Question 1

How many deck boards do I need?

Accepted Answer

Divide the deck depth by the board width plus the gap and round up to get the rows, then cover each row with the lengths you can buy so that every joint lands on a joist. With 145 mm boards and a 5 mm gap that is about 6.7 rows per metre. Add 5–10% for defects and mistakes.

Question 2

What joist spacing do deck boards need?

Accepted Answer

As a rule of thumb: 400–500 mm for 21–28 mm softwood, 400–600 mm for hardwood depending on thickness, and 300–400 mm for composite. The board manufacturer’s spacing always takes priority, and diagonal boards need closer joists.

Question 3

How many screws per m² of decking?

Accepted Answer

With 2 screws per board per joist, 145 mm boards and joists every 400–500 mm, count about 27–35 screws per m², plus a few at the joints. Use stainless steel: A2 in most gardens, A4 near a pool or the sea.

Question 4

What gap should I leave between deck boards?

Accepted Answer

Usually 5–8 mm between wooden boards, whatever the clips set for composite, and 10–20 mm to walls. Wood swells and shrinks with moisture, so check the movement of your species.

Question 5

Is hardwood decking dust dangerous?

Accepted Answer

Yes. Hardwood dust is classed as carcinogenic, and tropical species such as ipe can cause asthma and skin allergies. Cut outdoors with dust extraction and an FFP3 mask, and clean up with a vacuum, not a brush.

Question 6

Do I need a permit or a guardrail for a raised deck?

Accepted Answer

It depends on the height, the size and your region. Decks at ground level often need no permit, but raised decks may, and open edges that people can fall from need a guardrail. Ask your municipality before you build.