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A few weeks ago during the inspection on a house we are in the process of buying, the inspector made a recommendation that we should consider insulating between the joists in the mostly unfinished basement ceiling. The house has forced hot air with the distribution ducts wrapped in insulation and the seams taped over (Mike Holmes would be proud).
At face value, I thought this sounded about right, but after thinking about it I'm not so sure....
My take on it is that I don't see a need to trap any heat that might be there in the basement. If there is cold air coming through the foundation floor, it won't rise up to the 1st floor. The 1st floor is all hardwood, but with only a 10' x 10' finished room in the basement, sound deadening isn't needed.
Am I missing something here? Is it worth it to spend the almost $400 on insulation and a few hours of my time? Will it make a noticeable dent on our gas bill?
Assuming basic physics that hot air rises and cold air falls, why do I need to worry about cold air from the basement seeping into the 1st floor or warm air on the 1st floor dropping into the basement?
Like I asked in my original post - What am I missing here?
...such as poured concrete or high quality concrete blocks and windows that seal well I doubt you will see any measurable increase in comfort energy savings.
It is sorta like if you have on long underwear and good hat / gloves / coat pulling a over shirt on really won't make you warmer.
The quintessential multi-faceted question-
Answer: yes, no, and maybe.
I'm guessing this isn't new construction.
Currently, IRC (International Residential Code) the residential arm of ICC (International Code Council) requires homes that are built on a basement and the basement is unconditioned, the ceiling be insulated. It is explained as the "building envelope". A cocoon as it were- of the living area. The science behind it is transference. As you heat the "living area", that space wants to cool to the temp of the cooler basement temp (an equaling as it were). However, if you reverse the thought process- Cooling the "living space" (hot air rises- cool air falls) then the insulation should help maintain the temp without the transference of temperature.
Before this thinking came about obviously there was no insulation. Or if the basement was walk-out, whatever portion of framed wall would be insulated.
Concrete foundations (poured wall) are poor insulators (about R-1 for an 8-10" thick wall) onto themselves. And this is the only true consistent since soil types vary so much. But, the earth surrounding the basement does have an insulating value.
Some convening authorities only requires the perimeter to be insulated- the joist band and 4-5' of the ceiling were required.
A very good argument has come about in the insulating a basement debate. ICF's (insulated concrete forms) are stay in place forms- they are not removed when the concrete is formed. They create a foam sheathing on the outside and inside of the foundation wall. Giving a much enhanced R-value to the foundation wall. The negative has been damage to the exterior when backfilling (and some waterproofing companies will not treat ICF's because of the damage potential and/or incompatibility of materials) and it provides a dark moist travel highway for termites. So, the best alternative is to install foam board to the interior side of the foundation (1" minimum) with all seamed sealed with seal tape.
From the financial aspect- insulating a basement ceiling could be worthwhile depending on current/area fuel costs. But generally, it would be a long time return investment.
The important thing to remember here is this- unconditioned space. So, depending on the sq/ft would it be worthwhile to "condition" the space even though it's not finished?
Basements can most certainly pull warm air out of an upper level. Warm air does rise, but a cold floor is simply put, cold! If the air underneath the surface you walk on is cold the surface will be colder than would otherwise have been as well. If your feet are cold then you get cold, you will in turn, crank up the heat, even though the thermostat might say 70-72. In addition blowing warm air out of a vent across this cool floor cools the air some making it less effective in heating the room. So although warm air rises, remember a cool surface cools.
Insulation of any kind in any place is almost always a good idea.
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Assuming normal constuction methods...
