last year when we wanted to buy a house we decided to build instead so we could build a super energy efficient house with excellent tightness, energy efficient windows etc. As we are going down the path we are finding all these things that make energy efficient building not worth it financially. We are in a hot humid climate- a 33 seer mini split has a sensible heat ratio of .96 . it would never remove enough moisture from a tight, well insulated house. So now Im reading all these articles that say you have to have a dehumidifier. Have you seen how horribly energy inefficient those are? oh, you also have to have a hrv at added cost to add fresh air to your building that you didn't need before. I looked at high quality windows from Europe and they would cost about 5 times as much for nice windows than for inexpensive windows from here. If I build the house tight like I want now I have to worry about moisture intrusion because the house has no way to dry out and a rotting house becomes a real concern. then I measure all this in BeOpt and if I build a loose house, with cheap windows and code minimum everything, adding an extra 1000watts of solar covers everything Im a bit jaded right now

Were do you live?

If you do a good job on making the house tight and also add good vapor barrier (I would definitely do vapor barrier primer) then the moisture will have a harder time getting in. Then the AC by itself should be able to keep up.

You can also add a CO2 meter and have it run your HRV only when the CO2 levels get above your liking.

Well, like anything, something can be done well, poorly or anywhere in between... Starting with an integrated design appropriate for the specific building location is the first step. ROI should always be considered. Personally, I would never use high priced triple pane windows from Europe. I would first minimize the use of windows in general and increase insulation R-value in the ceiling, floor and walls. I would use passive solar cooling/heating design methodology to reduce cooling/heating equipment requirements. I would use an appropriate amount of interior thermal mass to buffer peak cooling/heating loads and further reduce the size of cooling/heating equipment requirements. Sealing the building is the most energy efficient solution in a cold or hot climate, but doing so will require an ERV or HRV. Sealing the building in temperate low humidity climates where you can just leave the windows open the majority of time makes little sense. You and all your descendants will rot out long before an ICF building ever rots out. Again, you definitely need to first model and design for the building location to determine the best integrated design solution BEFORE constructing the building. Too many people just start constructing the structure before even considering HVAC.

Sealing the building in temperate low humidity climates where you can just leave the windows open the majority of time makes little sense.

Thanks for that. This is the first time Im hearing this

You and all your descendants will rot out long before an ICF building ever rots out.

that's true but it makes my point exactly that before all the insulation and sealing, we built houses out of much more inexpensive wood that have stood the test of time.

Very true, wood buildings have been around for a long time too. When we started better insulating buildings in the 1930s, we ran into peeling exterior paint issues because of condensation inside the walls and we learned how to properly use vapor barriers while always still maintaining a drying path through a wall. However, vapor barriers are frequently miss-used even today and can cause even more problems.

History of Peeling Paint, Insulation & Vapor Barriers

Old houses are often sealed to improve performance. However, old house performance wasn't all that bad when they just used radiators which did not pressurize or depressurize the building. It was only when forced air furnaces were added to old houses that the performance went way down.

Bottom line, when you seal and use insulation and vapor barriers, you really need to understand what the consequences will be in different climates.

Thanks for the link. Inside that article is a Lstiburek article and is a little better. He is GOD, if you haven't seen him on youtube you should. I often wondered if he were Dana? hahaha

https://www.buildingscience.com/documents/insights/bsi-073-macbeth-does-vapor-barriers

It really depends on what you mean by "green building".

1: Relying on your AC to do whole-home dehum basically means building in an area with exactly ZERO shading and full sun day-round. Even then, most AC units won't be able to keep up with the load.
2: Yes, a separate whole-home dehumidification unit is a good idea. And yes, some of the very top-end ones are quite expensive.
3: Yes, you build a tight house to control the internal environment and you need mechanical ventilation. Again, not cheap. But do you really want to build a giant mold colony in your walls and rot out your building materials?
4: Windows beyond a certain point are "bling". If you can make do with dual-pane and low-e coating? Then yeah, you don't HAVE to go with tri-pane/quad-pane imported units that cost an arm a leg and every testicle within 1000 yards. Just take special care with your air and water sealing around the window units. Additionally, limit your glazing on the home to control solar gaine and look at overhangs and shading. Both for sun and for moisture control during storms.

Between a high-end HRV/ERV, a dedicated dehumidifier, and your AC unit, you can probably expect to spend between $4-8000. Or about 10-15% of your home's budget.
What you're forgetting is that in a tight, well-insulated, high mass home, these devices will NOT be on CONSTANTLY and your home will hold temperature and humidity levels for long low-to-no power cycles.
You build a "breathy" home, and your AC is basically on-duty 24x7. And most mini-splits simply WON'T stand up to that duty cycle.

You talk about building homes that stood the test of time.
Sure. Stuff that was built out out mainly old growth LUMBER.
Not plywood. Not OSB. Not recent-vintage pine. Not gypsum board. Not foam. Heck, not even Rockwool (it's treated to be hydrophobic).
These modern materials have a much lower ability to absorb, hold and dissipate moisture (the $100 term is "Hygric Buffer Capacity").
You want something that can handle moisture and breath? Look at straw-bale homes.

You try to build an old-style "breather" with modern lumber (or worse, engineered lumber), you're simply looking at a mold factory that'll rot out from under you.

Posted By sailawayrb on 18 Jul 2019 03:41 PM
Very true, wood buildings have been around for a long time too. When we started better insulating buildings in the 1930s, we ran into peeling exterior paint issues because of condensation inside the walls and we learned how to properly use vapor barriers while always still maintaining a drying path through a wall. However, vapor barriers are frequently miss-used even today and can cause even more problems.

History of Peeling Paint, Insulation & Vapor Barriers

Old houses are often sealed to improve performance. However, old house performance wasn't all that bad when they just used radiators which did not pressurize or depressurize the building. It was only when forced air furnaces were added to old houses that the performance went way down.

Bottom line, when you seal and use insulation and vapor barriers, you really need to understand what the consequences will be in different climates.

thank you for that link

Posted By newbostonconst on 18 Jul 2019 06:22 PM
Thanks for the link. Inside that article is a Lstiburek article and is a little better. He is GOD, if you haven't seen him on youtube you should. I often wondered if he were Dana? hahaha

https://www.buildingscience.com/documents/insights/bsi-073-macbeth-does-vapor-barriers

good information. thanks :)

Posted By Dilettante on 19 Jul 2019 12:26 AM
It really depends on what you mean by "green building".

1: Relying on your AC to do whole-home dehum basically means building in an area with exactly ZERO shading and full sun day-round. Even then, most AC units won't be able to keep up with the load.
2: Yes, a separate whole-home dehumidification unit is a good idea. And yes, some of the very top-end ones are quite expensive.
3: Yes, you build a tight house to control the internal environment and you need mechanical ventilation. Again, not cheap. But do you really want to build a giant mold colony in your walls and rot out your building materials?
4: Windows beyond a certain point are "bling". If you can make do with dual-pane and low-e coating? Then yeah, you don't HAVE to go with tri-pane/quad-pane imported units that cost an arm a leg and every testicle within 1000 yards. Just take special care with your air and water sealing around the window units. Additionally, limit your glazing on the home to control solar gaine and look at overhangs and shading. Both for sun and for moisture control during storms.

Between a high-end HRV/ERV, a dedicated dehumidifier, and your AC unit, you can probably expect to spend between $4-8000. Or about 10-15% of your home's budget.
What you're forgetting is that in a tight, well-insulated, high mass home, these devices will NOT be on CONSTANTLY and your home will hold temperature and humidity levels for long low-to-no power cycles.
You build a "breathy" home, and your AC is basically on-duty 24x7. And most mini-splits simply WON'T stand up to that duty cycle.

You talk about building homes that stood the test of time.
Sure. Stuff that was built out out mainly old growth LUMBER.
Not plywood. Not OSB. Not recent-vintage pine. Not gypsum board. Not foam. Heck, not even Rockwool (it's treated to be hydrophobic).
These modern materials have a much lower ability to absorb, hold and dissipate moisture (the $100 term is "Hygric Buffer Capacity").
You want something that can handle moisture and breath? Look at straw-bale homes.

You try to build an old-style "breather" with modern lumber (or worse, engineered lumber), you're simply looking at a mold factory that'll rot out from under you.

exactly. my 1987 average quality tract home, with old ac has no problem maintaining 38-45% relative humidity in north texas. so having to add a whole house dehu is not my idea of green. also the cost of building green is not limited to these three things you mentioned. If I wanted to build to passiv haus standards it would cost probably 75% more, which I would never recoup. I think I will build to code minimum and make up the rest with solar panels. That is the greenest option that exists today. less foam, fewer mechanical parts, and more harnessing of solar energy.