Insulation (house) advice please - The Hull Truth

Tireless · 07-28-2007, 10:38 AM

I need some professional advice on installing batt insulation between the floor joists in my crawl space. Currently we have no insulation under the flooring in a section of our house. The crawl space is approximately 3 ft high and there is no chance the insulation would ever come in contact with water. The ground is covered by a thick mil plastic sheeting. I have not placed insulation down here because someone told me many years ago the potential for mold forming on the insulation could become a problem. A friend just built a new house and he was advised to put the insulation in that area. Can you builders set me straight on this question? Thanks in advance.

CThomps · 07-28-2007, 10:51 AM

Use spray foam instead. It'll seal your floor ALOT better than fiber glass batts. It'll cost more. Fiber glass batts would be well suited for a basement situation or a sealed crawlspace I would think but not necessarily an open crawlspace. The fiberglass won't rott but the paper tabs on either side holding it to you floor joists likely eventually will. You could pay someone to do the spray foam or buy it in kits online as you can afford it. Tiger Foam is the main brand I always see. It's like R-6 per inch.

Maybe if you put the fiber glass in place and then put some sheets of 1/4" luaun or 1/4" ply over it. You could pre cut strips of it to fit in your crawlspace access. That 1/4" stuff is super light weight and easy to bend and handle. 1/4" luan is a more moisture resistant ply which might be better suited for a crawlspace. I don't think i'd use the paper faced batts though. HD also sells JM "closed cell" fiber glass batt insulation. It's wrapped in thin plastic rather than paper.

CThomps · 07-28-2007, 11:06 AM

Forgot to add...the JM insulation has tabs on the sides like the paper covered stuff does. But the tabs are plastic. Likely your floor joists are on 16's to the close cell stuff would fit perfect. I'd look to find out what code calls for as far as crawl space insulation goes. And don't over insulate. It's kinda pointless. Maybe caulk around any point that might let air infiltrate or escape from the rooms above the crawl space. This will help to seal the rooms. That's often one of the most important things. A sealed room goes a long way for reducing heating/cooling costs.

sixpack324 · 07-28-2007, 11:46 AM

I don't know about your area, but here in Jersey, by code that crawl space floor needs to have plastic sheathing (like you described ) AND a concrete floor, commonly referred to as a 'Rat-Slab'........

This slab and plastic is primarily put in place to force any ground gasses, like Radon, to ventilate to atmosphere outside the footprint of the structure. Also, here in Jersey, the foundation, weater block or formed and poured, needs to be ventilated. There is a formula that gives a ventilation sq. inch to crawlspace sq. ft ratio.

With that in mind, we use unfaced insulation, with 2" strips of 1/2" plywood run across the bottom of the joists to keep it in place.

Keep in mind, that when using kraft-faced insulation, (paper-faced) the vapor barrier (paper) is supposed to face the conditioned space. In-short, the paper faces the room, not the outside. It says so in the print right on the vapor barrier (paper) on the insulation itself. Although it is common for contractors to install the insulation with the paper facing the crawlspace, it is an incorrect installation method. It is common because it is faster and easier to just staple the paper tab rather than install plywood strips to hold it in place.

Think about your walls.......Does the paper face inside the house or the outside?
So why would the floor be different?

The plastic encased insulation mentioned above is a quality product, but it's more expensive than kraft-faced or un-faced fiberglass insulation. I believe it's called 'Comfort-Therm'. It's alot easier to work with, especially in close quarters like a crawlspace since the plastic encasement controls 95% of the fiberglass fibers, so it minimizes itching. As a DIY-er, I would use the Comfort-Therm and staple the plastic tab to hold it in place and add some 2" plywood strips at about 4' o.c. to add support when the installation is complete. If you use 1/4" plywood, one of those inexpensive electric brad nailer/staplers will not only staple the insulation, but will also install the strips.

maggie-mae · 07-28-2007, 12:12 PM

I wouldnt know my dad owns a painting bussiness and he works on roofs he knows about insulation and all that stuff if you really need the help with it you could email him at the5wings@aol.com and he should be able to help hes a professional. -hope this helps-

CThomps · 07-28-2007, 12:56 PM

Comfort Therm. That's the "closed cell" stuff I was talking about. Couldn't remember the name.

LI Sound Grunt · 07-28-2007, 01:33 PM

[quote]sixpack324 - 7/28/2007 10:46 AM

Keep in mind, that when using kraft-faced insulation, (paper-faced) the vapor barrier (paper) is supposed to face the conditioned space. In-short, the paper faces the room, not the outside. It says so in the print right on the vapor barrier (paper) on the insulation itself. Although it is common for contractors to install the insulation with the paper facing the crawlspace, it is an incorrect installation method. It is common because it is faster and easier to just staple the paper tab rather than install plywood strips to hold it in place.

Think about your walls.......Does the paper face inside the house or the outside?
So why would the floor be different?

[quote]

And, remember you only want ONE vapor barrier - whatever you put below the fiberglass cannot be a vapor barrier - no plasitc sheeting - otherwise you trap the vapor in to rot the floor joists.

That said I think that hi tech newest blown in foam stuff sounds great for your application - but again remember - one vapor barrier - on the living side.

Tireless · 07-28-2007, 10:43 PM

Thanks guys....no paper, air tight, non-molding material......I am inclined to do some research on local foam insulation contractors. I am assuming there are different products with different price points. It will be easy to get the equipment into the space. While the ceiling is low, the space is wide open. Does anyone have a range of sq ft charges I may be looking at?

CThomps · 07-28-2007, 10:53 PM

I've learned that EVERYTHING is locality specific. Just get multiple bids. Thats all you can do.

Or if you're thinking foam spray look into Tiger Foam. Just google it. Figure out your square footage and compare pricing with DIY'ing Tiger Foam vs. hiring a spray foamer.

Remember...always multiple bids.

katkt · 07-29-2007, 06:52 PM

Hire it done Tireless. The subs can often provide insul and labor cheaper then you can buy the material.
Check around with a couple of builders for a sub they use. Get a couple of prices. If its anything like here, they'll be pretty close.
I've got batts in my crawlspace, however the sub installed them paper up. I'm waiting for one of those days when I need something to do to go down, flip em over, and staple em to the joist. They installed pieces of wire between the joist to hold the batts in place
You know where I live, if I don't have a mold issue you shouldn't either. My crawl houses the duct work and Geo unit so between what passes for a tight seal in these parts, and the central vac that exhaust in this area, it is almost a conditoned space.
Unless you have water table or drainage issues around the house that could cause a moisture problem I wouldn't worry about it. If its dry now it always should be.