U values of building assemblies

Abstracted from ASHRAE (1989), with permission

Coefficients of transmission U for wood doors (W/m2·°C)

Thickness

Description

Winter

Summer

24 km/h wind
21°C inside temperature

12 km/h wind
24°F inside temperature

No storm door

Wood storm door (50% glass)

Metal storm door

No storm door

35 mm

Hollow-core flush door

2.7

1.7

1.8

2.6

35 mm

Solid-core flush door

2.2

1.5

1.6

2.2

44 mm

Solid-core flush door

1.9

1.6

1.4

1.8

44 mm

Solid-core flush door with single glazing (17% glass)

2.6

1.6

1.8

2.5

44 mm

Solid-core flush door with insulating glass (17% glass)

2.1

1.4

1.5

2.0

Coefficients of transmission U for steel doors (W/m2·°C)

Thickness

Description

No storm door

Metal storm door

44 mm

Fiberglass or mineral fiber core with steel stiffeners, no thermal break

3.4 -

44 mm

Solid urethane foam core with thermal break

1.1 0.91

Overall coefficients of heat transmission U of windows,
sliding patio doors, and skylights (W/m
2·°C)

 

Single Pane

Double Pane

Triple Pane

Plastic domes

No air space

5 mm air space

6 mm space

13 mm air space

6 mm space

13 mm air space

Single wall

Double wall

No low-E coating
e = 0.84

No low-E coating
e = 0.84

No low-E coating
e = 0.84

No low-E coating
e = 0.84

Low-E coating
e = 0.6

Low-E coating
e = 0.4

Low-E coating
e = 0.2

No low-E coating
e = 0.84

No low-E coating
e = 0.84

No storm sash

No shade

Winter

6.2

3.5

3.4

2.8

2.4

2.2

1.8

2.2

1.8

   

Summer

5.9

3.7

3.5

3.2

2.9

2.7

2.2

2.5

2.2

   

Indoor shade

Winter

4.7

3.0

2.7

2.4

2.2

2.0

1.7

1.8

1.5

   

Summer

4.6

3.3

3.1

3.0

2.7

2.4

2.1

2.3

2.0

   

Glass outdoor storm sash with 25 mm airspace

No shade

Winter

2.8

2.1

2.0

1.8

1.7

1.5

1.4

1.5

1.3

   

Summer

2.8

2.3

2.2

2.2

2.0

2.2

1.7

1.8

1.8

   

Indoor shade

Winter

2.5

1.6

1.6

1.4

1.4

1.2

1.1

1.2

1.1

   

Summer

2.8

2.1

2.0

1.7

2.0

1.8

1.6

1.7

1.6

   

Glass indoor storm sash with 25 mm airspace

No shade

Winter

2.8

2.1

2.0

1.8

1.6

1.5

1.4

1.5

1.3

   

Summer

2.8

2.3

2.2

2.2

2.0

1.9

1.6

1.8

1.7

   

Indoor shade

Winter

2.5

1.6

1.6

1.4

1.4

1.2

1.1

1.2

1.1

   

Summer

2.8

2.0

2.0

2.0

1.9

1.8

1.5

1.7

1.6

   

Acrylic indoor storm sash with 25 mm airspace

No shade

Winter

2.7

2.0

1.9

1.7

1.6

1.5

1.4

1.5

1.2

   

Summer

2.7

2.2

2.2

2.1

2.0

1.8

1.6

1.8

1.6

   

Indoor shade

Winter

2.4

1.6

1.5

1.4

1.3

1.2

1.1

1.2

1.0

   

Summer

2.7

2.0

1.9

1.9

1.8

1.7

1.5

1.6

1.6

   

Exterior horizontal panels (skylights)

Winter

7.0

4.0

3.7

3.4

2.7

3.0

3.2

   

6.5

4.0

Summer

4.7

3.2

3.1

2.8

2.0

2.4

2.6

   

4.5

2.6

Notes: