Decking without footings - bad idea?

[MarkH]

I'm planning a large (14.5m by 3m, elevated by a maximum of 800mm) decking outside the back of my house. The ground is solid, rocky clay - not fun to dig in at all. My thought was to cover the area with a weed-membrane and a few inches of aggregate, compact the aggregate and then rest the posts on paving slabs, on the agg.

 

The house is solid wall + 250mm EWI so the decking won't be attached to the house.

 

Is this madness? I really don't want to dig holes!

[JohnMo]

Just jumped into the planning portal

 

Planning Permission

Putting up decking, or other raised platforms, in your garden is permitted development, not needing an application for planning permission, providing:

 

The decking is no more than 30cm above the ground

Together with other extensions, outbuildings etc, the decking or platforms cover no more than 50 per cent of the garden area.

None of the decking or platform is on land forward of a wall forming the principal elevation.

 

Trouble with raised deck they may/likely require designing and structural engineering input. Ours did and the amount of timber involved was huge. We needed to go below ground and form pads out of concrete.

[MarkH]

The planning permission element isn't a consideration at the moment, just the practical things.

[Mr Punter]

Yes, silly idea.  You need a footing for each post.  https://www.wickes.co.uk/how-to-guides/garden-landscaping/plan-build-a-raised-deck

[MarkH]

3 hours ago, Mr Punter said:

Yes, silly idea.  You need a footing for each post.  https://www.wickes.co.uk/how-to-guides/garden-landscaping/plan-build-a-raised-deck

But why?

[Conor]

20 minutes ago, MarkH said:

But why?

That's how I did my deck, but with concrete blocks instead of pavers. Solid.

[Kelvin]

Our SE did a detail for our deck which consisted of a large concrete foundation which surprised me. We  (she) have decided not go with decking though. 

[TerryE]

The top soil / made up ground will have inconsistent ground bearing pressures across the footprint of the deck. Hence if you use pads that aren't footed on the virgin clay, then you should expect some degree of differential settlement across the pads, and some buckling of the deck in consequence. 

 

Pavers are a bad idea for pads unless you correctly load spread and the posts will tend to break them up and punch through them. The method shown in that Wickes video is about the simplest.  The holes really just need to go down to the virgin clay, which might only be 30cm or so, but you won't know until you've dug a few out.  

[Dave Jones]

you dont need to go mega deep with posts, 400mm is fine. 

 

The risk you run is having to take it all back up when it starts sinking/rocking.

[JohnMo]

With the planning requirements and the need for a ballastrade due to the drop, you may need a structural engineer input. Do it right once or why bother, my 25m X 3m (bigger but not much) deck cost me £2500 in wood alone for the support structure, plus ballastrade, plus decking boards.  It's a big cost to mess up, because you don't fancy digging a few holes (a day's work) and pouring some postcrete.

[MarkH]

Thanks all. 

 

I might dig shallow holes and concrete them in that case. But just to be clear - the ground was scraped down into the clay level some time ago and the area I'm decking is not topsoil, that would be daft. It's clay and rock, lots of rock. It's a massive pain in the arse to dig in. It would not be a day's work.

 

Ballustrade, structural engineer - I don't want a ballustrade as it'll get in the way of the view and without that there are no difficult structural considerations. 

[TerryE]

One last codicil.  It's worth covering the soil under the deck with a decent build fabric and a thin layer of gravel to keep it down, once the posts are in place; otherwise you might get problems with weeds, etc. 

[MarkH]

Update on this - I built the frame and deck without footings, posts resting on on slabs on clay with weed-fabric and aggregate. All seems good - no movement at all. I think it was important that the ground is clay and rock and therefore less prone to move.

 

No balustrade. The drop is over a meter at the highest point but a safety rail would really ruin the view when sat inside on the sofa. I've taken the view that anyone who wanders off the edge should have been looking where they were going.

[JohnMo]

24 minutes ago, MarkH said:

I've taken the view that anyone who wanders off the edge should have been looking where they were going

But you would always loose in court if it did happen.

 

Glass balustrade, safe but you keep the view!

[joe90]

41 minutes ago, MarkH said:

I've taken the view that anyone who wanders off the edge should have been looking where they were going.

I am not a big fan of health and safety but not protecting that drop is mad (you obviously don’t have any children visit your house) 🤷‍♂️

[ProDave]

I like "Yacht rigging" wire for an almost invisible balustrade, as long as BC are not involved.

[MarkH]

My nieces were round recently and whilst they were here we climbed the big oak tree behind the house and then later set up a slackline before finishing the evening firing my parsnip cannon into the woods... Safety glasses were worn for the parsnip cannon. 

 

All points accepted regarding railings!

[TerryE]

We put up posts and strung a thick rope between them using brass fittings. Looked nice, didn't really obscure the view and did the job.

 

Just whip the rope ends to look nice.