Breaching the DPC?

J

JMLanders

Between our lounge and the kitchen (extension), both of which having French doors, there is a pad of concrete about 4m by 3m set 150mm below the dpc. I want to put decking on top of this so that there is no step down from the two rooms into the garden. I propose to making the deck but leaving it approx 150mm away from the walls, with this trench being infilled with gravel. This will mean that the top of the gravel will coincide with the dpc

Any problems with this?
 
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Yes, you’ll most likely get excessive moisture in the outer skin rising up the wall above the DPC; this could track across to the inner skin if there is any debris in the cavity. Current Building Regulations require the DPC to be at least 150mm above the ground level to reduce the incidence of 'splashback' from rain but it should never be closer than 75mm or you’re just asking for trouble; the gravel will also act like a siphon for standing water under the decking.

If you really must have the level deck, loose the gravel & leave an air gap. This will also be better for the decking timber support which will otherwise be more or less permanently damp but you may still get damp problems arrising from rain splash back.
 
just use a ledger board against the wall with some washers for spacers. decking allows air to freely circulate and so it wont cause a problem.
 
why 150mm away from the walls thats a hell of a distance !! ok you wont have a step down but you might need to jump from the door to the deck !!! lol


or have i misunderstood ??
 
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The way it sounds to me is that the op wanted to avoid rain splashing up over the damp course and thought that this stone filled trench would be likely to be just the ticket. But I may be wrong.
 

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