Decking Foundations

CodeJACK

Im building two decked areas and looking for the best/cheapest option of doing posts/screws as a foundation. The garden soil I have in Walkinstown, Dublin is very dense clay and the garden is old and heavily compacted.

We had a garden room installed that used ground screws. Love them and they are solid but not really a DIY job and there is quite a cost to have them installed.

Has anyone used an auger to drill out a hole and then used this sort of pipe as a vertical insert to fill with postcrete?

https://tjomahony.ie/110mm-x-6-0m-750n-black-twinwall-unperf-inc-coupler-29100tpu.html

This seems like a handy enough way to get very solid posts in place quickly and these would be very solid in the soil. Maybe overkill??

For a 5m x 5m deck, how many of this sort of post would I need and what spacing/depth between them is advised?

Cheers

GreeBo

You could just dig a hole and then shutter the top and fill that with concrete? I dont think the pipe is getting you much.

In the US (and others) the use a sonotube for what you are doing, but thats basically to save having to shutter and also gets a nice round finish above ground. Depending on how you finish the deck, the posts probably wont even be visible?

Just keep the wood out of the ground (use a post anchor inserted into the wet concrete to attach the post to the concrete but keep it dry.

jack of all

Don't know how high/ elevated your deck will be but when building my own deck 20+ years ago I used a simple padstone arrangement. I dug out a shallow pad, filled with hardcore, well compacted and then bedded a 4" block (halved) on this with mortar, using string line and line level to level the individual conc. pads. I sat the timber plates these pads then fixed my joists at 400mm centres.

ted1

I’ve seen Concrete patio slabs used , and there’s been no issue over the years.

CodeJACK

Thanks all. I dunno if its just Walkinstown but the area around my house is like a wind tunnel. I know the weather has been bad in recent years but I'd like to know what im building is going to be excessively solid. Im considering making the covered pergola over the decking from steel but that could get pricey.

OK, so maybe ill skip the tube going down the hole and just use a section of 110mm standard pipe to form the bit thats out of the ground. What would be the correct type of cement to use in this case and how deep should I go?

Lumen

If your decking is seriously in danger of going into orbit like a trampoline (which I seriously doubt, you're not living in Kansas), small concrete feet won't make much difference, you're just making the deck slightly heavier.

Digging deep is a literal pain in the hole and completely unnecessary.

What makes sense is keeping the subframe out of ground contact, and having a stable footing so that the deck doesn't sink.

This is why it's normal to just use pavers or concrete blocks under the subframe. They're easy to reposition and will stop the subframe from rotting. For extra stability just remove the topsoil and then put some gravel in the hole (under the pavers/blocks) to get the levels right. Or use timber spacers under the subframe for levelling.