Expert: Dave Johnson - 8/12/2008

Question
QUESTION: I am buying a single floor 1979 built home that utilizes "site built" roof trusses.  All but a few in the living room have center span support from an interior wall that is directly over the center supporting beam in the basement. The site built trusses of that era don't have the reputation of todays engineered trusses according to my home inspector who, at one time, was a very successful builder.

In the living room there is a 10 foot span with no center support with an adjacent 12 ft span which has center span support from a half wall and spindles.

I would like to open all 22 ft and need some advice on sizing a beam for the 22 ft expanse with a center span column.  Built up sawn lumber would be easiest but  engineered lumber is an option.

There is no storage in the attic but living in Western Colorado we do have up to 18 in snow load occasionally.

Can you assist?

Regards,
Jim

ANSWER: Hi Jim,
There are a couple of ways you can go at this.
The beam you asked about will only be spanning 11 feet. (with the center support). I would use 2"x8" triple, with 1/2" plywood sandwiched between each.glued and well nailed or screwed.
Option 2:Go into the attic and add webbing to the existing "trusses"
making a "W" web. If this is already done, add to it and make sure everything is again, well nailed/screwed.
To add to this if you like, you could make a beam ABOVE the center
that is supported on either end and tie each bottom chord to it with
a Simpson tie. That would give you a clear span below with no beam or post.

I hope this is clear, if not, please mail me again...

Best of luck,

Dave

---------- FOLLOW-UP ----------

QUESTION: Dave,

I visited the Simpson website and got a little bewildered by the variety of ties.  Could you offer a suggestion as to which class of ties or specific ties I should look at to tie the trusses to a beam above them as you suggested in your third alternative.

Regards,
Jim

Answer
Oops, sorry Jim,
Use an "LTS" twist strap. There are a few sizes/weights but the light one is fine...use one on each joist (or bottom chord)
Dave

P.S. The 3rd option is good only if you are able to get the necessary lumber into the attic, scuttle hole/gable vent/etc.