Patio at Level of Internal Floor - Cavity DPC Sufficient

[Gaf]

Plan from the beginning of build was for our patio to be installed at the same level as our internal floor area. The patio is accessed from our open plan area through a large sliding door (3.5m). Open plan is an L shape and the patio is in the ‘gap’ in the L (if that makes sense) as the plan was to create a sense of the open plan ‘continuing’ out onto the patio. This was communicated to both the architects doing our drawings and the builder prior to starting. The plans have an Aco channel drain specified where the patio and sliding door meet. 

 

As the build has progressed and I’ve learned more about regulations, and I’m wondering if the makeup of the wall and DPC will allow us to do as planned with the patio being at floor level.

 

Attached image shows the makeup of the build at the external wall - it's 150mm cavity. The blue is the DPC – there is the DPC membrane running from high on the internal leaf down one block (215mm) to the external leaf, then an additional single piece of DPC running along the external leaf blockwork.

 

We had hoped to have the patio height set at the orange line. Does this DPC makeup allow this, or will we have to keep the patio lower (150mm below DPC) so somewhere approx. at the pink line?

 

The Paving Expert website only seems to include details where the DPC is just one horizontal piece on a single leaf, rather than double leaf house with the sloped DPC.

Edited April 16 by Gaf

[Temp]

I cant recall what the regs say but I would run the linear drain around the whole patio where it touches the house not just at the door. 

 

Normally a patio would slope towards the drain but I don't like the idea of sloping it towards the house in case the drain blocks. So I think I'd put another drain on the side furthest from the house and slope it towards that. 

[bmj1]

For my patio we did level threshold. We:

 

- sloped patio away from the house

- did a linear slot drain along sliding patio doors, and also on far side of patio

- fully hid the slot drain by the house/sliding doors, can share the drawings/detail if anyone is interested 

[Stu789]

10 minutes ago, bmj1 said:

For my patio we did level threshold. We:

 

- sloped patio away from the house

- did a linear slot drain along sliding patio doors, and also on far side of patio

- fully hid the slot drain by the house/sliding doors, can share the drawings/detail if anyone is interested 

Looking to do the same so yes please!

[bmj1]

1 hour ago, Stu789 said:

Looking to do the same so yes please!

You are doing sliding doors ? Which product ?

[Andehh]

Ours is like this, 2 years on never had an issue! (touch wood). Patio slopes away, linear drain is for driving wind and rain.

[Gaf]

3 hours ago, bmj1 said:

For my patio we did level threshold. We:

 

- sloped patio away from the house

- did a linear slot drain along sliding patio doors, and also on far side of patio

- fully hid the slot drain by the house/sliding doors, can share the drawings/detail if anyone is interested 

 Please share, thank you. What was the makeup of your DPC? 

 

 

59 minutes ago, Andehh said:

Ours is like this, 2 years on never had an issue! (touch wood). Patio slopes away, linear drain is for driving wind and rain.

 

Cheers for the image. Those thin linear drains look the business.

 

What is your DPC makeup? Is the patio level with the DPC (orange line in OP) or below DPC (pink line in OP)?

[Andehh]

DPC is below the doors then where it meets the walls either side uplifts to 2 bricks high and around the house it goes.

[bmj1]

Re: DPC, as per Andehh above.

 

Re: drainage detail, here is what we did:

• We did a triple track slider, and the system had drainage holes built into the bottom of the frame.
• We added a metal sill to carry water away from the house, and then added an aco slot drain in front of the sill (so a bit lower than the FFL)
• When we did the patio tiling, we used spacers to create 'channels' for the water to run from the slider drainage holes to the slot drain

This drawing and photo explains what we did - the result is an entirely invisible drainage by the patio doors (no visible slot). The flip side is that this approach requires careful attention to detail, and will take more time (cost more) than just putting a slot drain in.

 

 

 

 

This photo shows our prep work before laying the tiles. You can see we've tape up the slot drain, except where the drainage channels are:

 

 

And the finished product looks like this (taken this from the cctv, but shows that there is nothing visible)

 

 

[Stu789]

Thanks - Both look really good and added to the info file as we are looking to build step free and to Part M4(3) + some of the Living Home extras.

[Spinny]

bmj1,  So you have no surface drainage in front of your doors ?

 

 

 

 

 

 

 

 

 

[bmj1]

7 minutes ago, Spinny said:

bmj1,  So you have no surface drainage in front of your doors ?

 

 

 

 

 

 

 

 

 

The patio slopes away from the house, so the water is carried away from the house.

 

There is a drainage slot in front of the doors, but it is below the surface as shown above.

 

This is in London. Such an approach might not be suitable in more exposed/high winds areas.

[Andehh]

We have gravel between the slot drain and the slides for the same reason as posted above, triple slider drain points can drain into the gravel, which is then concrete and tiled over the top.

[Gaf]

@Andehh @bmj1 Just to check on the DPC. Are yours like the one on the right side of the attached image? So you DPC went up over two blocks high or was it two blocks above your internal floor level. So your DPC is one further block higher than the right hand side version on the attached?

 

My buildup is on the left side. I'm assuming I'm screwed now and won't be able to have the patio up flush with the internal floor level.

 

Edit: "Pation" should read as "Patio"

Edited April 18 by Gaf

[bmj1]

That looks problematic to me. But will defer to someone here with more experience.

 

Could you lower your internal floor level by reducing the build up, or too late ?

[Gaf]

8 minutes ago, bmj1 said:

That looks problematic to me. But will defer to someone here with more experience.

 

Could you lower your internal floor level by reducing the build up, or too late ?

 

Internal floors are all done and dusted at this stage unfortunately. Only when moving ahead with the patio did I come across the DPC requirement... would have thought the architects and/or builder, knowing we said we wanted this, would have flagged the need for the DPC to be higher.

[Spinny]

We are having a level walk out from our bifold doors to the patio when it gets built up. Here is a photo showing the outer DPM levels which are immediately above the faced block and then drops down to under the bifold threshold across the opening.

 

Internally we have a heated concrete slab which will have flooring on top. So the structure inside has a DPM running underneath the insulation layer which is under the concrete slab and this DPM (actually a red radon barrier) then runs up the sides at the outer edge of the slab where it meets the outer leaf and threshold across the opening. So any damp that might be lucky enough to to make it into the concrete block outer leaf below the threshold will be blocked by the dpm under the threshold and the radon barrier running up the edge of the concrete slab to meet it.

 

PS We also have a 500mm roof overhang above and it is east facing with prevailing winds from the west.

[Spinny]

Was going to mention that aquabocci do some nice threshold drains, very pricey though, and depends whether they will marry up with your threshold dimensions, which they don't for us sadly.

 

https://www.aquabocci.co.uk/?gad_source=1&gbraid=0AAAAABxVPQJ7xCa81KGd2rJKoo0mwGaEp&gclid=EAIaIQobChMIo6mn4IXijAMV9aJQBh32eRyCEAAYASAAEgIf2vD_BwE

[Spinny]

[Spinny]

What is your internal floor build up ? Do you have an underfloor DPM which comes up at the edges to meet the dpm level ?

[Gaf]

17 hours ago, Spinny said:

What is your internal floor build up ? Do you have an underfloor DPM which comes up at the edges to meet the dpm level ?

 Your buildup looks far better than ours and looks to have been well thought through to allow for the patio being at internal floor level. Your DPC looks nice a high on your walls.

 

Attached is our internal floor build up. We have an underfloor DPM (acting as radon barrier also, Moarflex RMB 400) which is unbroken and running from external leaf to external leaf. As in the blue line in the image is the DPM and it is one whole fully connected piece.

[Spinny]

And do you have a plan view showing your L shape and where the sllders are going ?

Presumably you have no inner leaf at the openings and the slab runs out to meet the outer leaf ? (Somewhat like my attached sketch)

 

I am just wondering because your DPM at the opening looks like it could be OK and would run under the threshold. The problem would seem to be your DPM level in the walls away from the opening(s). Perhaps you could put a step in your patio at this point, so you still walk out level, but then have a step down at the edge of the opening ?

 

I think normally your sloping cavity tray DPM should have weep holes at the outer leaf to allow any water in the bottom of the cavity to drain out.

 

Do you have any finish going on the outside e.g. rendering/cladding ?

Could a new physical DPM be inserted higher up the outer leaf at a higher mortar joint - there are videos on youtube of how they do that.

 

Given it seems to be the architects booboo they ought to help you find a workaround for free.

Edited April 19 by Spinny