I was thinking about using I joist for my roof framing. It’s a reasonably complicated roof – 12/12 pitch, two big gables and two shed roofs. It also has a large overhang, so I need about 3.5′ of joist beyond the bird’s mouth cut. In the end, I need a fair number of 24 and 26′ 2×10’s, which is the reason I started thinking about I joists.
I talked to my local supplier and his 9 1/4″ I joists are running about $1.44/lf. I haven’t priced 24′ 2×10, but they must be in that ballpark.
Couple of specific questions –
Anybody know about how much the metal hangers cost to attach the joist to the ridge?
Does the ridge have to be at least as big as the plumb cut on the rafter? With current engineering that wouldn’t be the case (double 11 7/8″ LVL ridge).
I can post a pdf file of my roof framing plan if that helps anybody.
MERC.
Replies
The ridge needs to be as tall as the plumb cut. Last time I did this, the ridge had to be loadbearing. A 4x16 lam. Not fun to install. A ridge board was not allowed. Can't just nail on rafter ties like you do with solid. This is not like using solid lumber and there are a lot of details. If your plan calls for solid lumber, you can't just substitute TJI and do it the same exact way. Roof has to be engineered for TJI. Make sure you use the schedule and hangers approved by the joist manufacturer.
You cannot do birdsmouth cuts. Bottom chord must bear on top plate. Rafter gets extended over a sloped top plate or use special angled hangers. Different hangers for different pitch ranges. You can sister on solid tails if you need something special. Web needs to be filled at each hanger or bearing point. Hangers were something like $3 each, but depends on which kind and pitch.
They're nice because they're straight and long, but they are not an easy cheaper alternative to solid lumber. Unless you absolutely need the length, solid lumber is way simpler.
I'd suggest going to the place you're likely to buy the I-joists from, and ask them for a book. That will have pictures of all the framing details you'll need, as well as all the framing options they allow.
Everything Bob said was pretty accurate. We don't sell many I-joists for roof framing for 2 reasons. First would be the requirement of a ridge beam. Some houses just don't have places to bear a ridge beam.
Second would be the hangers and ties needed at the ridge. They're not terribly expensive to buy (couple of dollars each) but take time and labor to install.
The ridge beam doesn't HAVE to be as tall as the I-joists. The manufacturers allow you to set the beam UNDER the I-joists, and rip a sloped plate for the I-joists to sit on. But most beams end up being fairly deep due to the lack of bearings in the house.
I would only consider them if you REALLY want the higher sloped ceilings inside. Otherwise scissor trusses sound better to me.
As far as comparing them to 2X rafters - They're a heck of a lot lighter and straighter that any 2X lumber I've seen in a long time. Their cost relative to 2X lumber varies with lumber prices, and the local market for I-joists. Sometimes there's little price difference around here between 2X12s and 11 7/8" I-joists. But that varies a great deal from market to market.
We judge ourselves by our motives, and other by their actions. [Dwight Morrow]
Thanks all to the replies.
I'm currenlty thinking the IJoist are cost prohibitive with all the hangers (my local guy quotes my $5.90/ridge hanger + $1 for a strap where pitch is >6/12). Plus my framer has never worked with them before, I'm not sure I want him learning while my house is open to the world (this is a remodel - tearing off the roof).
My local guy also tells me my ridge has to be at least as big as my plumb cut AND the ridge has to be double thickness LVL (not sure why doubles are required - seems kind of arbitrary). So that would really drive up the cost since I already own about half the 11 7/8" LVL I need, but with IJoist I would have to go to 14".
Thanks again -MERC