Building a Patio With Retaining Wall - Run Off/Fall

mandyraw

Hi there,

We are building a patio against the back of the house and are trying to get our heads around the best way to build the side retaining wall.

The intention was to fill the retaining wall with compacted hardcore, so that it lies flush with the wall, then lay the slabs on top of the whole thing.  The question is, given that the slabs need to have a fall of 1cm per every 60cm, how can the retaining wall follow the same fall?  The patio will be 360cm deep, so will need a fall of 6cm in total.

I understand that the retaining wall cannot be built sloped to match the patio, and that the obvious way would be to build a 'stepped' wall, but then the slabs can't be place on top.  It may be that we will need to forget about having it all lying flush, but how do other builders do it?  Especially when they incorporate the top of the retaining wall into the patio design.  How do they create the run off on the wall?

Any suggestions will be gratefully received.

Thanks

tacpot12

I've interpretted your description of the problem as being that you want to build a side retaining wall to support the patio slabs, i.e. the wall is under the slabs, and hence the top of the wall needs to have the same fall as you have across the rest of the patio (front to back)? 

The first thing to say is that some builders would advise against building the wall in this way as it creates a situation where you can fall off the patio. A better arrangement might be to build a wall higher than the level of the patio, to stop people falling off the edge. A low wall with a balcony/fence on top of it might also work.

If you do want to build the wall in this way, it needs a level footing and the wall needs to be built level (the fall is just less than the height of one brick, so there is no need for stepped footings). The final layer of bricks will need to be cut to form the fall. This can be done faily accurately with a diamond blade. The tool the blade is fitted to could be a small angle grinder, or a large cut-off saw. The slabs should be laid so that they project over the wall a little. This will help to hide any inaccuracies in the cutting.  

Sloping the patio and wall away from the house is a good idea, rather than having a drain next to the house and relying on the drain always working correctly. 

mandyraw

Thank you so much, tacpot12.  That sounds like the solution we need.

Cutting the bricks sounds a little tricky, but, as you say, inaccuracies will be hidden by the slabs.

The patio will not be very high, so no worries about falling off the edge.  :-)

I really appreciate you taking the time to respond.

Best regards.

stuart45

Just set the line at 60mm one end running to zero at the other and cuts the bricks as you go. You will find them more difficult to cut as they get smaller, and might find you can get away with just a thicker bed of mortar at the low end, especially as the slabs are overhanging the brickwork. 
When they finish inside the brickwork the cuts have to be more accurate. 
Brickwork can be built on a slight slope, but it can be more tricky to get right.

Section62

mandyraw said:

...
The patio will not be very high, so no worries about falling off the edge.  :-)
...

Smaller drops (level differences) can be some of the most dangerous - people can be less aware of them or perceive them to be less dangerous and take less care.  Bringing the edge wall up a few courses above the slabs a) avoids the problem you are asking about, and b) provides a visual cue where the edge of the paved area is.

What kind of height are you talking about?

mandyraw

stuart45 said:

Just set the line at 60mm one end running to zero at the other and cuts the bricks as you go. You will find them more difficult to cut as they get smaller, and might find you can get away with just a thicker bed of mortar at the low end, especially as the slabs are overhanging the brickwork. 
When they finish inside the brickwork the cuts have to be more accurate. 
Brickwork can be built on a slight slope, but it can be more tricky to get right.

Good point about the mortar.  It's said that it needs to be anything from 30-50mm thick, so should make it easier to fiddle with the brick height.

Thanks

Section62 said:

mandyraw said:

...
The patio will not be very high, so no worries about falling off the edge.  :-)
...

Smaller drops (level differences) can be some of the most dangerous - people can be less aware of them or perceive them to be less dangerous and take less care.  Bringing the edge wall up a few courses above the slabs a) avoids the problem you are asking about, and b) provides a visual cue where the edge of the paved area is.

What kind of height are you talking about?

Only about 20cm at the highest point and there is a fence just 10cm beyond the side wall.  Should be okay.

Thanks

casper_gutman

We have a similarly-sized step at one end of our patio. Instead of an actual brick wall we just put in heavy duty slabs on edge, bedded in concrete. At this small scale it was reasonably easy to lay these to the required fall, and we did that rather than cutting them. Whether that's good practice I don't know, but it's worked fine for us.

The best method probably just depends on the tools you have on hand and your preferences. If you do cut them make sure to take effective measures to control the dust. You don't want to be breathing it all in.