"Calvin Henry-Cotnam" wrote in message
m...
) said...

I searched for "trusses" on Firefox and found a great site from some
Canadian truss company. I do understand what a truss is, but what I
don't understand is why a home built with "engineered trusses" should
have anything to do with whether I tear down a measly 6 or 7 feet of
(joist-perpendicular) wall.

Stick-built roofs tend to only span about the same distance as floor
joists and would require load-bearing interior walls to support them.

Engineered trusses tend to be designed to span from exterior wall to
exterior wall.

We built our own home and it is about 33' wide. The first and
second floors have 13.5', 9', and 9.5' spans (add the 6" per bearing
wall and each exterior wall you get 33'!). The roof trusses span the
WHOLE distance.

In fact, most of the partition walls are steel stud walls and were
installed after the roof was in place. Almost all of the second floor
was ONE large room when the roof was first finished! Talk about open
concept! ;-)

We did install one partition wall made of wood in the back half of the
house near the centre to provide support when the trusses were first
craned up there and placed on their sides, but it provides no bearing
support for the trusses once they were installed upright.


A lesson learned about trusses.
Even though they are designed to span the whole distance this is not
without some flex. This is what happened to me.

36' wide house, trusses designed to span the whole width. The problem was
caused by the fact that there ARE other support walls. The only spot in the
house where the trusses actually span the whole width of the house is about
4 ft wide, after about 8 years the ceiling there cracked. The crack was
repaired and it would actually stay closed for a year or two. Final fix was
made by fabricating a beam out of plywood and 2x8 to span from the trusses
that were suported by the interior walls across those that were not . These
trusses were fastened to the beam with metal straps and the crack repaired
for the last time.

Beam is in the attic and the trusses hang from it.

If the interior walls had been built so they did not support the trusses
there probably would never have been a problem.