Adding an Extension - External Walls becoming internal walls.

17 Nov 2020
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United Kingdom
Hi guys, A bit of advice again please!

Please see the attached image.

Question 1: Is it ok to connect a new wall to an existing wall and have the outer leaf's flush?

In the picture, the red bricks are the outer leaf of the existing cavity wall, and the grey and green blocks will be the new cavity wall. Is it OK that the outer leaf walls (Grey and Red Blocks) are flush?

Question 2:
The red wall (currently external) with the Yellow Circle over it will then become an internal wall.
Are there any issues here with damp penetration or thermal bridging in the area circled in blue.

Question 3:
I am going to use a wall starter kit to link the walls together. For thermal reasosn, should I use mortar between the blocks or should I make it a thermal movement joint?



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    Extending Walls.png
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You need a vertical DPC where an external wall becomes internal.

The wall starter is a movement joint
Thanks woody.

so what is the best way to vertical DPC?

Do I run a disc cutter down the full height of the wall and slip in a DPC membrane and repoint?

Does that effect the structural qualities of the walls?!

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Yes to the first, and no you don't need to repoint as its in the cavity

No to the second

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