Q&A: A Forum for Green Building Experts and Beginners

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4 Answers
Can exterior foam be combined with interior spray foam?

If I have walls and/or an unvented cathedral ceiling that are insulated with closed-cell spray foam from the inside, can I also have rigid foam on the outside of the sheathing to limit bridging?
Just wondering if it's somehow a bad idea to have the sheathing sandwiched between two layers of foam.

Thanks, Chris.
(This is for Ottawa, Canada, equivalent to zone 6A.)

In Green building techniques | Asked By Christopher Solar | May 13 13
7 Answers
Thermal mass lessened with overlay over slab?

I have a passive solar off-grid home that works extremely well with a 2 in. concrete slab that is finished with decorative concrete stain/paint. However, the slab and stain/sealer are completely defective and very likely have to be replaced, but one party is proposing a concrete overlay product be put atop the existing slab. The overlay product (ArtCrete Deck Coat, I think it is) consists of two parts--1) Portland cement, aggregate, and a stain, and 2) a modified acrylic latex resin.

In Energy efficiency and durability | Asked By K Tot | May 13 13
3 Answers
Roxul

I am finishing a screened porch into a fully-insulated room, to be part of the house and used year round. I understand Roxul is an excellent choice for exterior walls. Is a vapor barrier necessary and, if so, can someone suggest how to install. Tks for your help.

In General questions | Asked By Roni Collier | May 14 13
9 Answers
Space and water heating for a micro-load house

I've been re-reading Martin Holladay's posts on water heating as I once again deal with a small-ish super-efficient house: 1900 ft2 with a heating load of less than 20 kBtu/hour. The homeowners have access to propane and electricity and here in MN, electricity is still generated by a lot of coal, although the homeowners are planning for a pv system.

At the moment I've narrowed heat/hot water system ideas down to three:
1. use a 6kW modulating electric boiler for space heat (hydronic radiant) and also to fire to an indirect tank for hot water. Also, use a drainwater heat recovery device.

In Mechanicals | Asked By Rachel Wagner | May 14 13
3 Answers
How to seal a Bilco door to prevent heat loss and moist air transfer?

We have a standard exterior Bilco door that leads to semi-finished space in our basement. We are having trouble with cold air coming in during the winter months and damp air in the spring/summer months. How can we seal this Bilco door without creating condensation issues around the door and/or seal? The air is coming from the cracks at the door hinges and around the doors themselves. It appears that the Bilco casing unit is sealed properly to the concrete. Home Depot sells polycarbonate domes that cover the doors.

In GBA Pro help | Asked By Jas Thurber | May 12 13
1 Answer
Wood choices for exterior use (siding & decking) - Green pro's and cons?

I'm working on a project to rehab and convert a garage building to a studio and living space and am looking at options for exterior wood siding and decking.

I will be using Hardie Panels with reveal strips for much of the siding, however there are some areas I would like to use a clear finished wood siding for an accent. In addition I'm building a small ground level deck and want to match the decking to the siding wood. The totally square footage of wood being used fairly low at around 500 sq. ft.

In Green products and materials | Asked By Kevin Hardy | May 11 13
154 Answers
Serious Windows vs. Thermotech, Fibertec, Inline, Accurate Dorwin

Does anyone have experience with Serious Windows or Canadian fiberglass windows? I'm having a difficult time finding high SHGC windows (with a U-value less than or equal to 0.30) for my passive solar home that are affordable. Looks like the fiberglass windows can give me the performance I'm looking for, but I can't find any local installations to inspect the quality of manufacture.

In Energy efficiency and durability | Asked By Claire Anderson | Oct 1 09
3 Answers
I was told that my central air conditioner needs a larger return duct

I was told that my central AC needs a larger return duct. The symptom was that the low pressure line at the compressor was icing up on the outside. Does this make sense? I had thought that if the system was low on freon that this was a symptom.

I am handy but need some input into the size requirements of a return duct versus the output ducts. I would assume them to be about the same size.

In Mechanicals | Asked By john friede | May 13 13
6 Answers
Spray-foam smell

Two weeks ago, We had Sealection 500 sprayed in wall cavities and under roof decking (metal roof) for our new home build. The smell seemed minor by 2 days after, then the ingition barrier - Blazelok IB4 was sprayed on entire roof deck. One week later, the smell is as bad a the day they sprayed the Blazelok IB4. Cure rate is 2-3 hrs so something seems wrong.
The chemical smell burns your eyes and nose, I can taste a metallic taste on my tongue and get dizzy after entering the home if any windows are closed.

In General questions | Asked By k s | Feb 25 11
2 Answers
Will some insulation need to be removed in a few years?

Our long-term plan is to add a deck/pergola/conservatory on top of a one-story room on our mostly two story house in Zone 5a. BUT, the roof on the single story leaks and will be unshingled/re-shingled NOW. We'll use this opportunity to remove decking of the flat part of the roof (it angles from the flat part down to the three walls), access the inaccessible attic, and air seal/insulate before re-shingling.

In General questions | Asked By Gordon B | May 13 13
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