perfectly well and at a much lower cost in materials and much less labor. I would also check the code in your area because using screws may not be acceptable to the inspector.
BILL
Wow! do I ever disagree with that statement,
my authority? a little company called Tauton press. they seem to know what they are talking about..
I refer to the chart on page 129 of the Best of Fine Homebuilding.Framing roofs A 3/8ths lag screw had an average load capacity of 2783 while a Simpson H4 had a capacity of only 547. pounds. and your typical toenailed rafter come off with just 208 pounds!
common sense should enter in here.
Take the oft sworn at sheetrock screw for example. We all know how others feel about it, but screw a piece of plywood onto a rafter with a number 6 sheetrock screw. Use one only an inch and a half long. Now take a 8p nail and nail it in. OK take your typical claw hammer and pull them apart. Which came out easier?
shear? fair enough, put a new sheetrock screw in place and a new nail in place and then beat the plywood on the side until the plywood either comes off or the nail/screw snaps.
Now I do not advocate the use of sheetrock screws in place of nails however a proper wood screw is a complete other matter.. Do that same experiment with a proper wood screw and you'll see what I mean!
Edited 3/1/2005 4:57 pm ET by frenchy
Frenchy:
You hit the nail on the head (no pun intended!). "The proper woodscrew"
Yes you can use screws in place of nails for CERTAIN uses but you must make sure that it is sized & installed correctly. I think that we'll just have to agree to disagree on the rest. As to the final result, the building inspector in my neighborhood would not accept substituting screws for nails (or the other way around), no matter what you or I may think, if it's not specifically called out that way in the code book.
BILL
Edited 3/1/2005 5:39 pm ET by wrohden
Regarding the approval of screws vs nails and your local inspectors approval. I regret to say that such things do occur. Evan though There is plenty of precident in the code to allow such. You simply must learn to read it and understand it completelty enough to answer a inspectors concerns. That is to say, not to argue with the inspector but to show where such usage is permitted and why.
Since it's well over 5 years since I learned the UBC and the UBC is no longer consider the final answer regarding construction I'd be at a disadvantage to site chapter and verse right now but trust me the language is there!
I agree.Also the idea that nails bend and screws snap and that nails have more shear strength are canards.Presently there are no testing programs for nails. Most come from China or Pakistan and are simple mild steel of undifferentiated quality. So while you, we, can usually enjoy the expected performance levels this is not guaranteed. I have seen 16d nails that could be bent by hand. These were so soft they tended to bend even when used by experienced carpenters. They took them back and got another, much better, box.The brittleness of screws is a matter of metallurgy, treatment and design. Drywall screws are cold formed and, as I understand it, not tempered. Which is fine for hanging drywall, their intended use.There are other screws easily available that closely match the ductility expected of common nails. Use of the right screws can easily match the bending strength of nails. A matter of using the right materials. These screws are less available because, generally and up to this time, few people used such screws for such jobs. If there is a major move to screwing down roof decks it can be expected that a supply of suitable screws will be made available.Similarly the shear strength of a fastener is a function of the metallurgy and the diameter of the screw body in shear. Given the right alloy, tempering and body diameter a screw should have a similar, or greater, shear strength.
Two words.Deck screws.
The person you offend today, may have been your best friend tomorrow It is easy to be friends with someone you always agree with.
Deck screws might work. My only doubt on a good quality deck screw would be the head. Most are bugle head. Designed to countersink quickly and efficiently. Essentially designed to go, to a limited degree, through wood. Not a major issue if the deck boards are an inch or more thick.The plywood on a deck is usually 1/2" or 5/8" so there isn't much wood to go through before the screw goes all the way through. Likely the remaining wood under the head, once the screw is countersunk, has been weakened by being crushed. A truss or washer head would better serve to spread the uplift load on a greater area. Lessening the risk of the plywood lifting up over the screw head.Deck screws, with bugle heads are relatively cheap. I have looked for truss head screws in bulk locally but they were not available. Those I found, in small packages, were not cheap. Many times what the price of a similar deck screw.
Agreed.
The person you offend today, may have been your best friend tomorrow It is easy to be friends with someone you always agree with.
Wow, this has really turned up some great discussion! For the record, I was planning on getting and adjustable depth autofeeding driver like the Quikdrive Pro 250. That way I can set it to stop driving when the head is flush with the OSB.
I have the Taunton Press "Framing Roofs", but it does not have anything about screws, nails, and lag bolts listed anywhere in that. As far as using lag bolts on the rafters, how and where are they positioned/driven? Having the bare rafters exposed gives me an opportunity to add strength to this critical area.
Also, I'm intregued by the "Glue and Screw" approach, but I am using foil faced radiant barrier OSB for the sheathing. With the foil facing the rafters, will the glue still hold?
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Edited 3/1/2005 11:38 pm ET by xxPaulCPxx
Rather than lag bolts on the rafters, I think most authorities would prefer hurricane straps.
Dan,
if an offical prefers an inferior method of rafter attachemt and the roof should fail I believe that he would find himself involved in a lawsuit.
I'm no lawyer but if I use Simpson H4 clips (547pounds) and the roof fails to hold and it can be shown that it would have held with a 3/8ths lag bolt (2783lbs) A building inspector who requires an inferior method of attachment over a superior method would be vulnerable. (IMHO)
The thing is, the rafter is apt to split around the lag bolt and pull off, leaving the bolt to hold 2783 pounds of nothing.
"if an offical prefers an inferior method of rafter attachemt and the roof should fail I believe that he would find himself involved in a lawsuit. I'm no lawyer but if I use Simpson H4 clips (547pounds) and the roof fails to hold and it can be shown that it would have held with a 3/8ths lag bolt (2783lbs) A building inspector who requires an inferior method of attachment over a superior method would be vulnerable. (IMHO)"No.There is 3 options for approval.1. As proscribed in the code which uses "standard" constrcution methods (all the IRC is starting to include more modern stuff such as metal construction).2. Installed per manufacture which as done testing and that testing is approved by the code officials.3. Specific design approved by an engineer.The H4 clips fall under #2.No matter how could any alternate methods are, if you don't have one of those 3 they don't have any liability in not approving it.
Frankly, I wouldn't use any methods proscribed by the code.
Page 126 thru 129 with the chart on 129 the source for the numbers I quoted..
I also vaguely recall reading the part in the UBC about fasteners but it's been too long for me to site chapter and verse..
I really have no experiance regarding the use of foil faced radiant barrier but I would suspect that the bond the foil has is far less than the bond a clean sheet of glued plywood would have..
Using screws to fasten OSB is kinda like putting a Rolls-Royce engine in a Yugo.
From a practical inspection standpoint, the big problem with allowing screws is telling the good non-brittle ones from ordinary drywall screws. There are so many drywall screws all over the place and the education of installers is so lacking that there would probably be lots of cases of "we ran out of screws, but we found these others".
The best solution would be glue for the real strength, and nails to satisfy inspection and hold things together while the glue hardens.
-- J.S.
"Using screws to fasten OSB is kinda like putting a Rolls-Royce engine in a Yugo."
HA HA! Oh, you couldn't imagine the engines we stuff into those tiny and inexpensive CRX's!
I was finally able to reach the building inspector, and his response:
"Oh I don't care. Just be sure to use the propper spacing pattern, 6 and 12 inches"
I'll see if I can't find a way to scrape the foil off at least on the edges where they make contact with the rafter so i can lay down a bead of adhesive.
Hey - nice post hijack on that tamarak! Now, if you would be so kind as to point out a link to a So Cal supplier of radient barrier tamark (or old growth locust) plywood or OSB - in a pinch, I guess 1" rough cut (but still foil faced) tamarack placks would work too.;)Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Were you suggesting using 3/8" lags to set roof sheathing?
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>> Were you suggesting using 3/8" lags to set roof sheathing?Now remember, his roof is probably decked with unplaned 2" black walnut or something like that. 3/8" lags wouldn't surprise me a bit.
No,
1 inch thick (actual not nominal ) tamarack
OK so I'm indulgent but I paid less for my tamarack than you would for 1/2 OSB...
Where, oh where has my UnderDog gone...
No I believe I was talking about using them as a method to hold down rafters vs the typical toenailed rafter connection. I hope that wasn't too confusing. and as You read I really didn't recommend screws to anyone since it took so long to do relative to nailing.
Granted I don't need to earn a living building my house so I'm free to indulge whatever whim strikes me without regard to speed. If cost and time were no object you might want to consider it but I know of almost no one who's in that position..
I am surprised that no one mentioned fire or flooding etc. after all screwing wouldn't improve the homes surviability under those conditions.
The funny thing is that with the roof decking of1 inch thick skip sheathing (actual 1 inch not nominal) it would be possible to use lag screw, counterbore them and still have a flat surface to put the roofing material on..
I see you are in California. I tend to doubt that you local codes enforcement people would allow screwed sheathing on a roof, given the seismic and other high standards out there. I like screws in a a lot of applications, especially in remodeling work, but roof sheathing seems like one of the last places I would wan tto see it.
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Piffin, why do you think that seismic activity should preclude the use of screws?
Regards,
Tim Ruttan
Screws tend to be harder and more brittle than nails, and thus don't hold up as well under shear -- they'll break before they bend.Of course the "true" solution is to use 20d nails and "clench" the ends after they're in place. This more than doubles the pull-out force.
Dan,
Either Tauton Press is wrong or you are. read the best of fine homebuilding framing roofs starting at page 126 note partucularly the chart on page 129
Maybe you could give me a hint as to what it says, so I'll know what I'm being accused of?
Most screws do not have a shear strength to compare to that of the appropriate nails
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>> Most screws do not have a shear strength to compare to that of the appropriate nailsHow much shear load are roof sheathing connectors subject to?
In numbers? I don't know that, but it is lots. Ever been on aroof in an eighty MPH wind?The officials responsible for the decisions don't allow screws in a alot od structural and shear applications, so I'll go along with that..As for Frenchies test, I've done plenty of that in demo fro remo owrk. The screws will almost always break before they pull out. Often enough, they break easier than a ring nail will pullout. I'll stick with the ringers
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Piffan,
Would you be willing to test my boards? I do take care to install them correctly. Thus holes are predrilled for the shank, the minor thread diameter and counter bore the wood for a head if it's intended. And no I don't use sheetrock screws for anything but sheetrock. I can understand how easy it would be to improperly screw items in place. For example, hold the board a 1/2 a thread off the joined material. or over drive the screw, etc.
all expenses paid? Be right there.
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I'll tell you what, If you'll do an actual test and publish the results I'll mail them to you.
A shear load would be trying to push the sheathing along or across the rafters. I have not (praise the Lord) been on a roof in an 80 mph wind. I can well imagine that it would tend to push me sideways pretty hard. That's understandable; even lying flat on the deck and screaming for mercy, I would be presenting a much larger cross sectional area to the wind than the 1/2" or 5/8" edge of a sheet of plywood.I don't see how an 80 mph wind, or even a 318 mph wind (Frenchy's F5 tornado), blowing across the surface is going to work up enough friction to impose a significant shear load on the sheathing fasteners. And if any plausible fastener schedule had been followed, the load per screw would be minimal.
Interesting discussion. Can't help but to throw my .02 in. (You may value it differently)
Given that proper screws are selected - ie, adequate shank diameter, non-brittle steel, with proper head design - and your ability to convice your local inspector, I can't see any reason why screws wouldn't work.
HOWEVER, I completely agree with DIRISHINME. It's a waste of time and money.
If you want to improve your roof deck, switch away from that OSB to Ply. It's not that I think there's anything WRONG with OSB, but ply will hold fasteners better. It doesn't make much sense to increase the strength of your fasteners beyond the sheathing's ability to hold it.
Use 5/8" T&G Ply, glued and nailed on the schedule DIRISHINME decribed, and you'll have a roof assembly that's much, MUCH stronger than screwed-down OSB. Sheathing and/or rafters would splinter before that joint came apart.
I understand that you'd have to apply a seperate radiant barrior under the ply, but you could do that in less time than the "screwing" would require. And, as a bonus, you could do it after the roof sheathing has been protected from the elements.
Of course, you could also use 1" tamarack sheathing with 1/2" SS lags and 1 1/4" washers and 12"x12" rafters. I don't know if you considered that option or not.
BTW Frenchy, I'm surprised you skimped on your sheathing material. Black Locust or White Oak would have been significantly stronger than Tamarack:)
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
regarding Black Locust or Tamarack You are only partially correct. Locust has a higher work to load of 15.4 pounds per cu .ft. over Tamarck's 7.2 pounds per cu. ft. but Tamarck has 800 psi strength perpendicular to grain over locusts 770 psi. Thus once the tornado gets the edge of a board up Locust would be stronger before it broke however Tamarck would have a higher resistance to being pulled out in the first place.
Besides Black locust doesn't grow here and Tamarack does! <G>
My text lists Tamarack with a transverse tensile strength of 260 psi green/400 psi at 12%. I'm seeing Locust at 770 psi green/640 psi at 12%, W. Oak at 770 psi green and 800 psi at 12%.
- Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material. Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 463 p.
That's consistent with the overall reputation of softwoods being weak in this application - Doug. Fir being notorious as a poor material for TF posts. Longleaf pine is about as good as softwoods get, coming close to 500 psi. Some species of oaks approach or exceed 1000 psi.
Either you have a superior reference, or you picked off the value for transverse COMPRESSIVE strength, which is 800 psi for Tamarack.
I'm sure your 4/4 tamarack is more than sufficient. I was merely poking fun at the degrees of overkill being discussed. Half-inch lag bolts through 1" decking is a long way from the original discussion of screws vs nails in OSB.
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
Edited to remove some unneccessary "smart@ssness"
Edited 3/3/2005 1:40 pm ET by JJSHAW
I knew that you were poking fun at me 'cause I had a smile on my face as I looked things up.. My referance offers differant numbers based on the closeness of growth rings.. the old growth Tamarack I use I assumed would be at the top of the strength charts.
yes I used dried numbrs for the Tamarack but I used them for the locust as well. (however to be fair I didn't use the old growth numbers since I didn't assume you would have much old growth Locust)
By the way is Tamarack a hardwood or a soft wood? I mean it sheds it's needles every year and it is listed in the hardwood section of my book...
I love annal stuff like this!
I'd never heard of tamarack until I looked it up today. It's in the softwood section of the US Dept of Ag. reference I have.
"All species of pine, spruce, hemlock, fir, cedar, redwood and larch are softwoods. Nearly all softwood trees have another common characteristic: their leaves are actually needles or scales and they remain on the tree throughout the winter, which is why they are also called evergreen trees. Exceptions are larch (or tamarack) and cypress, whose needles drop in the fall, leaving the trees bare during winter."
So you DIDN'T grab the comressive number by mistake? C'mon! fess up, Frenchy!
By the way, here's my source online...
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf
Check pages 11-13 or so"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
God himself..just told me.PLpremium on every other rafter, hardend black oxide scres of 1.5" in length, at 6" OC ..everywhere. Followed up with 8d galrs nails hand driven in between ..osb or ply..He dont care.
See..Noah had the same questions..and GOD said.." It is not the roof NOAH, it's the hull" " now we wanna tussel or do you think you can tread water?"" you have wood, you have a hammer..why? try to reinvent my practices? is it a nature of questioning ?"Farg it, get the 40 days and 40 knights..in real time thats whem you will be gone..use the overbuild for peaceful purposes..
Spheramid Enterprises Architectural Woodworks
Restoring, Remodeling, Reclaiming The Quality..
JJSHAW,
I think I wrote that it was compression strength (I probably should look back at my old posts <G>) but isn't that what would resist fastener pull thru? IMHO
This is purely subjective, but I have twice been on a roof when gusts got high enough to lift me physically an inch or three off the surface.It is hard to hear with that kind of thing going on, but I had the distinct impression that I heaard a lot of sqealing going on, like nails being torqued loose.
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A bit of speculation about the torque forces on the roof deck nails:
Wouldn't the squeaking you heard be the roof acting as a shear plane, as it resists the force of the 80mph wind on the outside walls? Windward walls are over pressured while leeward walls are underpressured. This would lead to twisting motions, which are transferred to the roof plane as shear forces.
right - and that point of transfer would be at the nails.
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A few years ago I read, in a magazine dealing with building construction I believe, that some engineers were claiming that the existing roofing systems could be significantly reinforced and made much more wind resistant by substituting screws for the nails.
Makes sense to me as I have made money a few times by betting a carpenter, a devout believers in nails, that a 16d nail would give up before a 2" screw. The pullout resistance of a screw being several times that of the nail I usually won.
I would think that, seeing as wind lifting usually starts at the corner, that you could use screws in the corners and get a good portion of the improvement at the least possible effort.
Of course I have long advocated gluing down roof sheathing. Glue and screw being the gold standard for fastening. But this may be overkill.
Edited to add last two blocks of text.
Edited 3/1/2005 1:52 am ET by 4LORN1
When I was in PR working with some experienced hurricane repair folks, they were pretty religious about screwing everything having to do with the roof, at least for those parts where hurricane straps couldn't be used.
I'd look at the old FHB issue that dealt with roof failures in FL during hurricane Andrew - do you want to use screws to use screws or is there an advantage to them? Most of the problems with the FL roof had to do with the sheathing being stapled and the staples missing the joists. If you really want to secure the sheathing, construction adhesive (aka "glue") on the joists with fasteners (nails, screws, staples, lags???) will make the whole roof essentially one piece. Of course, having the sheathing stay in place requires the framing stay attached. If you don't have a strong connection to your top plate, it won't matter much if the sheathing stays in place. Final thought - you could use T&G sheathing to get more strength.
I read about 1/2 of the replies. Here is mine, and I will be blunt:
Using screws on roof decking is a waste of time and money. If you want your roof fastened better than average, use 8d ring shank full round head nails 3" O.C. on supported edges and 6" O.C. in the field. A pneumatic nailer is pretty much a requirement and don't over drive the nails. If you really want to spend money, go to 5/8" t&g ply.
While sifting through the various replies, take a look at the individual responders profiles and try and determine who are the building professionals and who are the salesmen and office workers... I'd venture a guess that most of the later type people have never had to remove sheathing from a house nor repaired a storm damaged home.
Bingo!
We have a winnah!
Paul, I agree with this post 100%.
My one concern is the "OSB"...<sorry Mad Dog>
If you screw the sheathing down, I'd venture it's going to take you longer than nailing. By taking longer, you're exposing your roof to an increased probability of getting rained upon.
When OSB gets wet, it does tend to swell around the edges of the sheet, and when it dries the swelling does not recover to it's original thickness.
I've seen too many roofs where the 4' by 8' sheets telegraph through asphalt/laminated shingles.
It simply looks horrible. If you;re using another rofing material that may not be a factor, but I would never, ever, advise using redular OSB as a sheathing under asphalt shingles.
Advantek is better than standard OSB...<sorry Mad Dog> but T&G ply nailed down with ring shanks will go fast and will give you a superior roof.
Aside: The failure of roofs in FL had very little to do with the materials used, it was more the methods used to install them. ie, non-existant worksmanship.
You make an excellant point. I have no doubt that a screwed roof deck would be infinately harder to remove than a nailed roof deck. That supports my contention.
So far you are the first person to mention the end of the roof decking and that is certainly a valid point. The issue however was the roof security in the event of high winds and sysmetic activety.
To deal with your concerns regarding the replacement of roof decking I took particular care that at no point in the near future would such an event likely occur. I used skip sheathing (A time tested method of roof decking) made of tamarack (a decay resistant wood) In addition I took particular pains that the air trays would catch any errant rains drops and deposit them outside of the parimter of the house thus even should the roofing should start to fail moisture is prevented from causing decay and with it the requirement of replacing the roof decking..
Surprised at all of the arguments for the nail status quo. In a wind lift condition, shear strength (advantage nails) may not be as important as withdrawal strength (advantage screws). Once a single piece of sheathing gives way, the rest of the roof peels away quickly.
Recently read something in JLC about screwed-down sheathing being pushed for hurricane areas. Could not find it on the JLC site, but here are some other items on this topic.
http://www.clemson.edu/special/hugo/wind3.htm
"A third construction technique suggested by Clemson's Wind Load Test Facility researchers relates to the type of fasteners used to make roofing connections. While nails tend to be the fastener of choice in today's fast-paced construction industry, Clemson researchers found that screws do a better job of preventing roof systems from being lifted or damaged. With today's power-driven tools, using screws has never been easier."
http://www.savannahnow.com/hurricane2001/p_reinforce.shtml
"Keeping your roof in place is the single most important thing you can do to preserve the integrity of your home. Roof sheathing attachments (the number and type of nails) should be increased from those required by local codes. Experts suggest nailing to code requirements and then adding screws between the nails. A No. 8 screw 2 1/2 inches long gives five times the holding power of a comparable size nail."
http://www.seagrantnews.org/news/tips/tip_may97.html
"South Carolina Sea Grant Researcher Timothy Reinhold and his colleagues have found that connecting roof sheathing to rafters with screws rather than nails will reduce the risk of potential hurricane damage to homes. Through experiments conducted at Clemson University's wind-research facility, the researchers have found that roof sheathing held by screws withstood five times more wind-uplift pressure than roof sheathing attached by nails. Reinhold recommends using No. 8 screws, spaced eight inches apart, to attach the plywood underlayer of the roof to the rafters when re-roofing."
http://www.andrys.org/Building%20Guide.htm
"Whatever roof you pick, consider that this is hurricane country, and should be tied down to the highest degree possible. Tile roofs should be screwed down with stainless steel screws, metal roofing should have the seams mechanically adhered and the fasteners placed under the metal, not penetrating it. Shingles (if used) should be the laminated type with the first row set securely in mastic. The plywood sheathing should be secured with twist nails or screws. Finally, the best shape for a roof is a hip roof with an average slope."
Yeah, likely the nail/screw combo is the way to go, if you can't glue. With both you would satisfy most retentive inspectors, and would eliminate any worry about brittle failure. You could limit screws to the edges and near the ridge, and probably achieve 80-90% of what complete coverage would give you. A drywaller's autofeed screw gun would make quick work of the job.And using splice blocks at the horizontal joints between sheets would probably help a lot, though that would likely be more time-consuming than the screws.
Interesting comments. Screws may be a waste of time compared to ring shank nails but it's hard to deny that screws have much better pull-out strength than nails. I would like to see info on the pull-through strength for tapered screw heads and plywood. For gosh sakes, shear strength isn't the issue, except perhaps for earthquakes. How many roof sheathing failures occur because of shear forces -- my guess is almost none. Wall sheathing could be a different story.
Billy