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Hi All,
I'm trying to landscape my bare backyard but running into a bit of sloping problem. I was wondering if anyone could assist.
In the attached slope plan, you can see the natural slope of the ground from perimeter of my house to the rainwater drain.
I've got a good natural slope from any corner of my house to the drain (meets the required 1-2 cm per metre drop). However, I'm planning on adding topsoil and raise the level so that after putting down turf my alfresco matches up to the ground. This requires me to to increase the soil level by additional 12cm. As it needs to slope down to meet the drain level at the other end, I wonder adding this soil would make the slope too sharp since the land already got a 1-2 cm slope to it. Another reason I want to increase the soil level is to hide the visible slab of my house (see photos).
So, that's one issue which is bothering me at the moment.
Second issue I've got is that there's an added external slab to the left side of my house where AC unit and Rainwater Tank are placed on. For some reason these genius builders have set this slab lower than my houses slab (a lot lower, see photos). This slab is more or less same level as the rainwater drain. So, currently as it stands, the left side of my house is concaved down with two lower ground at the drain and AC slab and with middle part at corner of my house at higher ground. The drops from corner of my house to either end is around 8-9 cm over distance of around 6-7 m.
To make matters worse, I would be raising this high ground by 12cm as previously mentioned.
On the drain side this is not an issue, other than slope being to sharp to walk on maybe. But on the AC slab side this is a backward slope which will drain water towards the house, not away from it.
Only option so far in my mind which doesn't ruin the look is to create a wooden or stone steps which steps down from backyard to the side of the house, and then I can slope the side in correct direction (away from AC slab and house) basically creating two separate land zones.
Would love to hear what you all propose to tackle this issue or if I'm missing something here, please let me know.
Much appreciated.
A
Hi @ArashM,
It sounds like you’re on the right track with creating separate zones to handle the slope, and introducing steps or tiers is a practical solution to control water flow and avoid drainage issues near your house and AC slab.
For the area around the AC unit and rainwater tank, building a stepped or tiered section with treated pine sleepers is a great choice. By constructing a small retaining wall or step down here, you can direct water flow away from the house while creating a stable, controlled slope. Since this area has a lower slab height, adding a drainage line along the higher soil level is essential to prevent water from collecting around the AC slab. The drainage line will channel excess water towards the rainwater drain, protecting both the AC unit and the house foundation.
One critical point here is to avoid piling soil directly against your home’s brickwork, especially above the damp course line, as this can lead to moisture seeping into the walls. Moisture above the damp proof course can cause serious issues like internal dampness and wall deterioration. To manage this, use the stepped sleeper area to maintain a safe distance between the soil and your house’s walls, creating a natural barrier.
For the backyard slope that leads down to the rainwater drain, you could install a secondary retaining structure. Using timber sleepers to form a low retaining wall or sunken pit around the drain will allow you to raise the soil level for your turf without over-steepening the slope. This design will create a visual step down to the drain, giving you a gentler gradient across the lawn and a level transition from your alfresco area. Raising the backyard soil against the retaining sleepers will also visually cover the house slab, blending it seamlessly with the landscape.
In summary, by creating distinct zones with treated pine or stone retaining features, and ensuring proper drainage lines, you’ll control water flow and prevent unwanted moisture buildup around your house. These adjustments will also allow you to maintain an appealing landscape and achieve a level alfresco area.
Please let me know if you have any questions.
Mitchell
Hi Mitchell,
Thank you very much for taking the time to provide me with a detailed response.
I would like some further clarification to your advice if you don't mind, please see below.
"For the area around the AC unit and rainwater tank, building a stepped or tiered section with treated pine sleepers is a great choice. By constructing a small retaining wall or step down here, you can direct water flow away from the house while creating a stable, controlled slope."
Should I build the step down from the corner of my house (option C in attached photos)?
Or Should I build it right at the AC slab (option B)?
Or Should I follow the natural step down of the house slab and build the step down there (Option A)?
Should i take the width of the step from house wall to the outer perimeter of AC slab (i.e. A1) or from house wall to the fence (A1+A2)
"Since this area has a lower slab height, adding a drainage line along the higher soil level is essential to prevent water from collecting around the AC slab."
There's currently downpipe (i assume it is) is passing around the AC slab and there's a pipe with 100mm dust cap on it. Can i just replace the dust cap with surface drain cap? Or do I need to run an ag pipe next to this down pipe? ( See attached photos marked in blue and pluming plan)
"One critical point here is to avoid piling soil directly against your home’s brickwork, especially above the damp course line, as this can lead to moisture seeping into the walls. Moisture above the damp proof course can cause serious issues like internal dampness and wall deterioration. To manage this, use the stepped sleeper area to maintain a safe distance between the soil and your house’s walls, creating a natural barrier."
I'm not able to see a damp proof course between slab and the bricks. The only thing I can see is a plastic membrane embedded deep inside the slab itself. Assuming that would be the damp proof course (please confirm this for me, see photos attached), the soil level is already at or above the plastic membrane. Does that mean I need to lower the ground level to below that from all sides? If so, what do i do with the exposed slab sides?
"For the backyard slope that leads down to the rainwater drain, you could install a secondary retaining structure. Using timber sleepers to form a low retaining wall or sunken pit around the drain will allow you to raise the soil level for your turf without over-steepening the slope. This design will create a visual step down to the drain, giving you a gentler gradient across the lawn and a level transition from your alfresco area. Raising the backyard soil against the retaining sleepers will also visually cover the house slab, blending it seamlessly with the landscape."
Would the surface water be able to run to the rainwater drain if the drain is boxed off from all sides using sleepers?
I know I'm asking lots of questions, so once again thank you Mitchell for all your help and support 🙏.
For the side, I'd go with the step down at position A to align with the house slab @ArashM. For the width, I'd go right to the fence, which appears to have been constructed as a retaining wall. However, you might like to investigate whether it is only supported by the fencing posts and not separate retaining wall posts. If it is just the Colorbond post supporting the sleepers and fence, then it is not truly a retaining wall; it is merely a fence and should not have soil piled up against it. Check the neighbour's side to see if they've piled soil up against the sleepers. If so, it's likely not going to be a problem if you do, too. If they haven't, the additional soil you'll be adding on your side could eventually push the fence over. To avoid this, you'd need to run an actually retaining wall on your side just in from the fence to retain your soil effectively.
It would be a good idea to add a surface drain to the drain pipe and/or connected your drain pipe which you will be using in the stepped section.
Your dampcourse is a line of plastic material in the bricks; it is not the plastic exposed on the slab. You can raise your soil to the top of the slab, but I would not go any higher above the bricks.
For the drain, if you raise the sides around it, water will not flow as efficiently into it. However, any subsurface water running in that direction will flow through the sleepers towards the drain. It's not optimal to box in the drain, but given you need to flatten the area, there are not a lot of options. You might like to enlist the services of someone who specialises in drainage for their opinion.
Mitchell
