1. LawStack
  2. Title 24 - Housing and Urban Development
  3. Subtitle B - REGULATIONS RELATING TO HOUSING AND URBAN DEVELOPMENT
  4. Chapter XX - OFFICE OF ASSISTANT SECRETARY FOR HOUSING—FEDERAL HOUSING COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT
  5. Part 3280 - MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS
  6. Subpart F - Thermal Protection
  7. 24 CFR § 3280.509
24 CFR § 3280.509
Criteria in absence of specific data
February 22, 2021
CFR

In the absence of specific data, for purposes of heat-loss/gain calculation, the following criteria shall be used:

(a) Infiltration heat loss. In the absence of measured infiltration heat loss data, the following formula shall be used to calculate heat loss due to infiltration and intermittently operated fans exhausting to the outdoors. The perimeter calculation shall be based on the dimensions of the pressure envelope.

Infiltration Heat-Loss = 0.7 (T) (ft. of perimeter), BTU/hr.

where: T = 70 minus the heating system capacity certification temperature stipulated in the Heating Certificate, in F.

(b) Framing areas.

Open Table
Wall 15 percent of wall area less windows and doors.
Floor and Ceiling 10 percent of the area.

(c) Insulation compression. Insulation compressed to less than nominal thickness and loose-fill insulation in sloping cavities must have its nominal R-values reduced in compressed areas in accordance with the following table:

Table to Paragraph (c)—Effect of Insulation Compression and Restriction on R-Values

Open Table
Original thickness
(%)		 Non-uniform (a) restriction Uniform (b)
compression batt
(%)
Batt
(%) 		Blown
(%)
0 20 15 0
1 26 21 1
2 32 25 2
3 36 28 4
4 38 30 5
5 41 32 7
6 43 33 8
7 45 35 10
8 46 36 11
9 48 38 13
10 49 39 14
11 51 40 15
12 52 42 17
13 53 43 18
14 54 44 20
15 55 45 21
16 57 46 22
17 58 47 24
18 59 48 25
19 59 49 26
20 60 50 28
21 61 51 29
22 62 52 30
23 63 52 31
24 64 53 33
25 65 54 34
26 65 55 35
27 66 56 36
28 67 57 37
29 68 57 39
30 68 58 40
31 69 59 41
32 70 60 42
33 70 60 43
34 71 61 44
35 72 62 45
36 72 63 47
37 73 63 48
38 74 64 49
39 74 65 50
40 75 65 51
41 75 66 52
42 76 67 53
43 76 68 54
44 77 68 55
45 78 69 56
46 78 70 57
47 79 70 58
48 79 71 59
49 80 71 60
50 80 72 61
51 81 73 62
52 81 73 63
53 82 74 64
54 82 75 65
55 83 75 65
56 83 76 66
57 84 76 67
58 84 77 68
59 84 78 69
60 85 78 70
61 85 79 71
62 86 79 72
63 86 80 73
64 87 81 74
65 87 81 74
66 88 82 75
67 88 82 76
68 88 83 77
69 89 84 78
70 89 84 78
71 90 85 79
72 90 85 80
73 90 86 81
74 91 86 82
75 91 87 82
76 92 87 83
77 92 88 84
78 92 89 85
79 93 89 85
80 93 90 86
81 93 90 87
82 94 91 88
83 94 91 88
84 95 92 89
85 95 92 90
86 95 93 91
87 96 93 91
88 96 94 92
89 96 94 93
90 97 95 93
91 97 95 94
92 97 96 95
93 98 96 95
94 98 97 96
95 98 97 97
96 99 98 97
97 99 98 98
98 99 99 99
99 100 99 99
100 100 100 100

Note: To use this table, first compute the restricted insulation thickness as a fraction of the uncompressed (full) insulation thickness. Then look up the R-value remaining from the appropriate column (Non-uniform Restriction, Batt Non-uniform Restriction, Blown or Uniform Compression, Batt). Example: Assume a section of loose-fill ceiling insulation went from R-25 insulation at a height of 10 inches to a minimum height of 2 inches at the edge of the ceiling. The ratio of minimum to full thickness is 0.20 (2 divided by 10). Look up 0.20 (20 percent), read across to column 3 (Non-uniform Restriction, Blown), and read 50 percent. Therefore, the R-value of the loose-fill insulation over the restricted area would be R-12.5 (50 percent of 25).

(a) Non-uniform restriction is that which occurs between non-parallel planes, such as in the ceiling near the eaves.

(b) Uniform compression is compression between parallel planes, such as that which occurs in a wall.

(d) Air supply ducts within floor cavity. Air supply ducts located within a floor cavity shall be assumed to be heating or cooling the floor cavity to living space temperatures unless the duct is structurally isolated by the framing system or thermally insulated from the rest of the floor cavity with a thermal insulation at least equal to R-4.

(e) Air supply ducts within ceiling cavity. Where supply ducts are located in ceiling cavities, the influence of the duct on cavity temperatures shall be considered in calculating envelope heat loss or heat gain.

(f) The supply duct loss (and/or heat gain where applicable—See §3280.511) shall be calculated using the actual duct surface area and the actual thickness of insulation between the duct and outside of the manufactured home. If there is an air space of at least 1⁄2 inch between the duct and the insulation, heat loss/gain need not be calculated if the cavity in which the duct is located is assumed to be at living space temperature. The average temperature inside the supply duct, including ducts installed outside the manufactured home, shall be assumed to be 130 F for purposes of calculation of heat loss and 60 F for heat gain.

(g) Return air cavities. Cavities used as return air plenums shall be considered to be at living space temperature.

[40 FR 58752, Dec. 18, 1975. Redesignated at 44 FR 20679, Apr. 6, 1979, as amended at 78 FR 73984, Dec. 9, 2013]

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§ 3280.508 Heat loss, heat gain and cooling load calculations
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§ 3280.510 Heat loss certificate

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