I am working on a new house and am concerned with the wall
sheathing/subfloor/roof sheathing right now. Many new houses seem to be
totally sheathed in 1/2 inch OSB. I can buy 1/2 inch CDX plywood for
$1/sheet more. Is it any better, or is OSB a better product for this.
The subfloors will be 3/4 inch plywood so that I can nail 3/4 inch oak
floors to it. What about the roof. I often see roofs that sag between
the trusses over time. Is 1/2 OSB adequate or should I use 1/2 or 5/8
OSB is cheap, which is why builders use it. OSB is OK as sheathing, but as
roof decking it has a tendency to 'telegraph' through shingles in this heat
along the Gulf Coast.
I much prefer CDX, in any case. I always spec 1/2" CDX with a radiant
barrier and taped joints for sheathing, and 1/2" CDX Tech-Shield for roof
decking. For plywood subflooring I generally spec 1 1/8" CDX T&G.
Yupper. I just put 7/16 OSB on my roof as part of a build up process. The
original deck was 3/4 T/G plywood and we built up over top of that. The OSB
spans 2x4's which are 24" on center and I used clips between each 2x4. The
result is a deck that is almost as rigid as the original deck. The very
slight difference between the two is not worth mentioning. Where I live the
snow loads are very heavy. Very heavy. Houses are, and have been for quite
some time, constructed with 7/16 OSB on 2 foot spans, with no problems - as
long as you use the clips.
Until it gets wet a few times. Also, think of how each will behave in
a fire; all that extra glue in OSB is a substantial additional fuel load.
A OSB and truss roof is an unsafe location for a firefighting crew, so
we won't go on one if the roof is badly involved. This limits
vertical ventilation, which limits fire attack options, which limits how
well the fire can be stopped before gutting the house.
For a buck a sheet, you might buy 'em 5 minutes longer on the roof, to make
the firefighting that much more effective. Better yet, lose the trusses
and use real rafters. Even without considering the World Trade Center,
truss construction kills more firefighters than anything else.
Looks like some companies are trying to change that. With the available
technology, I'd think it would be mandatory to have some sort of retardant
either on or in it.
It this because of the flamability of the roof, or the loss of sthrength
from being wet?
Buck a sheet? That explains a lot. Buck a sheet can add 50 bucks to the
cost of a $300,000 house.
If I ever build a new house, the walls won't be wood. I'd use insulating
concrete forms (ICFs) and have 6" of concrete and more +R40 performance
Speaking as a contractor, do a simple test. Leave a sheet of OSB and a
sheet of CDX outside. for a couple of weeks. The decision will be obvious.
OSB will turn to mush. Now, onto the roof. You can use 1/2" material but
you will see the sags. I ALWAYS use 5/8" cdx on the roof. I ALWAYS use
1/2" cdx on the sidewalls. However, I do use Weyhrhouser brand 7/8" t&g
Edgegold (kinda looks like OSB but is a better product) for the subfloor.
Make sure to use construction adhesive for the subfloor no matter what
product you use and leave an 1/8" gap for shrinkage and swellage (new word).
SH - From the North Oregon Coastal Region
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.