I have space over a garage I'd like to convert to a 4th bedroom for an
upcoming child. The space is trussed and I was thinking of sistering
conventional framing beside all the trusses then cutting the obstrucing
portions of the trusses out. I don't want to tear down the entire
garage and throw away a perfectly good roof and siding and I don't want
to disrupt the neighborhood with a month's worth of torn up house. The
roof line is a simple A frame. I've built another addition on my house
after which the building inspector said I did a very good job so I'm
not a complete novice. The real question: is this idea crazy stupid
or has it been done before?
Just remember that the truss does two things, it holds the
roof deck up, and it keeps the walls that the roof rests on from
coming apart. As long as you replace BOTH those functions
(joists and rafters) you should be ok.
Is the garage door in the gable end, or one of the load bearing
walls? 'Cause if your new rafters rest on the wall with the
door in it, you'd best make sure that whatever beam goes across
there is sized to take half the floor.
(Scratching head) It sounds weird at first but I can see it working
with some problems.
Fastening the joists and rafters to the sill plates would be a problem
due to nailing room. I wouldn't trust just sistering to the bottom/top
chords of the trusses but it might work.
Your framing lumber would have to be much larger than the truss sizes.
Trusses are funny things. I strongly suggest you get a real structural
engineer to take a look at the situation and make a recommendation. You are
going to need to resize the structural units and make sure they are large
enough. With trusses it is not easy to judge since they are complex units
that relay on each other for strength.
This sounds like the perfect place to use the ole "Opportunity cost" in
other words, what will you give up, to gain something else.
Due to the structural uncertainty you may cause, the question of code as
to whether a bedroom above a garage is plausible, and the time it will
take to fiddle with what you have it may be WAY better to remove the
roof and get what you really need. I suspect the reduction in headaches
and I am sure it will take far less time to take down the roof and do it.
However, I'd check code first about a bedroom over a garage.
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