Who's our?

Truss engineer???

When I was working....

Worked for TrusJoist, so only open web trusses, nothing plated. Still have a few friends there, though.

Ok Rennie that means tag your it.
What we got is a stair well going up through the trusses 42" wide. This messes up layout. The truss company has build two beam trusses one for each side of the stair well. Than they had us building a ladder between the truss at the top cord to carry the roof over the well.
What we would rather do in the future is put in the two beam trusses. Than put in a truss on the 2 foot center and cut the bottom cord off for the well and head it off to the two beam trusses.
Is this doable? If not why?
Thanks Chuck

Chuck,

I'm not an engineer, but I've worked with one on special problems and special builds for the last 9 years. I've seen this done several times (or something similar). I've worked with building/repairing roof trusses, modifying trusses, beam trusses, floor trusses (open web joists), and TJI's.

The only reason I can see that they don't want to do this is the added cost of the build, engineering change, and approval, for carrying a short beam, or double 2x6/8 etc depending on span of the short truss and adjacent trusses.

You should be able to give dimensions and idea to the engineer and should be no problem. 2 double hangers for the header and basically a modified jack truss and your in business! Just get the engineer to build the bottom cord the way you want it to save on all the blocking for sheet rock etc if that's a concern. Some of the guys I've dealt with just seem to forget that the truss does a little more than just support a roof load (like making it easier to have the sheetrock look flat on the transition of 30' trusses,built with camber, to a girder, built with no camber, to short trusses on a popout with 1" of camber!!) Well, it looked good on the computer I'm sure!

If you lived in washington I could give you the name of an excelent engineer...

Thanks Brian,
The problems with the design we keep getting are
1 The blocking in that ladder (42" wide 2' OC ) Blocks the air flow for the ridge vent in that area.
2 they have the same blocking detail for the floor which means you have to put that blocking in than block it the other way to have nailing for the strapping on the ceiling below.
3 You have to lay the blocking out on both the floor and the rook so the plywood lands on the edge seams. (Not really a problem just an unnecessary pain)
Where as if we could head that bottom cord off to the beam trusses on each end all the rest of the parts for all the rest of the stuff that has to be hooked to them would be in place and on plane.
As for cost the one extra truss (About $200,00 for this job) would have saved 20 peaces of 2x8x42" and the time to cut and install them. 40 joist hangers and the time to install them. So the actual cost would be just about a wash.
But the time spent not having to mess with all the blocks would be priceless.

I understand what you want to do and it can be done but ONLY before the trusses are ordered and built. The trusses have been designed with a constant load factor built in for the area that will be ladder framed. In essence, they should have beefed up the design for the length of the ladder. By installing a header and placing an additional truss between the two beam trusses you are introducing a very large point load where the header attaches. This culd lead to failure of one, or both, of the beam trusses.

Such design considerations must be taken care of prior to designing the trusses. Now, if they are still in the planning stages, you're in luck!

If you are stuck with the ladder framing and are worried about air circulation there are alternatives. Depending on the depth of the ladder members you could use small plated trusses or TJI's with holes cut into the web to facilitate ventilation.

Does that help?

Yes it does Rennie
That makes 2 people that have told me I can get them the way I want them.
Now if this truss shop does not want to make them how I want them made It time to find another truss suppler.

There are other design considerations - span, depth of truss, loading - all play a part in the design. In most cases it is easier to to accommodate the ladder framing rather than a large point load out in the middle of a truss. It still might not be possible without adding a lot of cost to the job. Besides the additional (short) truss, they might have to design much beefier trusses for either side of the stairwell. Even so, what you want might not work from an engineering standpoint. Just a word of caution.

Rennie is deff right in his considerations. It would be kinda neat to see the plan. Don't know if you can, but snap a pic from the diff pages from ground floor to the trusses. It would be fun to see what your up against.