Have you ever met an EE who didn't _think_ he understood every
other engineering discipline?
Sure they will, if he sisters enough of them (like built up to about 4"
thick) alongside all of the existing 2x4 members in the present
That certainly wouldn't be my first choice about how to do it...
Notice how the OP didn't mention the connections, gussets nor anything
else? If he bolted 1/2" by 3 1/2" steel plate to the existing truss
members it wouldn't triple the strength of the trusses. The weak
point, the limiting factor, is the existing gang nail plates.
Yes but I assumed he wasn't so ignorant as to assume that
a series of unconnected segments would add strength to the
He may be thinking about adding them to make a T- section,
rather than sistering them. That might do what he wants,
provided he joins them all properly where all the pieces
intersect but it would be a major pain compares to just
sistering them. Sistering them with 2x6 (properly connected
with nailers might triple the strength too, keeping in mind
that by nailing the 2x6 to the existing 2x4 (again with
proper connections at the joints) they become
one truss, not two trusses sharing the
load unequally due to unequal stiffness.
I am with you on giving people the benefit of the doubt...on matters
that won't cause big problems. On those matters I prefer to err on the
side of caution.
The operative phrase being "proper connections at the joints". Those
are the areas where someone will run into trouble.
length 2x6s into the attic? How would you cut them to allow fitting
around the ridge and plates?
In any event, the OP will do what he wants based on what information he
has and what he believes to be the important factors. He will then
make up his mind that he either did or did not do the right thing. If
the thing fails, well, that's clear, if the thing doesn't fail, he'll
believe that he did the right thing - whether he did or not. That's
simply human nature.
IF you understand the principles around which beams are designed
it is trivial to make a homemade beam that is better than
a pre-manufactured I-beam. Instead of an OSB web, join
the flanges with plywood sides instead of a 2x3 flange, use a
2x4, instead of #2 SPF, use #1 hem-fir. Viola, a better beam.
It will cost you more in both materials and labor, but it will be
To be cost-competative the manufacturers
have to make their product as cheaply as possible while still (barely)
meeting code. They are so good at this, that the material cost of
homemade beams will almost certainly exceed the cost of pre-
manufactured beams of the same stiffness.
OTOH if you do not understand the relevant principles it is easy to
design beams that are heavier and not as stiff as the pre-manufactured
For the existing roof, it would be trivial to double the strength and
stiffness by sistering a new truss next to each old one, exactly
duplicating the dimensions and materials of the old. This is
where there may be an advantage to the do-it-yourself
approach as it will not be necessary to take the whole roof
down and rebuild it from scratch.
If that is not good enough, then probably the thing to do is to replace
the old trusses with new, designed to carry the new load. Here the
problem will not be with the roof, which OP is going to redo anyhow,
but the interior ceiling which is likely to be slung from joists that
are integral to the trusses.
Either way, the local building codes will probably require a
PE to sign off on the design. Pre-fab trusses will usually be
pre-approved having already been designed by an engineer, as
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