Floor joist insulation

[Arky217]

I am still pondering what would be the best way to insulate my floor joists.
My house is in western Arkansas. It has a pier/post foundation and will have no skirting. In other words, the perimeter of the foundation will remain open. The bottom of the joists are about 3 to 4 feet above the ground and are on 19.2" centers.
The subfloor has not been installed on the joists yet; it will go down after the house is dried in.

Unless I come up with a better solution, my current plan is, after installing the subfloor, to glue/staple polypro mesh to the bottom of the joists. I would then dense pack blow cellulose between the joists through strategically cut slits in the mesh. Following that, I would cover the mesh with 1/4" hardware cloth for rodent protection and to support the cellulose.

Since the foundation is completely open and the location is on a high, dry ridge, I don't anticipate the underfloor moisture problems that are sometimes associated with an enclosed crawlspace.

One concern, however, is what would happen if there were a water leak in the house and some of the insulation were to become soaked. I have read that cellulose has good wicking properties and would wick excessive moisture to it's surface. I just don't know if it would do it fast enough to prevent the joists from starting to rot.
I do know from experience that fiberglass batts do not wick well, and tend to hold wetness for quite a length of time. For that, among other reasons, I have ruled out fiberglass batts. Besides, they seem to be about twice the price of the cellulose.

I've read that sprayed foam may be the best insulation, but for me it's too expensive and the house is probably too remotely located to get a spray rig in.

Hard foam sheets, sealed at the edges with cans of aerosol spray foam is another method, but again it's very expensive compared to the cellulose. Also, what would happen if water became trapped between the foam sheets and the subfloor ?

Anyone know of a reasonably priced solution that may be better than the cellulose ?

Thanks,
Arky

[John Raabe]

I think you are on the right track. The material you put on the bottom of the joists should be an air barrier but not a vapor barrier. I think cutting slits is a good idea to allow a plumbing leak to drain. This should not greatly increase heat robbing air movement inside the insulation.

[Grouseman]

Arky,

Check around a bunch you may only need 2" of spray foam under your subfloor.  That might be enough.  Don't discount the foam until you get several opinions/bids on it.  You can also buy the kits to do it yourself.  I did alot of checking into it recently because of a house I'm rebuilding.
If I build anything new it will have FOAM everywhere.


Grouseman

[JRR]

I like the idea of cellulose, though I have not use it yet.  You might try a hybrid concept.  Around the piping use a thick fiberglass wrap that is wrapped with poly film ... the idea is to have a sacrificial fiberglass wrap that will handle the liquid leaks ... the poly film will keep the water channelled to the ground and away from the cellulose.  Foam spray or foam boards might instead be used around the piping ... still film should be used to protect the cellulose.  Just a thought.

[Arky217]

I think you are on the right track. The material you put on the bottom of the joists should be an air barrier but not a vapor barrier. I think cutting slits is a good idea to allow a plumbing leak to drain. This should not greatly increase heat robbing air movement inside the insulation.

The polypro mesh is an open weave mesh designed to be glued or stapled onto joists, (or studs if you're doing walls), and is made just for this purpose. It lets you dense pack the cellulose by inserting the blow nozzle at several points instead of just one.
Supposedly, by dense packing, the cellulose will not settle enough to leave an air gap below the subfloor (or at the top of wall cavities).
The slits are just to insert the blowing hose to install the cellulose, maybe 2 to 4 per joist cavity.
It's like a screen, except made from polypro and should not inhibit the wicking ability of the cellulose.

As far as an air barrier, I've always read that one of the features of cellulose is it's ability at limiting air movement, at least when compared to fiberglass.
In fact, the cellulose manufacturer recommends against using a barrier of any kind with their product, whether it be in a floor, walls, or ceiling. They say barriers will tend to defeat the wicking properties of the cellulose and that air movement through the cellulose is negligible.

The plumbing is going to be a rather unorthodox installation.
There will be only one pipe (well insulated) coming up from an underground run to cistern tanks. This pipe will go to a pump (housed in a water containment box) in the utility room at one corner of the house. Then all piping to the bath and kitchen will run behind a protruding baseboard trim at the juncture of the joists and studs along one long wall. Everything that uses water will be along that wall and all fittings, etc. will be accessible by removing the trim.

[HoustonDave]

The plumbing is going to be a rather unorthodox installation.
There will be only one pipe (well insulated) coming up from an underground run to cistern tanks. This pipe will go to a pump (housed in a water containment box) in the utility room at one corner of the house. Then all piping to the bath and kitchen will run behind a protruding baseboard trim at the juncture of the joists and studs along one long wall. Everything that uses water will be along that wall and all fittings, etc. will be accessible by removing the trim.

Clever.  I will have to look at something like that.  The tradeoff between excellent insulation in the floor and access for plumbing has been on my mind as well.