I have a question about my roof truss that I hope someone has some
thoughts about.
About 15 years ago I built a garage 24 x 24 foot. Roof truss is
24 in o/c. 7 x 12 pitch. W style truss (2×4 material) sheithing is
1/2 cdx. Braced both ends with x supports. Asphalt shingles.
The manufacturer of the truss is unknown, but I do remember asking
for a heavy duty truss.
The wood has premium stamped on it.
I am now converting the garage to a shop.
I have insulated the ceiling and strapped it.
No one can tell me what the ceiling will support.
I know I can support a ceiling, lights, and heater.
What about dust collection, materials, etc. All the things a typical
shop collects.
As I live in snow country (Vermont), we do get some eight up there.
Any thoughts or ideas?
Jeff
Replies
I'd ask around for a local structural engineer who you can pay for a couple hours of calc time. Otherwise, your local lumberyard might have somebody who can do it for you, especially if they buy alot of trusses & they know you.
Very likely if you distribute your load across several trusses, it'll be fine. Snow load does raise concerns though so I'll sit tight to see if anybody else offers an idea.
Hope that helps
Boss Hog should weigh in on this one, he is the truss expert. FWIW before he gets here, you are talking about bottom cord loading. Unless you specifically ask for a bcl of over 5 pounds per sgure foot, that is ussually what you get. May be slightly higher for "heavey duty" trusses.
Dave
I'm not all that worried about the normal snow load, as I haven't
had any problems about that, and the local supplier said the normal
snow load was already accounted for in our area.
I called a couple of manufacturers and asked for help. All I got was
a very large apology, and no one was interested in helping me even
if I offered to pay. (though, one company suggested a $500. to $1000. cost to come and inspect it, and work up a number for me)
I also asked about strengthening up the current trusses to improve
the load factor, and no one would touch it.
I couldn't find a truss engineer anywhere around here, only some
architects who had no idea.
My father is a civil engineer and he had no idea either.
Jeff
Willingness to pay will help alot.
If you don't feel likey they've already abandoned you - try talking to the truss company's Engineer who stamps their calc sheets/shop drawings - they'll certainly be able to help. In fact, any structural PE who does the least bit of wood design would be able to help you out in very little time at all. You can certainly beef up any truss - just gotta know the loads & the right person to design it. Not difficult at all.
What kind of "heel height" do you have available over your bearing walls? If there's enough depth, there might be room to add some joists that can span 24' (depth available will control whether this is feasible - and most likely beefing up trusses will be much more cost effective). If you want to beef up the bottom chord for specific loads, you probably can get a free analysis from a lumberyard that sells Paralam or TJI type products.
I know a few engineers who could tackle this in no time - where are you?
These Architects you spoke with should also be able to refer you to a PE if they're not interested in tackling it themselves. I would have to crack some books and call my dad (a structural PE for 35 years who hasn't designed anything in wood, ever) to come up with an answer I felt good about - and I still wouldn't want you walking under it based on what I've said on a message board.
good luck. it's didn't seem like it'd be this complicated, did it?
SPHAUGH
Thank you for the advise.
I thought about adding some support underneath, but don't have enough
height.
I also forgot to mention that we have no real permits, inspectors, or
engineers around here. You can build anything you want for personal
use without needing approval. (not the same for commercial)
I'm in Vermont just south of Manchester, VT.
Jeff
Jeff,
Much like where I grew up, out in OH in the sticks...
One of the PE's I had in mind, coincidentally, works out of Willison, VT. I dunno where that is in comparison - but if you're interested - I can email him monday & see if he'd help out with something like this.
Totally up to you, I'm just as happy if you work it out some other way.
SPHAUGH
Williston is the other end of the state, about 2 - 2 1/2 hrs away.
But yes, give him an email, maybe we could at least discuss it.
thanks
Jeff
I'd have to know a heck of a lot more about your situation to give you a specific answer. Things like local codes, loading requirements, lumber grades and species, and plate sizes and manufacturer.
In general, trusses are designed for about 10 PSF on the bottom chord. This is typically to account for ceiling material, insulation, miscellaneous loads, and the weight of the truss itself.
The fact that you asked for a "heavy duty truss" may or may not mean anything. They might have designed it for added storage loads, or they might have done nothing. If you wanted something specific, you should have asked for something specific.
I am curious - If you ordered the trusses yourself, how could you NOT know who the manufacturer was?
I don't have any problem thinking your truses can support dust collection ducts and lights like you mentioned. But I wouldn't go stacking materials in them. I'm pretty certain a 2X4 truss wasn't designed for that.
When two egotists meet, it's an I for an I.
Boss
I understand all you said.
Unfortunitly, when I ordered the trusses, I did it thru a local
lumber yard. I relied on their expertise when I placed the order.
I really was only building a storage garage at the time and didn't
specify anything other then a typical heavy duty garage truss.
I remember them asking if I wanted the normal truss or the Heavy duty.
They also said the normal was rated for our area and would meet all
the needs, but I ordered the heavy duty anyway.
I asked the lumber yard if they had any records or who was the supplier and they don't know which of the ones they use who supplied
it 15 years ago.
My own fault.
I've used the trusses to store material for years; wood, metal, etc.
I've removed everything before insulating.
I know the nailer plates on these units are about 4x6 inches, and could probably find some specific info somewhere on the bottom
chords for the type of lumber.
I'm not planning to hang any real heavy material, just things like dowels, trim, dust collection ducts, heater, lights, dust collector,
power cables, etc.
All real heavy stuff; lumber, shelves, tools are on the wall studs.
Any suggestions or thoughts would be a help.
Jeff
What you're're talking about putting on the trusses doesn't sounds like any big deal to me. Lumber would be the real killer - The weight can add up quick.
If they offered a "standard" truss and a "heavy duty" truss, it could be that the "standard" truss had 2X3 webs or somehting like that. Hard to say without reviewing the exact designs.
The truss plant and lumber yard probably have records somewhere, but will probably NOT be interested in digging for them. Often the old records are kept in dusty cardboard boxes in an attic somewhere. They're not going to look through them unless they HAVE to.Born free (my father's a doctor).
Boss
Sounds just like my old records.
Yes, I don't think stacking heavy lumber would be a great idea.
I don't have the space anyway.
Originally, I would have loved to store wood there, but I gave that
idea up last summer.
So you think I'll be ok with what I want to do?
Thank you
Jeff
Boss, you're the truss man but Jeff lives in a snow area and I suspect the difference between a "normal"and a "heavy duty" truss would most likely be related to the expected snow load. Something like "normal" can cope with 15in of snow and "heavy duty" can handle 6 feet. Alternatively, the difference may be it how many nails were (should have been?) used in the connectors. It should be fairly straight forward to reinforce the bottom chord of each truss with a steel strap - there was a discussion along these lines in the last coulple of months in respect to floor joists. Without seeing the truss or doing the calcs, reinforcing the bottom chord will substantially increase the load that can be slung from the bottom chord.
However, Jeff wants to line and insulate the space, and 24x24 is pretty large. I'd look to keep the lumber within the insulated space not outside.
"I suspect the difference between a "normal"and a "heavy duty" truss would most likely be related to the expected snow load.
What you say is basically correct. But that's also what I said earlier - A "heavy duty" truss could be just a gimmick, or could really mean something. No way any of us can tell without reviewing the designs.
"reinforcing the bottom chord will substantially increase the load that can be slung from the bottom chord."
That may or may not be true. If the heel or peak plates are maxed out, it won't do a thing. Again, this is impossible to determine without reviewing the design of the truss.
Time is the best teacher. Unfortunately, it kills all its students.
Boss, help me clarify something in my own mind that has come up in this thread. I had understood that a truss is designed as a whole such that, if your roof live load is fifty #/sf. ceiling dead load is ten and roof dead is fifteen, you have a total design load of 75#/sf. It matters little if that is applied to the bottom chord or the top chord so long as it is applied evenly, not putting a tremendous point load in one place. Am I wrong here or must morer of the loading be applied to the top chord?
I don't really think any of this really applies to this instance because he is not talking about adding a whole pile of green black walnut to the attic space to store , just a few appliances like lights and fans, with the heavies supported by the floor.
I agree, the heavy duty might be just a marketing ploy as much as anything else. It could be that the regular is the skimpy, "justbarelygoodenough to make it past required design loads for the area" truss to sell to tract builders who count every penny in a competitive environment and the heavy duty is the "this one really meets the standard in the right way that we would always like to build them for anyone willing to pay to have it done right to last more than fifteen years" truss. Probably same design numbers but in reality the better truss for a couple bucks more.
I remember too that a lot of quality suffered in the seventies for various reasons, (general cultural standards, energy crisis and inflation, wage and price controls, environmental lawsuits, etc.) so it may be that it is especialy good that he got the heavy option..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
" It matters little if that is applied to the bottom chord or the top chord so long as it is applied evenly, not putting a tremendous point load in one place."
Technically, you're wrong. But I'm not sure it realistically matters a great deal. If the top chord is maxed out in bending with the standard design loads, you can't incease the loading on the top chord without overstressing it. But it's unlikely to cause a catastrophic failure.
Keep in mind that the weakest link in the truss is typically the plates, not the lumber. Add a lot of weight on the bottom chord, and the plates attaching the webs to the bottom chord may be inadequate. Or the splice plate(s) may fail in bending.
"...the regular is the skimpy, "justbarelygoodenough to make it past required design loads for the area" ......and the heavy duty is the "this one really meets the standard in the right way ...... to have it done right to last more than fifteen years" truss. "
I don't really think there is such a thing. What exactly does quality mean in a truss? That the lumber looks nice? Or that the plates are on straight? What is it about a truss that makes it so it "really meets the standard in the right way"?
FWIW - Trusses around here aren't built any different for tract builders than for everyone else. I always kinda bristle a little bit when someone suggests stuff like that. I can't say for sure that it doesn't happen in other parts of the country, but it hasn't in the 6 plants I've worked in. The plant guys don't typically know or care whom the truss is for - All they see is the job number on the paperwork.
"...I remember too that a lot of quality suffered in the seventies for various reasons,"
Mostly because everyone wants a cheap truss. (Or cheap everything) Quality costs money, and the vast majority of the people buying trusses aren't willing to pay for it. Stamp out crime - abolish the IRS.
Didn't mean to make you bristle and thanks for the truth. It's why I asked and then speculated. I knew the weak link would always be the connector gusset plates.
As to slightly lower standards for some, If you could get the same design load with 2x3s that had a few more knots than with select 2x4s, wouldn't it be likely to happen in some places? I know I've seen a few scary ones down south in the 1970s. Grading standards have gone downhill for all lumber in my lifetime, IMO. Is there a check to prevent a knot from ending up used in a chord right at the gusset joint location? I haven't been around trusses for a lot of years, as you know, so I;m not throwing stones but speaking theoretically or acedemically for my own education. Maybe someone else can learn from the conversation too..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
I suspect that you meant equal design loads between higher grade 2x3 vs lower grade 2x4's, (pif>>>"with 2x3s that had a few more knots than with select 2x4s,").
I don't think you are allowed defects so large that you would be able to downsize 25%. As for a check for knot location, have you ever seen the monkeys that build these things? <raises hand, I were one> Besides, I can think of worse places for a knot than at the gusset. Either way, I don't remember very many pieces, if any, getting rejected by the assemblers. My main job was handling pieces off the cut machine, and if the piece was solid it got stacked.
I have seen truss gussets that were visably undersized on a job a few years ago. I was doing finish and happened to be goofing off drinking coffee in the garage. I look up and say, "hmm, small gusset". Look around and find 4-6 failed joints. I'm sure the trusses were fine to the truck, but suffered from there to installed. Small minded economy, but got by engineering.
What I think people can learn from this conversation, before my input of course, might be how marginal trusses are. Even hanging a heater would make me think installing a strongback to spread the heater load.
That's the kind of personal, reality based obsevation I'm looking for. I'm one who overbuilds anyway so now I've got me wondering why I got into this thread but I'm learning.
I know they do get some rough handling at times..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
You got into this thread because you haven't learned everything...yet. I would be curious what Boss has to say about the mini-gussets, at least when I built the things the gussets covered the joints.
Speaking of overbuilding, my brother got nothing but grief about that shed I built on his shop when I was up there, and I was pushing spans. Unamimous, and continuous, but he just explained that I was a contractor and they all nodded and said "Ya, they don't know anything, they all read some code book or something".
Me bad...
Oh, another thing about the mini-gussets. Somehow they engineer them to work on paper, but have you ever seen what wood does when you aren't looking?
Truss stock comes and goes from lifts in controlled conditions, then twists, cups, warps and gets handled in the real world. The more I think about those failed trusses, the crazier I get, but I have enough battles.
LOL,
So even tho the trip is finished, you are still breaking things?.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Nope, it was just that one stretch. Glad you think it was funny, some people might not get it.
And hey, the grief was I over built the shed. It seems I could have done it with sticks and twigs, 2ft on center. ARGH, he used all new wood!!! I remember a temporary shelter for a mason I built one time with strapping. 1x3 rafters and studs, no collar ties, blue plastic roof and walls. They would have liked that one.
Anyhow, I am banned from building in Maine until I get my act together. Oh ya, I am never going to hear the end of having a Chevy break. What do you expect, it was probably the first time they heard of such a thing. ;-)
To all
I guess when I started this question, I needed more insight.
SO FAR, I've learned alot more then I knew before
I also tend to overbuild, and that's one of the reasons I asked for
help.
I also wondered about the plates.
To me, they all look good and solid. but was wondering if gluing
and screwing plywood on either side of the plates would strenghten
them up even more
I definitly won't hang any heavy lumber up there
The heater is strung between 4 trusses for strength, but really
weighs less the 100 lbs.
That's the only heavy item other then the garage door.
Thanks all, again.
I'll keep reading anything that comes in.
Jeff
ssssssssssshhhh!...
When I mentioned the fuel pump, I didn't say it was on a chevy. Now you've let it out!
;)
inside joke folks.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Several things have been brought up, so here's a shot at addressing them all.
Undersized plates:
The size of the plates needed is partly science, and partly subjective. Sure, there are all sorts of rules used to determine the minimum size of the plates required. But which plates do you oversize? And how much? There are no easy answers. Every shop does it differently. Some oversize a great deal, and some almost none at all. It also depends a great deal on the size of the trusses involved - You need to over-plate a 50' truss a lot more for handling than you would a 20' truss. The guys at the tables generally have a free hand to over-size plates if they see fit. So some do, and some don't. Depends on what mood they're in, and whether their Wife has PMS that week.
Qtrmeg, I'm not sure what you mean by "how marginal trusses are". I don't think they're marginal at all - Typically they're MUCH stronger than they need to be. Sure, they look spindly next to a 2X10 rafter. But they're typically designed with a 3X safety factor.
The situation you mention, where some of the plates were knocked out in the garage trusses - I think that speaks poorly for the framer and/or the GC on the job. Everybody knows trusses can get damaged in shipping and erection. But to walk off and leave them broken in pretty poor workmanship, IMHO. They should have been fixed. It's impossible to overplate or overdesign a truss to the point where it CAN'T be damaged in transit.
Next subject - 2X3 truss webs.
I personally don't see anything wrong with 2X3 truss webs. We typically use them in 24' stock garage trusses, and some hip jacks. Sometimes in small cap trusses too. (The top part of a piggy-backed truss) You certainly wouldn't want to see them in a 50' pole barn truss. But I don't see any reason NOT to use them in small trusses where they might only have 50# of force in them.
As for knots - Knots aren't allowed under truss plates. Not because they look bad, but because they reduce the effectiveness of the plates. Large knots in the chord and web lumber should be culled, but aren't always. Just exactly what knot sizes are acceptable and what isn't is subjective. Some are bound to get through the plant without being noticed."More hay, Trigger?""No thanks, Roy, I'm stuffed!"
boss , a lot of the truss mfr's here are no longer cutting bevels on the web struts.. they are all radiused and cut to length.. the diameter of the radius is 3.5" so the struts become point bearing & rely on the plate strength.....
the plates have all gotten bigger too..
i'll see if i can get a pic before we rock the ceilingMike Smith Rhode Island : Design / Build / Repair / Restore
They call them things "Turbo Webs".
The idea is that you buy a whole bunch of them in stock lengths, like 8' (Or whatever) Then you don't have to cut them - Just throw them in the truss. Supposedly saves saw time and labor.
I don't think much of the idea, but would have to admit I haven't tried them. I also have never seen a picture of a truss with them things in it, so I would very much like to see one. Q: What's the difference between a golf ball and a "g-spot"?A: Men will spend 30 minutes looking for a golf ball.
boss, dug thru the old pics of our current house addition... here's some pics of a 24' scissor truss with a 12" energy heel.... this is the roof of a 28' gambrel addition..
top pitch is 4/12... bottom is 1/12..
the specs for this one require wind uplift of 90 mphMike Smith Rhode Island : Design / Build / Repair / Restore
So - Are YOU one of the guys in the pic? Who's the lady?
I wonder if the wind uplift requirement has something to do with why the B.C. web is so far out from the center of the truss?
Thanks fer the pics - Always interesting to see how things are done in other place/by other companies.Five days a week my body is a temple. The other two, it's an amusement park.
I remember too that a lot of quality suffered in the seventies for various reasons, (general cultural standards, energy crisis and inflation, wage and price controls, environmental lawsuits, etc.) so it may be that it is especialy good that he got the heavy option.<<
WTF? This is what happens when you post while drinking!
If the garage was permitted the plans office of your inspection department may have a copy of the original drawings submitted. These, if they exist, might have the figure you are looking for. If not the actual figure they also may have the name of the company who built the trusses or the engineer who approved the design. If you can track them down they may have what you want.
Jeff, you shouldn't have any problem supporting materials that you have mentioned. I would do some blocking for some additional support and nail some 2x4's on top and in between if it's a really heavy item you are trying to support. Since some heavy items will actually cause the 2x4's to twist outward or bow dependant on where you locate the item and how far run of the joist is, and where its located in relationship to the span. I would always use bracing in between the joists. since most items are never going to line up where the joists are located.
To Jeff
Here's someone that may be able to help
Wood Truss Council of America
5937 Meadowood Drive, Suite 14
Madison, Wi 53711-4125
(608)274-4849
Jack
Thank you
I knew there was a truss group and will probably call them.
Thank you for the number.
I think from the feed back, I'm ok and on the right track now.
Thanks to all
Jeff
The WTCA will not do anything to help you. They'll just tell you to call an engineer.
WTCA is a trade organization that represent the truss insustry in political situations and such. They really have little to do with the general public.
I would expect them to be polite, but not very helpful.Old skiers never die - they just go downhill.
I sent you an email w/ my email address & that of the PE I referred to (from other end of VT). Post back if you did not receive the email.
We had an interesting conversation which reflected much of what has been covered here in this thread.
Good luck
Got the Message.
I'll contact him.
Thank you.
Jeff
Jeff,
That's great. You should find him quite helpful whether its to pick his brain or to actually hir him to help out. The two of us have got a very big project together about to start in southern RI.
Honestly, in my description of your issue - he basically talked "me" out of hiring an engineer based on his own experiences with a 24' garage w/ 2x4 chords top & bottom, from which he has all kinds of bikes, volvo hardtops, etc suspended.
One idea he mentioned to me that was particularly interesting was a suggestion to replace the roof with metal, thereby reducing snow load risk considerably. Real world insight from a structural engineer (normally the kings of conservative & overdesigning) was pretty refreshing.
I thought about the metal roof, and plan to do that when I need to
replace the roof in a year or two.
I might do it early.
Where in RI, I have friends in the Foster area.
Jeff
Just moved to a temporary place in Westerly, about to move to a house we're buying in Stonington CT if the house inspection goes through OK.
We HAVE to be conservative. We all add factors of safety to preclude against inferior materials, long term aging effect on materials, inferior workmanship, trades that bore excessively sized holes in structural members, homeowners who wants to use his garage trusses to lift engine blocks out of his cars, waterbeds, home offices that use home living space to store paperwork floor to ceiling (very heavy!), exercise rooms with heavy Cybex equipment, etc! I have seen it all!
Failure to do so means buildings can fail, folks get hurt, lawyers sue, etc. Better safe than sorry!
Are you for real? Or are you just trying to make a point that you overdesign, to a point?
That's understood - always gotta cover your arse nowadays. The 2x safety factor in the code is a good start, too. I've seen many, many designs that are way over done - so bad that I've started asking for calcs & seeing that they've added 3' to all spans, etc for "contractor factor". Others are not so egregious - I'll give you that.
To Jeff
Here..... Try this number
Edwin Lauts Roof Trusses
Sterling, IL 61081
(815)626-5656
Ed lauts has been in buisness for forty+ years. he designs and builds his own for any application. The software he has available should help you with your question.
I would think that the WTCA could help you. According to my sweets group catalog there are engineers available to answer your questions. Could be That Boss Hog knows something that I dont. Thanks and good luck!
No one can help without reverse engineering what is there. Anyone will help for a price, there is no doubt of that, and I am sure WTCA will be polite enough to help point you in the right direction, eventually. What is needed here is a re-design for new conditions, after engineering you have installation costs of said engineering. Kaching$!
At the risk of offending the engineering police, I could see some lightweight ceiling storage supported from the existing webs for the odd moulding or long piece of something you want out of the way. Hang dust ducts, garage doors? No problem, distribute the load. Start to throw a half a ton of wood up there and you get what you asked for.
have you considered installing a beam under the bottom chords ?
depending how it is placed, a beam can do damage to some trusses..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Yes, I thought bout that a long time ago.
But, thank you.
I think I'm all set now.
Jeff
With out seeing what you have over there I can't give you the perfect solution. From what you describe I would get some 1/2 inch plywood and glue and screw plywood to the web of the truss (both sides). Then I would gusset the center of the span with a 2x4 and plywood. A strong back with a 2x8 on edge may also help to stiffen your roof system.