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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
2 Answers

Insulation and air sealing on attic side of bonus room

I live in southeastern NC in zone 3. I have a bonus room above my garage. The room does not have typical knee-walls. The pitch of the A-frame was raised to pull most of it out of the room. What I have now is a bonus room that is essentially a normal room with a nearly 8' ceiling. when the house was built, batts were installed in the stud cavities of the bonus room but were not enclosed on the attic side. So I have batts that are open to the attic with no air barrier of any kind. My understanding is that this is not ideal and the batts should be enclosed on all six sides.

Asked By Jason Dennis | Jun 13 18
6 Answers

Spray foam vs. parging rubble walls

We live in a brick twin home with a rubble stone foundation with dampness issues (not flooding) and the parging in the basement is failing. I was planning to have it parged again but I am wondering if it would be a better choice to apply spray foam. It’s unlikely we will ever finish the space. Is 2” appropriate and should I consider open cell at all?

Asked By Anthony Yoder | Jun 12 18
2 Answers

Energy savings from better wall system / insulation?

I'm looking for charts indicating rough energy savings / heat load changes for various wall system decisions. E.G., going from a standard 2x6 wall (5.5" = R16.2 @ 16"oc) to a double 2x4 wall (7" = R20.1 @ 16"oc + less thermal bridging).

I've seen charts that show this but have been unable to find them. This is for what is effectively a simple two story woodshop with few windows and none on the north side.


Asked By W Ramsay | Jun 12 18
7 Answers

Vent or Not Vent

I was recently struggling with this question for the house we are building and found this article particularly helpful. I had decided to go with a non-vented roof assembly until I started to compare the costs. I then ran into the standard trade-offs that I'm sure most people find. I finally settled on using a vented roof assembly with batt insulation from below on my scissor trusses (gable and hip). I only have a couple of ducts that will be in the attic space and will use rigid duct.

Asked By Kevin Camfield | May 26 18
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