Bottom Chord of Roof Truss Cut 1

[Matt_02]

Hi all,

I am trying to retrofit and reinforce an existing roof truss that had a portion of its bottom chord cut for attic stairs. I am analyzing this truss in RISA and am having some issues with getting a repair to work. I have modeled trusses in RISA and by hand before, so I am confident that my model is done correctly. What I do need help with is some possible repair options. I have tried adding in some additional web members and reinforcing what is currently there and I expected there to be issues because we are basically changing the load path of the truss, but I was note expecting the members and joints to be this overstressed. See the sketch below and you will see the truss that I am dealing with. It is a wood roof truss made of 2x4 members @ 2'-0" o/c with a plywood roof deck, gyp board/drywall along the entire bottom chord, and some plywood in the top of the bottom chord for some storage. Any help is much appreciated. Thank you in advance!

 

[phamENG]

This is a good place to start:

MiTek Roof Truss Repair Details

 

[Matt_02]

Thanks for the reference phamENG. To clarify, they would like to keep the attic stairs as is and provide some 2x reinforcing to the truss. Now I wasn't able to come up with anything that was reasonable and worked, so that's why I reached out here. The truss also spans from bearing wall to bearing wall and does not have a continuous bearing condition similar to a lot of the MiTek Truss Repairs shown.

 

[jayrod12]

So they can't re-instate the bottom chord back to original? That certainly complicates things. How much clear space above the current bottom chord elevation do they need to keep?

 

[Matt_02]

Yea I know, that's the issues I am having. I would say about 5' to 6' of clearance would be preferred on their end. However, I am at the point where I might just tell them to reinstate the bottom chord with a lap and fasteners, remove the stairs, make them smaller and fit them in between (2) trusses. This is a nightmare trying to come up with a solution, I am not sure if there is anything "easy" fix for this.

 

[Pmtottawa]

Can the stairs be relocated so they fit between existing trusses.
This way you can reinstate the bottom chord.
Aside that thhe truss will need to be re analyzed with a raised bottom chord in that area and plywood gusset plates for connectors

 

[phamENG]

Sorry. Missed the part that it has to stay like this. To that I say: good luck. If they wanted stairs and an attic, they shouldn't have built/bought a house with trusses. Not all problems have a favorable solution. I find modifying trusses usually fall into that category.

 

[jayrod12]

How tall is the truss? This is likely not possible but if we can see the proportions, perhaps we might be able to think outside the box. The problem with outside the box solutions, is they're generally much more expensive.

If they want this cheap, then relocating the stair and reconstituting the bottom chord is the cheapest proposal.

 

[Matt_02]

Yea, I think relocating the stair is the best option, it seems like everyone in this thread agrees with that. As far as other options, I think you are right jayrod, I wasn't coming up with anything "reasonable" or cost effective. I thought about sheathing the entire truss (I know, crazy, but it would work) or some reinforcing scheme with additional web members, but it is really tight up there in the attic and I dont think they would be able to get long pieces of wood or sheets of plywood/sheathing to do either. So were going to have them remove the stair and relocate them in between the truss that will have lapped/scabbed/reinforced bottom chords with a large amount of screws.

Anyway, thanks everyone for the help and recommendations, I do appreciate it!

Matt

 

[SJBombero]

What if the two adjacent trusses were sheathed or otherwise strengthened and used to support the cut truss with cross beams?

 

[KootK]

This is conceptually simlar to pvchabot's solution. One might also do something similar on the bottom chord to bridge the opening there but I like this better.