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Insulating Basements

Makes sense to me, warm move to cold, moist move to dry, if the beer can is cold you get condensation
 
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Mostly a very good video!
Is why most in my location use closed cell foam applied directly to the interior foundation wall.
For my climate location, 1.5 to 2" is all that's needed for normal indoor RH levels.
No condensation and an amazing vapor barrier..

Exterior insulation hardly ever continues above grade, and when it does it needs to be covered.
It IS the best way to do it, BUT there are downfalls.
Forget about the foundation wall when there is an outside basement entrance.
Additionally, I know very little about termites (We seldom have them) or other burrowing insects, but exterior foam I don't believe can stand up to that well.

Lastly, every effort should be made to condition that area, which now has its own concerns...
atmospherically drafted appliances ? Radon ?
If appliances are natural draft, make a boiler room that has vents to the exterior.
 
For basement insulation, make sure to control moisture first. Closed-cell foam or properly installed vapor barriers on the warm side of the wall usually work best to prevent condensation and mold.
 
When insulating a basement, the key is controlling moisture first. Closed-cell spray foam or rigid foam board works well, and make sure to follow local R-value requirements. Adding a vapor barrier and proper finishing keeps the space comfortable and code-compliant.
 
If I wanted to insulate and uninsulated masonry basement wall where there was the possibility of moisture in the back fill - almost everywhere I'd live in US - I'd put a heavy air vapour barrier against the wall (and floor), at least 10 mil, and perhaps set that in mastic of some sort. I'd like to minimize any air pockets or gaps. Then frame inside - gapped from wall - and sheath with something that is very vapour permeable - like t&g pine. And then dense pack the cavity with cellulose. Stop the moisture on the moist side and build the wall so it dries inward.
 
bill1952 said:
If I wanted to insulate and uninsulated masonry basement wall where there was the possibility of moisture in the back fill - almost everywhere I'd live in US - I'd put a heavy air vapour barrier against the wall (and floor), at least 10 mil, and perhaps set that in mastic of some sort. I'd like to minimize any air pockets or gaps. Then frame inside - gapped from wall - and sheath with something that is very vapour permeable - like t&g pine. And then dense pack the cavity with cellulose. Stop the moisture on the moist side and build the wall so it dries inward.
Click to expand...
Vapor barrier on what side?
 
Canadian codes require a water-impermeable coating or membrane be applied to a below-grade frostwall if wood studs are used as the wall assembly. There are other general requirements along the same lines.... basically, grab yer XPS.
 
I don't think I mentioned the slab. Searching the page only you used the word "slab". Perhaps I misspelled it but I couldn't find it. I would wrap my hair barrier across the slab under the wall but don't think I mentioned that. And don't think I edited any posts in this thread. You could prove me wrong.

As the video says, the wall needs to be able to dry inward from the condensing surface. So not that it complies with code but a vapor impermeable layer on the otherwise uninsulated masonry wall - which could be rigid or spray foam or a membrane like stego 15 mil product - and dense pack cellulose inside that would be my choice living in northern climes.

The video doesn't mention air pressure but that's an important consideration as well. Keeping in mind I've never lived in a house with AC, generally in any house the basement will be negative pressure relative to exterior. I'm the 2 story houses I've lived in - all with full basements - the neutral pressure plane is around the middle of 2nd floor windows. I'm in a newer tighter house now and it could be a little lowered - haven't tested it like my 100 year old houses. That negative pressure can only help the basement we'll stay drier and lessen condensation.

So that's my story.
 
I did not check code to see if foundation walls are required to dry to the inside, so this section applies to only what I call sound building science, and not necessarily what code says. If the inside of the foundation has 2" of closed cell, AKA a vapor barrier, and say the typical damp proofing used in my area on the outside, Id say the foundation would dry to the outside but only when wetter then the outside. I also don't think the concrete minds being wet one bit, and we shouldn't mind it either. Basically, not everything is cast in stone.

I have done worst case depressurization testing on literally hundreds (if not thousands) of houses and what you write about with air pressure is not always the case, again, not everything is cast in stone. An example I saw many times is when the house had forced air heating (or cooling) and the duct work was located in the basement. Most houses with ducts in the basement have hundreds of linear feet of supply (under pressure) and tens of feet for the return. When supply and return duct work is equally sealed (or unsealed) the supply side (having more leakage area) can pressurize the basement.

Your 100% correct about depressurization when the an attic of a two story home (How its been done here for years) as the air handler.
This literally pumps air out of the house and into the attic (which is lost out through gable, soffit and ridge vents) causing the house to be short or missing that same amount of volume.

This issue, (leaky attic duct work) is exactly the reason people around the world say "Furnaces dry the house out too much"
I try to explain to them, no leaky ducts cause this. There's a heat exchanger in the furnace and the heated air really never mixes with the air in the ducts...
That's about the time when eyes glaze over, and all they start hearing is bla bla bla blaaa, bla blaaaa bla.....

Telling most folks something that's contrary to what they have been told over and over, for decades regardless of the actual truth is a tough thing.
We humans most of the times go into the "too many tabs open, cannot compute" mode.
I still to this day see HVAC contractors selling humidification systems to home owners who have 100% spray foamed homes with hot roofs....

Im not insulting anyone... (too much!)
I can't forget how I felt hearing someone say, the house doesn't need to breath, we do.
How I struggled and struggled with ventilation being at opposites of air sealing etc....

Here's one that took a while, Let some of the fine folks here chew on this one ;-)
The more you air seal a house and the more you insulate a flat ceiling( higher R value), the more important attic ventilation becomes...

Since you live in a newer tighter home, Im curious how you manage basement de-humidification or if you have to manage it at all ?
 
Enrgxprt said:
If the inside of the foundation has 2" of closed cell, AKA a vapor barrier, and say the typical damp proofing used in my area on the outside, Id say the foundation would dry to the outside
Click to expand...
I don't care about that part of the wall. I care about from the vapor barrier and in - which can't dry to outside.

I'm a victim of my experiences - have always lived in houses with hot water heat. No ducts. It's a condition when we are looking for a house. It still seems like I'm heating season the pressure is low I basement and relatively higher at the top of the thermal envelope - often 2nd floor ceiling.

If there's HVAC in the attic, bring the attic inside the thermal envelope. I'm interant of ducts in an uninsulated attic. Bound to be problems, even if just efficiency.

Yes the tighter the house the more you have to worry about interior moist air getting into the attic, air pressure from that bouyant air being a major factor. You can help it if fanatical on the air vapor barrier. I'm last project I put butyl tape on all of the ceiling rafters and then carefully installed a 10 mile vapor barrier with taped seems. The project allowed me to have 0 penetrations except one piece of Romex. 20+ inches of cellulose right to exterior wall sheathing. 12" of fiberglass in double stud walls. Attic is still vented, but not much high. Lot of soffit, one gable vent with less than 1/600 vent of time sq ft.

Our basement is ICF and it's always dry. :)
 
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