Roof Timber Sizes

The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction.

Roof timber sizes.

For pitched roofs flat roofs and ceiling joists. 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. For instance a 7 12 roof pitch means that the roof rises 7 inches for every 12 horizontal inches. If the extension length is half the extension length the 2 hips will meet at the existing wall and the roof will come to a peak with no ridge like half a pyramid.

It is often compared to slope but is not exactly the same. Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak. All the figures are based on roofing tiles or slates laid on timber laths over sarking felt. Outside of the u s a degree angle is typically used.

Surveyors span tables for designing roof rafters. Rafter run outer wall this should be measured starting from the center of the roof span and then extending to the very edge of the exterior wall. The imposed load should be calculated in accordance with bs 6399 part 3 1988 code of practice for imposed roof loads as a rule of thumb for altitudes not exceeding 100m you can use a uniformly distributed load of 0 75 kn m and for most other areas exceeding 100m but not exceeding 200m you can use 1 kn m for parts of scotland pennines north east england and heights over 200m you will need to refer to bs 6399 part 3. Here the number is 941 86 inches.

Here the number is 1166 66 inches. The roof extension length must be at least twice as long as its width or the 2 hips will meet before they reach the existing building wall. Plasterboard on the underside of the rafter. C16 timber is kiln dried timber certified to comply with the criteria of strength grade c16.

Pitched roof timber sizes. In the united states a run of 12 inches 1 foot is used and pitch is measured as the rise of the roof over 12 inches. Rough timber is probably the most popular timber in construction we stock both native imported rough timber so we have all you need buy online and collect at one of our 7 branches nationwide or choose home delivery. Your choice of batten size here will be determined by the weight and span of your metal roof panels.

C16 timber is commonly used in floor and roof joists for internal building work. Usually 400 450 or 600mm but any value can be used up to 610mm max are there any brittle finishes e g.