Floor joist insulation support
I have been considering for quite a while on what to use to go under my floor joists to support the insulation and seal it off from rodents and insects, yet not be a vapor barrier or retain water if there are any water leaks from plumbing.
The house rests on (36) 6″x6″x32″ red heart cedar posts which in turn rest on 10″ dia. x 3″ high concrete piers. The posts are crossed braced both ways and the crawl space will remain open, hence the need to insulate between the floor joists. The joists are 2″x8″ and the insulation will be batts of Roxul.
Well, I was able to get a good buy on 7/16″ osb for less than $5/sheet. (The cheapest price I could find for 1/4″ hardware cloth was twice the price of the osb per square foot, and that was just for 24 ga.)
So, not wanting to install the osb sheets tightly together so as to create a vapor barrier, my current plan is to:
Install the osb leaving about a 1/2″ gap between the rows of sheets and then staple 3″ wide strips of screen and hardware cloth over the gaps.
By doing this, I hope to not only prevent insect and rodent intrusion, but also to prevent a vapor barrier, yet minimize air movement through the insulation from the wind blowing under the house.
Any comments or suggestions on this method or on perhaps a better way to utilize the osb for this purpose will be much appreciated.
Thanks,
Arky
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Replies
Why not plastic bug screen, like used on tents? Or steel, otherwise.
"Why not plastic bug screen, like used on tents? Or steel, otherwise."
John, do you mean plastic screen in lieu of the osb or as a covering over the osb gaps ?
Regardless of which, I'm sure rodents would have a field day with plastic.
As for the steel suggestion, that got me to thinking; that just may be a good method, especially since I already have quite a few 26" x 8' and 26" x 10' panels of corrugated galvanized metal that I used to cover my lumber while it was drying. Perhaps that would work; and maybe drill a few small holes in them to make them more permeable.
I haven't taken delivery on the osb yet, so now I'll count the steel panels that I have and maybe consider using them and canceling the osb order.
Thanks.
Jim,
Use the OSB and don't worry. There will be no vapor transmission issues with the OSB -- and if you have a plumbing leak, you'll have a mess and a repair job no matter what you use.
Martin,
Are you saying that using the osb, that I don't need to worry about leaving a gap and covering it with screen and hardware cloth ?
And with the steel panels, what would be the downside of using them instead?
I already have most, if not all, of the steel that I would need and using the steel would save me about $200.
Jim,
Just as you can sheathe the outside of a wall with OSB, or the outside of a roof assembly, you can also use OSB to sheathe the underside of floor joists. Why not?
The problem with steel panels is that it's harder to get an air barrier than with OSB. Steel panels are likely to leak air at the seams, whereas the OSB is easier to caulk or tape.
Sheathing the underside of the floor joists is pretty common in some villages here. They are built on the tundra and are all on piles. The sheathing is installed tightly.
Just make sure that the insulation makes contact with the top and bottom sheathing, like in a wall...
Here they usually install 2" of EPS directly to the floor joists and then install the sheathing...
"Are you saying that using the osb, that I don't need to worry about leaving a gap and covering it with screen and hardware cloth ?"
I believe that what Martin is saying that not only do you not NEED a screened gap, you should strenuously seek to avoid any such air path. Your floor should be air-sealed, not air-vented.
James Morgan,
Exactly right.