DPC and level for patio? Advice gratefully received (Photo)

[dwall]

Afternoon All

I've attached a couple of photo's of the rear of my house where I have taken up an old patio which originally was split level (follow red line).

I would like to build a new patio which would be level all the way across the rear of the house with steps down at the end rather than in the middle (follow blue line)

The Orange dotted line shows the height I proposed to concrete up to with mortar and slate slab up to blue line which is finished height.

My only question having read numerous 'how to locate your DPC' articles is whether the DPC is level with the top of the air brick or the bottom? If its the top of the airbrick then I should be good to go as the airbrick is 2 bricks high (150mm) and the patio will be level with the bottom of the airbrick when finished (blue line)

House was built 1938, rendered. Right hand side of picture is extension (roughly from the right hand window to the fence line) with solid concrete floor level and French doors.

The rest of house is suspended wooden floor level with top of airbrick.

Any advice gratefully received. Most articles I've read say airbricks are generally under the DPC which is great for what I want to do, but a few have said that the airbrick sits on top of the DPC so am not sure. If I do have to get a specialist in to locate it for me, how much should this cost? I have no damp problems currently and don't want to give myself any going forward.

Thanks for taking the time to read.

Dan

Untitled

• dwall
• 5 Jan 2013
• 1

Untitled

• dwall
• 5 Jan 2013
• 1

 

[goldeagle]

In my house (built around 1900) the DPC is below the air-brick.

You should be able to find it with inspection - it should be a thin membrane between the mortar and brick, normally black in colour. It should be fairly clear against the mortar and brickwork. There is a chance it is well covered by the mortar (I have just had my wall repointed and now cannot see the DPC). In which case you may have to scrape out a small bit of mortar if you really want to be sure where it is.

I wouldn't bother getting someone out to tell you where it is - if you can't see it yourself, nor can they, and expect they would have to remove some mortar to find out. Not sure how else they would tell - but I'm not expert so maybe someone else has some other advice?

Have a search on the internet to get an idea of identifying a DPC in brickwork so you know what you're looking for.

 

[gregers]

if you really canot locate the dpc level,why not allow say a 2inch gap between the wall and the new patio and back fill it with shingle,that way you wont have any water sitting against the brickwork and leeching up.or go the whole hog and install a french drain all the way round.

 

[limerockconstruction]

Looking at the photos, although I wouldn't say for 100% sure, I would say that the DPC is either at the top of the lower air brick or at the top of the brickwork plinth - either being ok for what you want to do. I would have thought the lower air brick is for ventilation to floor void and the higher one being for room ventilation.

Its pretty easy to locate it if you look hard for it as goldeagle has already mentioned – also if the bit on the right is an extension, its quite likely that they have sat their doors on the DPC or 1 course below (to allow for the floor/up stand & sill), which would also tie in with the above.

Just to mention, would be sensible to get a good fall on the patio away from the house, a big flat area like that will collect a lot of rain given the weather we’ve been having!

 

[trowlerman]

agree with the others i would guess your dpc is at the top of your airbrick ,the best way is to check with a small screw driver and hammer, and chip a bit of the bed joint out,

you could also leave a gravel strip between house and patio if you overly worried .

 

[dwall]

Many thanks for the replays all, that gives me some reassurance. I've decided to repoint the brickwork and will have a good look around for the DPC. I'm hoping there is one there, I'm looking for a back membrane / slate I assume. Worst case, I'll leave a channel as I can't lower the height or the pergola and need to cover the bricks that the staddles sit on.

Cheers

Dan

 

[dann09]

1. The DPC is and was, by Regs. supposed to be below the joist tails on the inner brickwork skin ie. the joists sit on the DPC - If the DPC is above the vent it's in the wrong place, it should be below it. Unfortunately, its often in the wrong place.

2. The DPC, by Regs. must be a min of 150mm above ground level.

3. If you go ahead with your blue line proposal, you will use an awful lot extra on the pour, and still have the concrete plinths showing.
Perhaps pour to the red line, and keep well away from the wall, falling in the opp direction as advised above.
This FFL might save detail work on the RWP's and waste.

4. Something to keep in mind is that the max riser height is approx 7 1/2" in mm.

5. Your pointing appears to be in good nick, unless it's a shallow smear-on.

6. Suggest that you do section detail drawings for various points along the wall/patio slab, including the slider threshold & step-down, before work begins.

 

[dwall]

Thanks again for all of the helpful comments. I think I'm going to leave a channel between the house and the patio and fill with 40-80mm decorative cobble stone. This will negate any worry I have about the DPC which I think from what people have said should be and most likely is at the base of the lower airbricks.

Cheers

Dan