French Drain

[Robbrad]

I am after some advice, our Victorian house extension suffers from damp, there is no sign of an original DPC, it is not a suspended floor - just a concrete floor and brick foundations/footings

We had a damp survey done on the house and it revealed that the concrete slab level at the back of our house was to high and we would need a 15cm trench. We also had a DPC treatment done but didn't have a trench dug at the time as we were short on money.

I have now started to tackle this job on my own. I have done a fair amount of research on how to construct a french drain and will be digging a soak away in the middle of the lawn away from the house

My question is - should excavate, let the wall dry(how long??), paint with rubber, lay membrane and pea shingle, then pipe, fill with pea shingle.

Or should I not paint with rubber to help the wall "breathe"

I plan to lay the pipe next to the bottom footing - is this correct? I will have to go a little deeper than the footing (see image)

Untitled

• Robbrad
• 1 Feb 2014
• 1

Untitled

• Robbrad
• 1 Feb 2014
• 1

Untitled

• Robbrad
• 1 Feb 2014
• 1

Untitled

• Robbrad
• 1 Feb 2014
• 1

 

[stuart45]

I wouldn't paint it. What membrane are you using?

 

[Blagard]

I would recommend you stop there depth wise. Old footings sometimes need lateral support for stability. I have seen one collapse where the builder exposed a length of footing prior to underpinning works. It rained and the footing slipped out sideways causing a collapse.

 

[Robbrad]

Ok good advice. I was planning to leave it open to dry out, from what you have said that might not be such a good idea.

The membrane I was planning on using was a geotextile one, like they use for landscaping. This should hopefully block sediment but allow water to freely pas though, into the shingle and down the pipe.

Not sure how I'm going to tackle the drain and gully, go around or under...

I do need to ensure a slight drop for the drain away from the house

 

[stuart45]

Use a non woven membrane for a better flow into the drain. I usually try and be a bit further out from the wall. In theory you can go down at a 45 degree angle from the base of the footing, but if you are a bit wider you can get the pipe below the bottom. This makes sure a high water table is taken away from the brickwork.

 

[Robbrad]

I'd like to do it properly, however I think I'm limited by aesthetics and the shear scale of earth to remove. If I don't go right next to the footing and I going to be ok?