(No, this isn't a troll...)
Can anyone give me a hint as to how much load a very simply built howe
truss can take?
The relevant dimessions are something like this (standard pine
Bottom and top chords: double 2x6s
Vertical and diagonal webbing members: single 2x4s
Height: anything from 0 to 6ft is doable
Span: 10ft plus 1ft bearing surface on each end
If it were 6' high, the webbing would be three vertical members (each
end, and center), and two diagonal members at 45deg.
Could this hold about 2 tons dead load, evenly distributed across the
span? Or, could it hold as much as, say, just a simple pair of 2x10s.
Why you ask? Long story, but if you are curious, I'll tell you...
I am doing some work on a 15'x20' garage. It has a walk-in basement
made of (crumbling) block walls, and an upper story stick framed, with
a simple truss roof spanning the 15 ft between the side walls. The
upper floor is thick planks over 2x8 (actual size) rough cut lumber.
The side block walls each have 2 smallish windows (3'x2') with a poured
concrete header. I want to temporarily enlarge one of the window
openings to gain access for some work to be done in the basement. The
opening will be 10' wide and about 3' high, going right up to the floor
For a few weeks, while the work is going on, I need to support the
floor joists over this 10' span, and the wall above, and the roof
trusses and roof. There is a center beam for the floor, but even
neglecting that I have at most (10 linear feet of) approx 8' wide
floor, 8' of roof and trusses, and 7' high wood-framed wall. Live load
will be small, as the building will be basically empty and unoccupied.
Looks like doubled 12ft 2x12s would hold this fine, though I need to
double check at the lumber store. BUT, it would be much better if I can
put the beam ABOVE the floor so I don't loose 10 inches or more from my
cut opening. I could just rest the beams on the floor above, just
inside the wall, then use joist hangers right through the floor to
suspend the floor joists below the beam. And I could fasten it to the
wall studs and bottom plate too, for good measure. And, of course, put
a column on either side of the opening below, to hold the beam. But it
occured to me that I have a the full height of the upstairs in which to
build this beam, so why not make a simple howe truss, if it would be
stronger and less expensive. Or I have plenty of plywood, I could use a
doubled 2x6 on the bottom, and a doubled 2x6 on the top, and solid
pieces of plywood (say, two pieces 8' long and 2' high) as the webbing
sandwiched between them.
Don't bother telling me to get an engineer -- this is a temporary
support for an empty structure, no one will be in or under the
building, and if the howe truss idea is crazy I will just go back to
using a simple beam instead, even though it costs more... $60+ versus
some stock lumber I already have and can reuse later.