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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
There are two ways to insulate a crawlspace: at the floor above it, or around the perimeter walls with the space sealed up. This sizes both so you can compare material and price before you commit.
With these inputs:
| Result | Value |
|---|---|
| Perimeter wall area | 449 sq ft |
| Subfloor area | 1,232 sq ft |
| Vapor barrier needed | 1,288 sq ft |
| R-value at this thickness | R-10 |
| Wall material cost | $377 |
| Floor material cost | $1,035 |
| Installed cost (walls, pro) | $867 |
Wall area = 2 × (length + width) × wall height · Subfloor area = length × width · Vapor barrier = floor area × 1.15 for overlap · Cost = area × cost per sq ft-inch × thickness
If the crawlspace is dry and can be sealed, insulating the perimeter walls and encapsulating with a vapor barrier performs better — ducts and pipes end up inside the conditioned envelope. Insulate the floor above only if the crawlspace stays vented.
Yes. Bare dirt pushes gallons of moisture into the house every day. Use 6 to 20 mil sheeting across the whole floor, lapped 12 inches and run up the walls.
It depends on whether the crawlspace is vented. A vented crawlspace is outside the thermal envelope, so insulation goes in the floor above. A sealed and conditioned crawlspace is inside it, so insulation goes on the perimeter walls — which is usually less area and brings the ductwork and pipes inside the envelope too. Doing both is wasted money; doing the wrong one traps moisture.
On bare earth, yes, and it does more good than the insulation. Ground moisture evaporating into a crawlspace is the source of most crawlspace problems, and a sealed ground cover lapped up the walls stops it at source. Insulating a damp crawlspace without covering the ground first generally makes the damp worse.
They are common in floor assemblies but they are unforgiving there — batts installed under a floor sag over time as their supports fail, and a sagging batt with an air gap above it does very little. If you use them, support them properly with wire rods rather than relying on friction, and expect to inspect them.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.