How to regrade an L shaped backyard with slight slope?

Question

🖼️

The project:

we are DIY ing our small L shaped backyard (9x3m by 6x3m), and are stuck at regrading the L shape as the property is on a slight slope.

the lowest point is the garage door (pictured), so how do we regrade soil away from house with the L shape?

We removed all grass and debris and started regrading the long part of the L shape, which wasn’t too difficult, but then when we got around the corner, we noticed that there was a big drop on the short L shape (pictured) of about 6 inches.

We have gone back and forth but realise we need some expert help!

Also uploaded sketch (not fully to scale) of what we want to achieve in final product.

- Step 1:

removed all broken concrete and steps, used roundup to kill kaikuyu grass, raked existing soil to regrade

MitchellMc · Answer

Hi @lans

The key thing to keep in mind is that your weep holes should always remain well above finished ground level, not used as a guide to raise soil up to them. Typically, you want at least 75–100 mm clearance below the weep holes so water can escape the cavity and you don’t trap moisture against the structure. Also, you should never bring soil up above your dampcourse line in the bricks.

From what you’ve described, it sounds like the ground near the garage has likely been built up over time, which is why your measurements are so high there. So rather than bringing the rest of the yard up, the correct approach is usually to take material away, not add it, even if that makes your area slightly lower than the fence line.

Your concern about becoming a “sink” is valid, but this is where drainage design comes into play rather than changing your finished levels to match the neighbours. You’ve got a few options to manage that:

* Create a gentle fall away from the house and garage as planned
* Install ag pipe (French drain) along the fence line to intercept any water coming from neighbouring properties
* Consider a spoon drain or surface channel to direct water to a safe discharge point

In terms of levels, I wouldn’t recommend using the weep hole heights to create a slope. Instead:

* Set your datum near the garage (as Jacob mentioned)
* Ensure the garage edge is not allowing water in (you may even want a slight fall away from it)
* Grade the soil consistently away from the house, maintaining that clearance below weep holes all the way around

Because your block is L-shaped, you might end up with two planes that meet at the corner, rather than trying to force everything into one flat plane, and that’s completely fine as long as water is directed away from structures.

You’re on the right track, just don’t be tempted to raise levels to solve a drainage concern. It’s almost always better to lower and drain, rather than raise and trap water.

Please let me know if you have any questions.

Mitchell

lans · Answer

amazing! Thanks so much Jacob!

Just to clarify - the garage is concrete slab, but house is brick veneer on stumps. We are unit 4 in a group of 7 attached.

If we were to dig down to the datum point near garage door (pictured), the property would be in a sink compared to neighbouring fence lines - we are just worried that this would cause water to run into our property from outside. Have attached pictures of fence lines to show where we have already dug out and how low we now are.

Another reference point we were considering was from bottom of weep holes down to desired soil height? Assuming we would have soil flush with top of slab at garage door (bottom of grey concrete) see pic.

we measured the distance from bottom of weep hole to ground closest to garage door, height was 670mm, we then measured around property and weep hole furthest from garage (near fence) is currently 390mm.

the garage side weep hole heights were relatively even - ranged from 670-600mm, around the corner up the slope to the fence ranged 520-390mm (although we have moved this soil ourselves). Would you suggest a gradual increase in slope led by weep hole height?

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let me know if you need any further info! Really appreciate your help!

JacobZ · Answer

Hi @lans,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

With any landscaping project that involves grading, the most important thing to do is set a datum point, which is basically a surveyor's mark, and then work everything off of that datum point. In this situation, the logical point to work from is the corner near the garage door as everything needs to flow away from it, so it should be the highest point.

Assuming the slab was poured level, if there is a drop of 6 inches or so from the corner of the house to the garage door, then logic would say at least one, maybe even two courses of bricks have been buried.

If you inspect the brick line around the base of the house, can you see the top of the slab? Or your dampcourse? Or your weepholes? If not, could you dig out a small section of soil against the brick to see how deep the slab is and upload some pictures?

If my assumptions above are correct, it seems like the solution is going to involve removing quite a bit of soil if you want the ground to follow a single plane to ensure water flows away and there are no issues stemming from soil sitting against the brick.

Working from that datum point near your garage door, the best thing to do is stake out the space and set up string lines as a guide to measure off of to check your heights. Here is an example of a layout that you could use.

You can set this up with a pack of

https://www.bunnings.com.au/products/garden/landscaping/plant-support/timber-garden-stakes

, some

https://www.bunnings.com.au/grunt-100m-fluorescent-builders-line_p4310406

and a line level. Set the stakes in the locations shown above, then set up your strings using the line level to check for level long ways and for fall the other way.

You should set the strings up from that datum point at the garage door. The strings should be about 100-150mm above the desired height of the soil, so you can measure down from the string at any point to check your height, but you still have clearance to remove the soil.

Once everything is mapped out with your string lines, it is just a case of digging out and removing the soil, checking back against string lines as you go to ensure you are following the desired grade.

I hope this helps to guide you about where to start, but I understand that you may have more questions, so please don't hesitate to ask. We're more than happy to help.

Jacob