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Why are most basements insulated inside?

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May 03, 2013, 02:23 PM
Why are most basements insulated inside?
I asked this already a lot of contractors:
Why are basements built of concrete or concrete blocks insulated inside of the house?
In my opinion that is wrong! You wear a coat on the outside too to keep yourself warm.
To install the insulation inside you bring the dew point in the house. Condensate will occur and you have the a big chance to get mold the house.
Is there a explanation why the insulation gets installed inside?
May 03, 2013, 03:36 PM
I would suspect it's less costly and easier to do inside. more likely to be damaged by mice or whatever outside, because your only option is foamboard.

sig: if this is a new economy, how come they still want my old-fashioned money?
May 03, 2013, 07:35 PM
You do realize that your example just disproved what you are saying don't you?

If you are wearing a coat, you are the source of heat. The fill of the coat is the insulation. The outer layer of the coat is the waterproof part to keep everything inside dry.

House - interior heat source, insulation to keep it there, block or poured concrete foundation to keep all that from the weather. Of course it's more complex than that - a basement must use other methods to keep water from migrating inside but the basics are there. If you were to put insulation outside the foundation (which is needed to support the house) then you would have to add yet another layer of material that will not get damaged by moisture and dirt over time - something like......block or poured concrete.

May 04, 2013, 03:45 PM
Jaybee, I'd like to followup on your analogy.
Let's say I'm a cross-country (Nordic) skier. I generate a lot of heat and moisture even though I'm out in the cold. I'm likely to wear some kind of jacket to keep warm and the outer shell needs to protect me from the cold wind, but it needs to allow my moisture to dissipate. So, I'm likely to wear a breathable shell made of something like Gortex (kind of like wrapping a house in Tyvek). I'm not going wear an outer shell of plastic--it won't breath and my jacket will become soaked. That's why I don't understand putting non-breathable foam panels on the outer shell of a house.

And, I'm not going to wear plastic next to my body, then a jacket, and then Gortex. The moisture would stay right next to my body--not good. That's why I don't understand the (sometimes required) use of a vapor barrier on the conditioned side of insulation.

It puzzles me.
May 04, 2013, 07:16 PM
Easy answer there: The ski outfit comparison is exactly what you have in a house .... above ground. Even though a framed house will usually have a faced insulation on the inner surface and frequently an exterior barrier like Tyvek - both of those surfaces can breath a little to keep moisture from collecting within the walls.

Different story with a basement. While I am in total agreement that you are generating a lot of moisture and trapping it within the basement by a (mostly) waterproof wall, the volume of moisture pales by comparison of what you get from a rainstorm or snowmelt. Because of this, you cannot have a basement that 'breathes' - it must be a structure that will repel water. Since you must keep all the rainwater out, basements will rely on a dehumidifier if interior moisture is a problem.

The best 'counter analogy' I can give is that while you are out skiing in your breathable and water resistant Gortex you happen to slip and fall - right into a creek. You are now wet to the core and heading back to the house.

Until somebody develops a magic material that allows water vapor to migrate out from the inside while remaining completely waterproof from the outside, this is what we will have to deal with for underground construction.

And of course there are other concerns that make a house different than a nordic skier. Both the heat source of a house and the cooling source of a house can dry the air and lower humidity. If you are running a central H/A system then you have your interior drying system already in place. The bottom line is that you have to keep the weather related moisture out and avoid trapping any other moisture where it can develop rot and other damage.

This message has been edited. Last edited by: Jaybee,

May 15, 2013, 01:58 AM
Brian McCallister
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May 29, 2013, 03:57 PM
Times 5
Originally posted by Norbert:

To install the insulation inside you bring the dew point in the house.

In my opinion, this is where your reasoning lost steam. Buying a stain for the outside of the house that repels moisture and then having a de-humidifying system in the house, will greatly decrease the amount of moisture inside.