Damp proof course and patio

kjs31

I am in the process of buying a house and the survey identified that the patio has been laid right up to the back of the house and too close to the damp proof course. The surveyor is suggesting that a drainage channel should be placed between the wall and the slabs by cutting a channel. I’m ok with that but the estimate he has put on the work seems quite a lot. 

Provision of perimeter linear drainage channels around £6,000 

There are some other bits and bobs to do too which push the total up to 10k but the patio makes up the lion’s share of this. It’s only needed across the back of the house as there is no issue with the front and sides. None of the work is horribly urgent. It says in 12-18 months and no sign of damp is present currently. 

Just wondered what people thought about the estimate. 

tacpot12

The estimate does seem very high, as the channel is only needed at the back of the house, and only a light-0dty channel is needed  (the channel only need to be rated to Load Class A 15). They won't want to under-estimate, but I would not use them to do this work if that is their estimate. 

I expect any decent builder would be able to do the work for half the price. The water will need to be drained to a soakaway that will need to be 5m from the house (and ideally 5m from the closest edge of the patio).

The soakaway will need to be much bigger if the patio is level or has a fall towards the house. If the patio falls away from the house as it should, then the soakaway can be much smaller which will also reduce the cost. 

stuart45

I'd leave it for a year and see what happens. It's not far off the 150mm needed.
It's a cavity wall and the bricks look like West Hoathleys which are F2 and S2 rated, and low absorption.

Doozergirl

tacpot12 said:

The estimate does seem very high, as the channel is only needed at the back of the house, and only a light-0dty channel is needed  (the channel only need to be rated to Load Class A 15). They won't want to under-estimate, but I would not use them to do this work if that is their estimate. 

I expect any decent builder would be able to do the work for half the price. The water will need to be drained to a soakaway that will need to be 5m from the house (and ideally 5m from the closest edge of the patio).

The soakaway will need to be much bigger if the patio is level or has a fall towards the house. If the patio falls away from the house as it should, then the soakaway can be much smaller which will also reduce the cost. 

It doesn't need drainage to a soakaway, it just needs taking back slightly from the wall to protect the damp proof course and prevent splashing up against the wall.  

As stuart says, you could suck it and see for a while.  

EssexExile

My house has a very similar patio, way too high. The patio has been there for 8 years and we've never had a problem. I do envisage purchasers being concerned about it when I sell later this year though.

jonnydeppiwish!

Hire a disc cutter. Remove 150mm of the tiling from the wall. Removed the cement underneath. This will take you easily over the 150mm depth below DPC. Fill with shingle.

Even if you buy a decent branded cutter and additional disc, will cost you around £400 to do yourself.

Lots of videos on YouTube, however, do try and get some experience in using it first! 

Ps use eye protection 

FreeBear

jonnydeppiwish! said: Ps use eye protection 

And don't forget to wear a decent dust mask as well. Breathing in fine stone dust is very bad for your lungs.

jonnydeppiwish!

FreeBear said:

jonnydeppiwish! said: Ps use eye protection 

And don't forget to wear a decent dust mask as well. Breathing in fine stone dust is very bad for your lungs.

Absolutely!

kjs31

jonnydeppiwish! said:

Hire a disc cutter. Remove 150mm of the tiling from the wall. Removed the cement underneath. This will take you easily over the 150mm depth below DPC. Fill with shingle.

Even if you buy a decent branded cutter and additional disc, will cost you around £400 to do yourself.

Lots of videos on YouTube, however, do try and get some experience in using it first! 

Ps use eye protection 

I would if I was power tool adept but sadly I wouldn’t trust myself to do it. My DIY skills just about cover being able to paint internal walls! 

markin

If its protected from most rain it will be fine, and no sign of moss or water marks.

ThisIsWeird

A number of factors will affect the 'urgency' of sorting this, Kjs, and its likely cost should you proceed.
The potential issue is caused by rain bounce, which could soak that lower section of wall just above the DPC layer. But a wall and pointing in good condition, and using quality bricks such as Stuart suggests, is likely to shrug off such soaking, just as it does any rain that falls directly on it. In your example, although laid too close to the DPC, there is still some gap between the patio level that should cope with most rainfall, and only become heavily splashed in heavy downpours coming from that direction (which, fair enough, we are having more of!)
So, is that a prevailing weather side? If not, and it only occasionally gets hammered, there's every chance it'll never become an issue.
In any case, the actual solution - cutting a neat, straight channel around 150mm wide (I think?) along that side and partially back-filling it with gravel to disipate this splash-back - is a doddle for a general builder, competent DIYer, or ditto local handyperson. The potential tricky/awkward bit will be how to remove the rain that will collect there. Even this might not be an issue in practice, if the amount of water soaks away naturally by itself. But, if it doesn't, and good chance it won't since it'll also be collecting all the rain that hits the whole wall, then a means of draining it away will likely be required. If the land surrounding the patio is at a lower level, then this should be cheap and easy to do in any number of ways.
That estimate seems astonishingly high, then. I can only guess that it must include drainage to a suitable location away from the house such as a soakaway, which is almost certainly unnecessary. As pointed out by others, only another daft installation issue such as the patio sloping towards the house might necessitate a more dramatic fix like this. So their £6k estimate seems like a very worst case scenario. 
Might be a good negotiating point for a £ouple of k, tho'?