This issue has bugged me for sometime and wanted your thoughts.
The clearance between a patio surface and the DPC shall be 150mm minimum. However with the every increasing popularity of the large bi-fold patio doors opening up the living space to the garden there is often a tendency for the client to want the step out to the patio surface to be minimise. In fact many glossy magazines have a single level surface between indoor and outdoors. Quite often a linear drain is used to segregate between indoor and outdoor but what about the DPC clearance? It could be higher up the wall admittedly but l would suspect often not. Could be photos of homes in climate where it isn't a concern.
I am designing a garden where there are 3 sets of bi-fold doors creating an L shape living space. There are sections of wall generally in the corners obviously supporting the beam structure of the house and some other associated walls. All the bi-fold doors will open onto patio surfaces.
DPC is located at the base of the bi-fold doors. The builder has laid a temporary patio 75mm from the DPC to minimise the step down, probably at the request of the client and will have probably set an expectation.
What are the options?
Can you have 75mm clearance plus an linear drain between the building and patio?
Could you use a more discrete slot drain between the building and patio plus the 75mm clearance?
Small gravel edge between the building and patio plus the 75mm clearance? If so what is the minimum width and depth of the gravel edge.
Do l have to insist on 150mm clearance?
I don't believe a step would be appropriate for the client in this case as it would spoil the look their trying to achieve.
What solutions have you used as l don't believe this is an uncommon problem for landscapers with the every increasing popularity of these door and the every increasing expectation created by the glossy mags of the single level between indoor and outdoors.
I would say l am happy to maintain minimum of 75mm clearance and normally insist and construct patio with a 150mm clearance.
Thanks for you help
This is an increasing problem as part M of the building regulation require most new builds to have a level access somewhere.
The 2 systems i am aware of are 'Aco interceptor Step Drain' and hepworth do one as well i can't remember what its called and its a bit more low tech.
Really if the extension is being signed off by BC they are the ones you need to talk to as you can do leg work finding something suitable and then find they aren't happy with it etc.
In reality as long as there is a decent soffit overhang and the doors are not facing an exposed direction it won't be a problem but it's not good practise to take the chance.
Thanks Simon, that is a very important point regarding sign off by BC and the pointer towards threshold drains. Hadn't realised about the part M change - seems a little contradictory to existing requirements. As you say not good practice to take a chance hence the post... Thanks again
Just to clarify, i didn't mean part M applied to your project I was simply mentioning it because it has increased awwareness and number of products available to solve this problem,
I think having a word with Building Control is the right way to go as they all seem to have different ideas as to what is acceptable.
I have done used several different methods in the past to suit what Building Control in different towns are happy with.
Some are happy if there is enough soffit overhang to stop the water jumping the DPC to go in almost level, where others we have built a wall parallel to the house wall and left a 15mm air gap against the building with the paving and again come in almost level with the threshold.
Just so long as you can shed the water off with a good enough fall they should be all right with it as Simon has said above, you now normally put in one level access on a job to allow for everyone to enter a property easily and safely.
I too would love some advice on this:
As far as I was aware the DPC is more about the prevention of the migration of damp from the ground into the walls than it is about water from the sky resting anywhere; drains and run offs make sense of course but the 150.mm clearance, as far as I am aware, ensures the efficiency and effectiveness of the DPC against rising damp which is a different issue.
Am I right in thinking that drainage solutions do not solve the problem raised specifically?
Nicky @ GardenImprovements.com
It is a little confusing but you need a bit of an understanding of how openings like this are built.
In a cavity wall the windows or in this case the door are installed butting against the back of the outer leaf. But obviously you need something at the base to support it and stop it dropping in to the cavity. With level threshold doors like this you often remove the outer leaf (or don't build it in the first place) and instead insert a concrete lintel which effectivly sits where the cavity would be.
This lintel obviously bridges the cavity and so to damp proof it the lintel is sort of enveloped in dpc, By placing it down on a large strip of wide dpc which is then folded up the back of it and folded up each side with the front left open. Water will then be able to soak into the lintel as its open at the front but it will not be able to get past the dpc and on into the inner leaf/floor.
Of course when your having a concrete floor you bring the dpm up the back of the lintel anyway so its a to be sure to be sure sort of thing.
Does that make sense?
Thanks Simon, After a couple of reads it did make sense.... and did understand the Part M wasn't applicable but the clarification was appreciated.
Peter, thanks for the input. The 15mm air gap is a good solution too. Will seek advice from building control as the safest route.
Nicky, thanks for the interest. I'm a little surprised there wasn't more interest on this subject. With respect to drainage - l was considering that the ACO linear drain in essence extended the distance between the DPC and a surface both vertically to the bottom of the drain to create 150mm but also horizontally to the patio surface. Was using it more as a cheat and safety mechanism.
I'm going to add this discussion into the hard landscaping group as may create more comments.
I've just viewed this video from Stonemarket.
I'm not sure if this is a show house mock-up or a real application but note the levels from the house onto the outside terrace.
There appears not to be any form of interceptor drainage.
From pavingexpert.com http://www.pavingexpert.com/threshold01.htm
I need to revise methinks!!
I'm not sure if this helps, but I'm due to have an extension built next year across the back of the house with 4.8m worth of sliding doors to totally open the house onto a raised patio to bring the outside 'in' and plan have an 'infinity' type patio built (my garden slopes away down at the rear).
I have visited the major quality door providers and selected Sunfold after visiting their offices.
One huge area of discussion was just this as we want no level difference at the threshold. This is the sectional plan supplied from the maker to our builder for installation.
There is an alternative using narrow profile stainless steel drainage channel, but I can't find the sectional diagrams at the mo...
We use this sytem from Aco alot as it almost disappears to the eye and doesn't get full up with leaves etc as they don't fit in. We also use it alot on swimming pool jobs as its very gentle on the feet.