CLTDs for flat roofs with suspended ceilings

From ASHRAE (1989), with permission

Click here to see CLTD values for roofs without 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

9 (10) 0.134 (0.092)

2

0

-2

-3

-4

-4

-1

9

23

37

50

62

71

77

78

74

67

56

42

28

18

12

8

5

15

-4

78

82

2

1" wood with 1" insulation

10 0.115

20

15

11

8

5

3

2

3

7

13

21

30

40

48

55

60

62

61

58

51

44

37

30

25

17

2

62

60

3

4" lightweight concrete

20 0.134

19

14

10

7

4

2

0

0

4

10

19

29

39

48

56

62

65

64

61

54

46

38

30

24

17

0

65

65

4

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

30 0.131

28

25

23

20

17

15

13

13

14

16

20

25

30

35

39

43

46

47

46

44

41

38

35

32

18

13

47

34

5

1" wood with 2 " insulation

10 0.083

25

20

16

13

10

7

5

5

7

12

18

25

33

41

48

53

57

57

56

52

46

40

34

29

18

5

57

52

6

6" lightweight concrete

26 0.109

32

28

23

19

16

13

10

8

7

8

11

16

22

29

36

42

48

52

54

54

51

47

42

37

20

7

54

47

7

2.5" wood with 1" insulation

15 0.096

34

31

29

26

23

21

18

16

15

15

16

18

21

25

30

34

38

41

43

44

44

42

40

37

21

15

44

29

8

8" lightweight concrete

33 0.093

39

36

33

29

26

23

20

18

15

14

14

15

17

20

25

29

34

38

42

45

46

45

44

42

21

14

46

32

9

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

53 (54) 0.128 (0.090)

30

29

27

26

24

22

21

20

20

21

22

24

27

29

32

34

36

38

38

38

37

36

34

33

19

20

38

18

10

2.5" wood with 2" insulation

15 0.072

35

33

30

28

26

24

22

20

18

18

18

20

22

25

28

32

35

38

40

41

41

40

39

37

21

18

41

23

11

Roof terrace system

77 0.082

30

29

28

27

26

25

24

23

22

22

22

23

23

25

26

28

29

31

32

33

33

33

33

32

22

22

33

11

12

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

77 (77) 0.125 (0.088)

29

28

27

26

25

24

23

22

21

21

22

23

25

26

28

30

32

33

34

34

34

33

32

31

20

21

34

13

13

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

19 (20) 0.082 (0.064)

35

34

33

32

31

29

27

26

24

23

22

21

22

22

24

25

27

30

32

34

35

36

37

36

23

21

37

16