Flat roof slopes for two seperate roofs

[omph]

Me and the neighbour share a parity wall. My flat roof is about 2.7m from the ground, and his is about 2.4m from the ground. Due to the fact that his roof is lower means that our rain water drains onto his roof. This difference in roof heights has caused a lot of issues over the years and we have decided to raise his roof to our height and lay some EPDM over it and be done with it.

I am currently in the process of figuring out the slope to drain off the water. I have attached an image of the current setup. My current line of thinking is to slope the other roof to draining towards the middle (like ours) and then there is a small channel of water around the parity wall area which drain off. Good idea ? bad idea ?
I could rip out both roofs and create a single uniform slope but the problem is I have a flat roof light and this complicates things. Also, the joists run from each house to the parity wall, and any slope will need to run in the direction of the joists for maximum stability.

 

[Notch7]

I dont quite understand the reason for making your neighbours roof the same height.

I presume the cause of the leaks is the abutment between the 2 roofs -is his roof cut into your wall with lad flashing?

if both roofs are clad in EPDM including the upstand of the junction between the 2, then that is effectively a single roof of EPDM.

EPDM is very flexible so its quite easy to glue the sections of EPDM together to form one single piece of rubber.




if you slope his roof towards yours, you really need to form a box gutter and dishcharge it into a hopper -I think its creating more work and a box gutter is prone to getting full of leaves

Personally I say leave his roof as it is, with the neighbours having a fall to the rear and a gutter across the rear as it is now.

 

[omph]

I dont quite understand the reason for making your neighbours roof the same height.

I presume the cause of the leaks is the abutment between the 2 roofs -is his roof cut into your wall with lad flashing?

if both roofs are clad in EPDM including the upstand of the junction between the 2, then that is effectively a single roof of EPDM.

EPDM is very flexible so its quite easy to glue the sections of EPDM together to form one single piece of rubber.




if you slope his roof towards yours, you really need to form a box gutter and dishcharge it into a hopper -I think its creating more work and a box gutter is prone to getting full of leaves

Personally I say leave his roof as it is, with the neighbours having a fall to the rear and a gutter across the rear as it is now.

Thanks for the response.
He is going to perform an extension and this section of his house has an awfully low ceiling - he wants to fix that.
Our felt is also over 30 years old and has leaks which I have patched but it is also in need of replacing, so the timing is perfect.

He has no flashing on the parity wall, so that is one problem - but then he can't because we have a vent there.
The whole thing is a mess, and there have been arguments over the years over who can do what, and the best solution is to level the roofs, and have a box gutter and be done with it.

 

[omph]

@Notch7 If a box gutter is prone to more work, what are alternatives do I have ? If I am to do both roofs, I have no choice since the slope will have to run in the direction of the joists, and I don't plan to replace our joists.
Our joists btw, are sitting on the wall, his are attached to the wall with fixing.

 

[oldbutnotdead]

A box gutter between the rooves is a very poor idea- rubbish access to clear any blockage, if you do get any overflow it'll go straight onto the internal walls.
What are you going to do with your vent in your new plan?
(I'm assuming that your flat roof is older than your neighbours and whoever built it was a bit shoddy by nicking half the party wall and probably originally had a gutter on the neighbours side).
What sort of pitch are these flat rooves? And what sort of area? (If they are shallow pitch and quite small then an actual formal box gutter in the middle might not be necessary)