Can you use I-Joists in an Attic as Rafters? - InspectionNews

Christopher Kovac · #1 (**permalink**) 06-26-2008, 01:31 PM

Hi Everyone,

Ran across I-Joists today used as attic trusses / rafters (I'm not sure what to call them frankly since they don't look like a pre-manufactured / engineered system to me). Has anyone ever run across these and more importantly can you safely use these as roof framing members?

A couple of pictures are attached, one with a member sawed right in half and re-supported...

Thanks in advance,
Chris

Nick Ostrowski · #2 (**permalink**) 06-26-2008, 01:40 PM

Never seen that before and it looks whacky.

What's with the end of the I-joist in the 2nd pic in front of the type B flue vent? It looks like that cross braced 2x4 is being expected to prevent that I-joist from moving under the downward pressure of the roof. That's a lot to ask of a 2x4.

bruce m graham III · #3 (**permalink**) 06-26-2008, 01:59 PM

David Banks · #4 (**permalink**) 06-26-2008, 02:12 PM

http://i-joist.org/pdf/Asd_ij.pdf

Looks like they can be used as rafters. Should not be cut like near the B-vent. PDF says to consult with specific manufacturer for design installation specs.
2.2 Common uses.
6.8 Sloped bearing conditions.

Insulation should be 1 inch from B-vent.

Just found this interesting. No solid sawn conventional lumber should be used as Rim Joist with I joist.
http://i-joist.org/solid%20sawn%20rim.pdf

And another detail pages 18-19. Those mid range supports look suspect. If you looked for or found specific manufacturer you could do a google search for install specs.
http://www.ilevel.com/literature/TJ-4500.pdf

Scott Patterson · #5 (**permalink**) 06-26-2008, 04:07 PM

Yes you can use them for rafters, they have to be installed per the manufacturers guidelines. The diagram provided by Bruce is an example of special requirements.

The one that is cut might be a problem. The manufacturer would need to design the repair. It is possible that is the repair that was designed but you would need to see the documentation to say that.

Randy Clayton · #6 (**permalink**) 06-26-2008, 07:14 PM

Using them as rafters is ok but that picture #2 the purlin braces or struts do not appear properly installed. And the cut out along the b-vent is a question?

Brandon Whitmore · #7 (**permalink**) 06-26-2008, 08:50 PM

The APA website has some pretty good info. regarding this.

Publications Featuring I-Joists | APA - The Engineered Wood Association

Christopher Kovac · #8 (**permalink**) 06-27-2008, 05:53 AM

As always thanks for the great feedback and links, it really helps me finalize my recommendations.

Chris

Markus Keller · #9 (**permalink**) 06-27-2008, 06:14 AM

That's the kind of work that makes me very suspicious of who was working and running the job.
I looked into using I-joist on a job once and it was cost prohibitive compared to a truss system on the labor side. I have yet to see anyone around here using them on a typical load roof set-up.
From the picture it looks like they would have needed to move the B-vent over about an inch to not cut the I-joist. So much for a project management or thinking carpenters.

Jim Robinson · #10 (**permalink**) 06-27-2008, 04:50 PM

It's not too unusual to see that here, especially for the vaulted ceiling application. To get R-38, you need the depth of a TJI or similar instead of the traditional 2x12. The other advice on cuts, stiffener blocks, etc is all good. The manufacturer's instructions are what you'll need to reference.

Jerry Peck · #11 (**permalink**) 06-27-2008, 05:08 PM

Quote:

Originally Posted by Markus Keller

From the picture it looks like they would have needed to move the B-vent over about an inch to not cut the I-joist. So much for a project management or thinking carpenters.

Markus,

I suspect the I-joist was there first.

That would mean thinking persons installing the B vent.

But ... wait ... we did not have any elbows on the truck and we get paid piece work, if it is not done, we don't get paid, so ... we did it, then got paid. The aftermath is *your* problem.

Richard Franklin · #12 (**permalink**) 07-11-2008, 03:49 AM

I find this interesting. Having worked for Trus-Joist Corporation (inventer of the I-Joist) in its wee days back int he late 1960's and early 70's I find this interesting. After I developed JMD and could no longer design, my job with TJ was to go around and help Architects and Engineers design floor and roof systems. Some of the details used today are those that I developed back in those days.

1st. the Cutting of the top and bottom chords on the truss is a no no.
In this case there is no truss. It needs to be replaced by nesting another TJI next it. Connecting the two together with web stiffeners. This needs to be engineered by the Engineer of Record and the Manufacturer. This is a construction defect.

2nd. You need to check for the bearing support. There has to be full bearing support on the bottom of the wall and the top. Also a metal connector used on the bottom of the wall and a connector and strap used on the top. To get a full bearing support we would design and used a cant strip plate cut to the pitch of the roof which was placed on the top plate.

3rd. Shear panels at both the top and bottom bearing.

4th. Metal 'X' bridging continues through the span.

5th. Care has to be used in the number of holes cut into the joist. NO cutting into the chords. Depending on the span length, you can larger holes as you get closer to the middle of the joist. Check the table. And only one hole. I once had one where the HVAC people could not get the flex duct to work. 18 inch in a 14 inch TJI, that they cut ovals into the joist.

6th. TJI's can be used as any framing material. Just make sure you follow the details from APA or the manufacturer. And make sure the builder follows them as well. The 3 "B's". "Bearing, Bridging and Brackets (connectors)."