Patio above DPC?

Chev2010

Hi,

Looking for some feedback on my plan to raise the patio above the level of the DPC. In the image; I have about 100mm of hardcore laid and I'm trying make the patio match the internal floor level and also cover up that black piece of aluminium - ideally without causing damp issues!

My plan is to cement single blocks on their side (in closer to the wall than shown - just under the black aluminium to allow for grouting), on the left of this I will fill with ~220mm hardcore and on the right I'll leave it as is so there's be no bridging above the DPC level and any water that gets in there can soak away - there should be about 40mm from brick to wall and it'll remain an empty void.

There's a 1m overhang on the roof, but there will still be some water sheeting off the glass and that will come out between the black aluminium and the limestone (will be put in dry and not cemented at this end to allow water movement).

Slope of patio will be away from the house and will have a drain at the far end.

Thoughts?

Thanks!!

Lumen

It seems right dodgy to be building a full patio above DPC level. Isn't that a clear breach of regs?

I'm not sure how you can avoid one of (a) drainage gaps being a trip hazard, and/or (b) drainage getting fouled by debris and water breaching the DPC.

There are a number of "rule bending" workarounds on http://www.pavingexpert.com/dpc01.htm but none of them have paving higher than the DPC.

Why not just build steps down?

Chev2010

We initially thought about the step down, but we then need to step back up into the garden and you still have that step above the DPC and the level look from inside to out would be far nicer.

Attached is a better image of what I am thinking about and there's 60mm from wall to brick. I had a dig through photos of the build and the builder actually put in 2 DPCs (not sure why). One at lower level and one at the level of the sliding door base - the back aluminium sits on this DPC level.

We could also use a hollow block row instead of solids, this would take the level of the hardcore back another 200mm or so from the building..

BryanF

Insulation thermal continuity at threshold is important, change the threshold out for wider cover or slip an alu folded piece up under the existing and down into an aco channel to run full length of door.

A flush paving detail needs to be either completely sealed or preferably given a land drain to cater for any water that gets down at the threshold

Calahonda52

whats the plan for ensuring the 220 mm of new hardcore, plus existing, will be free draining at the 3 sides
under the aco channel suggested by BF, consider the use of land drain full width, with rodent free, drainage at each end

Chev2010

Seems that image didn't attach to the last post, see attached now - apologies. That piece of timber is coming back out (I put it in with the intention of supporting the aluminium if builders stood on it).

@BrianF - with the attached threshold design(s), do you think an aco drain is still required at the threshold? There's been no damp in the blocks above the DPC in the last few months with the hardcore open to the elements so assumed when closed in from elements more it would be drier again? There's a rainwater gully at either side of the patio so could look drain it into that if needed..

@Calahonda52 - For the other 3 sides, I had planned to have the whole patio slope away from the house with a full patio width aco channel at the end. The sides will join existing block garden walls and have no drainage.

Also drew up the current proposal - hopefully this clarifies things and have also put in a second option where I dig out the existing hardcore (~50-100mm) to increase the distance from ground level to first DPC. The void will be closed in, so minimal dirt should build up in there over the years.

From what I see in other designs and reported problem, the concern is bridging the DPC or allowing rain splash back.. think either of these designs will prevent this and rain in this area is minimal as we have a 1m overhang on the roof - I'd say 1 rainy day in 4 leads to the glass door actually getting wet.

I'm planning on getting a professional in to do this, but I want to be sure I don't get the "ah, it'll be grand" answer so intend to have some of the specifics thought out (and reviewed) in advance

Thanks again for the suggestions to date.

BryanF

Chev2010 wrote: »

1. with the attached threshold design(s), do you think an aco drain is still required at the threshold?
2. There's been no damp in the blocks above the DPC in the last few months with the hardcore open to the elements so assumed when closed in from elements more it would be drier again?
3. There's a rainwater gully at either side of the patio so could look drain it into that if needed.. .

4. I'm planning on getting a professional in to do this.

1. Yes
2. Don’t know. That’s not really relevant imo
3. Yes
4. Why not wait until they draw the detail for you. You’ve ignored insulation in your details above.

Mellor

It's possible to have a patio level with internal floor level.
But not the way you are doing it. It's a pretty standard detail for an terrace balcony.

Chev2010

Sorry for the delay, been away but took your advice also had a company come out and look at this in the mean time.. their take was that this would not be an issue as water will flow away from the house and with the half pipe drain below the DPC (effectively a 42mm PVC pipe cut in half and run into the rainwater drain for the house) it will catch any small amount or water that may enter there.

So I guess I have 2 questions:
@BryanF - we have insulation under the solid floor that turns up at the end of the room, under the door - do you propose I put insulation on the outside of the house too? Would this not bridge the DPC and cause potential damp issues?

@Mellor - do you have suggestions on how it could be achieved considering the extension has already been built?

Thanks again for all the help, really appreciate it.

Mellor

Chev2010 wrote: »

@Mellor - do you have suggestions on how it could be achieved considering the extension has already been built?

Raised pavers on a pedestal system as per terrace balconies

BryanF

Chev2010 wrote: »

Sorry for the delay, been away but took your advice also had a company come out and look at this in the mean time.. their take was that this would not be an issue as water will flow away from the house and with the half pipe drain below the DPC (effectively a 42mm PVC pipe cut in half and run into the rainwater drain for the house) it will catch any small amount or water that may enter there.

So I guess I have 2 questions:
@BryanF - we have insulation under the solid floor that turns up at the end of the room, under the door - do you propose I put insulation on the outside of the house too? Would this not bridge the DPC and cause potential damp issues?

@Mellor - do you have suggestions on how it could be achieved considering the extension has already been built?

Thanks again for all the help, really appreciate it.

Without a detail of what installed I can’t comment