How to build a gravel path and drainage?

[FernyG]

Hi Bunnings Community,

Long-time reader, first time poster, thanks in advance for any advice and apols … my photos got in first and questions are below 😊 👇

 

 

 

 

 

 

My problem

• Previous owners laid pavers and stormwater drainage pipes too high beside my house, plugged up the weepholes in bricks for years and caused rising damp inside lower level (just fixed professionally and quite spendy).
• Problem exacerbated by use of an ag pipe (also previous owners) for part of the stormwater beside the house instead of a PVC pipe, connected into downpipes.

The area

• We are in Queensland - not in a flood zone or any problems in that regard - but it rains a lot and storms can be big. 
• Some water flow comes down from the back garden (terraced) through this area when it rains but does not pool and has always drained off quickly through the pavers. Backyard drainage is fine.
• The side of the house is 11m long and 1.45m wide so not a lot of area to play with.
• Clay type of dirt, high water table after years of rain.

The project (see drawing)

1. Removal of pavers (partially done) 
2. Dig down to bring ground level lower than bricks (currently at least 15cm above the bricks, we're hiring a kanga)
3. Slope the ground away from the house and create fall down to where pipe will join stormwater (there is a nice existing fall once you get past the side of the house towards the front) 
4. Trench and installation of PVC stormwater pipe at correct level (will get plumber for connections) - will use 20mm drainage gravel all around pipe and wrap in geofab 
5. Create a gravel path with 600mm x 600mm paver steps 
6. Plan is weed mat + pins, roadbase or 20mm gravel (100mm deep), compact, sand (50mm? deep), compact, install pavers, decorative gravel (50mm deep).
7. Lift old pavers out front of the house and reuse side pavers, as well as another gravel path. 

Questions - apologies, there are a few  

Materials - There is a LOT of material there now - at least 150mm above the bricks in places so I believe we need to dig out 300mm then put in the base/sand/gravel for 150mm then we're ideally 150mm below the bricks. And how far we dig the trench for the PVC pipe depends on height of stormwater connection (don't know that yet as pavers are not up). 

As pictured, I think what is there now is sand and roadbase (see pictured). We are going to have to dig out so much to dump in a skip, and planned to buy new stuff, but is there a way to reuse? 

The problem is it'll be all mixed up and the material will have grass/weed seeds all through, weeds have been a real problem and want to resolve that as well. Could we maybe do the first 50mm layer old dirt and compact, then weedmat, then 50mm fresh roadbase or gravel? Gravel appeals more for drainage benefits. Then 50mm sand, then 50mm decorative gravel.  

At least then we'll only have to buy half as much roadbase / gravel. Is there a risk the flow from the garden will wash the gravel away if we get a big storm?

Slope

Slope away from house (side): 50mm for first metre I think, then what? The slope away from the house will be towards the raised beds. We had thought about an ag pipe there as well but want to keep it simple.

I'm not clear how we lay the pavers to be flat down the centre if there's a slope?I know the fall to the stormwater connection is minimum 100mm per metre.

Trench 

How far out from house to trench to install the PVC stormwater pipe but still connect to downpipes. The downpipes are new and the plumber said to angle out from the house as much as possible as the old ones were flush and have rotted wood in our cladding.

The trench may not be that much lower than the rest of the ground level depending on fall requirements. If we wrap geofab and surround in gravel does it need to have something to separate it from the 'rest' of the gravel / roadbase for the path? Otherwise it is just sitting all at the same level. But then if we put in a metal separator or something that might trap the water by the house (again) ... sorry I'm not quite sure how to phrase this question. 

Thank you for reading if  you got this far!!   

[JacobZ]

Hi @FernyG,

A warm welcome to the Bunnings Workshop community, it is fantastic to have you with us.

I'll start by saying you've done some brilliant work so far with your planning. I think you have already hit on every consideration I would make with this kind of project, and you are well and truly on your way to success.

Now, to answer your questions - 

Materials - 

Yes, you can absolutely reuse materials; they are exactly the same as what you would purchase, they are just all mixed together. If you are using a kanga, you should be able to scrape away in layers to keep distinct materials relatively separate. 

It does look like there is sand over the top of gravel or road base, so if you can do a first cut to take away the sand on its own as best you can, then run it through a sieve or wire mesh panel to remove any stones, you can then reuse it.

You could then do much the same thing with the next layer of gravel/road base, but the idea is more to remove the roots and weeds than to isolate stones from soil, as they will be mixed in together anyway. If you are concerned about seeds in the soil, it might be best to get rid of it and buy fresh material, but there is still some risk of seeds being in fresh materials anyway.

There is always going to be a risk of surface-level materials being washed away, but by compacting them, you are minimising that risk. You can use a product like Landscape Lock Concentrated Garden Glue to help lock the surface level stones in place.

Slope - 

I believe you are getting your 50mm over 1m figure from the National Construction Code Part 3.1.3 Drainage.

As long as the slope follows a consistent plane without any change in gradient, you won't have any issues laying your pavers. It's when you change the slope, you can run into issues. If you keep the slope consistent, you will have a slope of roughly 75mm over the 1.45m, which isn't huge. You want it to be reasonably level along the 11m plane, but the slope along the 1.45m side won't be too noticeable.

I would consider adding a channel drain against the garden beds rather than an agi pipe, as the slope will be directing your surface water towards that spot. You could then have a plumber connect that channel drain to the stormwater connection.

Trench -

You'd have to check these questions with your plumber, as regulations can be different in different areas. It's always best to check with them, but I imagine 200-300mm out from the house would be roughly what you are looking at.

If the pipe is encapsulated in gravel, which is wrapped in geofab, the geofab is all the separation you need. Its job is to keep soil from eroding between the gravel around the pipe while still allowing water through. I wouldn't overthink this too much; your plumber will do what they need to here.

I hope this helps to clarify a bit.

Let me know what you think and if you'd like clarification or have further questions, please don't hesitate to ask.

Jacob

[FernyG]

Hi Jacob - thank you so much for the reply, that is super helpful and I appreciate you taking the time to provide great details! 🙏🙏🙏

[JacobZ]

No worries @FernyG.

I'm sure you're going to have a successful project, but if you run into any other questions along the way, please don't hesitate to reach out.

If I don't have an answer, I can certainly point you in the right direction.

Jacob

[FernyG]

Thanks Jacob - May I trouble you with one more question? With the roadbase / gravel base, I keep reading varied answers about the depth required. Some say 50mm, some 100mm. Could I do the mix of 50mm old stuff seived / weed mat / 50mm drainage gravel 20mm size (or is roadbase better?) then 20mm sand / 50mm decorative gravel. How much base material is required? Also for a gravel path with stepping stones, is a sand layer required if the gravel is well compacted? Perhaps we could concrete the stepping stones? Thank you 

[JacobZ · Accepted solution]

Hi @FernyG,

Your gravel or road base is just there to act as a compactable material that will create stability while allowing water to drain through. The thickness is a bit arbitrary because it all comes down to how stable the Earth is beneath it. If you had soft soil, you would want to go with 100mm and compact it; if the soil beneath is relatively compact already, 50mm should do the trick.

I would mentally plan for 100mm of base material, but if you can stomp on the soil and your foot doesn't sink in much, you should be fine with 50mm

If you are laying step stones with decorative gravel around them, I would backfill with 50mm of the sieved material, compact it, add a weed mat, then add 50mm of road base and then compact it. I would then instead of sand, use mortar to set the stepping stones in place, then backfill around them with your decorative stones.

This will give you some solid compaction without the addition of too many new materials.

Let me know what you think.

Jacob

[FernyG]

Thank you so much, Jacob! Certainly I’m going to have a lot of big piles of materials sitting on my driveway so if I can avoid a big sand pile to shift as well, that’s desirable!! 😀

[FernyG]

 

Hi again JacobZ … just one more Q on this (promise)! Our plumber will work out the drainage connections but in terms of the gravel, I dug down through sand and roadbase to clay, and that’s the original I assume. BUT, the clay-like dirt is still next to bricks. I don’t know how to tell where the damp proof course is in order to go 150mm beneath it! Should we just go 150mm beneath the last brick - so next to the footing but making sure the footing remains covered? I read that for my 1975 house the DPC may be PVC or tin. Not seen it yet. The inside has 16 bricks to window and I’m down to brick 19 on the outside. I need to keep digging but waiting to get the machine to do it.i cleaned up the bricks a bit to see. I think I can see what looks like weep holes so 150mm down from bottom weephole brick? Or will the DPC be under the weep holes? 

 

Any advice on the DPC or should I ignore that and just go bottom brick? Thank you 🙏 

[EricL]

Hello @FernyG 

Generally speaking, the DPC sits under the weephole and if you see the weephole the DPC should be visible as well. So technically the top of the gravel walkway should be at least 150 mm below the weep holes, according to Australian building regulations. This clearance is crucial for proper drainage and ventilation, preventing moisture-related issues.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations. 

If you need further assistance, please let us know.

Eric

[Nailbag]

Hi @FernyG 

I also agree with @EricL comments regarding the weep hole clearances. These are very important for in-house air flow prevent possibly mould growth and rising damp.

Nailbag