What size timber to span 2m, 2.4m, 2.5m, 3m, 3.6m, 4m, 4.8m, 5m & 6m | what is timber do i need to span 3m | what is timber do i need to span 4m | what is timber do i need to span 5m | what is timber do i need to span 6m.

There are many species of wood/ timber or dimensional lumber used in house construction as wood frame structure. It is used as floor joist, ceiling joist, pitch roof rafter, flat roof rafter, purlin and Binder.

There are different depth of floor joist made of timber are used in floor construction such as 47×120, 47×145, 47×170, 47×195, 47×220, 75×175, 75×220 etc made of different species of wood (southern yellow pine & Douglas fir) and different grade such as grade – 1, grade – 2, grade – 3. Southern yellow pine is strongest species of wood that can span more distance compared to other species of wood. Grade 1 lumber have higher strength than other grade Lumber due to fewer knots.

Ceiling joists provide support for more than one surface in your home. The first surface is, unsurprisingly, the ceiling, the materials of which attach directly to the joists. The other surfaces are the walls, which the joists span the distance between, providing a source of support to keep the walls from shifting.

Floor joists can be define as several small beams. Floor joists are typically a horizontal structural member that runs across an open space of building on supporting wall or studs. Their function is similar as beams, except floor joists are supported by wall, foundations, or beams framing.

Floor joists usually run between walls or rafters to support a ceiling or floor. They transfer the dead load of the subfloor and floor finishes and live load of people, furniture and furnishings to beams, walls, headers, or foundation walls. It is like the skeleton/ framing of a building that supports the load which the floor is built to bear. Joists are technically beams that typically spans relatively short distances compared to beams and are made of wood, steel, or engineered wood or lumber.

Spacing between floor joist for different sizes are kept at 300mm, 400mm and 600mm apart. The joist which are kept at lower spacing can allow longer distance to span as compared to joist spaced further apart. Standard spacing between floors joist is 400 mm centre to center.

In this article you know about what size timber to span 2m, 2.4m, 2.5m, 3m, 3.6m, 4m, 4.8m, 5m & 6m and also know about what size timber do you need that will help you in better choose the correct size of timber.

What size timber to span 2m, 2.4m, 2.5m, 3m, 3.6m, 4m, 4.8m, 5m & 6m depending on different size of timber, species of wood, grade of wood, spacing between the joist, expected dead and live load of structure that coming to joist. The loading includes dead load of the weight of the frame structure & fixed weight and live load of People, furniture, appliances and a snow on the roof.

**What size timber to span 2m, 2.4m, 2.5m, 3m, 3.6m, 4m, 4.8m, 5m & 6m**

**What size timber to span 2m**:- as per general thumb rules and guideline, for flat roof, a 47×120 mm size of timber as floor joists can allows spans up to 2 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 600mm apart. Thus, for 2m span you will need a 47×120 mm size of timber as floor joists at standard 600 mm spaced centre to centre.

**What size timber to span 2.4m**:- as per general thumb rules and guideline, for flat roof, a 47×145 mm size of timber as floor joists can allows spans up to 2.4 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 600mm apart. Thus, for 2.4m span you will need a 47×145 mm size of timber as floor joists at standard 600 mm spaced centre to centre.

**What size timber to span 2.5m**:- as per general thumb rules and guideline, for flat roof, a 47×145 mm size of timber as floor joists can allows spans up to 2.5 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 600mm apart. Thus, for 2.5m span you will need a 47×145 mm size of timber as floor joists at standard 600 mm spaced centre to centre.

**What size timber to span 3m**:- as per general thumb rules and guideline, for flat roof, a 47×170 mm size of timber as floor joists can allows spans up to 3 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 3m span you will need a 47×170 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**What size timber to span 3.5m**:- as per general thumb rules and guideline, for flat roof, a 47×195 mm size of timber as floor joists can allows spans up to 3.5 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 3.5m span you will need a 47×170 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**What size timber to span 3.6m**:- as per general thumb rules and guideline, for flat roof, a 47×195 mm size of timber as floor joists can allows spans up to 3.6 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 3.6m span you will need a 47×170 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**What size timber to span 4m:-** as per general thumb rules and guideline, for flat roof, a 47×220 mm size of timber as floor joists can allows spans up to 4 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 4m span you will need a 47×220 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**What size timber to span 4.5m**:- as per general thumb rules and guideline, for flat roof, a 75×195 mm size of timber as floor joists can allows spans up to 4.5 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 4.5m span you will need a 75×195 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**What size timber to span 4.8m**:- as per general thumb rules and guideline, for flat roof, a 75×220 mm size of timber C16 class as floor joists can allows spans up to 4.8 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 4.8m span you will need a 75×220 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**What size timber to span 5m**:- as per general thumb rules and guideline, a 75×220 mm size of timber C16 class as floor joists can allows spans up to 5 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 5m span you will need a 75×220 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

What size timber to span 6m:- as per general thumb rules and guideline, a 75×245 mm size of timber C16 class as floor joists can allows spans up to 6 metres for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2 when spaced 400mm apart. Thus, for 6m span you will need a 75×245 mm size of timber as floor joists at standard 400 mm spaced centre to centre.

**Conclusion**:-

For flat roof, A 47×120 mm size of timber can allow to span upto 2m as floor joist, thus you will need a 47×120 mm size of timber to span 2 metres as floor joist.