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

Q & A Instructions

[Click map to enlarge]

The GBAGreenBuildingAdvisor.com web site has a wealth of articles on a wide variety of construction topics. Before posting your question, you may want to check out the articles on this page: How To Do Everything. You just might discover an article there that provides the information you seek.

Please register for a free account or sign in to ask and answer green building questions.

If you want to post a question, the usual rules of courtesy apply:
1. Be nice.
2. If you can't be nice, be polite.
3. If you can't be nice or polite — well, please be brief.

To attach a photo or illustration: Under the box labeled “More explanation,” look for the words “File attachments.” Click that, and you should be able to attach a photo.

Thanks for joining the conversation!


4 Answers

Zehnder ComfoTube code issue

I am an architect working with a contractor/homeowner who is currently building a new home for his family in St. Paul, Minnesota.

He has installed a Zehnder HRV with associated Comfotube piping and insulated air intake and exhaust according to Zehnder's layout and specification. However, our HVAC inspector will not approve the system as it does not meet their ducting requirements - it is not UL listed nor is it a type 0 or type 1 assembly.

Asked By L Alm | Aug 5 15
5 Answers

How to use rigid foam insulation in roof space

Context: Central Pennsylvania. Want to convert vented (sofit and ridge vent) cathedral attic space into conditioned space. No plans to replace the roof. Roof cavities are 7.25". Cost is important, but so is DIY-ability.

Plan so far: Cut and cobble XPS into cavities between trusses, sealing all the way to exterior wall. Assembly stack spray foamed in place:
1.25” ventilation
2 layers of 3” XPS
1.25" ISO on inside face covering roof trusses

Asked By Mark Sentesy | Sep 9 15
6 Answers

Unvented roof, Zone 3B, foam-free

Hi Martin,

First off, I have read a wealth of articles on the subject of unvented roofs, by yourself and Joseph Lstiburek. I started with your “How to Build A Cathedral Ceiling” article and read pretty much everything related to this from you and Lstiburek. The conclusion being that for an unvented roof you either install closed-cell spray foam between the rafters, or rigid foam above the sheathing at a thickness dictated by your climate zone to keep the sheathing warm enough.

Asked By Joe G | Aug 26 15
1 Answer

Insulating existing barn with board and batten siding?

Hello,

I have an existing post and beam barn in Massachusetts that my wife and I would like to convert to a workshop/studio space. It's clad with existing rough cut vertical pine siding to which I plan on adding vertical battens to seal it up better.

I would also like to insulate. Preferably with Icynene to get a tight seal and discourage rodents from nesting in the exterior cavities. The Icynene dealer suggested open cell and said that a weather barrier isn't necessary(?)

Asked By Evan Halstead | Sep 8 15
2 Answers

How long will closed-cell polyurethane foam retain its greater-than-5 R-value?

The laws of physics and thermodynamics state that a stable R-value higher than about 5 is impossible to achieve when using air as the trapped gas in an insulating material due to the thermal conductivity of air itself. Most materials using air will be lower than than due to the thermal bridging of the structure itself, which is why EPS has an R-value that tops out in the mid 4s. XPS, polyiso and polyurethane boast higher R-values than this because the trapped gas is not air, but rather, some blowing agent with a lower thermal conductivity than air.

Asked By Nate G | Sep 8 15
2 Answers

Why would someone buy a heating (gas fuel) and cooling package unit?

Hi!

I recently moved to CA and have started seeing a lot of homeowners installing heating and cooling package units, usually installed on the roof. These systems are gas-fueled, with a max AFUE of 81 or so. Why would someone buy one of these units instead of a full Air Source Heat Pump to do heating and cooling?

For example: http://www.lennox.com/products/packaged-units/LRP14GE/

Thanks for your help!
Whitney

Asked By Whitney Larsen | Sep 8 15
6 Answers

Cavity insulation with exterior rigid foam

I'm looking for advice on stud cavity insulation. Walls will be (from outside in) LP smartside lap siding, 3/4" rainscreen gap, 6" EPS foam (R-24), self-adhering vapor/water/air barrier, OSB, stud cavity, then interior wall covering which will be either T&G pine or drywall with latex paint. My main floor walls are 2x4 and the basement walls are 4' below grade ICF and 4' above grade 2x6. I live in zone 7a - eastern North Dakota.

Asked By Adam Emter | Sep 5 15
2 Answers

Is closed cell foam insulation worth the cost for a 75 year old home with 2x4 exterior walls?

I am remodeling my 75 year old home. I am gutting the interior walls and adding a full dormer. The exterior walls are 2x4. Is it worth the cost for closed cell foam insulation or is a traditional fiberglass insulation sufficient? Thanks, Paul

Asked By Paul Hanson | Sep 6 15
9 Answers

Improving hot water heat pump tank efficiency with free dryer heat

Hi. I have been thinking about how to improve my GE electric hot water heat pump efficiency, particularly in the winter months. It is located in a very well insulated utility room off the garage (larger than recommended minimum volumes). The by-product of using the heat pump is cool, dry air, which in turn creates a cold room calling for accessory heat to warm the room back up to temp for the heat pump to then work efficiently again. I find the room temp is fluctuating up and down in conjunction with the use of heat pump this not making it as efficient as it could be.

Asked By Matthew Michaud | Sep 7 15
4 Answers

Does anyone have updated (current product information) on water heaters with heat pumps?

I am looking for a DHW heater (with heat pump) which will service both DHW and a radiant floor system? The project in question has approximately 1300 sf radiant floor system and having one appliance to service both efficiently would be very beneficial.

I’ve looked at the Sanden Eco (good information here in this forum) but it’s too late for the current project to design an exterior heat pump into the residence exterior; but I will certainly consider this next for future cleints since they will be available (I'm told) at the end of this year.

Asked By Caroline Di Diego | Sep 7 15
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!