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7 Answers

Vapor permeance of thick foam sheathing and board seams

I have read that at a certain thickness, all foam boards (eps, xps, and polyiso) lose their vapor permeance, effectively rendering them vapor retarders with very low perm ratings. Does anyone have a link to the research behind these findings and if so can I be pointed in the right direction?

I am hopeful that the effective thickness at which this condition occurs for each foam is stated on the research but I will hold further questions till I have read up on it.

Asked By Sash057 | Jun 18 18
9 Answers

Ceiling insulation for a room addition to my house

I'm planning a room addition, 16 x 16 with a 6/12 gable roof and cathedral ceiling, zone 6. I'm not yet committed to anything specific so would like to run this scenario by folks for advice and opinion. I'm wanting to avoid the 5-6 inches of exterior foam (R-25) that would be needed if I went that route. And, I would like to go unvented. Would the following scenario work?

Asked By Howard Gentler | Jun 16 18
1 Answer

Reuse old fiberglass batts?

We are gutting and rehabbing an old house. We are pulling out the old fiberglass insulation from the walls and ceilings, and we have quite a large collection of the batts. Can the insulation be reused?

Some of it is obviously in bad shape, but a lot of it is still fluffy and pink with some discoloration. I know the batts acted as an air filter for the (very) leaky house over the decades, and so they have collected dust and dirt.

How much has that degraded the effectiveness of the insulation? Would it be worth salvaging some of the insulation?

Asked By James Fugate | Jun 18 18
2 Answers

Second Heating and Air

Where would be the best place to install the second unit (basement, 1st floor, upstairs)?

Asked By user-7084153 | Jun 16 18
9 Answers

Double Stud Wall & Basement Insulation Review - Climate Zone 5A

I've read practically every article on this site and many others related to 2x4 double stud walls and moisture. I want to have a wall that is low risk for moisture issues without introducing any more expense and complexity than necessary. The following seems attainable with my budget, and doesn't seem to cause much builder concern for construction. From exterior to interior:

LP Smartside Siding
1/4 rainscreen composed of either a mesh or furring strips with an insect screen at the bottom
Tyvek Drainwrap
CDX Plywood, seams taped

Asked By Shane | Jun 15 18
3 Answers

Thermal break for in-betweenie window box?

Hi, Peter in zone 5 (Boston), considering a PGH design with double stud walls (2x3's inboard, 2x4's outboard; 2.0 SPF at the outside wall and cellulose for the remainder) with about 10" of insulation space (shooting for R-40). (See case 10 of Bldg America report BA-0903:

Asked By Peter Staecker | Jun 14 18
22 Answers

Closed-cell foam thickness vs. R-value

We are in the Asheville area in the mountains of Western North Carolina (Zone 4A) where I am renovating a small 300 sq ft shed roofed cottage. I intend to use closed cell foam in the roof, walls, and floor. I want a well insulated tight envelope as we are going to try to heat with an electric space heater.

I have now had two different contractors recommending only 3" of foam in the roof (R-18-21) and tell me I don't have to worry too much about the R values, as there is a steep diminishing return curve after 3". Is this correct? Should I insist on 5 or 6"?

Asked By Ross Williams | Jun 11 18
6 Answers

Fentrim tape worth the expense?

Can anyone weigh in on this super tape? My client is balking at $2k in tape, vs $400 for grace vycor. We have euro windows with no built in flashing.

Asked By Lukas Schwartz | Jun 12 18
1 Answer

Installing fiberglass batts in attic

I have recently finished up air-sealing my unfinished attic, and am going to be installing R30 faced fiberglass batts in between the joists. My question is in regards to how aggressively should I be pressing down on the batts when I install them? Do I need to really push down on them to make sure that the vapor barrier on the batt is pressed closely to the attic "floor" made up of drywall?

Asked By DrJimesTooperMD | Jun 13 18
32 Answers

How to seal ventilation baffles in rafter bays?

If I use the "Smartbaffle" in my rafter bays, I would tape across the joints where two baffles meet, but do I need to seal the edges against the rafters also? What would be the recommended/cost effective way? Tape, caulk (messy), spray foam cans like great stuff (would add up with 54 or so 25ft long rafter bays from soffitt to ridge.


Asked By Joe Watson | Aug 5 15
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