Gap between extensions

12 Aug 2012
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United Kingdom

I'm planning to build an extension next to (as close as possible) neighbour's existing extension. I understand it will have to comply the Party Wall Act.
The question is of a technical matter. If the gap between the extensions will be about 150mm wide, it makes it impossible to render the blockwork on this side ..
Do I need to render blockwork at all? Should I use brickwork?
Maybe a better solution would be to close the gap?
Would cantilevered parapet be appropriate in this case? My extension has lower height.

Thank you for any help!
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Leave a gap, no need to render if the blockworks good. Ensure any water that runs down between the two walls can drain out. Ensure you can get a broom or pole or whatever in the gap to clear anything out that ends up in the gap like leaves etc.

You could join your neighbours extension but this can be a PITA with regards to future neighbourly relations.
Thank you, but what does it mean 'good blockwork'? Would building Control accept it?
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You shouldn't leave blockwork exposed to any sort of weather and, thus, you must render it or clad it with an external material. Over time, the slightest amount of rain will penetrate the external skin and damp patches will start to appear. The 150mm is academic, unless the blockwork is a facing block?

Is the blockwork solid 250mm, or does it have a cavity?

thanks Andrew,

it's a cavity. Facing block is probably more expensive and this wall will not be exposed, so doesn't need to have any decorative improvement.
Would it be better to use brickwork - there are millions of houses with exposed, not rendered brick... any other solution?
Yes - brickwork would be much better, and the pointing doesn't have to be immacualte if it is not visible (due to the gap you mention).

Blockwork is a funny creature - perfect for inside finish, not so for external. I've, in my career, seen MANY disasters with facing block. Don't take the risk.

What is the situation with Building Control?

The app had been submitted - they requested a solution for this part of the wall. I will go with the facing brickwork then - there is some range of the prices to choose from for sure.
You shouldn't leave blockwork exposed to any sort of weather

It wont be exposed, it will be sheltered by the neighbours extension

In any case, blockwork can be left exposed with no detrimental effects. Its purely aesthetic
In my opinion - they would be concerned - just ensure there is no encroachment over neighbours’ land - part wall issue etc.
If the gap is 150mm then fascia board then guttering there will hardly be any gap left if any to worry about weathering.
would be okay, but there is a flat roof with parapet walls to both sides.
Thank you

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