New patio above DPC and air bricks?

Hello everybody, I'm new to this forum so sorry if this post is in the wrong place. I work in Garden maintenance normally but have helped lay patios before. My friend has asked to help him with his patio and I am not sure if it is going to be possible to achieve what he (more specifically, his wife) is after.

As you can see in the image the DPC is one course below the threshold, and the air bricks sit on top of this.

They want the patio to be the same height as the indoor floor level, like you see in those glossy magazines.

I know that the patio should be 150mm below the dpc and that they could have a step but that isn't what they (she) wants.

The patio is already about 1m higher than the rest of the garden so a new retaining wall is going to have to be built.

I've seen various workarounds online that suggest leaving a 150 - 200 mm 'dry' area or a gravel channel with a perforated pipe in the bottom between the patio and the house. is this a suitable solution? would a surveyor be happy with this further down the line?

There is another bifold door to the right of this image and a downpipe comes down the rendered wall between them.

Thanks in advance for any help or confirmation you can offer.

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  • PRO

    Always tricky.. In outs as they're called. 

    the way you have suggested is certainly an option however I would consider applying some kind of water proofing to the brickwork before hand. making sure the paving is falling away from the house. perforated pipe will certainly help in terms of drainage. 

    And to keep ventilation I would re route/install some pipe work from the existing air bricks to new ones in the new retaining wall to keep a channel of unrestricted airflow into the property.  Alternatively you could use something like a telescopic air vent? that might be an option. 

    A lot of 'in out' projects I have seen have just run a channel drain across the door to catch any water regardless of how severe the fall away from the house is. Whatever you do just make sure you give ample water proofing to anything above the dpc. 

    • Thanks Matt,

      Would a bituminous paint do the trick or are we talking some kind of self adhesive tanking on the bricks above and below the dpc?

  • PRO

    Hi Stehan,

    I have this come up all the time. Clients seem to love patios and steps the same level as the threshold.

    My method as i was taught is a low retaining wall on a concrete footing. You can use mainly concrete block if you like as it will all be hidden. At end of run you may need to go back to brick if the wall end will be seen. Set the wall along the house the length of the patio leaving an air gap between it and the house wall of around min 25/30mm or so. As you are already going to be doing brickwork this should be an easy add on. Top of brick/blockwork level or slightly higher than the top of the scalpings. Then lay your paving slabs over the top of the brick/blockwork with an overhang as you would a step, and under the door sill, but again leave an air gap of say min 20mm between the paving slab and the house wall.  DO NOT fill the cavity/air gap with anything as you want the air to be able to circulate. Just remember that nothing should touch the wall to 150mm below dpc. Only drawback to this method is that debris can fall down the gap over time. That is why i do 20mm min and not 10mm as i was taught, as it's easier to clean out with a stick or a blower. Even though you end up with a gap between the house and the patio, when its all done and the rest of the patio is pointed it looks fine.

    Can't stress enough that you don't want anything touching the wall up to 150mm below dpc. Break this golden rule and any problems can come and bite you later.

    Hope that helps.


    • Thanks Ed, I like the sound of this idea and would still want to waterproof he brickwork etc im guessing. would the 30mm gap provide enough air circulation to the air vents? and is there a chance that water could end up filling the 30mm gap and be left sitting against the house....or should I create a fall at the bottom so that it goes to the existing drain?

      Thanks again

      • PRO

        Hi Stefan,

        Obviously i don't know the full situation of the site in terms of aspect but i have never waterproofed the brickwork. Remember that bricks above the dpc are meant to be able to breath so sealing them is a no in my opinion. I've always just made the air gap with no waterproof sealing.. If there is a drain it would be logical to fall the base of the gap towards it though for the bearing in mind the small amounts of water you could get i wouldn't worry too much as you are intending to have the bottom of the gap at least 150 below dpc. You will only be getting small amounts of runoff from the house walls in severe storms i would guess and plenty of houses i have seen have sodden soil right up against the house at 150 below dpc. so a bit of moisture there at times is never going to worry me. Just make sure the ends of the gap are left open and it will always dry out in the air. You should be falling the paving away from the house anyway to get rid of water that lands on there. As paving expert says you can do an increased fall along the wall and then revert to the standard fall you normally use though in practice i have never worried to much about this. 

        So long as there is an air gap the air bricks will be able to breath as intended.

        I have done a lot of jobs this way and also been able to over time check on how they have held up and in all cases i have not seen any damp issues.

        Good luck mate,


  • PRO

    Small point on what Matt said about channel drain. I've seen it used too but too often i'm unsure if it still breaks the golden rule of compromising the dpc.

    Here are 2 links to how to do it  properly. First link has section on doorway thresholds but is not clear where the house dpc is, so still leaves unanswered questions in my view.

    2nd link is not really suitable as the workarounds mean a big gully or paving that can't go higher than 75mm below dpc which is not really what your client wants, but its all good information though.

    Happy to hear any views on this as the more i read the more of a minefield it becomes, so i stick to y tried and tested method which have produced no problems yet and also save on drainage installs.

    Good luck.


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    • Thank you!

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