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-   -   Tyvek For Crawlspace? (https://boards.straightdope.com/sdmb/showthread.php?t=537422)

Duckster 10-26-2009 12:27 PM

Tyvek For Crawlspace?
 
I was recently in the crawlspace under my house. The insulation in between the joists in the floor is held in place with string stapled tightly across the joists. However, some of the insulation has settled a bit and a few strings are broken. I plan to add more insulation.

Instead of using the same approach, is there any problem if i covered the bottom of all the joists with Tyvek housewrap? After all, it's wrapped around the exterior walls of the house.

(FYI - The ground in the crawlspace is already covered with a thick ply plastic sheeting to meet radon protection.)

Thoughts?

Gus Gusterson 10-26-2009 12:39 PM

The housewrap won't prevent the insulation from settling. The usual way to support insulation on the underside of a ceiling or crawlspace is to use metal rods sprung between the joists to hold the insulation in place. They sell them in the insulation aisle.

crazyjoe 10-26-2009 02:03 PM

When I did this in my crawlspace I used foam board insulation sheets. I nailed them to the joists to keep the insulation in there.

Hakuna Matata 10-26-2009 02:14 PM

My gut feeling is that you shouldn't do this. Tyvek is lapped vertically so that water hits it and drops. But it isn't water resistant if you have water standing on it, it is permeable I believe.

So if you put it in a crawl space (which will be damp) it could allow water to penetrate in one direction and hold it for awhile wetting the insulation.

In addition insulation typically is vented and the Tyvek might make prevent this venting which could cause moisture to occur above the insulation, which then will cause issues.

Now I have never seen it done with Tyvek, so it might be okay, but my gut tells me this is not a good use for this material. You might browse their home page to see if they have anything to say about it.

Duckster 10-26-2009 08:30 PM

Quote:

Originally Posted by Gus Gusterson (Post 11704779)
The housewrap won't prevent the insulation from settling. The usual way to support insulation on the underside of a ceiling or crawlspace is to use metal rods sprung between the joists to hold the insulation in place. They sell them in the insulation aisle.

As it stands now, the string method isn't working. Metal rods probably will not either. I will look into them, though. Anyone can be wrong.
Quote:

Originally Posted by crazyjoe (Post 11705173)
When I did this in my crawlspace I used foam board insulation sheets. I nailed them to the joists to keep the insulation in there.

I thought of that and dismissed it immediately. The manhole into the crawlspace isn't big enough, nor the depth into the crawlspace sufficient enough.
Quote:

Originally Posted by Hakuna Matata (Post 11705231)
My gut feeling is that you shouldn't do this. Tyvek is lapped vertically so that water hits it and drops. But it isn't water resistant if you have water standing on it, it is permeable I believe.

So if you put it in a crawl space (which will be damp) it could allow water to penetrate in one direction and hold it for awhile wetting the insulation.

In addition insulation typically is vented and the Tyvek might make prevent this venting which could cause moisture to occur above the insulation, which then will cause issues.

Now I have never seen it done with Tyvek, so it might be okay, but my gut tells me this is not a good use for this material. You might browse their home page to see if they have anything to say about it.

My crawlspace is bone dry. If there was anything damp down there I would be having really bad problems. Actually insulation is not vented. Tyvek is normally wrapped around building to stop active moisture. It does allow water vapor to pass through.

Thanks to all.

ftg 10-27-2009 09:41 AM

Exposed foam is a major fire hazard and is most likely against code in your area. It would need to be covered with a suitable fire-resistant material. Like 5/8" drywall.

Don't try to skirt this and hope to not get caught. It's against code for a really good reason. Insurance companies love to use these sort of things as an excuse to not pay out in case of a fire.

Just go down to Home Depot and get the insulation support wires. Trivial to install.

NurseCarmen 10-27-2009 10:11 AM

Tyvek is expensive. Maybe you could use a roll of one of those mesh fabric temporary fences. They are breathable, but the holes aren't so large that the insulation can fall through. And it would be much cheaper.

crazyjoe 10-27-2009 10:30 AM

Quote:

Originally Posted by ftg (Post 11708234)
Exposed foam is a major fire hazard and is most likely against code in your area. It would need to be covered with a suitable fire-resistant material. Like 5/8" drywall.

Oh shit. Does that include the pink foam?

I forgot that I was able to install this when we remodelled the room the crawlspace was under. I simply cut a hole in the floor wide enough to get the foamboard through. I have no access to this crawlspace otherwise, and the room is kinda finished now....

Did I say "shit" yet?

Zulema 10-27-2009 10:32 AM

Just to be safe with the moisture issue you could use Typar, which is landscape fabric that you can get on a huge roll but can be stapled. It isn't waterproof and is relatively cheap.

johnpost 10-27-2009 10:38 AM

tyvek is an infiltration barrier, stops rain and major air flow though allows vapor to pass. though under siding there is a fair amount of air flow and solar heat to allow the moisture to get out.

in a crawl space it may just trap moisture against the flooring because of low air flow and heating from sun.

it is good to ventilate crawl space to keep dry.

use joist wide strips (so individual sections can be removed of maintenance) of chicken wire or plastic mesh (shaped like chicken wire) to support insulation.

Gus Gusterson 10-27-2009 10:44 AM

Quote:

Originally Posted by Duckster (Post 11706734)
As it stands now, the string method isn't working. Metal rods probably will not either. I will look into them, though. Anyone can be wrong.

The string doesn't work because it doesn't push the insulation upward. The metal roads do because they are sprung (they are slightly longer than the space between the joists so they have to be bent a bit to fit and thus they are always under tension).

It baffles me that you so quickly dismissed the tried and true method of solving the problem you face in favor of a method that doesn't do much to hold the insulation in place, has potential water problems, and isn't what the product you're using was intended for.


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