I have two 2x10’s 18 feet long supported in the middle by one
2x4. Windows are now in these openings. I’d like to remove the
center 2x4 and replace the windows with a 16’x 7’ garage door.
What size (thickness) flitch plate would be needed to strengthen
the 2x10’s to support the open span? (Keeping within the 9¼”
height.) Single story, 4/12 roof, rafters are perpendicular to
header. No live load, just ceiling joist. Snow load for western
NY. Next wall parallel to header is 22’feet away.
If the 2x4 post supports its maximum load, say 1.5x3.5x1000 = 5250 pounds,
the beam might have an equivalent uniform load of 583 lb/ft, according to
You may be out of flitch territory and into something like a 10"x5" I-beam.
Hard to picture that. What's the load on the beam?
You might seek professional help...
The calculations to determine the individual tributary loads and the
resultant header load are pretty straightforward, the flitch plate
calculations a little more involved. I don't think you are going to
find anyone on a newsgroup (even a PE) who will be willing to give
you an absolute answer.
I'd suggest you contact a local engineer...
And a more complete deescription would be needed-any roof overhangs,
roof style, stick or truss framed roof, etc. To many thngs not
If I'm not mistaken, a ceiling live load has to be applied to any
space with a headroom greater than 42 inches. I would imagine snow
load is at least 50 PSF in western NY. The local authority would tell
you that value.
Again, call a local...
Well, if two 9' 2x10s have S = 3x9.25^2/6 = 42.8 in^3 and M = 1000S
= 42800 in-lb = W9x12/8, W = 3169 pounds, it looks like the 2x4 post
(it might support 5250 pounds) isn't the limiting factor. The uniform
load on an 18' beam would be 2x3169/18 = 352 pounds per foot.
The 1981 NAHB ap note says an 18' 2x10 Hem Fir beam with a 1/2"x9" plate
can support 215 lb/ft of uniform load, so a 0.5x352/215 = 0.82" plate
(or 2 246 pound 7/16" plates) might support 352 lb/ft. They suggest
1/2" bolts every 20" near the top and every 40" near the bottom and
something like 2 2x6 jack posts with 3/4" plywood plates at each end.
Please apply the usual disclaimers.
This was my initial approach, too.
When you calculate the bending stress (Sg.7) and deflection on the
glulams specified, (E=1.8E06) with a 352 pounds/foot load, Fb is
about 2000 psi (2400 psi allowed) but the deflection is about 0.9
inches, assuming a 16 foot span (garage door width).
If you use the 1/360th of span as the limit, and 16 foot unsupported
span you get about 210 pounds/foot.
I was looking at the other side of the building. It has an 18’
opening with the same room dimensions. Of course same roof load.
There are three 2x12’s supporting the same ceiling attic
space. What would be the psf on that span? It has been there
for 17 years. I’m leaning toward the 3 LVL’s (glulam) because
I can’t seem to get a straight answer on a flitch plate.
Seems costly 4.45 per beam, per foot.
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