Should I insulate between floors?
Bob_3md2
| Posted in General Questions on
I am insulating a 1500 sq foot workshop that has a radiant heated slab. there is a 700 sq foot loft that will be conditioned with a min split to keep ambient temp between 55 -85 F. Building is sheathed with ZIP R10. 2 x 6 Wall framing. Walls (main floor and loft) have R23 mineral wool batts.
Plan on R49 blown cellulose in attic spaces. Should I install 11 1/2″ of blown in cellulose between floors (around R38)?
In SE Michigan – climate zone 5A
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Replies
If the space above and below the floor will be the same temp the insulation will have no thermal effect it may deaden some sound.
Walta
The space above the main floor (storage loft) will generally have a colder or warmer temperature. It won't be as extreme as outdoors but there will be a significant difference,
10 -15 degrees at times.
Bob,
"The space above the main floor (storage loft) will generally have a colder or warmer temperature"
Careful with that. Much like an unconditioned attic, you can easily have the air drop below its dew point and have moisture problems in the roof.
Malcom,
Does that mean if my main space temp is a constant 68 degrees and the loft varies between 55 -80 degrees i will have roof issues? the loft space has R23 wall insulation and R49 in the attic. Again, my main question is whether i should put insulation between floors.
Bob,
The caution is that the dew point of any assembly is highly dependent on the relative humidity of the interior air - and that RH is varies by temperature. So air that is fine at say 70F can drop it's moisture when it cools to 55F.
That's what dew is, and that's what you could have happen in the attic independent of how well insulated it is. Codes acknowledge this and require you to keep attics either in or out of the conditioned area of the house. If they are outside it they need to be vented. If they are inside they need to maintain much the same humidity and temperatures as the rest of the living spaces to avoid moisture issues.
A long-winded way of saying: don't insulate the ceiling.
Malcom,
Again thanks for your answer. Still one final question just to be sure. As stated my attic assembly for the scenario I have described is vented (above the main floor and the loft). So does that change my situation. My basic concern is will I get less heat loss and have a lower heating requirement if I insulate between floors. Obviously I don’t get any benefit and the cost of insulating isn’t worth it I should leave that area uninsulated?
Bob,
I would not insulate the floor - or insulate as you suggest with the understanding that you may find you need to heat that loft to the same temperatures as the rest of the space if you have moisture problems.
Yes, your idea would save energy but it is a risky code violation.
Yes, some people ignore the risks and do it anyway. If you live in a desert or someplace that does not get cold you are more likely to get away with this game.
If you are willing risk everything in the storage area getting wet and moldy how valuable is it really to you. Too much risk just to save 5% on your energy.
Walta