Adding Insulation Under Floor


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Old 11-22-17, 09:57 AM
W
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Adding Insulation Under Floor

I recently had an addition built on helical piles and had the underfloor insulated with spray foam (see attached image). The insulation does an "ok" job but I feel the floor is still a bit on the cool side in the winter. The crawl space in the image is still a ventilated space even although I have added lattice around the perimeter.
Would there be any benefit to adding sheets of expanded polystyrene board to the underside of the joists shown in the attached image ? The EPS Sheathing has a R8 value .
 
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Old 11-22-17, 10:34 AM
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Would it help. Yes. Would you be able to notice... maybe not.

How much insulation R value is in the floor already? Spray foam has an R value of about 6 per inch of thickness. If you already have 6 inches then you have an R 36 floor. Adding R8 insulation will help but is only about a 20% improvement to go from R36 to R44. 20% is significant but you might not notice it. If your floor had nothing it might have an R value of 2 and adding insulation with R8 would be a huge increase and very noticeable.
 
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Old 11-22-17, 11:36 AM
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Thanks Pilot. The insulation has an R value of 31. Would you say that the couple of inches of exposed joists could also be a cause of cold transfer ?
 
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Old 11-22-17, 12:44 PM
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The r-value affects the heat loss, double the r-value and halve the heat loss. But doubling the r-value only makes a small difference in surface temp and surface temp is what you share with those floors. Citations available.

Bud
 
 

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