Flat roof conundrum?

I have a very old flat roof that is in dire need of a replacement covering. It is shared with my immediate neighbour who has replaced their roof within the last year (before we moved in) so is very reluctant to replace again...

I have removed a section of ceiling which shows that there (unsurprisingly) is no insulation which I would like to rectify since it is freezing in the winter in this room, the kitchen (to give you an idea the cooking oil sets solid! )

Here's a very basic plan view to help illustrate, apologies!


Given the shared nature of the roof and the identical levels of the covering at the moment I assumed that a cold roof design would be simplest since I want to replace the ceiling anyway so could fit celotex or similar from below. The issue I can see with this is maintaining the necessary ventilation since I could only ventilate at one end of the joists and, from what I have read, this wouldn't be sufficient?

Warm roof would mean a step between my roof and the neighbour which would be unsightly and I would be unsure of how to appropriately finish?

The covering I was considering was cold lay (poss Wickes easyseal system or polyester reinforced). I'd appreciate any bright ideas on how to best add insulation to this arrangement.

Thanks for any suggestions/guidance

The step would be slight and hardly noticable let alone unsightly.The detail in question would not be a problem to cover.I have done this many times particulary on shared dormas.

Hi Cumbrianroofer

Thanks for your reply and apologies if I'm mis-understanding you.

I was under the impression that for a warm roof all the insulation would be above the joists thus meaning at least a 100mm step down to the neighbour?

If this is what you are suggesting then how would you recommend sealing the interface, would running the felt down the step and sealing onto their existing roof be acceptable?

Further searching on here has also suggested that if the void between joists is completely filled with insulation this would prevent any condensation so a cold roof approach could be employed??

Thanks

willmarsh said:

Hi Cumbrianroofer

Thanks for your reply and apologies if I'm mis-understanding you.

I was under the impression that for a warm roof all the insulation would be above the joists thus meaning at least a 100mm step down to the neighbour?

If this is what you are suggesting then how would you recommend sealing the interface, would running the felt down the step and sealing onto their existing roof be acceptable?

Further searching on here has also suggested that if the void between joists is completely filled with insulation this would prevent any condensation so a cold roof approach could be employed??

Thanks

Click to expand...

Yes felt the step,its only a small upstand 10 cm,onto the next door felt,up the isulation and onto the new felt,seperate flashings,starting and the low pint of the roof and working up..As long as the existing felt on next doors is cleaned,dryied and primed then getting a good bond wont be a problem and it certanly wont look unsightly.

Thanks for the further response, however, I have discovered a challenge for the warm roof not previously considered! Unfortunately there are two 40mm waste pipes and a cast iron soil pipe that will all require repositioning to fit the warm roof. The 40mm's are no problem but I will prob end up having to change the entire stack from cast to plastic to enable the soil to be re-sited and the fall will then be on the shallow side and I will end up with less than 50mm upstand/flashing height below the soil outlet...Just another consideration!! Cheers

Flat roof insulation may seem like a nuisance.Flat roofs have been a choice of homeowners for generations; they are aesthetically pleasing and lend themselves to a variety of architectural styles.

It does appear that way but I'm not sure the other half will let me not insulate given how cold it gets in there. I'm beginning to think that fitting a rad may be the simpler solution though