Raised Patio

[Toppers]

We have bi-fold doors on our newly built kitchen/dining room opening onto the garden, my original plan was to put a composite decking patio immediately outside these doors to create a level floor as you step out. At the moment composite decking is proving quite difficult to get hold of. I've changed tact and thought of building a brick retaining wall (approx 3no bricks high), infilling and tiling on top. So a few queries:

 

1. What sort of depth would the footing need to be 
2. Would the retaining wall need to be a cavity wall
3. I assume it would need to be concreted to lay the tiles on top, is that correct

[CC45]

Personally I would make it 6" deep (as long as you have already removed any topsoil) and twice the width of the proposed wall.  No to cavity.  I would fill the void with clean materials you have about - left over bricks, blocks etc - I would personally bed these in place (4:1 sand : cement mix) - straight onto a compacted base.  I then put a concrete skin ~ 3" over the top of this rubble - to give a solid surface to walk on while you wait for slabs to be laid.  If you haven't got rubble around then I'd do a weak (6:1) mix of ballast to cement.  Just my opinion.

[Toppers]

Another option is to cast a concrete slab if thats feasible.

[Temp]

+1 to @CC45 and @Toppers

 

After building wall (and allowing plenty of time for the mortar to full harden) compact the ground inside. I would hire a vibrating wacker plate for that. Then build up layers of hardcore (possibly MOT Type 1) until the right height. Each Layer compacted with the wacker plate. Then approx 3" layer of concrete. Depending on access and quantity needed I'd probably get ready mix delivered. Couple of friends and some beer to help rake and level it?

 

If you are feeling really  keen put a sand blind and membrane on top of the hardcore to stop water leaking out of the concrete potentially weakening the mix.

 

You could omit the concrete if using pavers instead of tiles. In that case compacting the base is even more important.

 

If you go for ready mix try and prep another job (steps?) to use any excess concrete. Then you can risk over ordering slightly.

 

Remember you shouldn't bridge the DPC or block under floor vents on the house. Might be an idea to leave a 6-8" wide gap filled with gravel to minimise rain splashing up above DPC.

 

Should also be a fall on the top surface so rainwater runs away from the house.

[Toppers]

37 minutes ago, Temp said:

+1 to @CC45 and @Toppers

 

After building wall (and allowing plenty of time for the mortar to full harden) compact the ground inside. I would hire a vibrating wacker plate for that. Then build up layers of hardcore (possibly MOT Type 1) until the right height. Each Layer compacted with the wacker plate. Then approx 3" layer of concrete. Depending on access and quantity needed I'd probably get ready mix delivered. Couple of friends and some beer to help rake and level it?

 

If you are feeling really  keen put a sand blind and membrane on top of the hardcore to stop water leaking out of the concrete potentially weakening the mix.

 

You could omit the concrete if using pavers instead of tiles. In that case compacting the base is even more important.

 

If you go for ready mix try and prep another job (steps?) to use any excess concrete. Then you can risk over ordering slightly.

 

Remember you shouldn't bridge the DPC or block under floor vents on the house. Might be an idea to leave a 6-8" wide gap filled with gravel to minimise rain splashing up above DPC.

 

Should also be a fall on the top surface so rainwater runs away from the house.

 

There are a few vents, whats best thing to keep the airflow, I assume some sort of duct?

[Ferdinand]

49 minutes ago, Toppers said:

 

There are a few vents, whats best thing to keep the airflow, I assume some sort of duct?

 

Yes you will be able to find matching ducts.

 

There are other possibilities such as offset air bricks that move the one on the face of the wall up by one to three courses.

 

This post from me last week discusses a sort-of related issue: