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I'd use 6"×2" or 150×45 or whatever.....
I don't think either of your options will be strong enough for a deck that size. (Even on the ground). I built a deck under a pergola (about 6m X 3m) and used 6x4s as that seemed the standard IYKWIM.
Looking at building some decking (4m X 6.5m) over the next few weekends. Can I use 45 x 70 or should I be using 45 x 95 please?
https://www.wickes.co.uk/Wickes-Trea...00-mm/p/190165
https://www.wickes.co.uk/Wickes-Trea...00-mm/p/190167
There a £55 difference between the two.
I'd use 6"×2" or 150×45 or whatever.....
I don't think either of your options will be strong enough for a deck that size. (Even on the ground). I built a deck under a pergola (about 6m X 3m) and used 6x4s as that seemed the standard IYKWIM.
Always the 4x2. You could use the 3x2, but you need more supports underneath as it will flex more.
I generally mortar pads on the ground, depends what depth you have, you can use block pavers, or anything as thin as a tile.
The important thing is that the joist is clear of any earth or concrete, so not in contact with any water.
I use the straightest joist you have and lay these the same way you want the boards to run. I go a joist every meter, with a supporting pad at the edge of said joist, and every meter apart.
Repeat this however far you are going out with deck.
Then just a case of cutting and screwing in joists between every 18”/450mm.
If worked out fairly accurately, these cross joists will sit on a pad roughly every other one.
HTH
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It really depends how many supporters you’ve got ,over that distance I think 4x2 would be ok if you had a support every 1-1.2m,if you can’t go for 6x2 .
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1.2/4ft the limit you can go, there’s minimal flex. 1m rock solid.
Fitted many decks over the years, never had a call back once.
As others have mentioned, elevate it off the ground. Old paving stones or similar are ideal.
Then buy a roll of damp proof course and pin that to the top of the joists before you screw the deck boards on top. Assuming they are not sat in water or on mud, the joists ultimately rot from the top where water is held between the deck-boards. Using DPC will materially lengthen the life of the joists.
Looks like great advice and the sketch and example help too. A genuine question because intuitively i’d have done the opposite, why do you run the joists the same way as you run your decking boards? ThanksOriginally Posted by deanlad
I used C16 at 400mm centers. laid down a weed membrane prior to construction, followed with a second membrane between the decking and the 4x2
Thanks for the advice guys especially the sketch from Dean.
I currently have block paving slabs so the plan was going to be to lay some weed matting down and then elevate the corners + every 80cm with some spare slaps to lift the wood away from any water.
The pic I posted partially decked shows it a bit better.
The main joists every 18” run opposite way you want the deck boards laid.
The ones that sit on the pads run same way as the deck boards, as these are the main supports.
I guess if it were like the floor in your house, it’s effectively the “sleeper wall” but rather than joists sitting on, cut and screw them between.
Dont go to wickes look for a Timber yard. i just checked the price of the timber in your first link to a local to me timber yard and it is £5.18 compared to wickes. £9
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And don't forget to use wood treatment for each cut end
You shouldn't be going out at all, of course delivery would be ok
Good shout - just checked the timber yard outside the village and the 4x2 comes in at the same price as the 3x2 from Wickes. Thanks.
Two additional questions please - how high can I go up to the house bricks DPC please as I have heard and seen varying reports?
Also, I was going to leave a 4” gap between the decking and the house bricks and fit a drain grate.
...or can I affix a length of 4x2 to the house bricks alongside some stainless washers as spacers and but the decking straight up to it?
Last edited by gavsw20; 29th March 2020 at 09:09.
Decking ideally 2 courses below DPC. If you fix timber direct to brickwork then put plastic packers between the bwk and timber
Personally when i built our Deck 14mts x 4.5 mtrs deep and 1.2mtrs from the ground across the back of our Bungalow i followed advice given by Lowes.com also a step by step instruction on Youtube from start to finish..
it is totally over the top construction i know but the Americans have been building Decks for many years and personally i wouldn't use anything less the 8x2 and even then mine are doubled up on 6x6 posts..and completely freestanding off of the house.it is rock solid and we had over 75 people on it at a recent anniversary party
I guess it all comes down to budget and how high from the ground you are.
and good luck trying to find a straight bit of Timber in Wickes...
Well that’s blown that idea out the water for now. Wickes’ delivery is 3weeks + and all my local timber merchants are closed incl. local delivery.
Thanks for all the responses though.
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