The size of timber needed for a flat roof span depends on various factors, construction requirements, design, imposed and dead load, including the intended use, load-bearing requirements, and local building codes and regulation. For general residential construction in wooden frame house, common sizes for roof joists may range from 38×120 mm for shorter spans to 75×240 mm for longer spans.
The International Residential Code (IRC) specifies that the timber used for flat roof as roof joists will typically be placed at 400 mm centers but no more than 600 mm centers. The common sizes of timber used for roof joist for flat roof include 38×120 mm, 38×145 mm, 47×170 mm, 47×195 mm, 47×220 mm, 75×220 mm, 47×240 mm and etc.
In general, the size of timber for roof joist to span 6m flat roof should be 75×245 mm, while the size of the timber needed to span 5m flat roof should be 75×220 mm. Moreover, the size of the timber needed to span 4m flat roof should be 47×195 mm, while the size of the timber needed to span 3m flat roof should be 47×170 mm. In addition, the size of the timber needed to span 2m flat roof should be 38×120 mm.
There are many species of timber or dimensional lumber used in wooden frame house construction like grade #1 and grade #2 of Southern yellow pine (SYP), Douglas Fir (DF), Hem Fir (HF) and Spruce pine fir (SPF) are used to provide timber which have much strength. They are used as floor joist, ceiling joist, pitch roof rafter, flat roof rafter, purlin and Binder. A wooden framing house very much popular in United kingdom, North region of United states, Canada and etc.
The flat roof are designed to carry all imposed and dead load of structure like self weight of roof, environmental load caused by water, snow and wind. All roof timber like different joists, wall plates, blocking, strutting, battens, firrings and nogging must be treated with preservatives to secure its durability.
In general, the flat roof joist span is typically measured horizontally distance between two support end. The roof joists span may be either 2m, 2.5m, 3m, 3.5m, 4m, 5m and 6m and so on higher. In this article you know about what size joists do i need for a specific span for flat roof that will help you in better understanding and to figure out or estimate of joist size and their depth according to span.
What size timber for 2m, 2.5m, 3m, 3.5m, 4m, 5m and 6m span flat roof
In common, the size of timber required for roof joist for a 2m span flat roof need to be 38×120 mm, while the size of timber for a 3m span flat roof need to be 47×170 mm. Likewise, the size of timber for a 4m span flat roof have to be 47×195 mm, whereas the size of timber for a 5m span flat roof need to be 75×220 mm. In addition, the size of timber required for roof joist for a 6m span flat roof need to be 75×245 mm.
What size joists do i need for a flat roof
The size of joists needed for a flat roof depends on various factors. However, the most common joists sizes are 47×195 mm, 47 x 145 mm, and 47 x 170 mm. The joists will normally be placed @ 400mmc/c but no more than @ 600mmc/c.
What size timber for 6m span flat roof
The size of timber required for roof joist for a 6m span flat roof need to be 75×245 @ 400c/c. This measure 75 mm wide by 245 mm deep. So, the size of the timber needed to span 6m flat roof as roof joist should be 75×245 mm is often suitable for standard residential applications.
What size timber for 2m span flat roof
The size of the timber needed to span 2m flat roof as roof joist need to be 38×120 @ 400c/c. This measure 38 mm wide by 120 mm deep. So, The size of timber required for roof joist for a 2m span flat roof should be 38×120 @ 400c/c is most suitable for standard residential applications.
What size timber for 2.5m span flat roof
The size of timber required for roof joist for a 2.5m span flat roof need to be 38×145 @ 400c/c. This measure 38 mm wide by 145 mm deep. So, the size of the timber needed to span 2.5m flat roof as roof joist should be 38×145 @ 400c/c.
What size timber for 3m span flat roof
The size of the timber needed to span 3m flat roof as roof joist need to be 47×170 @ 600c/c. This measure 47 mm wide by 170 mm deep. So, The size of timber required for roof joist for a 3m span flat roof should be 47×170 @ 600c/c.
What size timber for 3.5m span flat roof
The size of timber required for roof joist for a 3.5m span flat roof need to be 47×195 @ 600c/c. This measure 47 mm wide by 195 mm deep. So, the size of the timber needed to span 3.5m flat roof as roof joist should be 47×195 @ 600c/c.
What size timber for 4m span flat roof
The size of the timber needed to span 4m flat roof as roof joist need to be 47×195 @ 400c/c. This measure 47 mm wide by 195 mm deep. So, The size of timber required for roof joist for a 4m span flat roof should be 47×195 @ 400c/c.
What size timber for 4.5m span flat roof
The size of timber required for roof joist for a 4.5m span flat roof need to be 47×220 @ 400c/c. This measure 47 mm wide by 220 mm deep. So, the size of the timber needed to span 4.5m flat roof as roof joist should be 47×220 @ 400c/c.
What size timber for 5m span flat roof
The size of the timber needed to span 5m flat roof as roof joist need to be 75×220 @ 400c/c. This measure 75 mm wide by 220 mm deep. So, The size of timber required for roof joist for a 5m span flat roof should be 75×220 @ 400c/c.
Conclusions:-
In general, the size of timber needed for roof joist for a 5m span flat roof should be 75×220 @ 400c/c, 75×245 timber for a 6m span, 47×220 timber for a 4.5m span, 47×195 timber for a 4m span, 47×170 timber for a 3m span, 38×145 timber for a 2.5m span, and 38×120 timber for a 2m span.