Paving above DPC?

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Discussion

T5GRF

Original Poster:

1,675 posts

244 months

Sunday 8th March 2015
quotequote all
We have been talking to landscaping companies regarding a new patio. We would like to raise the level of our new patio to bring it above DPC to keep the floor level of our new extension the same height as the hard landscaping outside. We would look to install a French drain or Aco drain to carry water away from the wall but I understand that covering over air bricks is not a good idea so will need to find a solution to keeping the air bricks free of obstruction.
I have asked 3 landscaping companies to quote for the job. I got a mixed response from them regarding raising the level of the paving above DPC level and in relation to drainage and keeping the air bricks open.
Is it just a bad idea to raise the level of the patio up in terms of damp issues even if we use a French drain and have the patio falling away from the house? If we do put a French or Aco drain in, what is the best way of keeping the air bricks un obstructed?

wolfracesonic

5,637 posts

107 months

Sunday 8th March 2015
quotequote all
Have a look here, some food for thought dry area construction Laying anything touching the brickwork above the dpc, be it gravel or acos is just asking for trouble imho.

Hoover.

5,965 posts

222 months

Sunday 8th March 2015
quotequote all
I personally would not recommend putting anything above DPC, no mater what is a constructed as a watertight structure always seems to have issues.

I'm company I am currently working for is building some new houses for a well known house builder, and we were asked to price the substructure brickwork...... the site is sloped, so keep the gardens level muck/spoil will built up against the outside skin, and where this happens the internal floor is lower then outside levels....... I then looked at the waterproofing detail, and it was useless, advised directors that we would be forever coming back to damp problems caused by bad design which the house builder would be blaming us for bad workmanship...... we didn't price the works.

I would not do it, you are just asking for problems

m3jappa

5,695 posts

198 months

Sunday 8th March 2015
quotequote all
Only way to do it IMO is to slightly pull the patio away from the house and have a thin gravel trap. Make sure this is free draining. Air bricks can be extended to come out the other side of the patio or another point. Obviously the paving has to clearly fall away from the house.
I have done this and it was on a newly built extension with bifold doors. Apparantly building control was ok with this.

For me I would do it and I'd construct it to the best of my ability and agree everything with you. However I wouldn't want to give any guarantee it will be no trouble, though it shouldn't be.

Little Lofty

3,019 posts

131 months

Sunday 8th March 2015
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I've just had a patio dug out and lowered by 150mm as the existing was above DPC, tbh it hadn't caused a bad damp problem internally due to the cavity wall but I dropped it anyway as it would just come up on a survey when I sell. I had to do a similar thing to some decking last year, it was too high and the house had solid walls so it was causing a severe damp problem internally, some poor guttering was also contributing to that damp.
It's always good practise to keep below DPC wherever possible.

T5GRF

Original Poster:

1,675 posts

244 months

Sunday 8th March 2015
quotequote all
Thanks for the advice. It looks like a no then however, so many projects I see on line seem to adopt the approach if raising the height of the paving to match the inside floor height, I just wonder how they achieve this without damp problems!

wolfracesonic

5,637 posts

107 months

Sunday 8th March 2015
quotequote all
A lot of pics you will have seen of where the internal/external floor levels are the same are probably new builds or new extensions where tray dpc's have been built in at brickwork stage in anticipation of any likely damp problems. Or they haven't and are suffering damp problems. Doesn't the 'dry area' idea appeal to you?

SAB888

2,961 posts

187 months

Sunday 8th March 2015
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We have to provide level access to many doorways these days because of DDA. Raise level externally but have a gap adjacent to the wall with a gravel area at normal level (150 below dpc). We also use ACO drains at the doorway or even along the wall depending on the structure and design.

popandu

5 posts

96 months

Wednesday 1st April 2015
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Really this should have been in the specification for the extension and the DPC installed 2 brick courses above its current level. The solution is now a work-around...

Taking a general stance by raising the ground level to above DPC you are increasing the risk of water in contact with the house regardless of the method of drainage, channels and falls etc...

The solution would depend upon the design of the method of access i.e. the door unit and threshold; assuming you would want some kind of contemporary concertina/ bi-fold door access the external patio could adjoin the house only for the length of the door and then you could revert to a 200mm channel elsewhere around the patio as it adjoins the house infilled with a cosmetic gravel.

The join of the patio along the length of the doors for access could be minimal using a hollow design approach to build up the level. It could be possible to use a channel along the door length itself but there would have to be an invert pipe running to an appropriate method of disposal depending on the area to be drained.

Hope that helps.

Andy