Building decking

[arcon5]

So building some decking off the back of my conservatory and wanna run the design by you more experienced guys and ask leg and support intervals...

- 4.5m wide x 2.85m projection
- Slight slope so raised about 5cm off the ground one end and about 20cm the other end.
- One end is gonna be a ledger board off the conservatory using 5x m12 studs and chemfix.
- Joists connected from ledger to other end using galvanised joist hangers.

So my question...

What intervals shall I support the frame..
For the legs being concreted in, what depth should the legs go down in to the concrete?

I want planning on cutting a birds mouth in 100x100 and placing 4 legs across the width of the end plate. Then 1x 100x100 at the 1.4m point of each end joist.
Then was gonna use concrete blocks to support across the center of the frame.

 

[John D v2.0]

What size joists and beams are you using?
If you're using 4 by 2 you would need an intermediate support along the joists that span nearly 3m, but if you're using 6 by 2 it would be fine.

I don't quite understand how you're going to use a bird's mouth unless you're making a ramp?

Don't forget to use UC3 timber or if you can find it UC4, rather than just grabbing the "treated" timber that's designed for indoor use off the shelf. Even wickes can deliver the proper stuff for you if you can't find elsewhere.

 

[arcon5]

Thanks for the reply.

It's 4x2 tantalised/c24 timber for joists and beams.

I've attached pic of birds mouth (if thats the right terminology). So gonna do this so the weights carried by the timber and not a bolt

I'm just not sure how many supports to do for the end beam.

For the center supports, how many should I be looking at across the width?

 

[John D v2.0]

Ok see what you mean now with the birds mouth. That's sensible although you will have cut through the treatment so will need to retreat the section that's cut.

There are tables you can look up online but i would personally think you'd need a support every metre or so on the end beams on 4 by 2s. Depends how much bounce you want to put up with really. I think the middle support will make the biggest difference.

 

[arcon5]

Good point regarding the treatment.

Yeah span tables I read point to it being borderline within at actually 2.8m but I don't really want the bounce.

Under it is block paving on a slight slope so could potentially use that to my advantage so dig down for the end beam and use 5 posts cemented in, so approx 1.1m. But then support every joist... like the two examples in the photo.

First one a small piece of timber sat on a brick and screwed to the joist.
Second one I have some left over 6x2 off cuts I can screw to it, but then it would be sat on the floor...

Both bedded on some concrete.

What are your thoughts on this setup with the digging for the center support?

 

[freddiemercurystwin]

Is your decking going to be over existing block paving?

 

[arcon5]

Yes it is.
It's currently block paving, and a slight slope and we're decking over it. But raised it up a few cm to match the conservatory height

 

[freddiemercurystwin]

Then why do you need to dig big holes in it to bury some posts? When you can just rest your decking on some pedestals or similar on the presumably stable block paving?

 

[John D v2.0]

As above i agree and Regarding 2.8m i very much doubt that is within span for 4 by 2s unless they're made of steel. It will be very bouncy.

Personally for my decking I'll be bedding level pads out of offcuts of paving slabs and sitting it on those, to avoid having any timber in direct ground contact. And I'll have similar ish dimensions but I'll be using 6 by 2 uc4 c24 timbers, but mine will be on the diagonal because the decking will go diagonally too and i don't want rows of fixings in line with my eye.

 

[arcon5]

So the existing block paving will end where the decking ends so the thought process is that sitting on the edge of the paving would make it vulnerable at that end as its gonna go straight from decking to play bark.

Which is why I was thinking of using one of the two methods to secure the middle of the joists on top of block paving and digging in the posts for the end board.

Reading the comments I think I'll go with the first method of timber sitting on a brick to avoid contact with the floor for the joist and will do that with every joist.

So for the end board, would 4 posts be suitable or should I whack a fifth one in?