residential soakaway for extension flat roof

[johnhenstock83]

hi all,

 

I'm digging a soakaway for my new extension. it's a 6x3.5m extension with a fibre glass flat roof, nothing fancy. the down pipe is already laid and I've dug the hole for the crates, but I have a few questions:

 

1. I know the crates have to be wrapped in some form of geotextile membrane. I'm seeing a lot of pictures of nicely done soakways wrapped in a black membrane, also used as a weed membrane. they sell it in toolstation for £11. will that do or do I need something more specialised?

 

2. it's not entirely clear if the soakaway crates (1000x500x400 times two) must be filled with pebbles etc. or whether I leave them "empty", creating a huge void that fills with water. I believe the answer is no fill, but I'm not 100% sure, can someone confirm please?

 

3. where the down pipe joins the underground pipe, I'm looking to add a leaf guard, there's some moss on the roof from the main roof, small pieces every now and then. is it worth adding some sort of a cleaning outlet next to the soakaway, just before the pipe enters the crates or is that not necessary? there's good access from near the extension, I can easily remove the leaf guard and rod the pipe, it's 5 meters long.

 

thanks all

[torre]

Pretty sure the geotextile membrane's heavier duty than weed fabric, it needs to keep soil etc out for the lifetime of the soakaway.

 

No fill (if you go for rubble instead of crates you need approx x3 the size of soakaway.

 

What you're looking for is a silt trap before the soakaway (that site's got quite a bit more useful info too, including for a percolation test to establish size if you've not done one)

[johnhenstock83]

Thanks a lot, that’s helpful. I was hoping not to have to buy another membrane, I only need a small quantity and they’re sold in long rolls.

 

as for the silt trap, that’s exactly what I have in mind, I’ll install one, thanks!

[johnhenstock83]

me again.

 

soakaway done, I ended up buying a non-woven membrane in the end, even though building control would've been happy with the weed barrier one. it's all installed and nicely connected, hole is backfilled to replicate the soil structure (sand/pebbles up to where top soil starts, then top soil). BCO is happy and he signed it off, but I still need to level the soil in preparation for turf.

 

there's only about 150mm of top soil on top of the crates and I'm just wondering what will hold the weight of the soil. I know the creates are very strong, but they do have holes, so essentially, the membrane is holding everything. should the membrane tear, the soil will start falling in the crates and destroy everything.

 

is there anything that normally goes on top of the crates? a piece of MDF, maybe?

 

any advice welcome