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12 Answers

Please explain how foil-faced roof sheathing works

Some say that foil-faced roof sheathing can reduce the temperature in an attic. I'm unclear how this works. Considering two types of attic designs:

1 - The attic is ventilated, and the insulation is laid on top of the ceiling drywall.
2 - The attic is not ventilated, and the insulation is attached tight to the roof sheathing.

In Energy efficiency and durability | Asked By Robert Feibleman | Dec 13 12
9 Answers

Blown Cellulose vs Blown Fiberglass

Hello Everyone. I own a four family apartment building in St. Louis and I'm considering having insulation installed in the attic, first floor ceiling, and basement ceiling. I

The attic contains original R-9 (roughly) insulation. The first floor ceiling probably contains little to no insulation and I'm looking more for noise reduction. The basement double as garage parking for the tenants with existing unfinished drywall installed. There is no existing insulation underneath the drywall.

In Energy efficiency and durability | Asked By RICK LEPPO | Dec 12 12
3 Answers

Rigid Insulation Retrofit and Vapor Barriers

I've spent hours researching my new wall detail and I'm down to one question, should I tape the 2" XPS Rigid Foam or not.


I am in Rochester NY (Climate Zone 5)

I have an existing home where I am taking the exterior down to the studs. I'm adding 1/2" OSB to the exterior (none now), 2" of XPS Rigid, Housewrap, 1x4 strapping and then a mix of cement siding and vinyl. The existing walls are 2x4 with R-11 Kraft Faced.

In Energy efficiency and durability | Asked By Matt Convery | Dec 9 12
4 Answers

Building modified Trombe wall -- How to stop heat from sinking into foundation?

Howdy planning a modified trombe wall but wondering how to stop the heat from migrating threw the 8 " stem wall an down into the foundation an soils of the crawl space. Is there a method of installing say a 2" isolation foam wedge to isolate the wall above the main floor ?

In Green building techniques | Asked By tim miller | Dec 14 12
2 Answers

What's a good way to detail an exterior corner with rigid foam?

I'm planning on improving an existing 2x4 wall by installing 2 layers of 2" polyiso or 4-1/2" nail-base panels. I've found good pointers on this site for most of the details, but am still unsure about how to handle the exterior corners so that the rain-screen strips and siding corner-boards have something solid to attach to. The corner-boards will likely only be a few inches wide, so not wide enough to catch any framing. I'm assuming a butt-corner with nail-base, so there would be OSB on only one side of the corner. How do you do this without creating a thermal bridge?

In Green building techniques | Asked By Andrew Thompson | Dec 12 12
5 Answers

MiniSpilt or PV

I am building a single story house in the Pacific NorthWest which is 1800sq ft. I am using Pretty Good House/PassivHaus principles. The house will be well sealed and insulated, it will use good quality glazing for some solar gain.

I had been planning on using a MiniSpilt to heat the house. Only electricity is avaiable.

In Energy efficiency and durability | Asked By Stephen Carlton | Dec 14 12
5 Answers

Can closed-cell foam insulation be used to entirely fill double-stud exterior-wall cavities?

Can closed-cell foam insulation be used to entirely fill double-stud exterior-wall cavities (i.e., about 7" deep) for an entire wall? Other than higher cost, does this plan suffer from technical drawbacks?


In Green building techniques | Asked By Martin Hughes | Dec 13 12
4 Answers

Cellulose vs. fiberglass batt cavity insulation with rigid foam exterior in zone 5 central NJ

I'm looking at cavity insulation options for a new 2200SF house that will have 1-1/2" polyiso on exterior walls and 3" on the roof. Cavity insulation prices are coming in at roughly $4500 for fiberglass batt (R21 walls/R38 roof) and about 3 times that for cellulose. While the benefits of cellulose have been well covered on this blog, I'm having trouble justifying the added cost for cellulose and wonder to what extent the short comings of fiberglass are mitigated by the addition of the foam on the exterior.

In Energy efficiency and durability | Asked By Scott Schaub | Dec 12 12
3 Answers

Not damp/waterproofing a foundation?

Would it be foolhardy to not damp/waterproof our foundation? We have a very sandy site and low water table. We will be putting 6 inches of foam on the foundation (the foam is ship lapped).

In General questions | Asked By jessie pratt | Dec 13 12
4 Answers

Design for upgrade: Where are the debates or standards? 100 year buildings.

The timber is old growth and thick, the structure sound, the outside and inside is beautiful. The building is 87 years old and nothing is wrong with it... except it's been hacked to bits through upgrades to plumbing, electrical, telephone and (now) wireless internet.

In Green building techniques | Asked By Bryce Nesbitt | Dec 13 12
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