The Brew Cabin

Posted: **Fri Aug 17, 2012 12:42 am**

First of all congratulations on the very informative & helpful site.

I want to extend some paving in front of my house:

https://docs.google.com/open?id=0B4ubkI1JMkLQREJ6cngtNTRkNzA

The existing paving is level with the dpc. It slopes slightly away from the door & also towards the wall on the left of the photo. I'd like to extend the paving to the area shown by the red outline.

The landscaper I had round for a quote was going to lay a "concrete pin kerb retaining element situated 100mm from the building wall to prevent dpc breach & spread clean decorative gravel to the drainage strip between the newly paved area and the building walls".

However, I've been looking at the first Dry Area arrangement on page http://www.pavingexpert.com/dpc01.htm

What I'd like to know is:

1) Does it matter how wide the channel is? My landscaper said 100mm. The diagram shows it as 200mm but in the 2010 Building Regs I couldn't see any specification for this. So I'm wondering where it comes from. Is it just from experience?

2) Are the falls of the channel away from the house wall & longitudinally something I should press the landscaper about. He didn't mention anything about them. Come to think about it, he didn't even specify a concrete base to the channel...

3) Does it matter how high the gravel in the channel goes? On the diagram it is slightly more than 1 brick below the dpc. I guess the main consideration is that the top of the concrete channel is at least 150mm below the dpc?

Thanks in advance,
Jim

Posted: **Fri Aug 17, 2012 7:26 am**

1) Does it matter how wide the channel is? My landscaper said 100mm. The diagram shows it as 200mm but in the 2010 Building Regs I couldn't see any specification for this. So I'm wondering where it comes from. Is it just from experience?

It is said that rain can bounce 150mm in height, 200mm is a good bet to counter that effect. 100mm not so effective.

2) Are the falls of the channel away from the house wall & longitudinally something I should press the landscaper about. He didn't mention anything about them. Come to think about it, he didn't even specify a concrete base to the channel...

He is probably thinking of using the gap as a french drain, and allowing water to pass directly down through the ground below, last time i used this work around i installed a linear drain at the bottom of the channel and directed to water to a soakaway, the french drain isnt held in high regard here as after a period they can become blocked with leaves and junk and lose effectiveness (is that even a word?)

3) Does it matter how high the gravel in the channel goes? On the diagram it is slightly more than 1 brick below the dpc. I guess the main consideration is that the top of the concrete channel is at least 150mm below the dpc?

Correct, rain can still bounce off gravel and breach the dpc. 150mm is the golden number

Posted: **Fri Aug 17, 2012 10:03 pm**

Thanks for taking the time to reply.

last time i used this work around i installed a linear drain at the bottom of the channel and directed to water to a soakaway,

I have a drain from my roof gutters nearby so I could ask the landscaper to direct any water to that. Did you put anything on top of your linear drain?

the french drain isnt held in high regard here as after a period they can become blocked with leaves and junk and lose effectiveness

So would you say "The Dry Area arrangement" on page http://www.pavingexpert.com/dpc01.htm is a French drain? The page says it is the preferred method of dealing with a conflict between level of paving / ground and dpc. Is that only provided it is installed to those exact specifications (which I guess many aren't)?

Out of interest, what stops your linear drain from getting blocked with leaves and junk if it's in a similar channel?

Correct, rain can still bounce off gravel and breach the dpc. 150mm is the golden number

So you mean the top of the gravel should be at least 150mm below the dpc? In which case the gravel needs moving down a bit in "The Dry Area arrangement" diagram on page http://www.pavingexpert.com/dpc01.htm...

Once again, many thanks for your help.

The Brew Cabin

Best practice for paving & dpc