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How far can a 4x2 decking joist span?

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).

qualitydecking.co.uk - Deck Subframe Design Guidance –Tips for Laying a Decking Subframe

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Decking Subframe Design Guidance

Decking Beam Span Guidance

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%.

Joist Spacing (centres)

Maximum joist support centres for Q-Deck deck boards

Deck Board Size

(mm) Joist centres (mm) for C16 grade joists - S D 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

Maximum support centres for Q-Deck Twinson® deck boards

Deck Board Size

(mm) Joist centres (mm) for C16 grade joists - S D 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.

C16

Table A: Maximum joist spans - Strength Class C16

Imposed load 1.5kN/m2

Joist centres (mm) Imposed load 4.0 kN/m2

Joist centres (mm) Joist section (mm) 400 500 600 400 500 600 Width Depth Maximum clear joist span S J (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

Table B: Double member beam spans - Strength Class C16

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Imposed load 1.5kN/m2

Joist centres (mm) Imposed load 4.0 kN/m2

Joist centres (mm) 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 S B (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)

C24

Table A: Maximum joist spans - Strength Class C24

Imposed load 1.5kN/m2

Joist centres (mm) Imposed load 4.0 kN/m2

Joist centres (mm) Joist section (mm) 400 500 600 400 500 600 Width Depth Maximum clear joist span S J (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

Table B: Double member beam spans - Strength Class C24

Imposed load 1.5kN/m2

Beam centres (m) Imposed load 4.0 kN/m2

Beam centres (m) 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 S B (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)

qualitydecking.co.uk - Deck Subframe Design Guidance –Tips for Laying a Decking Subframe