![]() The major axis of the purlin is perpendicular to the rafter slope. These span tables do not apply to trussed rafter roofs. The dead loads shown at the top of span table above do not include the self weight of the purlin, however, the purlin self weight is included (in addition to the dead loads) in the calculations used to determine permissble clear spans. The allowable clear spans have been calculated in accordance with BS 5268-2:2002 Structural use of timber - Part 2: Code of practice for permissible stress design, materials and workmanship and BS 5268-7.6:1990 Structural use of timber - Section 7.6 Purlins supporting rafters. ![]() Where preformed insulation board is used as the air-impermeable insulation layer, it shall be sealed at the perimeter of each individual sheet interior surface to form a continuous layer.Dead load per square metre (in kN/m²) supported by purlin The vapor diffusion port shall protect the attic against the entrance of rain and snow. The vapor diffusion port shall serve as an air barrier between the attic and the exterior of the building. The vapor-permeable membrane in the vapor diffusion port shall have a vapor permeance rating of greater than or equal to 20 perms when tested in accordance with Procedure A of ASTM E96. Where there are multiple ports in the attic, the sum of the port areas shall be greater than or equal to the area requirement. The port area shall be greater than or equal to 1:600 of the ceiling area. An approved vapor diffusion port shall be installed not more than 12 inches (305 mm) from the highest point of the roof, measured vertically from the highest point of the roof to the lower edge of the port. In Climate Zones 1, 2 and 3, air-permeable insulation installed in unvented attics on the top of the attic floor or on top of the ceiling shall meet the following requirements: For calculation purposes, an interior air temperature of 68☏ (20☌) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months.ĥ.2. Alternatively, sufficient rigid board or sheet insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45☏ (7☌). The air-permeable insulation shall be installed directly under the air-impermeable insulation. Where both air-impermeable and air-permeable insulation are provided, the air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing in accordance with Item 5.1.1 and shall be in accordance with the R-values in Table R806.5 for condensation control. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing in accordance with the R-values in Table R806.5 for condensation control. ![]() Where air-permeable insulation is provided inside the building thermal envelope, it shall be installed in accordance with Section 5.1.1. Where only air-impermeable insulation is provided, it shall be applied in direct contact with the underside of the structural roof sheathing. Item 5.1.1, 5.1.2, 5.1.3 or 5.1.4 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |