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19 Answers

Alternatives to foam under slab or no slab?

Are there any alternatives to foam under a slab that might be "cost effective". I realise that CE is a very loaded term, so don't get bogged down in that term.
Obviously, I am not interested in VIP's. But how about the cost and performance of Perlite? Are there other alternitives?
I am looking at a Passive House in a 5, maybe 6, climate zone.
XPS may be available to me at a reduced cost because my wife works for a large company that makes the stuff. Am I wasting my time looking at alternative insulation products if I can get XPS at a discount?

Asked By Steve Young | Aug 23 12
11 Answers

Looking for help on our cathedral ceiling insulation detail

I'm the owner and builder. 1300 sq. ft. addition in southern Maine, Zone 6. Simple salt box design. Rear roof 3/12 pitch. Front roof, 6/12. 17' high at ridge beam, sloping to about 8' in rear.

Thanks for your time,


Asked By user-6941533 | Oct 25 17
8 Answers

Foundation wall poured incorrectly: can this be salvaged?

First major hurdle of the build : the concrete contractor poured an inner foam ledge all around the foundation, but it was not shown on the plan in the front, where I have dimensional stone (see picture for correct stone cross-section, and siding cross section for visual of the foam ledge ). Bottom line is my wall is now 2" too narrow at the top on the front of the house, to accept all the thickness stack up I was planning with dimensional stone.

Asked By Mai Tai | Oct 26 17
5 Answers

Is 1/2 inch foam insulation on outside advisable?

My wood frame house in Brooklyn, NY is being re-sided. I wanted to have foam insulation installed in order to increase the R rating. The plan was to have housewrap, with foam insulation on top, furring strips on top of that (for rainscreen) and then Hardie siding attached to furring strips.

My contractor says that I can only have 1/2 inch thickness of foam. Given this, is it even worth it to or advisable to install foam? If OK to install 1/2 inch foam, what is the best material?

Asked By BrooklynW | Oct 27 17
0 Answers

Looking for local GBA contractor in Chicago IL

Hello, I am looking for someone in the Chicago IL area to help guide me in building an underground roof. Do you have a list of contractors that are Green Builders in the IL area? Thank you!

Asked By bawhitn | Oct 19 17
3 Answers

Venting and finishing an attic of a timber frame home

I'm hoping some folks wiser than I can chime in with their thoughts on how to properly finish off the attic space of a former New England Barn.

In a nutshell here are the existing conditions:
-A 200+ year old Post and Beam building near the ocean. (good breezes)
-An unaccessible dirt floor crawl space with No vapor barrier
- Wall insulation : 1-2" Encompassed Balsa wood insulation snaking between offsetting 2x3's (airflow from the crawl space up thru the walls is good for air circulation and bad for R value.)
-2 finished floors of existing living space

Asked By Tates23 | Oct 3 17
2 Answers

I have a very old wood burning stove with an oval chimney outlet.

Can i use an oval to round adapter and seat the oval end OVER the oval opening of the stove and then continue to install the rest of the chimney?


Asked By dtikberg | Oct 5 17
2 Answers

Insulating a 2/12 roof above the roof deck

My first house, purchased a couple of years ago, needs a new roof. We recently had a major storm in the area and all roofers seem to be so busy that it is difficult to have someone over to discuss my case. So far I spoke with 3 roofers, each with a different idea, so I am doing my own research to see my options.

I have done some research but none of discussed roof setups was identical to mine.
- Zone 5 (Chicago), cold winters and hot summers,
- Basic gable roof, two slopes only,
- 1 story ranch on slab,
- 2/12 roof pitch,
- Unvented roof,
- No attic
- No ceiling insulation,

Asked By Bary_g | Oct 3 17
3 Answers

So poly is bad, and in to out vapour diffusion is a myth : what about wet rooms?

If read enough articles about the dreaded old school polyethylene vapour barrier that it is likely not a good idea for most walls of my building (zone 5.5, 2X6 wall with 2" xps). If I go dense pack cellulose, will likely have to use membrain to appease the inspector (or convince him the special paint is ok).

Even with all of this bad press, does poly still have a place in my zone? I routinely see it specced on the attic sealing (just above the drywall)by well informed people, is that still the norm? Why is the ceiling different?

Asked By Mai Tai | Sep 29 17
10 Answers

Insulating my slab

Climate zone 4a. I am in the process of insulating my basement walls with 4" of xps and had been planning on insulating my slab with 1/2" or 1" xps but as I read more and more on GBA I am now wondering if it's even worth it. I will definitely insulate the exterior of my slab with 2-3" of xps depending on how much I can get away with before it extends beyond my siding but after reading some of Martin's comments to other people's questions I am leaning towards forgoing the slab insulation. To one person he wrote that 1/2" of xps is "fairly insignificant" and 1" of xps "isn't much".

Asked By Matthew Seabolt | Sep 25 17
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