Decking structure layout

[daiking]

This is a bigger job than erecting the log cabin. First of all I’m in the ground already so I’m going to have to dig it all out. Even so I think I’ll stick to 6x2s as my spans can be bigger and I’ll need less supports in/on the ground.

 

The composite decking boards I have are 3600mm long so I’m basing the plan on a deck 5400mm wide (1.5 board length) and nominally 5400mm deep. 
 

I’m thinking of using staggered frames that are 3600 x 1800 and 1800 x 1800. Also due to the board joints I’ll need double joists in whatever frame is sitting at 1800 and 3600 from each side.

 

Typically I’ll be using 400 centres for the joists but the top left 1800 x 1800 frame will be 300 centres to take more weight.

 

What I’m looking for is guidance on how much support my main beams will need. Supporting these every 1800mm as shown looks a bit light. Would the 3600mm frames be ok with 1200mm support? I.e 8 posts per frame and the 1800mm frames with 900mm supports? (6 posts per frame).

Edited April 14, 2021 by daiking

[markc]

If you are using 6x2`s 1800mm will be more than enough.

[TonyT]

And once you have done the joists, and you have any left over timber add some mid point noggins to stiffen it even further.

looks good

 

https://www.trada.co.uk/media/3809/design_a_deck_planning.pdf

 

some good info in the link

[Gus Potter]

Hello Daiking.

 

Is the deck more than 600mm off the ground level, if so then it becomes a structural deck (in Scotland). If so we need to have a look at the lateral stability and so on.

 

You may or may not need a hand rail, you do if more than 600mm off FGL in Scotland. You may want one anyway even if less than 600mm off FGL.

 

Surprisingly you can end up with quite a lot of load on a deck, party time and folk sometimes put planters etc on them too.

 

For your main beams, say the rim beams around the perimeter you may want to go for double 170 / 195 x 45 timbers. This gives you a stiff edge for attaching handrails to say. Also, if you make the rim beams a little deeper you can hide the hangers if you can see under the deck. The deeper edge beam can also form a bit of a drip and this can be helpful.

 

If you can it's good to draw up a detail showing how the edge beams etc rest / attach to the posts. A good way of doing this is to have the heavy beams resting directly in bearing on the posts, maybe take a check out of them. This way you have a direct bearing contact rather than relying on the shear capacity of any bolts / screws.

 

If the deck is only say 200mm off the ground then you could just support thing on small concrete pads and a few blocks?

 

 

 

 

[daiking]

4 hours ago, markc said:

If you are using 6x2`s 1800mm will be more than enough.

It just looks a bit skinny at 1800mm along the beams, I know it’s fine for joists. I’m not committing to anything until I’ve dug a bit out. Might drop it to 4x2 if it’s too hard and have far more supports.

[Gus Potter]

Daiking.

 

All the best with the digging. Remember that sometimes the journey can just as important as the getting there.

[daiking]

3 hours ago, TonyT said:

And once you have done the joists, and you have any left over timber add some mid point noggins to stiffen it even further.

looks good

 

https://www.trada.co.uk/media/3809/design_a_deck_planning.pdf

 

some good info in the link

Thanks for that link, I’d been looking for something like that but not come up with anything. Of course noggins are essential.

[daiking]

3 minutes ago, Gus Potter said:

Daiking.

 

All the best with the digging. Remember that sometimes the journey can just as important as the getting there.

I’ve already dug out about 6m3 of earth for my cabin.

 

Not many worries about the deck height it is a low one so you can’t fall far and not intending to put handrails. I would still like to concrete some posts into the ground so it is fixed rather than just resting on supports. 
 

There will also be a small reinforced area for a hot tub. I’m already conscious of loads with that as I’ve had to put one on decking in the past.

 

 

[daiking]

Lovely lovely. Being quoted £90-£120 per sq m for decking structure and fitting the decking I have previously bought. (£40 per sq m)

 

?