Floor Construction Templates
Floor Type 1: Wood-Frame Floor Over Unconditioned Space
Typical raised floor over crawlspace or garage
Interior
Hardwood flooring
3/4"
19 mm
k = 0.080 Btu/(hr·ft·°F)<br>λ = 0.138 W/(m·K)
R-0.94 (RSI-0.16)
Subfloor
OSB or plywood
3/4"
19 mm
k = 0.077 Btu/(hr·ft·°F)<br>λ = 0.133 W/(m·K)
R-0.93 (RSI-0.16)
Structure
Floor joists (16" OC)
9-1/2" (2x10)
241 mm
k = 0.080 Btu/(hr·ft·°F)<br>λ = 0.138 W/(m·K)
R-11.9 (RSI-2.09)
Insulation
Fiberglass batt
9-1/2"
241 mm
k = 0.027 Btu/(hr·ft·°F)<br>λ = 0.047 W/(m·K)
R-30 (RSI-5.3)
Air barrier/vapor
Rigid board or membrane (Class III)
-
-
-
-
Exterior
Ventilated crawlspace below
-
-
-
-
Total Assembly: R-30 hr·ft²·°F/Btu (RSI-5.3 m²·K/W)
Notes: Insulation goes between joists with the vapor control facing up toward conditioned space. Hold it tight to the subfloor or you'll get air washing through it. The crawlspace below should be vented (old school) or closed and conditioned (new school).
Floor Type 2: Slab-on-Grade with Perimeter Insulation
Ground-supported concrete slab
Interior
Finished flooring (tile, etc.)
Variable
Variable
Variable
Variable
Slab
Reinforced concrete
4"
100 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-0.5 (RSI-0.09)
Poly vapor barrier
Polyethylene (Class I)
6 mil
0.15 mm
-
-
Sub-slab insulation
XPS rigid foam
2"
50 mm
k = 0.020 Btu/(hr·ft·°F)<br>λ = 0.035 W/(m·K)
R-10 (RSI-1.76)
Capillary break
Crushed stone
4"
100 mm
Variable
Negligible
Perimeter insulation
XPS rigid foam (vertical)
2" × 24" deep
50 × 600 mm
k = 0.020 Btu/(hr·ft·°F)<br>λ = 0.035 W/(m·K)
R-10 (RSI-1.76)
Below grade
Compacted soil
-
-
-
-
Total Assembly: R-10 sub-slab + R-10 perimeter (RSI-1.76 + RSI-1.76)
Notes: Most heat loss from slabs happens at the perimeter, not through the center. That's why the vertical insulation at the edge matters more than you'd think. The poly goes under the slab to stop moisture vapor, not between insulation layers where it creates condensation problems.
Floor Type 3: Radiant Heat Slab
Hydronic in-floor heating
Interior
Tile or engineered hardwood
1/2"
13 mm
Variable
Minimal (conductive)
Topping slab
Lightweight concrete or gypcrete
1-1/2"
38 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-0.19 (RSI-0.03)
Tubing
PEX tubing (embedded)
1/2" dia
13 mm dia
-
-
Structural slab
Reinforced concrete
4"
100 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-0.5 (RSI-0.09)
Poly vapor barrier
Polyethylene (Class I)
6 mil
0.15 mm
-
-
Sub-slab insulation
XPS rigid foam
3"
75 mm
k = 0.020 Btu/(hr·ft·°F)<br>λ = 0.035 W/(m·K)
R-15 (RSI-2.64)
Capillary break
Crushed stone
4"
100 mm
Variable
Negligible
Total Assembly: R-15 sub-slab (RSI-2.64)
Notes: You want the heat going up, not down, so the sub-slab insulation is critical. The topping slab provides thermal mass and protects the tubing. Don't use high-R-value flooring over radiant or you'll defeat the whole point.
Floor Type 4: Suspended Concrete Slab
Post-tensioned or reinforced concrete floor
Interior
Finished flooring (carpet, tile)
Variable
Variable
Variable
Variable
Structural slab
Post-tensioned concrete
8"
200 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-1.0 (RSI-0.18)
Below
Conditioned space or parking
-
-
-
-
Total Assembly: R-1.0 hr·ft²·°F/Btu (RSI-0.18 m²·K/W)
Notes: This is a thermal boundary only if there's unconditioned space below, which is rare in multi-story buildings. Usually both sides are conditioned so thermal performance isn't the concern. Sound transmission is, but that's a different conversation.
Floor Type 5: Raised Access Floor
Commercial computer room or office floor
Interior
Carpet tile or stone
Variable
Variable
Variable
Variable
Floor panels
Steel or aluminum panels
1-1/4"
32 mm
k = 314 Btu/(hr·ft·°F)<br>λ = 543.5 W/(m·K)
Negligible
Air plenum
Adjustable pedestals (6"-24")
12"
305 mm
-
R-1.5 (RSI-0.26)
Structural slab
Concrete slab
6"
152 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-0.75 (RSI-0.13)
Total Assembly: R-2.25 hr·ft²·°F/Btu (RSI-0.40 m²·K/W)
Notes: The plenum is for cabling and HVAC distribution, not insulation. You access it by lifting panels, which means the thermal boundary is really at the structural slab below. The air space provides minimal R-value but excellent cable management.
Floor Type 6: Timber Frame Floor
Heavy timber construction
Interior
Tongue & groove planking
1-1/2"
38 mm
k = 0.080 Btu/(hr·ft·°F)<br>λ = 0.138 W/(m·K)
R-1.9 (RSI-0.33)
Structure
Timber beams (48" OC)
10" × 12"
254 × 305 mm
k = 0.080 Btu/(hr·ft·°F)<br>λ = 0.138 W/(m·K)
R-12.5 (RSI-2.2)
Insulation (between beams)
Rigid mineral wool
10"
254 mm
k = 0.025 Btu/(hr·ft·°F)<br>λ = 0.043 W/(m·K)
R-40 (RSI-7.0)
Air barrier
Vapor-intelligent membrane (Variable)
-
-
-
-
Below
Exposed timber ceiling or conditioned space
-
-
-
-
Total Assembly: R-40 hr·ft²·°F/Btu (RSI-7.0 m²·K/W)
Notes: Heavy timber is exposed for aesthetic and structural reasons, which means insulation goes between beams. The timber itself provides some R-value but creates thermal bridging. Trade-off for the look.
Floor Type 7: Insulated Concrete Form (ICF) Floor
Foam form stays in place as insulation
Interior
Finished flooring
Variable
Variable
Variable
Variable
Top insulation
EPS foam
2"
50 mm
k = 0.024 Btu/(hr·ft·°F)<br>λ = 0.041 W/(m·K)
R-8 (RSI-1.4)
Structural slab
Reinforced concrete
6"
152 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-0.75 (RSI-0.13)
Bottom insulation
EPS foam
2"
50 mm
k = 0.024 Btu/(hr·ft·°F)<br>λ = 0.041 W/(m·K)
R-8 (RSI-1.4)
Ceiling finish
Gypsum or exposed foam
1/2"
13 mm
k = 0.096 Btu/(hr·ft·°F)<br>λ = 0.166 W/(m·K)
R-0.45 (RSI-0.08)
Total Assembly: R-17.2 hr·ft²·°F/Btu (RSI-3.0 m²·K/W)
Notes: Same concept as ICF walls but horizontal. The foam formwork remains as permanent insulation on both sides of the concrete. Sound transmission through the concrete is still an issue despite the insulation.
Floor Type 8: Insulated Above Parking Garage
Separation between unconditioned parking and conditioned space
Interior
Hardwood or tile
3/4"
19 mm
Variable
Variable
Subfloor
Concrete topping
2"
50 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-0.25 (RSI-0.04)
Insulation
Rigid mineral wool or XPS
3"
75 mm
k = 0.025 Btu/(hr·ft·°F)<br>λ = 0.043 W/(m·K)
R-12 (RSI-2.1)
Waterproofing
Membrane
-
-
-
-
Structural slab
Post-tensioned concrete
8"
200 mm
k = 0.90 Btu/(hr·ft·°F)<br>λ = 1.56 W/(m·K)
R-1.0 (RSI-0.18)
Below
Parking garage (unconditioned)
-
-
-
-
Total Assembly: R-13.25 hr·ft²·°F/Btu (RSI-2.3 m²·K/W)
Notes: The waterproofing membrane protects the structure from parking garage moisture and chemicals. Insulation goes above it to stay dry and effective. Getting the drainage right matters more than you'd think, because pooling water finds every weakness in the membrane.
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