Adding flat roof against neighbour's sloping roof

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Hi, first time poster but regular 'searcher'!
I am looking to turn an old single block (small) building into an office. The current roof is corrugated cement (containing chrysotile asbestos) and the back wall is also the garage wall of my neighbour (rear joist rests on the walls and is not fixed to the garage). I want to remove the current roof and add a 'flat' warm-roof; however, this will be next to my neighbour's (sloping corrugated bitumen) garage roof. I'm unsure if this is 'do-able' in order to maintain 'warm' and dry. We've just moved into the property so want to stay on our neighbour's 'good side'! I've attached a couple of pics of the current set up and a 'Sketchup' of my proposed idea. Any thoughts or advice (constructive!) are appreciated

sketchup.png2 roofs.jpg
 
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The removal of the asbestos filled sheets will obviusly need to be done using lots of caution, protective gear etc.
I have seen suggestions to paint it first to lock in the fibres.
It will need to be triple wrapped in plastic sheeting before it can be disposed of at your local recycling center (check with them first).

Why not add a few layers of bricks at the higher side so that you can have a sloping roof to match next doors and also drain off any rain?
You will also need to incorperate a gutter then, have you somewhere to drain it off to?
 
Thanks Mattylad but I was trying to keep it as simple (and cheap) as possible and because of the slope already in place, was hoping to just follow that. However, if that seems to be the best/only way then perhaps I need to rethink.
Also, yep, the ACM roof will be removed and managed iaw HSE guidelines.
 
Make the party wall extention wall first on the ground, and then fit it in place. Make the frame and line the external face with a single piece of suitable deep uPVC board, fit this in place tight up to the pitched roof, and then flash the neighbours roof, and the bit of wall that will be above your new roof level.

Where the pitched roof intersects the flat roof will need careful detailing with flashing. Not difficult but needs care.

Don't forget the flat roof needs a fall, which does not appear to be on your sketch.

The rest of the roof is standard.
 
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Hey Woody
Firstly, thank you for taking the time to respond. Could you explain what you mean here (I'm easily confused!) "Make the party wall extention wall first on the ground, and then fit it in place"?
There is a slope already in place which is at right angles to the neighbour's garage.
Cheers
 
Yeah, it’s doable, but you’ll need to sort out the junction where your flat roof meets your neighbor’s sloping one. Flashing it properly with lead or GRP should keep it watertight. Best to have a chat with your neighbor first to keep things smooth. And with that asbestos roof, don’t mess around—get it removed safely by the pros if you're not sure. Better safe than sorry!
 
Build the new wall first on the ground then fit it in position, as that is easier. It may need to be on a beam spanned front to back, or fixed to the party wall face, if it can't physically fit on top of the party wall. No need to adapt the neighbour's roof.

This is the principle, not the detail....

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Daaamn sir you're good!
The garage roof (neighbour) is also corrugated which slightly overhangs where my roof will go so I might be able to 'utilise' that to aid the rainproofing. Hugely appreciate the time you took to send that Woody, many thanks; it's given me a lot more confidence.

Just FYI, I had a roofer planning to work on it but the the day before, he actually fell off one he was working and is now out of commission for at least a few months. I've got all the materials sitting in my shed but I need to get this done so going 'DIY' (I understand 150mm PIR insulation is deemed 'minimum' for warm roofs but is it overkill for this project?)
 

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