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chigundo 06-29-2010 09:57 AM

Insulation method 2x4 walls?
Gutted our den, which apparently used to be a porch, 3 or 4 season at some point. The insulation used to be R-11 fiberblass, aluminum foil faced batts, and then at some point they blew in cellulose on top of that.. some stud cavities were tightly sealed, but most were a mess with the fiberglass sagging and all sorts of insects living in them. Already found one batch of carpenter ants and the search for the nest is still on.

3 walls are exterior, 2x4 over a concrete slab. The room is freezing in the winter so I'm trying to do my best with insulating. First quote from spray foam is over $1200... given the cost of fiberglass batts and a few cans of Great Stuff for the visible cracks in the bottom sill and electrical holes, i don't know if that's worth the cost. I understand there are R-15 batts for 2x4 walls now, so do you think if I got paper-faced R-15 batts I should be in pretty good shape? I'm in Connecticut.

Scuba_Dave 06-29-2010 10:02 AM

What did they give you for an Rvalue on the spary foam ?
I'd bet the concrete slab is where you are losing most of your heat
If the ceiling is high enough I'd consider a floor w/insulation added

I used R15 on our 2nd floor existing walls & a few other places
Worked for me

chigundo 06-29-2010 10:06 AM

Before we gutted, the floor was carpet.... concrete, carpet pad, carpet.

It sucked. The ceiling height is 7 1/2 feet right now..not sure how we can insulate the floor at ALL let alone properly.. any tips in that department would be appreciated. We were thinking an engineered wood/laminate flooring instead of carpet.

Jim F 06-29-2010 10:29 AM

I second addressing the concrete floor problem. What about furring out your walls with 2x2's interiorly to give you an adaquate 6" wall?

chigundo 06-29-2010 10:33 AM

Do you think a 1/2 inch rigid foam board directly over the concrete will be a big enough improvement ?

chigundo 06-29-2010 10:34 AM

realistically trying to make the room as insulated as possible without really shrinking it anymore than we need too, considering it's not terribly big to begin with

there's that fine line trying to find

Scuba_Dave 06-29-2010 11:21 AM

Ah, somehow the walls looked taller in the pic
I've never put rigid on the floor, but have seen it done on TV
Not sure on the method, results etc

KennMacMoragh 06-29-2010 12:21 PM

I would identify the cause of those carpenter ants, that means there is way too much moisture in the walls, you may have a leak somewhere.

There's three methods of vapor barrier that I've seen and used:
- Faced insulation
- Unfaced insulation with plastic stapled to the walls
- PVA primer

My preferred method is PVA, that way you are totally covering the walls with a vapor barrier.

As for the floor, there is a company in Canada that manufactures insulated floor tiles for what you are doing. I've never tried them, but you can take a look here

Gary in WA 06-29-2010 09:17 PM

You lose twice as much through the walls as the floors.

Tape a 2' square piece of clear plastic on the floor, check for moisture after 2 days. This will possibly tell if there is a vapor barrier under the slab (highly unlikely).

At time to cover, seal the wall/floor joint with caulking, caulk the drywall everywhere against air:
Seal the sheathing/bottom plate joint with caulk to stop air/bugs.
Plug each wire hole with foam to stop air movement:
As mentioned by Jim F, furring the walls , or at least adding foam board directly to the studs after batts for a thermal break:

1. Why are the top plates installed short of the ceiling?
2. Did you find any moisture in the stud bays?
3. Is the bottom plate of treated wood?
4. Can you see a sill sealer under the bottom plate?

Be safe, Gary

chigundo 06-29-2010 09:31 PM

1. Why are the top plates installed short of the ceiling?
-Good question, no idea. I'll be removing the ceiling drywall tomorrow to see what else is up there.. what are the problems with how it is now?

2. Did you find any moisture in the stud bays?
-None, the stud bays seemed pretty dry. If there was any evidence of moisture, it was towards the bottom in some stud bays and that's where you could see outside looking between the bottom sill plate and the exterior sheeting.

3. Is the bottom plate of treated wood?
-I think so, and I only say that because there's no sign of rot.

4. Can you see a sill sealer under the bottom plate?
-No and I highly doubt there is one considering when this could have been built.

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