I just moved into a relatively new (4 years old) townhome. The attic has a
small area (about 15 sq ft) that has been decked over the joists with 3/4"
particle board for extra storage.
I have several questions:
1. If I want to deck the rest of the attic for storage, is 3/4" particle
board the way to go?
2. How can I know the attic will support the extra weight of the decking
plus the boxes/etc. to be stored on top of it?
Regular joists or trusses? Size? Regular joists can take more weight than
a truss that is designed to take the roof weight, but not floor weight.
If joists, then particle board, plywood, other cheap material is OK. Just a
couple of nails to keep it from moving is OK.
Older houses used joist for both the floors and the attic. Floor joists
are usually 2 x 8, 2 x 10, etc, that run across the room to support the
A truss is usually made from 2 x 4s, in a triangular unit of both the roof
support and ceiling support for the room below it. . It will have cross
bracing and a sort of web design. Very strong, they can support a lot of
weight from a roof, but are not designed to be used as a floor. Couple of
boxes of curtains, OK, but not for real hefty storage, like you gold bar
See a truss here http://www.cwc.ca/products/trusses/gable_system.php
No, it isn't for storage- it is to give a place to get in and out of the
access hole without stepping through the ceiling. 15 Sq. Feet is 3x5, not
counting the access hole. 3/4 particle board is lousy decking material.
Heavy, fractures with no warning, soaks up water like a sponge, etc. Builder
used that because they had scraps laying around. Use 1x pine or 1/2"
plywood- the cheap stuff is often on sale. You'll probably need to rip into
18" or 24" strips to get it up the access hole. Don't nail it down hard- 4
or 6 roofing nails per board is plenty, and makes it easier to pull up when,
not if, you need to get to wiring underneath. <Always> put the decking
joints over a joist. Forget about decking if you have insulation higher than
the joists- it'll cost you big time on your heat bill, from compressed
insulation. Forget about decking if the joists are smaller than 2x8- you
will get nail pops and cracks on the ceiling below, from flexing. If you
have trusses (attic looks like a forest, with lots of vertical members in a
row), forget about more than a stripe down the middle to store empty boxes
and Christmas decorations, and similar basically weightless stuff. Truss
attics are not rated for heavy storage. They might hold, they might not, and
no way to tell without an engineering survey.
Although wouldn't the flexing be even more if one goes around the
attic just stepping on the joists. A piece of floor spreads his
weight ovef more than one joist. I had a lot to do up there when I
first got the house. Running electrical, phone, burglar alarm wires,
tv cable. Even putting in insulation requires one to move around. I
put some pieces in the middle and used 2 or 3 other 16"x8' pieces,
which I moved around, to reach outlying areas of my attic, sometimes
lying on my belly. I couldn't lie on my belly on tthe joists alone.
And yes, one phone wire failed, so I have to move the plywood.
I agree that particle board will just break some day. Even 3/8"
plywood, which is not enough for my weight so I have to put my feet
above a jooist, one piece cracked once, but only one layer, and it
still held. Later when I got more plywood, or T-111, I put a second
layer, so in that area I can stand anywhere.
Trusses are really designed to hold nothing more than the ceiling on
the bottom chords, Something like 2 PSF. They will perform better than
that because of walls that are not load bearing on the plan but still
will transfer load.
Try to do your "storing" on decking that is over the walls below.
DO NOT nail the decking, use deck or drywall screws. You can get them
back out if you have to and you have a whole lot less chance of
cracking the drywall on the ceiling below.
That's an excessively general observation.
the type of truss that you generally find
in a ranch-style house with a low-slope roof,
is as described. But trusses are also
designed with "bonus space" in the attic
planned for, and those would be designed
for a minimum of 30 PSF live load.
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