Need advice! Rear extension up to line of junction

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Hello!

We are building rear extension at the moment, our roof is pitched roof (gable roof) and our neiboughour is shed roof (slope roof), so our roof edge is generally lower than the neiboughour's

Our builder said that it's better to have around 100-150mm gap between our extension wall to the neiboughrs extension wall, so it allows air bricks ventilation to work to prevent damp etc. He also said that it will allow the hanging gutter to fit on the roof, also not to seal with the neiboughour's wall? ? He told me that will use bricks to finish off so shouldn't have damp issue.

However, my thoughts are:

- I don't want too much gap as it will lose my internal space for extension part.

- The gap could potentially be a pest / leaves trap and it's impossible to clean

- The rooftop should seal using lead flashing with neiboughour's extension wall.

- Use parapet gutter design to be used rather than the hanging gutter?

However, I also have concerns:

- If we leave minimum gap, would it like the builder said, the air brick ventilation wouldn't work and have risk of damp?

- If there's heavy rain, will the water level go up because of the narrow gap between the walls of extensions?

- Will parapet gutter even more easier to block by leaves then have penetrating or rising damp?

- if use minimum gap, say less than 50mm, would it cause more issue in the future? If the lead flashing/weather proofing is done properly?



So my questions:

- If we only build up to the line of junction, should we only leave minimum gap (say less than 50mm)or more gap is recommended?

- What type of gutter/drainage design should we use for this kind of roof with the neiboughour?

Sorry for so many questions as I'm really stuck! I've googled and asked the party wall surveyor and building regulation but they all have different opinions, I'm really confused and would like to get some advice from experienced builders.

Many thanks
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Our builder said that it's better to have around 100-150mm gap between our extension wall to the neiboughrs extension wall, so it allows air bricks ventilation to work to prevent damp etc. He also said that it will allow the hanging gutter to fit on the roof, also not to seal with the neiboughour's wall? ? He told me that will use bricks to finish off so shouldn't have damp issue.

So how did they build the original houses without this magical 100mm gap? The hanging gutter is a valid argument but this can be overcome with a parapet wall and tapered box gutter.
 
I'm curious how an extension can be started and then out of the blue, this crops up.

Are you literally making it up as you go along, with no plans?
 
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I'm curious how an extension can be started and then out of the blue, this crops up.

Are you literally making it up as you go along, with no plans?

I thought this should be part of the building reg plan but it seems it doesn't include and they are charging me extra for that... Is this responsible by building reg, building control, or structure engineering drawing? I'm really confused...
 
So how did they build the original houses without this magical 100mm gap? The hanging gutter is a valid argument but this can be overcome with a parapet wall and tapered box gutter.
Do you mean the parapet wall as a party wall? Building party wall is out of option as requires foundation changes and not part of the planning permission
 
I thought this should be part of the building reg plan but it seems it doesn't include and they are charging me extra for that... Is this responsible by building reg, building control, or structure engineering drawing? I'm really confused...
You've been conned. It's bog standard part of planning and building regs design.

Where the wall goes is directly dictated by how the roof is drained or finished.
 

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