What size joist to span 3m, 3.5m, 4m, 4.5m and 5 meters | what size joist to span 3m | what size joist to span 3.5m | what size joist to span 4m | what size joist to span 4.5m | what size joist to span 5m | What size joist for 3m, 3.5m, 4m, 4.5m and 5 meters span.

There are different depth of floor joist are used in floor construction such as 47×95, 47×120, 47×145, 47×170, 47×195 and 47×220 mm 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.

Floor and roof joists can be define as several small beams. 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.

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.

What size joist to span 3m, 3.5m, 4m, 4.5m and 5 meters depending on different size of Lumber, 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.

Not all the type of species of wood created equally strong and type of tree used to make joist affects the span allowed. 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.

Spacing between floor and flat roof 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 400mm.

**What size joist to span 3m, 3.5m, 4m, 4.5m and 5 meters**

What size joist to span 3m, 3.5m, 4m, 4.5m and 5 meters depending on different size of Lumber, 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.

The thumb rule for the depth of common joists is to take half span in meters; to this number add 50mm for the depth of the joist in mm. Example, for a 4m span, half this is 2m, add 50mm, which gives 250 for the depth. So a 50×250 joist will be required. it’s important to use the actual engineered wood dimensions, not the nominal dimensions).

Typically, this thumb rule work better for permanent loads are assumed to be 50 kg/m2 and imposed load of 150kg/m2, and this rule of thumb will work for loading conditions that don’t exceed that value. If the floor system is to be tiled or there are any other unusual loading conditions, I’d recommend having an engineer review the conditions.

**What size joist to span 2m**:- as per general thumb rules and guideline, a 47×95 mm size of floor or roof 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 400mm apart. Thus, for 2m span you will need a 47×95 mm size of joists at standard 400 mm spaced.

**What size joist to span 2.5m**:- as per general thumb rules and guideline, a 47×120 mm size of floor or roof 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 400mm apart. Thus, for 2.5m span you will need a 47×120 mm size of joists at standard 400 mm spaced.

**What size joist to span 3m**:- as per general thumb rules and guideline, a 47×145 mm size of floor or roof 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 47×145 mm size of joists at standard 400 mm spaced.

**What size joist to span 3.5m**:- as per general thumb rules and guideline, a 47×170 mm size of floor or roof 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 joists at standard 400 mm spaced.

**What size joist to span 4m**:- as per general thumb rules and guideline, a 47×195 mm size of 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 47×195 mm size of joists at standard 400 mm spaced.

**What size joist to span 4.5m**:- as per general thumb rules and guideline, a 47×195 mm size of flat roof 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 47×195 mm size of joists at standard 400 mm spaced.

**What size joist to span 5m**:- as per general thumb rules and guideline, a 47×220 mm size of flat roof 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 on flat roof, you will need a 47×220 mm size of joists at standard 400 mm spaced.

**Conclusions**:-

For a span up to 3m, you will need 47×145 mm size of floor or roof joists, for 4m span – 47×195 mm, for 5m span – 47×22 mm and for a span up to 3.5m, you will need 47×170 mm size of floor or roof joists at standard 400 mm spaced.