Instead of searching for very long dimensional lumber, why not make some
Its common practice to use 2x3 or so for the top and bottom plate of the
joist sandwiching 1/2" osb in an I-Beam configuration.
XXXXX <---- 2x3 Top Plate
X <----- 1/2" OSB Sized to carry load needed.
XXXXX <----- 2x3 Bottom Plate
Just dado the 2x3 to take the OSB. Makes for a very strong joist and
inexpensive joist. If you are willing to build them. Or buy them for that
All depends on what type of load is being carried above the ceiling.
Just one possibility
A 21' 2x6" isn't going to hold much load without a fair amount of
deflection, so it should be "hung" from the rafters by nailing a vertical
2x4 from joist to rafter. You also can use 2- 12' 2"x6"s butt jointed with
another 2x6 nailed to overlap the joint to make the 21' joist. It is also
easier to install. You can also add a "rat run" as we call it around here.
Run a 2x4 or 6 horizontal across the joists at the center of the span. To
the 2x4 nail a 2x6 or 2x8 vertically to the 2x4 to form a right angle. Now,
by nailing the rafters to the rat run, you space them on the proper centers,
you level the ceiling and you add more strength by tying the rafters
together and the 2x6 or 2x8 acts somewhat as a support beam.
When I was building houses, I occasionally needed lumber to 26' or so. My
lumber supplier had to order it and it took a few days, but it was
I sisterd my sagging rafters with the box beam approach. I had to span 20
feet and had a clearance of 10" from top plate to roofing. A heck of a lot
of nails, but them things are dead flat and incredibly strong!
for one site that has joist span tables.
Spanning nearly 21' is asking too much of a 2x6, and you can't add any
load, even a ceiling (assuming drywall). You probably should look
into getting an LVL beam (the wood I-Joists required here are nearlt
12" deep also). You could get away with something 7-1/4" deep, if
you're not planning on storage in addition to the ceiling. See
Also see http://www.apawood.org /
On Sun, 17 Aug 2003 21:04:45 GMT, charlie groh
The inspectors around here would require "engineering" if you tried to hang
anything from the "collar ties". These are structurally in tension and could be
replaced with steel cable in the design. The purpose is to prevent the walls
from bowing out when the lateral load of the rafters is presented.
When you start adding members to carry vertical loads you are creating a truss.
That requires load assessments (AKA engineering).
Perhaps you should consult with the building department to see what they are
going to expect. They may accept diagonal bracing with a bunch of nails or they
may want to see how you determined what to use.
I went down to building code today. I learned a lot, and between us we worked out
a plan that they would accept. However, I have not filed it as yet.
What they proposed is to take #1 or better 2x6es on 16" centers, or #2 2x6, 12"
Looking through a book I have, that appears to be on the very edge of the span
for absolute no load attics. Also, it does nothing to correct the perceptable
exists in the collar ties that are there. I also discussed the midspan support
with them, such as tying to the rafers above (would bow the roof), and placing a
traverse to the collar ties and effectively halving the span (needs engineering
Ive been thinking about it all day, and I am not happy with this solution. A
with an identical house changed the 48" OC 2x6es to 24" OC 2x6es (by adding every
other one), but also arranged a beam across the garage as well. I would really
do this as well, and am thinking I might have to involve an engineer at this
point. Its my
house, I want it solid, I don't like the idea of being at the edge of what the
and I would like to reduce the sag from front to back just as I wanted to reduce
the sag between joists. With the beam, the 21' span is effectively halved, and
fits the span table well. Ideally, I would like to mount the new beam above the
the reason being the garage is to be a shop, and I like to have maximum
Whats the best way to get a plan together that building permits will sign off on
Thanks in advance.
Scott, go back to the lumber yard and ask for 22' engineered beams, they are
wafer board between two 2X2s
can span up to 24 feet with no sag. They are light and easy to work with and
very strong. Also meet codes. Cost about the same as regular 2bys.
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