Usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size automatically calculate sizes suitable for supporting the loads below.
Roof joist sizes uk.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1.
These tables can help calculate whether floor joists are strong enough to support themselves and the load they carry without the help of any walls underneath.
This is the distance between joist centres.
Surveyors span tables for designing roof rafters.
The range of joist sizes used in homes varies though between 2 by 4 inches and 2 by 12 inches.
Standard size of joists though there is no standard joist size for the ceilings in all buildings most average homes use ceiling joists in a board size of 2 by 6 inches.
The lengths and sizes of joists vary depending on the species and quality of the lumber used.
3 23 inc vat per metre.
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 04 2 75 3 47 4 20 4 93 5 66 floor joists flat roof joists assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2.
Permissible clear span metres.
Fsc standard kiln dried regularised c16 treated carcassing 145 x 45mm.
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.
Fsc standard kiln dried regularised c16 treated carcassing 195 x 45mm.
Pitched roof timber sizes.
All the figures are based on roofing tiles or slates laid on timber laths over sarking felt.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction.
For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine.
Rafter and joist span faq.
Dead load per square metre in kn m supported by joists.
Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600.
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.
For pitched roofs flat roofs and ceiling joists.
