Do I need a vertical DPC?

17 Oct 2020
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United Kingdom

I'm building a kitchen extension where the extisting DPC will match / be at the same level as the new extension wall. We'll be using wall starters between the old building and the extension.

Will I need a vertical DPC too?

Is it preferred to open the existing cavity and join there or on the facing brickwork? (The new cavity will be wider by about 50mm).

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Yes generally recommended to have a vertical DPC to stop moisture from transferring from one part of the structure to another, especially if the new structure has a different type of wall construction or insulation.

It can be done either way, depending on what you are up for and what's possible. Its a balance between thermal performance, structural stability, moisture risk, and ease of construction really.

Given the wider cavity in the new extension, it may be simpler and safer to join on the facing brickwork rather than opening up the existing cavity but you'll have to deal with the downsides of that approach.

Ideally your SE or architect should have already thought about this and not left it to builders to make it up.
You don't need a vDPC just because you're using a starter, but you do need one if an external wall becomes an internal wall.

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