I’m starting the roof on my house next week. I’m trying to balance cost vs. time, and I’ve figured out that 14″ I-joists at 2′ on center is similar to 2×12’s at 16″ on center (the span is about 22 feet, 10 pitch). Since the main part of the house is 40′ long, the I-joists would save me about 20 2×12’s (ten on each side). My concern is with sheathing that 2′ span. We live in Maine, and the total load (minimum), including snow, is 45 psf. My framing book says that the appropriate rated plywood will cover a 2′ span, but I wonder if that will be 1) too spongy or 2) a beast to get up on the roof, thus negating any labor savings.
My other problem is simply that I’ve seen so much warped, crowned, and twisted spruce as we’ve raised the walls that I can’t stand the thought of 24 ft. 2×12’s at $46 bucks per coming in the same condition.
I’m looking for advice about the best way to go with this… And, by the way, this is my first attempt at roof framing, although I have done sheathing before.
Replies
Trusses are typically installed 24"o.c. I suggest going to 5/8" sheathing. 10:12 pitch helps.
Boss Hog can probably help.
Wood is Good
Adam Greisz
Owen Roberts Group
10634 East Riverside Drive # 100
Bothell, WA 98011
http://www.owenrobertsgroup.com
What about 19.2" ?
I'm sorry, I thought you wanted it done the right way.
The 2x12s come from a better part of the tree than the 2x4s do, but you can still count on having a couple bad ones.
I would not hesitate to go with the TJIs for that span. I assume you are planning a cathedral cileing is why you aren't diong trusses, so the TJIs also give you room for insulation and ventilation.
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weaf... anytime we frame 24" oc, we go to 5/8 sheathing....
now.. with our new wind uplift requirements, we use 5/8" T&G....Mike Smith Rhode Island : Design / Build / Repair / Restore
Actually, we have a cape with a shed dormer on one side. I assumed that the amount of living space under the roof ruled out trusses. No place to put the bracing, and all that.
I haven't ever tried giving someone my opinion yet, since I'm just building my first house, but I figured if you're doing your first roof too....
We used I-joists on the main part of our roof. You mentioned cost vs. time. I found that for me it took a lot longer to frame with the I-joists. FHB had an article about working with them - I think framing a roof in particular - not too long ago. Unfortunately, since we've been building for two years now, I didn't see it until we were done. If time really is a issue, it might be something to consider.
Shauna
For what it's worth, I had our addition floors framed with wooden I-beams but the flat roof was comprised of 2x12's. The span was not that long (17') but we did have to take the snow loads, etc. into account. The 2x12's also give you a lot of room to run utilities.
I preferred a solid beam in said application due to the fact that sooner or later a roof will leak. When it does, I put a bit more faith into a solid piece of wood to hold up its end of the bargin than something that was glued together. Undoubtedly, they have brands where they use marine-rated glue, etc. but for whatever reason I place more faith in intra-cellular walls.
One big drawback to using I-joists for rafters is that a structural ridge beam is required. (No exceptions) You didn't mention if you have that or not.
The 24" O.C. thing wouldn't bother me. Upgrade to 5/8 plywood if you don't like the 1/2 stuff.
The cost of the I-joists and related hangers and other hardware might make them more expensive, even if there is less pieces. If you take your prints to a lumberyard they should be able to give you a takeoff and price.
Yeah, the hardware will make it more expensive. The total cost for the rafters themselves would be about the same, but I have to figure spending more on sheathing and hardware.
From the sound of things, you are doing this on your own house (correct me if I'm wrong). Are you doing this project in your spare time? If so, weather would have to come into play.
My wife & I are buiding our own house & we ended up choosing dimensional lumber (2x12 floor joists) instead of I-joists mainly because I wasn't sure how they'd hold up to a whole summer's worth of rain. Same thing will apply once we get to the roof.
Just finished putting the subflooring down on the second story. Time to throw up another set of walls...
Yes, we're doing it ourselves. I've used a lot of Advantec for the exposure issue, but I'm a teacher, so I'm working every day. My folks built their own house in the 80's, and they'll be up for the roof. Hopefully we can get it covered before our current dry spell breaks.
we ended up choosing dimensional lumber (2x12 floor joists) instead of I-joists mainly because I wasn't sure how they'd hold up to a whole summer's worth of rain.
And lumber yards think nothing of leaving these things out in the rain.... Last time I got some I-joists I was picking through the pile to get something at the bottom that was not POS.... Cut a bit off the end when I got it home and the flanges fell away from the webbing..... Mr Weyrhauser said not to use it.....
At the risk of thread hijack: I've put I-joists under my bath tub. How extreme would it be to use a waterproofing membrane like Redgard to protect the flanges?
I've put I-joists under my bath tub. How extreme would it be to use a waterproofing membrane like Redgard to protect the flanges?
Not extreme at all. I think it sounds like quite a reasonable precaution.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Chris talks about the wet snow
hey chris , in the winter, no problem
but after 3 or 4 years, in the middle of summer, wavy gravy
stick to your stonger thicker roof
and if anyone complains about 3/4 roof and the wieght of plywood ,,,,,,, chumps
I used I-joist for the cathedral roof over my great room. After 8 years I can tell you the framing is as straight as the day I framed it. Its an 8 pitch 30 ft from plate to plate 19.2 o.c.
That said, It took a week to frame it. Something that could have easily been framed with dimensional lumber in a day. The rafter tail detail took the longest.
Also the cost of hangers like Boss said was staggering.
In my opinion any horizontal or semi horizontal space of more than 12" needs 3/4" ply or the minimum would be 5/8 T&G . For a few dollars more you can have a nice solid roof that does not spring your hatchet back at you while nailing shingles between rafters.
In my opinion any horizontal or semi horizontal space of more than 12" needs 3/4" ply or the minimum would be 5/8 T&G . For a few dollars more you can have a nice solid roof that does not spring your hatchet back at you while nailing shingles between rafters
Wouldn't you say that's a little overkill Don?
Are you saying that every roof you sheath 16" o/c you use 3/4" or do you space your rafters 12" o/c and use 5/8"?
Joe Carola
I don't think of it as overkill , but just kill. I hated shingling on roofs that bounced my hatcet back . Really liked the solid feal of hitting a nail over a joist . Just a tap and swat the nail is set . But on a flimsy roof the rebound was a killer , sometimes had to hit the nail three times .
For the extra you're paying for that 3/4", you could probably buy a compressor, some hose, a decent nail gun and a couple boxes of nails, speed things up a tad, get off the roof quicker and push the aches and pains of old-age wear and tear out a few years.
I think it would take a few roofs to pay for a comp., gun ,hose and nails but I try not to do roofs any more . When I quit the roofing gig the guys were just starting to use air staplers and many had wind failure problems . No pnumatic roofing nailers at that time . But I still think that floors and roofs need 3/4 ply
My recommendation is you go for solid wood rafters, and use 5/8" plywood sheathing, as Mike and some of the other guys have suggested.
Reasons:
On the framing:
1. You won't get this blacked in as fast as a pro crew, so the length of time those I-joists will be sitting exposed to weather is an important factor. The more often they get rained on, the sooner they're gonna distort and/or disintegrate.
2. If you do your framing with solid wood you may be able to dispense with a structural ridge beam. A ridge beam a big deal, a lotta wood, and very heavy and difficult to put up with a small family-type crew.
3. You will find it more difficult to work with the joists than with dimensional lumber as even simple cuts become more complicated when you have to set a jig in place to make them.
4. If you spoil an I-joist because you cut it too short or whatever, you will have to re-order and wait for a replacement to be shipped. OTOH, if you mess up a 2x12, you just drive over to the yard and pick up a new one.
On the sheathing, it's been said by a couple of other guys, but here it is again:
(1) ½" sheathing laid over rafters spaced 24" OC will wave-out between rafters after a very short time period unless the roof is very steep (by very, I mean upwards of 24:12).
On a rare framing job I did as a sub, I was obliged by the GC to put ½" OSB on a 4-in-12 shed roof over trusses set 24" OC. About mid winter, I got called by the HO to fix a roof leak in that new section (the GC had gone tits-up and vanished). I shoveled it clear and found it already scalloped after less than even one full winter. This scalloping had pulled the chimney flashing away from the chimney, which was the source of the leak. In your area, your snow loads are similar to those here. You will have more severe scalloping than someone further south, and you will have it sooner rather than later.
(2) ¾" sheathing, on the other hand, is overkill. It's also a waste of money and a parasitic load on the roof framing. Remember that a roof is not a floor. It does not have to be that stiff because it will not be supporting moving live loads...only static ones.
(3) Go with the 5/8, but use plywood, not OSB. There is a world of difference in longevity, nail-holding, and weatherability.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
I'd like to thank everyone for their suggestions. 2x12's it is. The structural ridge beam and te added expense of brackets puts I-joists out of the picture, and I hadn't thought through the difficulty of dealing with the trim end of a 14" I-joist. The 2x12's will have to be 16" o.c. I'm thinking 5/8 sheathing ought to do with that spacing. We will have a metal roof, so the roof will be lighter and shed snow better than asphalt.Weaf
If you're gonna use pre-fab metal roofing, you can put skip sheathing on the roof and forget the sheet goods entirely. I'd use rough-cut 1x hemlock if you can get it. If you're lucky, one of your local mills will be doing a run of 6x6's and 8x8's and will be glad to unload the offcuts cheap. For skip sheathing, it doesn't matter if the planks aren't all exactly the same thickness.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
In the early stage it seems prudent to deal with savings of 50 bucks a rafter. In the big picture, that is chicken feed. You'll spend that much buying a bag of latex modified tile mortar, or a light fixture, or a towel bar.
Step back breath deeply and say "my estimate is only 60% of what this house / cabin will really run."
As for the I-Joists. Do it. Dimensional lumber is good for vertical support (studs and even headers) however as rafters or Joists Engineered products with glue on the mating surface make for a better solution. They are easier to place although there is need for blocking at the ends.
I used a set of Plans and had the design firm change it to I-Joists form the dimensional lumber that originally was specified. Big spans onthe rafters or 28' from top plate of the wall to the ridge beam. Man, that product is very predictable and to this day the structure is straight as a rule. We had a long build cycle as well. It took fully 4 months of Midwestern (WI) summer to get all of it under shingle.
I believe we have a traditionalist vs 'new-fangled-product' conflict on this thread so you, at some point, will have to make your own decision. Although I have to suggest the heavier weight of dimensional lumber vs Engineered would make my decision easier. Contrary to some, this isn't rocket science to make the jointery. Then again you'll have to get some fast instruction if you are hanging rafters in 2 weeks.
Don't scrimp on the structure in any case. It is awfully hard to cure a whoops in that area. It is relatively easy to replace a cheapo light fixture with your dream fixture later. Slipping in another beam is a nightmare.
With a 2 foot span on rafters you'll need to use the sheathing clips inbetween sheets in the area between the rafters. Or as someone suggested T&G sheathing. They (the clips) look like a square cut saddlepoint that physically slips in to tie the sheathing together. If you are a math teacher you are on to this description.
As for the sheet goods and the I-Joist rafters, I hooked up a pulley on the ridge beam (16/12 pitch) and used support people on the ground to pull up the sheet goods and rafters with a rope thru the pulley. I attached the rope to the goods using a pair (one was a safety) of visegrips. It keeps you from becoming a monkey on a ladder or a hangglider pilot and lowers your workload.
All the best.
Edited 7/28/2005 8:47 am ET by Booch