CLTDs for flat roofs without suspended ceilings

From ASHRAE (1989), with permission

Click here to see CLTD values for roofs with suspended ceilings.
Click here to see construction details for the different roof types.

Roof No.

Description of construction Weight, lb/ft2 U value, Btu/hr·ft2·°F

Solar time

Hr of max. CLTD

Min. CLTD

Max. CLTD

Diff.
CLTD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

1

Steel sheet with 1" (or 2") insulation

7 (8) 0.213 (0.124)

1

-2

-3

-3

-5

-3

6

19

34

49

61

71

78

79

77

70

59

45

30

18

12

8

5

3

14

-5

79

84

2

1" wood with 1" insulation

8 0.170

6

3

0

-1

-3

-3

-2

4

14

27

39

52

62

70

74

74

70

62

51

38

28

20

14

9

16

-3

74

77

3

4" lightweight concrete

18 0.213

9

5

2

0

-2

-3

-3

1

9

20

32

44

55

64

70

73

71

66

57

45

34

25

18

13

16

-3

73

76

4

2" heavyweight concrete with 1" (or 2") insulation

29 0.206 (0.122)

12

8

5

3

0

-1

-1

3

11

20

30

41

51

59

65

66

66

62

54

45

36

29

22

17

16

-1

67

68

5

1" wood with 2 " insulation

9 0.109

3

0

-3

-4

-5

-7

-6

-3

5

16

27

39

49

57

63

64

62

57

48

37

26

18

11

7

16

-7

64

71

6

6" lightweight concrete

24 0.158

22

17

13

9

6

3

1

1

3

7

15

23

33

43

51

58

62

64

62

57

50

42

35

28

18

1

64

63

7

2.5" wood with 1" insulation

13 0.130

29

24

20

16

13

10

7

6

6

9

13

20

27

34

42

48

53

55

56

54

49

44

39

34

19

6

56

50

8

8" lightweight concrete

21 0.126

35

30

26

22

18

14

11

9

7

7

9

13

19

25

33

39

46

50

53

54

53

49

45

40

20

7

54

47

9

4" heavyweight concrete with 1" (or 2") insulation

52 (52) 0.200 (0.120)

25

22

18

15

12

9

8

8

10

14

20

26

33

40

46

50

53

53

52

48

43

38

34

30

18

8

53

45

10

2.5" wood with 2" insulation

13 0.093

30

26

23

19

16

13

10

9

8

9

13

17

23

29

36

41

46

49

51

50

47

43

39

35

19

8

51

43

11

Roof terrace system

75 0.106

34

31

28

25

22

19

16

14

13

13

15

18

22

26

31

36

40

44

45

46

45

43

40

37

20

13

46

33

12

6" heavyweight concrete with 1" (or 2") insulation

75 (75) 0.192 (0.117)

31

28

25

22

20

17

15

14

14

16

18

22

26

31

36

40

43

45

45

44

42

40

37

34

19

14

45

31

13

4" wood with 1" (or 2") insulation

17 (18) 0.106 (0.078)

38

36

33

30

28

25

22

20

18

17

16

17

18

21

24

28

32

36

39

41

43

43

42

40

22

16

43

27