Can basement walls to dry to the inside with foam board?
I'm planning to install and seal 2 inch eps foamboard to my basement foundation walls. From all of my reading it says that your basement foundation walls can only dry to the inside. If I put foamboard on the concrete and seal it everywhere, when moisture comes through the concrete it will have nowhere to go.
Perhaps I am missing something here but seems to me over time behind the eps will be wet as this moisture has nowhere to go?
I have also read attach it directly to the concrete with no air gap, lately I'm reading leave a tiny air gap. Looking for thoughts on these 2 options.
Yes, below grade basement walls can only dry to the inside, but I would add as a caveat – they don’t actually need to dry. We say they can only ‘dry to the inside’ because they simply can’t dry to the outside, which is what builders must assume is going to happen when the put poly vapor barriers on basement walls.
The straight answer is that it’s fine if concrete stay wet. Virtually every concrete foundation wall will stay wet indefinitely, even those with exterior dimple membranes, unless there has been a footing membrane included and I’ve never seen one installed that was at my doing. You an image of what a footing membrane looks like (capillary break) in the following page-
Best practices for durable basement construction to avoid mold
As for applying the EPS rigid insulation, I wouldn’t worry too much either way about air gap or no air gap, because concrete walls aren’t perfectly uniform, so unless you spread a thick coat of adhesive evenly over the whole surface of the EPS and press it firmly to the wall until it sets, there will be minor air gaps. Whether you try or not you’ll probably have one : ) Here is another good page to read -
Why basements are moldy and how to prevent it
Thanks for the great info Mike.
I am planning to use a good dehumidifier as part of my basement solution so I can monitor humidity and keep it within a good range.
would there be any point in cutting maybe 6x12 inch squares out of the bottom of the foam about the size of a cold air return. In winter I would put the cut piece of foam back in place and seal it up tight but in summer I could remove it and allow any moisture back there to dry to the interior of the basement with my dehumidifier system?
No, nothing good will come from that I think. Without inspecting it I would still say it is almost a foregone conclusion that your concrete walls will always stay wet, so any drying that may happen by you letting moisture into the basement (which will be an anecdotal amount at best anyway) will just be replaced by more as it is surrounded by an endless supply. All that would serve to do would be give your dehumidifer a bit of extra work to do for no reason. Best is to seal it up so the moisture stays on the other side and leave it.
I know this is a few months ago but i have a similar question,
We only use our basement for laudry and storage and over time our stuff smells like the tipical basement! I can see white residue on different areas of the foundation but no actual water or puddling anywhere.
Am i best to just drylock foundation or can i just install 1" xps sealing it on top and bottom?
I did air seal all sill plates already and installed new windows. My dehumidifier is an 80gallon heat pump hot water heater which makes the room colder, i figure this unit could work better having the basement walls warmer with the xps installed. The boiler is down here also but i am a big wood burner so it doesn't come on very long.
Basement walls are 77' total and 7½ high, i figure the xps board would be cheaper and actually insulate.
Let me know your thoughts! Im on east coast longisland, thanks, Chris
The best solution suggested in this diagram is using Mineral Board (Vapor permeable and water resistant)? If it's true, no wet wall?