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!

6 Answers

SIP roof with roofing sleepers

I want to create an air space between the SIP roof panels and the finished roof. I am taping the SIP roof seams with SIGA tape and installing a breathable roof membrane (Majcoat).

I want to create an air gap between the finished metal roof and the SIP. I was planing to use 2x's but the problem is which way to run the boards?

In GBA Pro help | Asked By Peter L | Feb 10 17
3 Answers

Hydronic radiant heat over concrete slab

I'm building an addition that partly includes an extension for an existing room off one side of my house here in Connecticut. Existing floor is 2 1/4" x 3/4" oak strip hardwood floor. Addition floor will be slab-above-grade with poly and rigid foam underneath the slab. Need to "marry" the existing oak floor (conventional wood subfloor/structure) to new concrete slab using new oak strip flooring. Because I'm building this addition myself, there will be more than sufficient time for the slab to dry (perhaps a year or more) before new finish flooring needs to be installed.

In General questions | Asked By John Rooney | Jan 14 17
6 Answers

Re-roof insulation upgrades for a cathedral ceiling with polyethylene

Hello GBA Community,

I have a re-roof coming up. What are my options for improving the insulation in my cathedral ceiling that has an interior poly vapor barrier? I'd like to do this work without tearing up the internal finish.

In General questions | Asked By Pavel Gorelik | Feb 5 17
3 Answers

New home wall assembly

I am currently designing a new single-family home in Northern Virginia (Zone 4, Mixed-Humid Climate) and am looking for some feedback to my tentative plans for wall and roof assemblies. I am not trying to build a passive house, just a more durable house. My primarily concern is controlling/managing air and vapor movement.

Walls: 2x6, 24" oc w/ open-cell spray foam insulation in the cavity, ZipSystem R3 sheathing on the exterior and 5/8" drywall foamed to the studs.

In Energy efficiency and durability | Asked By Michael Winn | Feb 11 17
5 Answers

Persistent condensation on ERV fresh air supply duct

I have a deep energy retrofit here in Chicago and discovered to my dismay that I have a lot of condensation on my ERV fresh air supply duct. The rigid duct from the outside fresh air intake into the ERV closet is insulated with foam and doing fine. The problem lies with the 36 inches of insulated flex duct, which connects the ridged duct to the ERV. The fiberglass at the bottom of the flex duct was soaking wet (see image).

I did follow the installation recommendation for the flex duct piece and made sure I had it zipped up tight. It seems like that’s not enough!

In Energy efficiency and durability | Asked By Marcus de la fleur | Feb 9 17
4 Answers

Heating and cooling load calculations

I wanted to get a 2nd opinion from the knowledgeable readers of this site about what an accurate heating/cooling calculation would be for my new house. Both programs I have used(BEOPT and RemDesign trial version) say 18-24,000 btu heating load and 12-14,000 cooling load. I made a spreadsheet and calculated about the same as well.

In General questions | Asked By Brad Depies | Feb 11 17
1 Answer

Little heat transfer to 2nd story floor

Instead of forced air heat on 2nd floor, there are PEX loops stabled to the underside of the sub floor. The upstairs floor does not get the heat transfer, but the ceiling does so 1st floor rom are noticeably warmer than the 2nd floor. Imagine that? The ceiling is finished, but I do have access to the floor cavity though passive floor grates... enough for blow-in insulation. What would you recommend?

In General questions | Asked By Greg J | Feb 11 17
12 Answers

Engineer ambushes salesman, or "what do we do about HVAC?"

So at this point, I have done a Manual J load calc for my house that puts the heat load at around 20,000 BTUs. I know that I want an electric heat pump so I can eventually go net zero. I *think* that I want it to be the Bryant Evolution 280a, which has the highest HSPF (13) that I've been able to find in a ducted heat pump. Seems simple enough, right? "Quote me an installation for this unit."

But so far I have been unsuccessful in getting any HVAC companies to bid. Not one. Four salesmen have come by, and no bids. Zero.

In Mechanicals | Asked By Nate G | Feb 7 17
3 Answers

Insulating around heating ducts running between floor joists

I'm in the process of renovating an older bungalow home in climate zone 7a. It currently has an unfinished basement but I am in the beginning process of retrofitting this. It is a heated basement and plan to finish it into a living space.

I've been taping the seams and joints of all ductwork with foil tape and then planning to insulate the ducts. ALL of the heating ducts run under the main floor between the floor joists.

In Energy efficiency and durability | Asked By user-6759891 | Feb 10 17
2 Answers

Second story hydronic radiant floor system

We notice that the hydronic system for the 2nd story tends to warm the ceiling of the 1st floor rooms below rather than the floors as was intended. Our second story was built with hydronic loops between the floor trusses on the underside of the subfloor using thin metal (not aluminum) heat transfer plates. Laminate flooring and some tile in the bathroom cover the floors. I read and others suggested to blow insulation between the floors and insulate the ceiling cavity to force the heat upwards.

In GBA Pro help | Asked By Greg J | Feb 10 17
Register for a free account and join the conversation

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