The Brew Cabin

Hi Tony
I'm putting a patio at the back of the house outside a conservatory. the local 'expert' came round today to have a look at the base and suggested putting a linear drain along the conservatory wall to catch any surface water. It would connect to a gulley already there. His suggestion was to place the drain one brick course down from the DPC. The reason being that the garden level is slighty higher, 60-70mm, than the patio level would be, if laid at 150mm below DPC. By installing the drain the patio would be 'almost' level.
Is this acceptable or am I going to have problems later, like surveyors etc.
Excellent site!!!

Some expert! The linear drain must be 150mm, that's 2 courses of brickwork, below dpc, to comply with Building Regs. If doing this means that the garden is higher than the patio, then you need some way to deal with the surface water, and my preferred method would be to omit the linear drain around the conservatory itself, and lay it (or some other form of drainage) at the garden/patio interface, with a step up to the garden if necessary, and fall from the conservatory to the linear drain. This would allow you to keep to the requirements of the Building Regs, keep any future surveyors off your back, and effect a workable solution to draining both the garden and the patio.

On the DPC page on this website it states that a linear drain may be laid to within 75mm of the DPC. Could you clarify which is correct?

I have a similar problem around a small extension where I want to install some paving, although the ground slopes up transvesely across the house from left to right (looking towards the house) as well as sloping up fairly sharply towards the garden. The ground at the RHS is nearly up to the DPC but we have no problems with damp. The nearest drain is the LHS side of the extension.

It would be easier for me to install a linear drain against the house and around the extension to comply with building regs than having to dig out a load of earth to make the ground slope away from the house and ensure the finished paving level is 150mm below DPC.

Any advice would be most welcome and many thanks for the very comprehensive & informative site!

Laying a linear drain just 75mm below dpc is stretching the limit to the very edge of breaking point, and should only ever be countenanced when there's no other option - perhaps I should make that clearer on the dpc page.

The issue of using Linear drains in this manner is complicated, as some BCOs are quite happy to accept a linear drain laid in this fashion, while others will reject it out of hand. Part of the problem comes from the implementation of Document M of the Building Regs, which requires disabled access to new buildings. One of the supporting documents shows a linear drain laid to within millimetres of the dpc as one possible solution. Some BCOs I've spoken with, claim this is acceptable only for the width of the doorway (1200mm) and would not be acceptable for extended runs of a few metres, while others, as I said, are happy enough for it to be used wherever.

In your situation, where there's no overwhelming obstruction to complying with the 150mm below rule, I'd stick with that, as it's less likely to arouse the interest of a surveyor if you ever come to sell the property or make a claim on your insurance for any damp damage (even if it's nowt to do with the linear drain). Once the linear drain is in, you can backfall the paving towards the house, and save yourself a good bit of work (and a skip or two of spoil), as long as you have somehwre to outfall the linear drain.