Are Damp Proof Courses worthwhile?

Question

I have some building experience – was suspicious of Damp Proof Courses from a structural viewpoint, but I’d like to be sure if this is the case. I’ve has some experience with building work in the past and have heard about various issues with using DPC’s.
 I know they are typically just black plastic sheets between brick/stonework a few courses up from the foundation, to stop the damp rising from the ground up, but I don’t know how much of a problem this really is. I’ve been told about they can cause a wall that is in construction to be knocked over with a small bump. It worries me that the wall integrity is affected by these sheets. It worries me how easy they can cause a wall to be shifted – I don’t want to use them if they are an additional risk. Does anyone know any more about whether DPC’s compromise the integrity of the walls? Have you had any issues that they have caused? Are they worthwhile for the sake of just avoiding damp?

Tim · Answer

Hi, The issues that you may have heard about may be due to DPC’s not being installed correctly. They should not be dry laid – the need to be bedded on mortar underneath.  Often builders get this wrong, which can be the cause of these issues – when the DPC isn’t bedded properly, it will have weak spots, which still means damp can happen to the walls. DPC’s are worthwhile due to how effective they are at preventing damp for walls. Without any DPC’s a wall will begin to show signs of damp within 12 months quite easily. (IE – turning green with moss, consistently wet.) If you were to see the difference side-by-side you’d agree that it is effective with damp prevention. As for the structural integrity, the weight of the above building structure will keep it in place – so for any fully constructed building, the DPC is inconsequential and won’t make the building any weaker. 
Granted, this would be different for an outdoor freestanding wall – which could also be knocked over easier than building structure walls anyway. It would likely need some additional protection or alternative preparation to prevent damp. For some possible examples; using two courses of engineering bricks (150mmm) at the base of the wall,  using sand/cement rendering or using a damp proof membrane, rather than a DPC, with a fixed mesh and sand/cement tanking system (using mechanical fixing). The choice of method will be yours, depending on your outdoor wall’s circumstances typically. A minimum recommendation would be to include sand/cement rendering regardless of any other methods being employed, as It will prevent the breakdown of the mortar over the long term which would make the wall fall apart. I recommend taking whatever precautions you can, to ensure the longest lifespan for the wall. Best of luck

Lee · Answer

Definitely required. It's the only way to stop rising damp. And if built properly and consistently using wall tiles in the correct spacing it will be structurally sound.

Best regards 
Lee

Are Damp Proof Courses worthwhile?

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