Level Threshold patio

[jimmbo]

Hi, guys.

I know there’re several topics already about this, but I still can’t get my head around it!

I’ve seen several drainage channels (threshold drain/threshold interceptor/step drain/brick slot drain) which allow for a level threshold between inside floor and patio to comply with Part M of building regs.

If we were to have a level threshold patio, installing one of these where the doors are (we’ve got French doors and bifolds) what do we do with the adjacent areas of exposed brickwork where the patio will be level with (or at least less than 75mm below) DPC?

I had thought that I could have threshold drains where the doors are and French drain/gravelled channel in the other areas, but that wouldn’t really work because I can’t see how there would be a continuous flow between them all. Unless I’m missing something??

Many thanks

 

[^woody^]

Why do you need a drain across the doors, when you the rest of the surface is lower?

 

[jimmbo]

I don’t understand, why is the rest of the surface lower?

I’m saying the patio will be level with threshold, therefore level with DPC or just below DPC!

Here are some examples of what I mean:



The threshold/step/channel drains are just in front of the doors to create level threshold access (complying with part M) but surely the areas adjacent to the doors are breaching the min 75mm below DPC?!

 

[Leofric]

Dpc in outer skin of external wall should be minimum 150mm above adjoining ground level

 

[^woody^]

I’m saying the patio will be level with threshold,

And you're saying

the adjacent areas of exposed brickwork where the patio will be level with (or at least less than 75mm below) DPC?

So which is it? Are you ramping the patio up to the doors? If so how is water going to travel up hill into a drain across the threshold?

 

[Leofric]

The patio shouldn't be level with the threshold if the threshold is at the same level as the dpc , the patio should be at least 150mm below the dpc .

 

[jimmbo]

At least LESS than 75mm! Ie not conforming to minimum 75mm below DPC! 150mm best case, but 75mm at worst!!!!!!

 

[jimmbo]

The “at least” was just a figure of speech, if that’s what you’re confused about?

 

[^woody^]

I'm confused about the whole thing.

Level, at least, minimum, 75mm, 150mm, worst case, best case, threshold, adjacent brickwork ....

 

[jimmbo]

Patio level with threshold, therefore level with DPC. Which means not conforming to 150mm below DPC (which apparently is best practice , ie best case scenario) (or 75mm at worst - but bending the rules and still being ok’d)

Again, which is ok where there’s doors (part M building regs - disabled access etc) but next to (ie adjacent) the door threshold there is usually exposed bricks. Which means that if the patio is at the same level as the door/internal floor then the exterior floor level is not going to be a minimum of 75mm below DPC!

Is that clearer?

Now look at the photos (one of which is given as an example of threshold drainge on pavingexpert) and tell me that the external floor level is lower than 150mm from DPC.

Or are you telling me that the threshold is actually lower than DPC level

Cheers

 

[Leofric]

Which means not conforming to 150mm below DPC (which apparently is best practice , ie best case scenario) (or 75mm at worst - but bending the rules and still being ok’d)

the requirement if you take any notice of bldg. regs is that the dpc should be at least 150mm above adjoining external ground level ( not 75mm being ok if bending the rules )

Which means that if the patio is at the same level as the door/internal floor then the exterior floor level is not going to be a minimum of 75mm below DPC!

Where do you get this min 75mm from ? There is no such stipulation.

 

[Leofric]

You can't always comply with current Part M disabled access to existing buildings. If you have a level threshold disabled access with external patio level same as finished ground floor level, the dpc should be 150mm min above patio/external ground/paving level and therefore 150mm above fin grd floor level.
Can't see where your 'paving expert' shows the dpc but if it isn't as I just explained they are wrong.

 

[23vc]

I had thought that I could have threshold drains where the doors are and French drain/gravelled channel in the other areas

That’s what you’ve gotta do. Wherever you’re not meeting your 75/150/whatever ground level below dpc rule, you need a drainage channel. Whether that’s on the door threshold or anywhere else. Which lines up with what paving expert and other posts on this forum say.

 

[jimmbo]

Yeah, that’s what I thought.

If I had French/gravel drain leaving a gap away from the wall and threshold drains at the doors, I’m just not sure how I’d fit threshold drains coz they would be directly above said French/gravel drain!

Cheers

 

[^woody^]

A drain is for draining. A drain is not required just because paving level is a DPC level.

In and case, "150mm below DPC" is an anachronism to the time of solid walls. And it has no affect on cavity walls due to what is known as .... a cavity.