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!


22 Answers

Flat roof (TPO over polyiso build-up) insulation guidance

I am trying to figure out the best insulation build up under this roof situation.

- 27'x29' flat roof with 5/8" plywood sheathing.
- There is polyiso over the plywood built up 1/4:12 on all four side to the the center. There is 1/4" of ISO at the edges built up to approx. 3.5" in the middle.
- There is no ice/water or vapor barrier under the ISO. The ISO is covered with 60mm TPO.
- The plywood seams where not tape or sealed
- The ceiling joists are 14" TJI 360 at 16" OC.

In General questions | Asked By Eric | Jan 17 16
1 Answer

Interior foam insulation in Climate Zone 4 (marine)

We are currently renovating our house and wanted to get some help on adding interior insulation. Our house is located in Seattle and is a single story rambler with 2' eaves.

It has has brick facade, drainage gap, 2x4 framed walls, and no current insulation. The great room that we are currently renovating has a vented cathedral ceiling where the rafters start out with a 5" depth and increases to 23" depth as it gets closer to the ridge.

For the exterior walls:

brick facade > drainage gap > 2x4 framed walls > 3.5" roxul batt > 1" rigid foam board > 5/8" drywall

Ceiling:

In Energy efficiency and durability | Asked By User-7029106 | May 8 18
2 Answers

Manual J and second floor heat loads

I am working through sizing a multi-split for a 2-story house and I have had both my engineer and my mechanical installer perform their own Manual J,D and S for the project. A large part of the 2nd floor is open to below and I am wondering if Manual J takes into account the heat gains coming from the 1st floor when determining the 2nd floor heat loads in a situation like this. Does anyone know if that is the case?

In Mechanicals | Asked By Jonathan Lawrence CZ 4A New Jersey | May 8 18
3 Answers

Location recommendations for minisplit heads

I know it's been asked many times, but would appreciate suggestions on locating the head units for two minisplits in my 'pretty good house'. I have attached the floorplan. Some things to note on the house:

- Climate Zone 6b, southcentral Montana
- majority of windows are on the east side for the river view
- windows and doors are double-pane. South windows are high SGHC for solar gain
- first floor concrete slab
- underslab = R20, walls = R40, roof = R60, windows = R4

In Mechanicals | Asked By Brian Croston | May 8 18
4 Answers

Understanding BEopt DView outputs

OK, so for some of you this is going to seem like a "duh" question. I'm using BEopt to model the energy use of our new home and I'm more than a little confused as to which toggles I should be using in the DView output.

For example, if I want to see the BTU output of my heating equipment, in this case a GSHP, what toggle do I use to show the actual BTU output over time? This is imortant for equipment sizing, but there are SO many options:

Source Energy
-Total (*) (Btu)
-Total (E) (Btu)
-Heating (E) (Btu)

Site Energy
-Total (E) (kWh)
-Heating (E) (kWh)

Delivered Energy

In Energy efficiency and durability | Asked By Lance Peters | Jan 31 18
1 Answer

Ultracell Insulation

Has anyone heard anything about the status of Ultracell insulation? I'm particularly curious, since I live close to Buffalo. The website still says its coming this year, and it sounds like they've gotten several million of funding. However, it looks like Bill Hulstrunk, National Fiber's old technical guru, has moved on to another company, and has filed a lawsuit against them.

In Green products and materials | Asked By John Ranson | May 8 18
2 Answers

Foundation wall drainage

To create better drainage, I'm considering extending the aggregate from around the drain tile up the foundation/basement wall closer to grade instead of just using regular soil backfill. I can't find much info regarding this technique online. How is this accomplished? How close to grade is the aggregate brought, and how wide is it in the trench? Trenches are a couple feet wide; that's not all stone, right?

In Green building techniques | Asked By Bryanw511 | May 7 18
14 Answers

Review mini-split setup

good afternoon folks,
I'm building a 2000 sqft bungalow with conditioned, semi finished basement. 9' ceilings on both levelss, to a little below "pretty good house" standards. R70 attic, R30walls, R7 triple pane windows, R5 doors, R30 basement walls, and R16 subslab, aiming for excellent air tightness. Fully ducted ERV, ventless dryer, recirculating range hood, and the achillis heel, a wood burning fireplace, "sealed" combustion with outdoor air supply kit.

In Mechanicals | Asked By Ryan Magladry Ottawa, Ontario | Apr 30 18
11 Answers

Certainteed Membrain: Reviews and opinions, please

New build, climate zone 6a. High altitude snow country. My insulation contractor is really pushing me away from doing a ccSPF on the underside of my sheathing and very strongly suggesting I use this certainteed membrain. Here are my options for roof design for my un-vented 2.5/12 pitch cathedral ceiling shed roof:
A) 14" TJI rafters with 5.5" of ccSPF and 8.5" of netted and blown in insulation
B) 16" TJI rafters with 16" of netted and blown insulation but using Certainteed Membrain - a nylon smart vapor retarder.

In Green products and materials | Asked By Steve Mackay | May 7 18
6 Answers

Insulating top of basement slab - Is moisture still a problem with a barrier?

Is insulating the top of a non-walkout basement slab floor in climate zone 6 really valuable if the slab has a moisture/vapor barrier beneath it? Goal is carpet on top for most to the space. What happens in the event of water flooding from a toilet or clogged drain?

In General questions | Asked By BobTheWeekendWarrior | May 4 18
Register for a free account and join the conversation


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