Insulating basement ceiling

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  #1  
Old 07-15-08, 11:27 PM
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Insulating basement ceiling

We are in the process of purchasing a house and the heat loss analysis showed we are losing a lot in the floor. The basement isn't finished but also isn't dark dank and dingy if you know what I mean. The laundry room is down there so I want it to be fairly warm, anyway what kind of insulation should I use in the basement ceiling between the floor joists???

I was also wondering if I need to put up some kind of insuation on the concrete walls or since it is below ground will it keep out the cold??
 
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Old 07-16-08, 04:50 AM
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Insulating the ceiling will have no effect on comfort. It will never pay back. Insulating the walls will be a good idea and will have pay back.
 
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Old 07-16-08, 07:49 AM
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Won't it keep heat upstairs??? How would that not effect comfort? My main concern is keeping heat/air from escaping throgh the floor to the basement *energy saver*

What kind of insulation should I use for the basement walls?
 
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Old 07-16-08, 08:07 AM
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Heat will rise. So insulating the basement will not keep heat up stairs. How will you be finishing the basement?
 
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Old 07-16-08, 08:16 AM
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You need to decide if the basement will be in or outside of the building/insulation envelope. I would recommend keeping it inside. In that case, insulate the basements walls and forget about the ceiling.

I would agree you probably don't have a great heat loss through the floor, although you could have a comfort issue (cold floors). This will improve if you insulate the basement walls and add registers/returns to the basement, if not already there. This will reduce the temperature difference between the floors and the costs will be minor.
 
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Old 07-16-08, 09:26 AM
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I'm not going to finish it as far as drywall carpet etc (unless insulation & drywall will help keep some heat in)

It has some registers in the ductwork already to heat the basement but i'm not sure how many so I don't know how warm it will stay.

So what kind of insulation should I use on the walls??
 
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Old 07-16-08, 10:19 AM
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Here is a lot of good info on the subject.

http://www.nrel.gov/docs/fy02osti/26455.pdf

It's usually best to find out what's common practice in your area (batts or foam). Also check on fire codes, some products may need to be covered with drywall for fire safety, depending on your local codes.
 
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Old 07-21-08, 07:51 PM
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Ground temp is 58 degrees year round.
In the summer it is cooler then outside, in the winter it is warmer then outside. Putting insulation in your fllor joists will only keep that natural energy in the basement and not change your main floor conditions. In fact it could make it worse.

the best bang for the buck is expanding foam in all the openings through the wall. Fiberglass insulation around teh top of the basement wall. That space between the cinder blocks and floor joist only has one 2x pieces of lumber and your outside siding between the outside world and your basement. R value of like 5-8.
 
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Old 07-21-08, 08:23 PM
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I wonder why everyone (everyone in the AC/heat forum) said I was losing most of my heat through my floor....??

What about putting insulation on the basement walls?? Will that keep some of the heat in/cold 58 degree temp out in the winter??
 
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Old 07-22-08, 02:04 PM
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Yes.

There is no reason to insulate teh floor joists unless they are over a crawl space, or other un insulated, HVAC controlled space.

Your HVAC system is just that a system. I t draws air from all over the house and pumps it to all over the house.

Your home is one big box. Insulate it as such and everything will be fine. No need to insulate between floors or section off rooms provided the house is insulated properly.

Couple of sources of information.
This old house, and the government.

Notice the recommendation to insulate your rim joist. That is your biggest bang for teh buck in the basement insulation.

http://www.thisoldhouse.com/toh/askt...131829,00.html

http://www.eere.energy.gov/consumer/.../mytopic=11470
 
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Old 07-22-08, 05:32 PM
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What is he rim joist?? Is that where the concrete wall ends and the upper floor starts?
 
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Old 07-23-08, 10:06 PM
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Yes. The rim joist is the rim around the top of the basement cement walls and the bottom of the first floor. When tehy frame the house they lay the 2x12 on top of the support beam / cement wall (floor joists). Then attach a 2x12 all the way around the outside of the house (rim joist). You can see the 2x12 from inside the baement. The only thing attached to the outside of the 2x12 is a vapor barrier, sheet of plywood and/or insulation (depends on year of house) and your siding. It is not insulated very well. Plus this is above grade (above ground level), which means it is exposed to the outside elements, air heat,cold, etc. You get what is called thermal transfer.

When you insulate the rim joist you severly reduce the amount of thermal trasnfer, heat gain (summer), loss (winter) in the basement. IF you also insulate the top of the block walls down to below frost line you will greatly reduce heat transefer through the block wall. There is a portion of your block wall that is also above grade. Frost line is how deep your ground freezes in the winter. In other words the ground is froozen solid to a certain depth. The further north you go the deeper the frost line.

Your rim joist and cement block should stop air movement, howver they wont stop thermal transfer, a piece of plastic will also stop air movement just like your blcok wall. About the only difference between the block wall and the sheet of plastic is the R value, and that isn't much of a difference. Hence the recommendation to insulate your rim joist.

That is the long version. I gave you not only where the rim joist is, I also explained why it is important to insulate it.

Got any more questions, post up.

Based on your original comment and recommendation from your other thread, sounds like there is some mis information going on. Hopefully this will help other to understand it as well.
 
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Old 07-24-08, 01:15 AM
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That was an excellent explanation!! What is usually used to insulate the rim joist and wall down to the frost line (bats, foam, etc) and what R value??
 
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Old 07-27-08, 05:57 PM
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Typical will depend on where you live in the US. Teh federal government has recommendations. They have different recommendations for walls and attics.

http://www.energystar.gov/index.cfm?...sulation_table

R-11 to R-19.

The most important one is the rim joist. IF your going to finish the basement, then figure insulating the basement walls as part of the job. I also highly recommend you use expanding foam to fill all holes leading to the outside. A/C lines, electrical wires, plumbing (outside faucets), sewer drains/vents (even if tehy are on interior walls, tehy run into the attic and trough the roof. Basically if you see spider webs, you got an opening to the outside world. Seal it, then insulate it.
 
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Old 07-27-08, 07:35 PM
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If your bsement is a heated space, then you do not insulate between floors. If it is not heated, then you absolutely insulate the bottom of the first floor. You won't loose heat through the floor, but you will have a colder space bellow you to transfer up through the floor and make it feel colder at foot and make your heating system work harder than it has to.
 
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Old 07-30-08, 08:50 AM
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Originally Posted by Kremeriky View Post
If it is not heated, then you absolutely insulate the bottom of the first floor.
This isn't particularly good advice. The amount of money spent on insulating materials would take a long time to recoup in any potential energy savings.

Cold first floor surfaces will not automatically become warm with a layer of fiberglass under them. Try as you may, warm air will not settle at the floor. If you want warm floors you either heat the space below (i.e. the basement), or put in radiant in-floor heat.
 
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