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!

3 Answers

Turning off/setting back ductless minisplits, kwh, efficiency, and more

So I talked to an LG engineer today (hint: if you have questions about minisplit performance, don't call tech support, find the number to a local manufacturer and ask to talk to their engineer).

My 4 ton LG LMU48HV condenser can cool down to 14,400 btus. At that minimum, the system will use around 900 watts. This was actually verified by my Efergy Elite monitor, which showed that during 82 degree outside temperature, 3 of my indoor units were on, and it showed a pretty constant energy use of 900 watts for the 8 hours that it was on (2 pm - 10 pm).

In Energy efficiency and durability | Asked By Jimmy Nguyen | Sep 15 17
4 Answers

Air-sealing a metal chimney

Hello GBA community, I have a question about air-sealing an ICC Excel chimney servicing a woodstove in Manitoba, Canada:

In Green building techniques | Asked By Benjamin Pries | Sep 12 17
4 Answers

Door flashing detail

We are in Minnesota (Zone 6a). 2200 sq/ft single level (9' walls), slab on grade.

Is a recess in the slab the preferred method for pan flashing a slab? I have several innie doors, 1 outie doors and 1 sliding patio door. How deep should these be? 1/2"?

In General questions | Asked By Scott K | Sep 14 17
1 Answer

Price for replacing roof

We had a couple of leaks through our tiled roof. A roofing (limited) company would not give a quote before starting the job, saying they needed to see what the roofing felt etc was like and needed to removed areas of tiles to find out.

They quoted us £15,000 to do the job, but they had already removed several areas of tiles and started replacing battens before giving me the price, so I was not able to dispute it at that stage. I negotiated the price down to £14,250, and they made me sign a "quotation" at this price.

In Project management | Asked By Jonathan-123 | Sep 15 17
4 Answers

4x8 Sheathing on 9' wall

We are in Minnesota (Zone 6a). 2200 sq/ft single level (9' walls), slab on grade.

I was planning on doing 4 x 9 sheets of plywood on the exterior of my double stud wall. The 9' sheets are about double the price of 4 x 8 sheets. What is the best strategy for applying 4 x 8 sheets on a 9' wall? Staggered horizontally? Lot of extra seams to tape...and is it counter productive to even consider 4 x 8's if I have those extra seam that aren't backed by a stud. I REALLY don't want to pay $35 a sheet for 4 x 9 cdx.

In General questions | Asked By Scott K | Sep 14 17
10 Answers

Air-source heat pump for heating, cooling, and domestic hot water

We are working on a net zero project here in Dauphin, MB (Western Manitoba) and are interested in reducing our annual electrical usage (thereby minimizing the size of our required PV system to achieve net zero 'status'). I have been encouraged by our energy modeller to consider a cold climate air source heat pump for space heating and cooling. I am seeking to know if a practical solution exists to use air source heat pump technology for space heating, cooling AND domestic hot water with a single outdoor unit.

The annual usage is estimated as follows:

Space Heating 2100 kWh

In Mechanicals | Asked By Eric Bjornson | Aug 31 17
5 Answers

Sizing a furnace

I was reading an article about HVAC sizing with Manual J & D.

Here is my question:

If you have data for an existing home -- heating-only therms, furnace run-time (from smart thermostat), HDD, etc for the coldest days of the year for multiple years -- can you calculate furnace sizing in a different way?

In Mechanicals | Asked By mtaylor12345 | Sep 12 17
4 Answers

Sub-slab insulation

I was planning on using 4" of Type II EPS covered with 10 mil Stego under my slab and 2.5" of EPS on the basement walls. I spoke with my concrete guy today and he told me they have been using this product:


In Energy efficiency and durability | Asked By Jonathan Lawrence CZ 4A New Jersey | Sep 13 17
2 Answers

How much do oil-based stains affect vapor permability?

Hi guys,

I stained my siding recently (bevel siding) with oil based stain.

Since my house is built fairly vapor open, I am curious how much oil stains will affect the vapor permability of the building's envelope and ability to breath?

I am guessing it leaves the wood still semi vapor permeable because almost every house has paint/stain.

How do you guys approach this when building a vapor open house? Even if it makes it vapor closed, I do have 1/2" furring strips behind my siding, so would that be suffecient to allow vapor to escape from the house?

In Energy efficiency and durability | Asked By MichaelBa | Sep 13 17
6 Answers

Vapor barrier

I have read that with me putting two layers of 1 1/2 inch foil-faced rigid foam with staggered joints on the outside walls, I don't put a vapor barrier on the inside.

Now on my low-slope roof, I have 2x12 rafters. Starting at the top, I have:

15 lb. felt paper-
ice shield over the full roof-
1/2 inch plywood sheathing-
1 5/8 inch air space to vent-
1 inch foil-faced rigid foam, caulked at the edges-
1 1/2 inch foil-faced rigid foam, caulked, with staggered joints-
2 inch foil-faced rigid foam, caulked, with staggered joints-
5 1/2 inch Roxul insulation.

In Green products and materials | Asked By Gary Ovens | Sep 13 17
Register for a free account and join the conversation

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