This is the distance between joist centres.
Roof joist span tables uk.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
Span tables for ceiling joists to bs 5268 7 3 span tables for flat roof joists to bs 5268 7 2 imposed loads of 0 75 kn m for maintenance and snow load are applicable where there is no permanent access no fixed ladder or staircase and most areas where the altitude does not exceed 100 metres refer to bs 6399 3.
Permissible clear spans for flat roof joists to bs 5268 7 2 find the column for your dead load and spacing and the row for your timber size to find the permissible clear span in metres.
Solid timber strutting to be at least 38mm thick and be a minimum of three quarters of the joist depth.
This should be compared to the table.
Size of joists mm clear span c16 joist m clear span c24 joist m 47 x 95 47 x 120 47 x 145 47 x 170 47 x 195 47 x 220 1 77 2 40 2 89 3 38 3 87 4 36 2 05 2 67 3 22 3 77 4 31 4 85 assumptions at 400mm centers.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
If your old joists do not meet the requirements set by the table they are either supported.
Click on a span to generate a full calculation you can adjust the exact span.
Joist spans up to 2 5m no strutting required.
Where the tables do not apply or where there are concentrated loads floor joists should be designed by an engineer in accordance with technical requirement r5.
You need to measure the complete span of your floor joists together with the distance between them the centres and the size of the timbers.
Floor joist span tables for surveyors floor construction.
Usually 400 450 or 600mm but any value can be used up to 610mm max usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size.
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.
Rafter spans can be extended slightly beyond what the rafter tables suggest when there is a cantelever extending beyond the supporting wall.
For pitched roofs flat roofs and ceiling joists.
Joist spans 2 5m to 4 5m provide strutting at mid span.
Ceiling joist span use this table to determine the maximum lengths of ceiling joists based on species of lumber joist spacing and joist size.
They also tell you what the maximum spacing should be between each section or timber member.
Surveyors span tables for designing roof rafters.
Span tables can be used to determine the size of a timber member of a particular strength class required for a given span.
