Decking: gap between joist ?

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bacchus

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What is the recommended gap between joists (150mm * 44mm) when using deck boards that are 32mm tick (red wood but do not know the type of wood)?

Timber suppliers say 40cm (the more wood they sale the better ), while builders say 60cm (the less wood they use the better )....
 
Hi ,

The most common gap your talking about which is univerally used and advised by books and diy manuals is 16 inches.The smaller the thickness of the deckboard the smaller the gap between joists....if not they will bend when standing on them and risk breaking.

My decking joists are 16" (40cm) wide and my boards are 32mm and their as solid as youll get......any wider and again , refer to the above

If your decking is raised make sure your joists are a minimum 5x2
 
I would apply the same criteria to joist spacing in a garden deck as would be used to gauge joist spacing on an internal floor. 600mm or 24" is a gap too far in my opinion, regardless of decking thickness. 400mm centres (or 16" in old money) should give a good firm deck when used with any board thicnkess of 25mm or more. 400mm (or 16" to be more exact) is the spacing universally used in framing floors anyway. Intermediate supports (posts or plates) for your joists should probably be spaced at 1350mm to 1500mm based on your joist size.
 
Finaly going to start the deck this week-end, and hopefully Carpenter in online....

Even though the joist deck are pressured threated, i am thinking of giving them a protective coat before fitting the deck boards as it would be simple/cheap and quick to do now.

What product should i use? same stuff as for fences/sheds ?
 
Noooo don't use the stuff you use on fences! I did that last year and it makes the decking slippy and the finish is brutal! Spend more money and get a proper decking treatment!
 
Lauren said:
Noooo don't use the stuff you use on fences! I did that last year and it makes the decking slippy and the finish is brutal! Spend more money and get a proper decking treatment!
Click to expand...

My query is about protecting the deck joists (frame structure) not the deck boards.....
 
Carpenter is indeed online! I would definitely treat the joists with a quick brush on of Cuprinol Green or similar (you can get cheaper products that are similar like "Panabond" or "Larsen"- they all contain copper sulphate AFAIK). At the very, very least you should treat all cut ends and any endgrain and especially where you may have cut/ chiselled or otherwise worked the wood. It won't take long and you'll have the satisfaction of knowing that you're deck is going to last. A little tip for you- you'll need two drills for fixing down your decking, one to drill pilot holes and a driver to drive home the screws. Rub each screw thread on a bit of candle wax and you'll sink them extra easy and extend the battery life of your drill. Some of that treated timber can be rock hard and is hard work with power tools. If your timber is CCA treated (not so popular now I believe) don't burn the offcuts in your fire- it's hazardous waste. A chalk line and some speed clamps are your best friends for this job. Good luck with it, you've got the weather on your side anyway.
 
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