French drain, DIY job?

TheCyclingProgrammer

Our surveyor suggested that some damp on a property we are buying may be caused by a bridged DPC due to high ground levels. It's a semi detached with a paved driveway to the front, paving and a Tarmac driveway along the side of the house amd patio/paving to the rear.

He suggested a French drain and improving ventilation might be all that is needed. We have had a "free" survey by a damp proofing company and they have said that some of the damp is caused by a leak in a downstairs shower but recommended a small amount of chemical DPC and re plastering amounting to about £1600 inc VAT (most of that is for the plastering).

However they were quite open about the fact that reducing ground levels and monitoring it might be enough. Apparently the existing air bricks were blocked by the construction of a conservatory extension.

If a French drain was to be built, would this go around the entire perimeter of the building? Is this something that can be done properly as a DIY job or is it worth getting a professional in? I assume it's a job for any decent builder who does driveways, drainage and other ground works?

If so, how much would we likely be looking at? House is just over 6m wide, about 12m long down the side. Not bothered about digging up paving in the garden as planned to level it at some point but want to make sure the driveway isn't damaged.

wallbash

Is this something that can be done properly as a DIY job or is it worth getting a professional in? I assume it's a job for any decent builder who does driveways, drainage and other ground works?

yes/no and yes!

French drain is not rocket science, but the end result is very visible.
So yes to construction by a diy'er but would you be 100% happy with the look ?

would this go around the entire perimeter of the building?

Unlikely

TheCyclingProgrammer

Thanks, sounds like it's worth getting a builder with experience of this kind of thing out to advise and quote then.

The quote for the chemical DPC was about £300 plus VAT which isn't too bad, the bulk of the cost was replastering and I'm skeptical of the need for it. If the plaster isn't blown and has no staining is it worth just monitoring would you think? If we can avoid the cost and disruption that would be preferred.

I'm guessing it might be cheaper to get a quote from somebody other than the damp specialist?

wallbash

I would always get the advice of a trusted experienced builder over a damp specialist? who is touting for business.

pleased to read

However they were quite open about the fact that reducing ground levels and monitoring it might be enough. Apparently the existing air bricks were blocked by the construction of a conservatory extension.

One step at a time.

tony6403

I wouldn't install a french drain around a dwelling and have never seen it done.
Doing so probably will have the effect of directing more water towards your house.
If you need drainage (instead of sorting out the levels) then contain the excess water using this type of channel

adouglasmhor

tony6403 wrote: »

I wouldn't install a french drain around a dwelling and have never seen it done.
Doing so probably will have the effect of directing more water towards your house.
If you need drainage (instead of sorting out the levels) then contain the excess water using this type of channel

They are often buried around the foundation wall of dwellings. that's a traditional use of them. If you don't have it feeding a steep enough run off you need a sump pump to drain it regularly though.

tony6403

adouglasmhor wrote: »

They are often buried around the foundation wall of dwellings. that's a traditional use of them. If you don't have it feeding a steep enough run off you need a sump pump to drain it regularly though.

I have never seen foundation french drains (presumably not much use at that depth without further drains to a soakaway) as you describe and have never come across a pump installed outside a house to take away excess water from the foundations.
Anyway , as far as I know, a near to surface french drain would not be allowed right next to a wall under Building Regs. which state that " water should not be discharged adjacent to buildings where it could damage foundations" and that "surface gradients should direct water draining from a paved area away from buildings. Where the levels would otherwise cause water to concentrate along the wall of a building a reverse gradient should be created for at least 500mm away from the building to divert the water away "

TheCyclingProgrammer

Well we had our damp report back and it too has recommended a French drain along the side of the property, so that's two recommendations.

We will probably get an independent survey when we move in but it would be useful to know how much this will cost.

adouglasmhor

tony6403 wrote: »

I have never seen foundation french drains (presumably not much use at that depth without further drains to a soakaway) as you describe and have never come across a pump installed outside a house to take away excess water from the foundations.
Anyway , as far as I know, a near to surface french drain would not be allowed right next to a wall under Building Regs. which state that " water should not be discharged adjacent to buildings where it could damage foundations" and that "surface gradients should direct water draining from a paved area away from buildings. Where the levels would otherwise cause water to concentrate along the wall of a building a reverse gradient should be created for at least 500mm away from the building to divert the water away "

I did describe a "soakaway" but in non jargon terms, and I have seen pumps installed. My father was a civil engineer specialising in drainage since before I was born and he probably has forgoton more about drainage than both of us together will ever know.
"As far as you know", means you are admiting you don't really know.

What reg do you think applies? Chapter and Verse.

zaax

Sounds like the driveway was put in with out much care for house.
The only other way to go it to lower the drive / tarmaced area back down to the original soil level - very expensive.

Air bricks must be cleared and you will have to check for rot in the timers under the floor.
How long have the air bricks been blocked?

TheCyclingProgrammer

zaax wrote: »

Sounds like the driveway was put in with out much care for house.
The only other way to go it to lower the drive / tarmaced area back down to the original soil level - very expensive.

Air bricks must be cleared and you will have to check for rot in the timers under the floor.
How long have the air bricks been blocked?

Yes, lowering the driveway is going to be prohibitlively expensive I think and it also would cause an issue as the properties at the rear of our house have right of way over it.

The conservatory blocking the rear air bricks was installed about 9 years ago I think.