Patio above dpc level

[JoanneT]

Hi
We are laying a patio in front of a new extension, to join up with an existing patio in front of the existing house. The new patio will be on two levels - a higher area which is level with the threshold of the bifold doors, and a step down to a lower level which is level with the existing patio.
The higher part will be edged on one side by the existing house wall.
We know we need a drainage channel between the door and the patio slabs.
However the higher part of the patio is 2 brick courses above the level of the dpc of the existing house. I've found the dry area suggestion on your drainage pages of a 20cm wide trench filled with gravel - however I'm concerned this will be a hazard for people/our children to put their foot down - is there any other solution? Can this gap be covered over with anything, or could we lay the drainage channel which we'll be using in front of the doors around the edge of the higher part of the patio too where it meets the wall of the existing house?
Thanks
Jo

[lutonlagerlout]

something has gone askew in the planning Joanne

there are ways around this problem but they need to be thought through and executed at the build stage

if you go 2 course above DPC you will have damp problems for sure

is it the old type DPC of slate?

sometimes this would be 140mm below finished floorlevel to allow the joists and floorboards to sit on DPC?


all i could suggest is install code 4 lead from 2 courses above the new patio height to 2 courses below DPC

its going to cost a few quid

LLL

[JoanneT]

Hi, not sure if it is slate but it is definitely below internal finished floor level, about 2 courses, hence why that is the level we need the top part the new patio to be so it is level with the patio door threshold.
Jo

[Tony McC]

Would a threshold drain work?

[JoanneT]

Hi,
Do you mean running the type of drainage channel that we need along the threshold of the bifolds all around the edge of the house wall too?
This kind of thing?

www.screwfix.com/p/floplast-flodrain-ch ... k-1m/95012

If we were to do that, would we need to leave a dry trench with gravel at the bottom underneath it or could we fill that with pea shingle or similar? The channel obviously needs to sit on something or be fixed to something. Just concerned about having stuff against the house above the dpc. Could we fix damp proof membrane and /or paint with water resistant stuff from below the dpc to above the level of the paving to help prevent water from seeping into the bricks?

Thanks

[Tony McC]

No, a *threshold drain* as shown on the page link I provided.

[JoanneT]

Sorry there are several types of drain shown in that section. Are you referring to the Hepworth threshold drain in the bottom pic? And suggesting we use that all round the edge of the patio that is bounded by the house wall? Or just in front of the doors?
Thanks

[Tony McC]

Choose the one which you like or is cheapest or match the colour of your curtains - it really doesn't matter, and then use it just outside the door.

If you need a channel elsewhere (because of the levels problem) you should find that the standard linear u-channel is much more cost-effective for non-threshold locations.

[JoanneT]

Ok thanks

[John156]

LLL what detail do you do at the build stage?

[lutonlagerlout]

if we know a flush threshold is coming we run a 900DPC up from the internal blockwork @DPC up 2course of blocks = 450mm then we put in 2 DPCs on the exterior skin

got a pic somewhere 1 sec




like this there is zero chance of damp penetratng,but it is a PITA detail to build
LLL

[John156]

Sorry for the delay- yeah, looks good. I imagine getting the membrane around the corner is a bugger. So you reckon the best way for a retro fit is lead up the wall? I always abide or get close to the 150mm below dpc rule but I have seen a fair few existing paving levels above dpc with no problems.