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We have a new house, well built, spray foam insulation, tight seals. My daughter's room is over an unfinished area of the basement and is COLD this winter. There are vents in the unfinished area, but we have them closed because we don't want to heat that area. We probably wouldn't ever finish that room because it is our main storage space. The whole unfinished space is below ground. My husband and I are having a debate. Do we install foam board insulation on the walls in the un finished area or do we spray foam or use other insulation in the ceiling of the unfinished area? Or both? Our HVAC is not the issue, we have checked that out.

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What kind of insulation is in the floor of the bedroom? –  markthegrea Jan 13 '13 at 2:37
    
The ceiling below the floor is uninsulated...The floor in the bedroom is hardwood –  Candice Jan 14 '13 at 1:01
    
I don't remember what insulation we put in the floor. Going back and putting insulation under the floor probably won't be a viable option right now. The floor isn't just cold, the whole room is cold. We don't care about chilly floors, we wear socks or slippers! –  Candice Jan 16 '13 at 5:27
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2 Answers

If the ceiling of the unfinished space is the floor of the bedroom and is uninsulated, the floor of the bedroom is going to be cold. It would help a lot if that floor was insulated. There is not any real downside to insulating that floor or the unheated space. Insulation on the walls of the unheated space would help a bit, but you will see much better results if you insulate the ceiling/floor first. Doing both would be great.

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Thanks...we have been debating for a while about the first thing to do. –  Candice Jan 14 '13 at 1:02
    
I was watching This Old House the other day and they had a segment about this. They made a comment that whatever you do, if it is unheated below, you will never have a comfortable floor. I believe you are fighting science: Heat rises. Since you have a hardwood floor it will never be warm, even with insulation. They suggested heating elements of some sort. I believe they installed a small hydronic system. In your case, if you had a duct underneath the floor, you might just heat the basement room in the winter... –  markthegrea Jan 14 '13 at 16:00
    
Thanks - I will check on the duct....I honestly have never paid attention. –  Candice Jan 16 '13 at 5:25
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There is no point in insulating a cold unheated room! Concentrate instead on keeping the heat inside the warm bedroom. The best way to insulate a cold floor is, to lay sheets of tightly butted polystyrene or similar closed cell insulation on the existing floor and to then cover them with glued t&g oriented strand board. This way you have a fully floating floor, there are no heat bridges to syphon away your heat

To have a really warm floor (no cold feet) have sheet polystyrene, OSB, underlay, carpet. This will give you a carpet surface temperature the same as the room air temperature at floor level. ie; with an air temperature of 22C you will have a carpet surface temperature of 22C.

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The bedroom is over unfinished basement space. What you describe is a lot of work in a finished bedroom, compared with simply insulating the bedroom floor from below. In my mind, the answer is simple. If the basement is to be an unheated space, the "ceiling" of the basement space, which is the space between the joists for the floor above, should be insulated. –  Tim B Jan 15 '13 at 12:51
    
Thanks everyone. The house is 6 months old so I am not going to do what is suggested for the floor above. Let me clarify - the floor isn't "cold", the entire temperature of the room is 5-10 degrees colder than the house. No leaks in walls, windows, etc... spray foam insulation in all exterior walls. We have wood floors to help with allergies so carpet is not an option. Also -the finished space is pretty small so the cost of insulating isn't going to be huge. Maybe a 10X10 or 10X12 space. –  Candice Jan 16 '13 at 5:28
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