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Should we tear out our pink fiberglass (above grade) and EPS (below grade)?

Our entire basement (800 sq ft?) has pink batt insulation above grade covered with vapour barrier and then drywall. It doesn't seem terribly damp down there, but I'm just wondering if we really should tear it all out and replace it with spray foam, rigid foam, or Roxul.

Secondly, about 30% of our basement has Expanded Polystyrene Foam (EPS), I think about 1/2"(ish), below grade, covered with drywall. Should we rip all that out as well and redo it with spray foam or rigid foam? Or just leave it?

I am wondering from both a heat cost savings, as well as a moisture benefit. We leave in the East Coast of Canada (Nova Scotia). If the benefit is minimal, then we don't want to bother. For the rest of the basement that has currently no insulation below grade, we are going to get spray foam.

Asked by Sarah Poulin
Posted Jun 19, 2017 5:36 PM ET

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8 Answers

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1.

It's probably worth doing some exploratory partial demolition to see if the studs are getting moldy, or have an unacceptably high moisture content. Buy a <$100 two-pronged moisture content meter. If the studs at both the above grade section and the bottom plate of the pink-fluff section are below 20% moisture content, re-assemble it in an air tight manner and be thankful! (Let's not go out of our way to steal defeat from the jaws of victory!)

If the section with the polyethylene and pink stuff is OK, and the half inch EPS section is in a stud wall, insulating the cavities of the rest with fiberglass or rock wool would also be low risk. But rather than polyethylene, "vapor barrier latex" or 2 mil nylon (Certainteed MemBrain) would offer more drying capacity. If the wallboard is tight to the EPS, it's better to add 2-3" of EPS (or polyiso), strapping it to the wall with 1x4 furring through-screwed to the foundation, then hanging the new wallboard on the furring. That solution would not need any vapor retardent paints or membranes- the EPS would be good enough.

If 30% of the basement has only the half-inch EPS behind wallboard, it could be that s much as 5-10% of the entire heating bill is from the basement. It could even be higher than that if the furnace or boiler is in the basement, with uninsulated ducts or pipes.

Air sealing the basement is also critical for lowering the heat loss of the home. Air leaks in the basement are more important than air leaks on the first floor, and on par with air leaks to the attic, since the top & bottom air leaks are what defines and drives the stack effect infiltration.

Answered by Dana Dorsett
Posted Jun 19, 2017 6:06 PM ET

2.

I'm not sure I follow your recommendations about the EPS.

"half inch EPS section is in a stud wall" - It's against the concrete, then there are studs infront of it, then there is drywall covering the studs.

"insulating the cavities of the rest with fiberglass or rock wool would also be low risk" -- insulate the cavities where the EPS, studs and drywall are? But it's all covered with drywall... we would have to rip out the drywall, and if we rip out the drywall, we might as well rip out the EPS as well. If you mean to insulate the rest of the basement, there are no cavities. There are no studs. Just bare concrete.

"If the wallboard is tight to the EPS, it's better to add 2-3" of EPS (or polyiso), strapping it to the wall with 1x4 furring through-screwed to the foundation, then hanging the new wallboard on the furring" --
When you say, "wallboard," you mean drywall, right? There's the EPS, then the studs, and there is a big open gap, then the drywall. We know this because an electrician had cut a tiny hole to fish some wire previously. There is also a tiny section at the end of the laundry room that has no drywall in front either (so that's how I know how thick the EPS is). And again, if we have to rip out the drywall, we might as well rip out the EPS.

We also have electric baseboard heating the in the basement, and a heat pump + electric baseboard heating (supplemental) upstairs. No furnace or ducting.

What do you mean by air sealing the basement?

Answered by Sarah Poulin
Posted Jun 19, 2017 6:17 PM ET
Edited Jun 19, 2017 6:19 PM ET.

3.

Sarah,
Q. "What do you mean by air sealing the basement?"

A. The answer can be found in this article: Air-Sealing a Basement.

Answered by Martin Holladay
Posted Jun 19, 2017 7:00 PM ET

4.

Ah, I see. Our basement must be well sealed. Our whole house, actually. We had a blower test done and it did really well.

Answered by Sarah Poulin
Posted Jun 19, 2017 7:33 PM ET

5.

Sarah,

Can you define "really well?"

Answered by Steve Knapp CZ 3A Georgia
Posted Jun 19, 2017 8:15 PM ET

6.

I don't know. I don't have the numbers. We qualified for a free blower test for the Home Warming Program. All I know is that the guy was insistent that our biggest issue is a need for proper ventilation (need an HRV) and that our 1986 split entry home is pretty well sealed. So we are getting that done first. But the basement is next up after dealing with having proper air exchange.

But I just really want to know whether we need to start demolition in the basement, or to leave alone and just spray foam the bare concrete spots.

Answered by Sarah Poulin
Posted Jun 19, 2017 8:19 PM ET

7.

Sarah,
Whether or not you want to improve the insulation levels in your basement depends on your goals and your budget. It's probable that thoroughly upgrading the insulation levels in your basement to the best modern standard will cost more than you can ever expect to gain back in energy savings.

If the fiberglass batts are in framed walls that are above grade, then these walls aren't any different from the walls in 90% of U.S. and Canadian homes, and they are at no particular risk for problems. They may not be insulated well, but they are typical. The fact that these above-grade framed walls are part of your basement doesn't change the recommendations for insulating the walls (compared to ordinary walls on the other floors of your house).

Concerning the concrete walls insulated with 1/2-inch EPS -- that's pretty minimal. It's probably about R-2. What you really want is R-10 or R-15.

If this were my house, I might remove the drywall from the areas with 1/2-inch EPS, and add some closed-cell spray foam between the studs. But I would do that with my eyes wide open, fully aware that the expensive work would never yield enough energy savings to justify the investment from an economic perspective. (And if I did this work, I would seek out a contractor who offers closed-cell spray foam with a blowing agent that is environmentally friendly -- for example, Demilec's Heatlok XT HFO, Lapolla Foam-Lok 2000-4G, or Elastochem Specialty Chemicals Insulthane Extreme. For more information on this type of foam, see Next Generation Spray Foams Trickle into the Market.)

Answered by Martin Holladay
Posted Jun 20, 2017 6:23 AM ET

8.

It doesn't require anything like complete demolition to inspect how the fiberglass wall is doing. Find the studs with a stud finder, and use a hole saw to cut a 2.5-3" hole in the drywall where the stud intersects a top plate, and another where it intersects a bottom plate. You will then have sufficient access to test moisture content, but have clean hole small enough to air & vapor seal and patch up easily. Doing this in a few locations would give some confidence if they're all coming back reasonably dry, and there is no visible mold or fungus-smell.

Answered by Dana Dorsett
Posted Jun 20, 2017 12:11 PM ET

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