Insulating below a floor

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I've mentioned in other posts about our 135 yr old house we're working on. At this point I'm rebuilding the floor on the lower level. This house basically sits on the ground. My new joists will be about 4" off the dirt. I've been through the "to vent or not to vent" threads about crawl spaces. I've decided not to ventilate. It's been closed for 135 years, it can keep being closed. My question is, IS there any reason why I shouldn't fill this space will insulation? Whether it be fiberglass or blown cellulose? In a few days I'll have all new joists and proper center support and will probably insulate unless there's some reason I shouldn't.
thanks!
--
Steve Barker





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I don't see how that insulation will do much insulating. A shallow unvented crawl space makes for a reasonable insulator by itself. However, it could provide a bridge/path for moisture or bugs to cross from the dirt to the joists and floor. It might also make subsequent jobs a little harder (e.g. pulling some new power or CAT-5 cable).
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Malcolm Hoar wrote:

I concur with Malcolm. I'd just insulate the perimeter walls, making very sure to use appropriate flashing or whatever to make a barrier between the ground and the insulation (which would otherwise provide a termite/bug/stuff path). Maybe you also want to put down a sturdy vapor barrier over the entire dirt floor, if you haven't already.
Other than that, the air itself will provide decent insulation.
-kevin
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If that is true, why don't they just leave the air space between the sheathing and drywall in a house? Why do we waste money putting up all the fiberglass?
I'd insulate with two inches of foam board at a minimum.
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Now any moisture passes up through the house that comes up from the ground, who knows how much water the insulation might hold possibly leading to rot. 1st put down a plastic moisture barrier on the dirt. Your location, amount of rain and soil humidity need to be known first. If its to high you will have problems.
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1. There's typically a lot more outside wall than there is floor (in terms of square feet). More heat loss.
2. Because warm air rises and the walls are therefore normally a lot warmer than the floor. More heat loss.
3. And most of all, because the outside walls are subject to the wind chill effect. More heat loss. The floor is insulated by the dirt and rock -- quite a few feet of it too ;-)
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But the earth is cooler than the inside air. As long as it is cooler, is not Insulated, it is drawing heat. Insulation helps. Energy efficient homes are built with 1" or 2" of insulation under the slab.
I agree that other places have much more heat loss, but over time, loss is loss and if you can stop it you save money. Don't just take my word for it.
http://www.hgtvpro.com/hpro/bp_insulation/article/0,2617,HPRO_20150_3463250,00.html
http://www.buildingscience.com/resources/foundations/renovating_your_basement.pdf
https://www03.cmhc-schl.gc.ca/b2c/b2c/init.do?language=en&shop=Z01EN&areaID 00000042&productID000000420000000051
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Sure, more is always better. Insulatio ad absurdum.

But the OP doesn't have a slab.
Besides, what is 1" or 2" of insulation under a slab? It's effectively 1" or 2" of air.
The OP already has that and more.

It generally costs money to insulate and some of those investments can pay for themselves very quickly. Others never recoup the initial cost.
And if inappropriately installed insulation creates or contributes to moisture problems, rot and mold one has a highly negative return.

Since the OP doesn't have a basement or a slab I'm not sure what point these links are trying to make.
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Malcolm Hoar wrote:

As far as venting etc, you are chinging things from what they were over the last 150 years, so things will change....
If you are worried about moisture etc, use foam.
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Been there done that, pointless waste of time and materials. The floors were nearly, if not, as cold after the install. We did a good job & hung R-19 between the joists with chicken wire to hold it in place. Warm air rises, cold air sinks you aren't really changing anything.
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You certainly are changing things. Heat moves three ways, conduction, convection, radiation. You are addressing only convection. While hot air is rising, heat can also be conducted to the ground that is a lower temperature. Heat always moves to where there is less of it. Laws of physics, not opinion.
Were the floors as cold after you insulated? Any flat smooth surface is going to feel cool at room temperature. It has to do with skin contact to the smooth surface. Your body is about 97 degrees. The floor is about 70 degrees. Following the laws of physics, the heat from your body is drawn to the cooker surface. A flat wood, tile, or concrete floor is going to feel cooler than a carpeted one because of the greater surface contact as compared to a bumpy one with air pockets.
Putting insulation under the floor reduces the amount of heat that can pass as it is drawn to the cooler area.
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All I know is that any other improvement to insulation, (better doors, better windows, walls stuffed, attic R level raised) have shown a marked and noticeable difference both in utilities and comfort. The floor joist job was a 1 on a scale of 1-10 with 1 sucking and 10 as fantastic, if I had it to do over, I'd just have thrown the same amount of insulation into the attic.
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Bingo! Air pockets.
Still air is an excellent insulator. Most insulation materials are largely comprised of ummmm, air.

The OP already has some of that under the floor. His crawl space is sealed (not vented) and shallow. Additional insulation will help in theory but the effect will be insignificant in practice, in my view.
If his crawl space was 3 foot deep and ventilated, that would be a very different situation.
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IF my crawl space was 3', I'd be in hog heaven!! LOL! It's amazing the planning you have to do with plumbing and electrical if you don't want, (or can't get) ANY of it below the floor.
Steve
PS. THANKS for all the replies. I think I'll plastic the dirt, and perhaps foam board around the perimeter and be done. I'll post pictures someday. <G>
s
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Then again, we have shoes, and a small foot surface.
Nick
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But air conducts and heat radiates downwards. A vapor barrier on the ground to avoid moisture and a layer of foil over the joists with air gaps above and below can save energy.
Nick
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wrote:

..less than almost anything other than a vacuum. Check the thermal conductivity of air in a suitable reference work.

And a floor, which is generally not very warm to start with, isn't going to radiate very much (in any direction).
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Indeed!
I recall from eons ago class that the radiation amount varies as the (absolute!) temperature TO THE FOURTH POWER.
David
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put your zipcode in the manufacturer's blank at: http://www.owenscorning.com/around/roofing/zip.asp?ckie=complete
and read up at: http://www.buildingscience.com/resources/homeowner.htm
Steve Barker LT wrote:

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thanks for the links. I need all the mold info i can get.
steve

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