Decking flush with bifolds.. Building Regs issues?

[itsallaboutyou]

Evening all.

As part of our lockdown madness, the boss has given me the go ahead to start looking at replacing our knackered patio. We have 5m bifolds at the back of the extension and a 200mm drop to the current patio and between 150mm and 170mm below the DPC.

I'm far from an expert - but my concern would be if we ever came to sell that a surveyor would notice any non compliance with the 150mm rule.

I know that Part M effectively bins this off for steps and ramps etc... but surely a 5m 'step' would be taking it too far?!

Even if I introduced a channel drain flush with the finished floor level of our extension - the unit would still be higher than the existing DPC - and would probably even make the issue worse...

Surely it can't be that much of a unique issue - how to people solve this... I'd like it to be a completely flush transition - but don't think that it's possible...

Should add that this extension was on when we bought the house... I'd have been asking for the DPC to be higher.. although dunno if that's even possible at that stage!?

Any ideas!?

Cheers.

 

[Derek W]

Can you upload a picture through imgur.com and link to the area in question.

I personally wouldn't see an issue with it. I've had jobs where path / patios / ramps are level with the floor so above the dpc. The only real thing you may have to do is where the patio will be up against the outside wall just put a bunch of gravel down 150 wide so any water can still drain below the dpc.

 

[Abyss]

I'll have a look at our patio tomorrow. It's a new build with 2 sets of french doors onto a patio with level access so 3/4 of the rear elevation if flush with a slot drain. I've never really noticed where the DPC is.


I would however suggest that a well designed decking with ventilation space shouldn't be an issue with the DPC. It's a temporary structure. I installed decking in the previous house pretty much flush to the back door without any problems.

Edit: Just checked the developers drawings for our current house and it looks like the DPC comes level with the thresholds but I'll check tomorrow.

 

[200sols]

Its known doing this can cause issues, even with ventilation and designed drainage you can still get damp issues. It makes zero sense to build above the DPC the drop is there for a reason.

 

[Maccapacca]

You'll need to properly extend the dpc as a dpm up the face of the brickwork which will mean chasing into the dpc and lapping and sticking a dpm then up to the threshold. Then install a threshold drain across the front. Check you're not blocking any weep vents or air bricks.

We built our patio up a bit which covered the air bricks so I pulled them forward with 4" drain pipe to the new end of the patio.


If it's done right it's okay

 

[itsallaboutyou]

Cheers all.. sorry had a very restless night with the kiddiwinks - so I'll try and plonk up a photo later.

I'll have a read up on extending the DPM, there are 4 air bricks on the same wall - but on the upside - there are two gully grates for the surface water - so hopefully with a bit of jiggery pokery something can be sorted...

Might be that I install a step with slot drain / dry zone and go from there down to the finished height..

Ta!!

 

[Jez]

I laid a patio up flush to our kitchen door, along the edge with the house i dug a ~200mm wide trench to well below DPC (~300mm below) and put a line of large grade gravel filling the trench. Not had any issues at all, any water clearly has to drain to well below DPC, it cant ride over a french drain like that. The patio obviously drains naturally away from the house anyway due to the slope of it, so there is no ground soaking up to the house wall. I'd bet the soil (and therefore the house wall) under the patio is virtually bone dry due to the slabs carrying it all away from the wall anyway.

Piqued my interest actually, after the next big downpour (nothing forecast for ages!) i will scoop some gravel out of the trench to the bottom and see if its wet at all in there. I bet nothing even drains that way.