insulation Levels FOR attics, WALLS, FLOORS AND BASEMENTS in cold, mixed and hot climates

Recommended R-value and U-value
Insulation materials and rated by their R-value or R, or by their U-value or U. A higher "R" (or a lower U) means more resistance to heat flow, that is, the higher the R-value (or the lower the U-value) the greater the insulating value of the material.
Wall, attic or floor Insulation requirements are also specified by R-value (or U-value). Building codes may require an attic insulation of R-40, or R-50 or R-60 (Metric U: U-0.14, or U-0.11 or U-0.09) , for instance.
U and R-values can be expressed in Metric units (Europe, Australia) or in Imperial Units (America). See: Insulation materials are rated by their R-value or U-value

Insulation requirements vary with the climate and the part of the house where the insulation is going to be installed: attics and ceilings, exterior walls, floors and slabs, basement walls...

In some mild climates, with low heating and cooling bills, you do not need very high levels of insulation in the walls or floors.

And the same goes in hot climates, where you need high levels of attic insulation but relatively low levels of wall insulation (and no slab insulation).

There are also a few cases, involving some hot climates, where cooling is mainly done by natural ventilation, breezes and shade, and where thermal insulation has a circumscribed role (rather restricted to air-conditioned rooms).

However the more general rule, for climates with high heating and cooling bills, is very high levels of insulation all over the envelope of the house, above common standards.

It's critical for comfort and energy conservation.

See: American and Australian Climate Zones

Recommended Thermal Insulation in new construction and In existing homes

Do it right the first time.

Increasing the levels of thermal insulation in new construction is relatively inexpensive and very rewarding.

recommended rvalues department of energy

Recommended Attic insulation levels (Super-insulation approach)

Recommended attic and roof insulation, for all climates: US R-50 to R-60 (Metric System: U-0.11 to U-0.1).

Thickness (approximate) for R-60 (U-0.1):
Loose-fill cellulose (R-3.5 per inch): 17 inches (44 cm)
Expanded polystyrene (R-4): 15 inches (38 cm)
High-density polyurethane (R-6,5): 9 inches (23 cm)

See: Roof vs Attic insulation .

Recommended Exterior Wall Insulation for cold, moderate and hot climates

The difference of temperature between the interior and the exterior sides of exterior walls doesn't reach such a high level as in the attics, and since it is this difference that drives the heat flow, wall insulation doesn't need to be so high in walls.

Anyway, wall insulation is critical in all climates, and as important as attic (or floor) insulation.

Recommended wall insulation levels:
Cold climates: R-30 to R-40 (U-value, Metric system: 0.19 and 0.14)
Hot climates: R-10 to R-20 (U-value, Metric system: 0.58 to 0.28).
Temperate and mixed climates: R-20 to R-30 (U-value, Metric: 0.28 to 0.19 )

Thickness (approximate) for R-30 (Metric: U-0.19):
9.5 inches (24 cm) of fiberglass
7.5 inches (19 cm) of expanded polystyrene
8 inches (20 cm) of low-density polyurethane
4.5 inches (12 cm) of polyso
Thickness (approximate) for R-20 (Metric: U-0.28):
6.3 inches (16 cm) of fiberglass
5 inches (13 cm) of expanded polystyrene
5,5 inches (14 cm) of low-density polyurethane.
3 inches (8 cm) of polyso
Thickness (approximate) for R-10 (Metric: U-0.57):
3 inches (8 cm) of fiberglass
2.5 inches (6. 5 cm) of expanded polystyrene
3 inches (7 cm) of low-density polyurethane
1.5 inches (4 cm) of polyso

More: External Walls Insulation Guide

Recommended Floor and Slab Insulation for cold, moderate and hot climates

Heat also flows through slabs and floors. In hot climates, underfloor and slab insulation may not be advantageous, but that's not the case in other climates.

Slab insulation is advantageous in moderate, mixed and cold climates, but since the ground temperature is relatively stable and moderate, the amount of required insulation is smaller: no insulation in hot climates and between R-5 and R-10 in other climates (higher in colder climates).

The recommended levels of insulation for floors over crawl spaces and basements are about R-30 (Metric system: U-0.19) in cold climates and R-10 to 20 (Metric system: U-0.56 to U-0.28) in mixed and moderate climates.

Recommended insulation materials: rigid foams or dense-rigid mineral wool boards.

Thickness (approximate) for R-30 (Metric: U-0.19):
Rigid polystyrene (expanded) or mineral wool: 7-8 inches (18 cm)
Thickness (approximate) for R-20 (Metric: U-0.28):
Rigid polystyrene (expanded) or mineral wool: 5 inches (13 cm)
Thickness (approximate) for R-10 (Metric: U-0.57):
Rigid polystyrene (expanded) or mineral wool: 2.5 inches (7 cm)
Thickness (approximate) for R-5:
Rigid polystyrene (expanded) or mineral wool: 1.2 inches (3 cm)

More: Under-floor insulation and Slab insulation

Recommended basement wall insulation for hot, moderate and cold climates

Basement walls require relatively low levels of insulation - compared to other walls, in cold climates. Insulation levels around R-10 are probably enough in most climates, with the exception of cold and very cold climates, where they should be increased to about R-20.

Thickness (approximate) for R-20 (Metric: U-0.28) (cold climates):
Rigid polystyrene (expanded) or mineral wool: 5 inches (13 cm)
Thickness (approximate) for R-10 (Metric: U-0.57)(other climates):
Rigid polystyrene (expanded) or mineral wool: 2.5 inches (7 cm)

See, for details:
Basements Interior Wall Insulation: Yes or No
Basements Exterior Wall Insulation
Slab Concrete insulation
Underfloor insulation

Addendum US Climates

Climate zones usa, energy star Cold, mild and warm climates & Recommended Insulation Levels

North American “cold climates” include Canada, and much of the northern half of the U.S., including the northern half of Missouri and the northern edge of Kansas, northern New Mexico, northern Arizona, most of  Nevada, the northeastern corner of California and most of northern Oregon and Washington. 

climate zones australiaNorth American "hot climates"include the hottest areas in the U.S.: most of Florida, the areas up to central Texas, and a large part of the Arizona and a small part of southern California. 

The other areas (the orange areas, in the first map) are included in the "moderate climates".


Canada climate zonesFor more details:
North America & Map with the recommended insulation levels per climate zone: NAIMA
Australia (second map): Your Home Australian Gov.








Top or Home PageRelated Content
Contents Top .... Home Page