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6 Answers

Insufficiently thick exterior foam: Remove, increase, ignore?

Hi there,

I've been reading the articles on GBA about exterior foam and I think mine is too thin to keep the sheathing above the dew point. I'm wondering your opinions as to the best remedy. I'm assuming that removing or increasing the thickness will both be expensive. I believe my wall assembly is risky, but have no evidence it is actually a problem. Given that I'm wondering if the best course of action is to live with it. Here are the details:

- 2 x 4 walls
- .75" polyiso
- Plywood sheathing
- No rain screen
- Stud cavities filled with fiberglass batts

In Energy efficiency and durability | Asked By Jeremiah Breer | Mar 19 17
10 Answers

ERV vs. HRV Efficiency - Humidity Loss Considered?

I've been looking into Heat/Energy Recovery Ventilation and comparing specifications of different models. As we know, HRVs transfer heat and ERVs transfer both heat and humidity to incoming air from outgoing air in cold/dry conditions, and do the reverse in hot/humid conditions.

I was looking at the specs and I couldn't really figure out how the latent recovery of an ERV was being accounted for when compared to the efficiency of an HRV. Perhaps the specs indicate this and I'm just not getting it?

In Mechanicals | Asked By Lance Peters | Mar 15 17
4 Answers

With a drainage membrane on exterior of foundation walls, is backfilling with gravel still recommended?

We're in an area where gravel runs pretty high in cost (monopoly effect.) On the exterior of our basement walls we'll have sprayed in place Tremco Tuff'n'dry H8, with Tremco Warm'n'dri drainage board installed prior to back filling. So is it still a no brainer to backfill with gravel or might we be able to skip this and save some cash? We haven't excavated yet, but soil in this area is classified as "silt loam" - in other words it's not a heavy clay, but it's not light, sandy soil either.

In Green building techniques | Asked By William Costello | Mar 19 17
8 Answers

Where should I apply polyiso in an attic? South wall?

My budget is $2000. Built in 2002. I have average R40 attic insulation a combination of blown pink and rolled pink. My thought is to add R10 poly iso to the attic but I wondered the best way to do it. R10 would be from two layers of 3/4" R5. The attic is large and ventilated with 2x6" joists 24 OC. I has an existing radiant barrier that looks to be properly installed on the underside of the top of the attic I live in 3A W/H Dallas TX.

My first and best solution was to

In Energy efficiency and durability | Asked By user-6799229 | Mar 19 17
6 Answers

Maximum CFM for range hood without makeup air

In a tightly sealed house, what's the maximum CFM that you could consider in a range hood without supplying makeup air. I know that the IRC allows up to 400cfm without makeup air, but is that actually advisable? Any personal experiences about 200-400cfm fans in tightly sealed houses?

I'm considering putting in a fan that goes up to 350cfm, and opening a window if I need to run it at full speed.


In Mechanicals | Asked By John Ranson | Mar 18 17
11 Answers

Electric vs. Propane Direct Vent Water Heater

Hi All,

My water heater is nearing the end of its lifespan and I am trying to decide the best option for replacement. My main criteria is lowest energy cost. Secondary criteria are installation cost and overall efficiency/greenhouse gas emissions.

Right now, I am limiting my search to storage units (no on-demand).

The unit I have right now is a direct vent propane heater. I pay about $4/gallon for propane (well over 4X the wholesale price ! Don't get me started about the unjust economics of residential propane). My electric rate is about $0.20/kWH.

In Mechanicals | Asked By Pierre Donner | Mar 18 17
3 Answers

Cathedral Roof: To Vent or Not To Vent?

I'm building a vacation house on some rural property in Montana. It can get very cold in the winter and very hot in the summer. And we have a fair amount of wind in our area. The walls of the structure are going to be built using Faswall ICF blocks. The roof will have two sections with a single pitch roof design separated by a middle section with a more conventional two-pitch roof.

In Energy efficiency and durability | Asked By David Williams | Mar 18 17
4 Answers

Indoor air quality and wood heat

Hi All,

The primary source of heat for my home is a wood stove. This is an economic choice (cord wood is free) but I sometimes wonder if it is a healthy choice.

Wood stoves produce some nasty stuff. Conventional wisdom says that everything goes up the chimney, out of the house and stays out of the house. This seems like it might be an oversimplification. Wood stoves depend on draft to keep the nasty stuff out of the house and draft is not entirely reliable. Once the nasty stuff makes it out of the house, there are routes for (some of it) it to come back in.

In Mechanicals | Asked By Pierre Donner | Mar 18 17
7 Answers

Reclaimed and factory second rigid foam

I have seen a couple of recommendations here and there on obtaining reclaimed rigid foam. One post actually mentioned the Syracuse area, close to where I live, so I checked craigslist as they suggested and sure enough there was--new, reclaimed and factory second rigid foam.

In Green products and materials | Asked By Nina Saeli | Mar 16 17
2 Answers

External wall layers comparison question

External wall layers comparison question: Zip R Insulated sheathing vs. 4" rigid foam (atop and exterior to) OSB sheathing?

This is going to focus strictly on exterior, above grade wall layering without concern to climate zone or other factors for the moment.

From the beginning of our building project, we have had in mind to use Huber's Zip- R Insulated Sheathing (comes in 1" to 2 1/2" insulated panels, each performing at various R-Values) and Zip tape. (Our project thickness is not yet determine, and I do not to be believe to be relevant to the upcoming questions)

In Energy efficiency and durability | Asked By Nina Saeli | Mar 19 17
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