Unfinished/Unheated Basement Ceiling Insulation

mcusumano

I've heard that putting insulation between rafters of an unheated and unfinished basement is a waste of money. I have a stone foundation and my basement floor is part cement and part dirt. With the basement windows closed in the winter the basement never gets cold enough to freeze pipes but it is cold and my first floor wooden floors are cold. So, my question is--Would it make a difference in floor temperature for me to put 1 inch insulated sheathing on the basement ceiling between rafters just to keep the floor a little warmer? I live in central Pennsylvania. Again, I understand it will not make the upstairs warmer, I am only interested in knowing if the insulation would keep the cold off the basement ceiling and thus allow the floor to stay warmer? Will there be less radiant cold?

Gary in WA

Where are you located?

Is there HVAC in the basement?

Gary

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mcusumano

I live in central PA and the basement is unfinished and not usable. It has a stone foundation and the floor is part dirt and cement. There is no HVAC--just 2 windows and a door.

Windows on Wash

Be careful with the insulation of the floor.

The issue is that there is enough heat loss from the space above right now to keep the crawl space/basement warm enough (even though it is not conditioned space) to keep the pipes from freezing.

Properly adhered rigid foams will work as will spray foam. The issue with slowing the loss of heat to the basement is going to be that the pipes need to be properly insulated in conjunction with any basement insulation.

I would also encourage you to place a vapor barrier across the floor of the basement and seal it to the basement walls to prevent the migration of any moisture, radon, and smell from the dirt floor.

You could also insulate the basement walls and convert the space to conditioned space with some supply and return side air. Sealing of the floor needs to be done with this application as well.

Gary in WA

I agree. Also, weatherstrip the windows and door down there- first.



The floor is cold due to the incoming outside air in the basement (making up the escaping attic air from the “stack effect”) permeating the joist bays and dropping the temperature of the floor joists, transmitting their temperature to you. Check your attic insulation R-value and air sealing of wiring/plumbing holes. Check the 1st floor above you (while in basement) for any similar holes that let air through. The decking is acting as an air/vapor barrier due to the exterior glue in the material. Any hole in an air barrier, no matter how small, will let through a lot of air due to the pressure difference between the basement/attic. The holes usually go through all floors and the wall top plates right to the attic; http://www.wag-aic.org/1999/WAG_99_baker.pdf
So you want to insulate the floor and treat the basement like a crawl-space; http://www.buildingscience.com/docum...ce-insulation/

Now you already have a basement….. some ways to insulate it; http://www.buildingscience.com/docum...g-your-basment


If dead-set on insulating the floor; http://www.buildingscience.com/docum...n-crawlspaces/


Either way, air-seal and insulate the rim joists- first; http://www.buildingscience.com/docum...m-at-rim-joist


AND, cover the dirt; http://dirt-crawl-spaces.com/crawlspace-dirt.html


Gary

Gary

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