{"data":{"id":"us/24-cfr-3280.509","jurisdiction":"us","citation":"24 CFR 3280.509","heading":"Criteria in absence of specific data.","body":"In the absence of specific data, for purposes of heat-loss/gain calculation, the following criteria shall be used:\n(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.\nInfiltration Heat-Loss = 0.7 (T) (ft. of perimeter), BTU/hr.\nwhere: T = 70 minus the heating system capacity certification temperature stipulated in the Heating Certificate, in F.\n(b) Framing areas.\nWall 15 percent of wall area less windows and doors.\nFloor and Ceiling 10 percent of the area.\n(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:\nTable to Paragraph (c)—Effect of Insulation Compression and Restriction on R-Values\nOriginal thickness (%) Non-uniform (a) restriction Uniform (b) compression batt (%)\nBatt (%) Blown (%)\n0 20 15 0\n1 26 21 1\n2 32 25 2\n3 36 28 4\n4 38 30 5\n5 41 32 7\n6 43 33 8\n7 45 35 10\n8 46 36 11\n9 48 38 13\n10 49 39 14\n11 51 40 15\n12 52 42 17\n13 53 43 18\n14 54 44 20\n15 55 45 21\n16 57 46 22\n17 58 47 24\n18 59 48 25\n19 59 49 26\n20 60 50 28\n21 61 51 29\n22 62 52 30\n23 63 52 31\n24 64 53 33\n25 65 54 34\n26 65 55 35\n27 66 56 36\n28 67 57 37\n29 68 57 39\n30 68 58 40\n31 69 59 41\n32 70 60 42\n33 70 60 43\n34 71 61 44\n35 72 62 45\n36 72 63 47\n37 73 63 48\n38 74 64 49\n39 74 65 50\n40 75 65 51\n41 75 66 52\n42 76 67 53\n43 76 68 54\n44 77 68 55\n45 78 69 56\n46 78 70 57\n47 79 70 58\n48 79 71 59\n49 80 71 60\n50 80 72 61\n51 81 73 62\n52 81 73 63\n53 82 74 64\n54 82 75 65\n55 83 75 65\n56 83 76 66\n57 84 76 67\n58 84 77 68\n59 84 78 69\n60 85 78 70\n61 85 79 71\n62 86 79 72\n63 86 80 73\n64 87 81 74\n65 87 81 74\n66 88 82 75\n67 88 82 76\n68 88 83 77\n69 89 84 78\n70 89 84 78\n71 90 85 79\n72 90 85 80\n73 90 86 81\n74 91 86 82\n75 91 87 82\n76 92 87 83\n77 92 88 84\n78 92 89 85\n79 93 89 85\n80 93 90 86\n81 93 90 87\n82 94 91 88\n83 94 91 88\n84 95 92 89\n85 95 92 90\n86 95 93 91\n87 96 93 91\n88 96 94 92\n89 96 94 93\n90 97 95 93\n91 97 95 94\n92 97 96 95\n93 98 96 95\n94 98 97 96\n95 98 97 97\n96 99 98 97\n97 99 98 98\n98 99 99 99\n99 100 99 99\n100 100 100 100\nNote: 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).\n(a) Non-uniform restriction is that which occurs between non-parallel planes, such as in the ceiling near the eaves.\n(b) Uniform compression is compression between parallel planes, such as that which occurs in a wall.\n(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.\n(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.\n(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.\n(g) Return air cavities. Cavities used as return air plenums shall be considered to be at living space temperature.","path":["Title 24—Housing and Urban Development","Subtitle B—Regulations Relating to Housing and Urban Development","CHAPTER XX—OFFICE OF ASSISTANT SECRETARY FOR HOUSING—FEDERAL HOUSING COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT","PART 3280—MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS","Subpart F—Thermal Protection"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-24.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:24:55Z","sha256":"268181eae413147b7038c734e8d2570d9c32c2b7fc3a11ff75643fc1016ff68e","source_id":"us-cfr","stale":true,"prev":"us/24-cfr-3280.508","next":"us/24-cfr-3280.510"},"notice":"GroundRules: Original legal text. Not legal advice."}