We recommend beams are constructed from two 44 x 145mm Q-Deck deck joists and are placed at maximum centres of 1.8m. In this instance the maximum span between deck post centres is 2.07m (C16) or 2.24m (C24).
Annotated decking diagram
Joist and Deck Board Spacing Guidance
The table below shows figures for domestic applications (uniformly distributed load 1.5kN/ m2) and commercial applications (uniformly distributed load 4.0kN/ m2). Dimensions stated represent the maximum length of unsupported joists (ie. between beams or slab etc). Please note: Decking laid at a 45° angle will require a reduction of joist spacing centres of 30%.
Deck Board Size (mm) |
Joist centres (mm) for C16 grade joists - SD | Description | |
1.5kN/m2 - Domestic | 4.0kN/m2 - Commercial | ||
20.5 x 95 | 300 | - | Cambridge |
20 x 138 | 400 | TBC | SmartBoard |
27 x 144 | 500 | 400 | Winchester, Canterbury |
33 x 120 | 600 | 500 | York |
Deck Board Size (mm) |
Joist centres (mm) for C16 grade joists - SD | |
1.5kN/m2 - Domestic | 4.0kN/m2 - Commercial | |
28 x 140 | 500 | 350 |
PLEASE NOTE: This information has been prepared to assist in the preliminary design of timber decks, eg for species selection and initial member sizing. The detailed structural design for an individual deck will need to be confirmed by an appropriately qualified engineer. Reproduced with permission from TRADA (Timber Research and Development Association).
Joist and Beam Span Tables
Strength Grading.
For decks 600mm or more above ground level, support posts should be of strength graded material. If you need strength graded components please consult your Q-Deck® retailer who will pass the enquiry onto Hoppings Softwood Products for consideration.
Imposed load 1.5kN/m2 Joist centres (mm) |
Imposed load 4.0 kN/m2 Joist centres (mm) |
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Joist section (mm) | 400 | 500 | 600 | 400 | 500 | 600 | ||
Width | Depth | Maximum clear joist span SJ (metres) | ||||||
45/47 | 97 | 2.00 | 1.86 | 1.75 | 1.47 | 1.33 | 1.22 | |
45/47 | 122 | 2.51 | 2.33 | 2.20 | 1.85 | 1.66 | 1.51 | |
45/47 | 147 | 3.02 | 2.81 | 2.64 | 2.20 | 1.97 | 1.80 | |
45/47 | 170 | 3.49 | 3.24 | 3.05 | 2.52 | 2.26 | 2.07 | |
45/47 | 195 | 4.00 | 3.71 | 3.50 | 2.87 | 2.57 | 2.35 | |
45/47 | 220 | 4.20 | 4.18 | 3.94 | 3.21 | 2.88 | 2.63 |
Imposed load 1.5kN/m2 Joist centres (mm) |
Imposed load 4.0 kN/m2 Joist centres (mm) |
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Beam Size (mm) | 1.2 | 1.8 | 2.4 | 3.0 | 1.2 | 1.8 | 2.4 | 3.0 | |
Width | Depth | Maximum clear beam span SB (metres) | |||||||
2 x 45/47 | 122 | 1.99 | 1.72 | 1.55 | 1.43 | 1.45 | 1.22 | 1.05 | - |
2 x 45/47 | 147 | 2.39 | 2.07 | 1.87 | 1.73 | 1.74 | 1.46 | 1.25 | 1.02 |
2 x 45/47 | 170 | 2.76 | 2.40 | 2.16 | 1.99 | 2.02 | 1.67 | 1.44 | 1.18 |
2 x 45/47 | 195 | 3.16 | 2.75 | 2.48 | 2.29 | 2.31 | 1.90 | 1.64 | 1.35 |
2 x 45/47 | 220 | 3.56 | 3.10 | 2.80 | 2.58 | 2.61 | 2.13 | 1.83 | 1.53 |
Imposed loads 1.5kN/ m2 - domestic applications (single occupancy) 4.0kN/m2 - commercial applications (dining areas, cafes, restaurants, balconies)
Imposed load 1.5kN/m2 Joist centres (mm) |
Imposed load 4.0 kN/m2 Joist centres (mm) |
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Joist section (mm) | 400 | 500 | 600 | 400 | 500 | 600 | ||
Width | Depth | Maximum clear joist span SJ (metres) | ||||||
45/47 | 97 | 2.15 | 1.99 | 1.87 | 1.58 | 1.47 | 1.38 | |
45/47 | 147 | 3.24 | 3.01 | 2.83 | 2.40 | 2.22 | 2.08 |
Imposed load 1.5kN/m2 Beam centres (m) |
Imposed load 4.0 kN/m2 Beam centres (m) |
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Beam Size (mm) | 1.2 | 1.8 | 2.4 | 3.0 | 1.2 | 1.8 | 2.4 | 3.0 | |
Width | Depth | Maximum clear beam span SB (metres) | |||||||
2 x 45/47 | 147 | 2.57 | 2.24 | 2.02 | 1.86 | 1.88 | 1.62 | 1.37 | 1.09 |
Imposed loads 1.5kN/ m2 - domestic applications (single occupancy) 4.0kN/m2 - commercial applications (dining areas, cafes, restaurants, balconies)