Timber Sizes For Pitched Roof

Surveyors span tables for designing roof rafters.

Timber sizes for pitched roof.

Roof pitch between 15 and 22 5 degrees with rafter spacing. C16 timber is commonly used in floor and roof joists for internal building work. It will be all be warm roof insulation above and between with the ceiling plasterboard nailed under the rafters so no ties. It s often chosen as the standard timber for roof extensions or joist refurbishment as it s the most cost effective internal structural timber.

For pitched roofs flat roofs and ceiling joists. The wider the gap between the rafters the thicker the rafter and lath timbers need to be. 12 5 15mm plasterboard should be fixed at a maximum support spacing of 600mm. Plasterboard should be fixed as follows.

Rafters are nailed to a wall plate at the top of each supporting walls these are normally 100x75mm 4x3 inches timber embedded on cement mortar on top of the inner skin of a cavity wall or the inner part of a solid wall. The building control officer won t specify the timber sizes but seems to be easy going and would be happy to accept generous sizes with c24 timber. Roof pitch between 15 and 22 5 degrees with rafter spacing strength. Roof pitch between 15 and 22 5 degrees with rafter spacing strength class c16.

To meet the requirements of the c16 timber grade timber is machine graded or visually graded. Surveyors and structural engineers utilise data from tables below to help calculate the correct size strength and centres of roof timbers for the required spans and loadings. Ceiling finishes should be fixed according to the spacing of the support members and the thickness of the sheet. A new timber ring beam is fitted alongside the existing windows to support the new roof structure.

My builder would also be delighted to over specify the timber. Step 2 the conservatory roof is carefully removed leaving only the windows doors and and brickwork in place. 9 5mm plasterboard should be fixed at a maximum support spacing of 450mm.