Cold flat roof abutment with sloping roof

[David R]

Hi Folks,

 

 

I have an issue with abutment detail on my cold flat roof where it meets the existing sloping roof.

 

There is not enough height on the wall to allow for a 150 mm upstand. The height above the new flat roof joists to the existing roof tiles is only 120mm max. With 18mm for my OSB and 80mm for firring, it does not leave anything to pay with.

 

Has anyone encountered this issue before?

 

I cant drop the joist height as the ceiling is low enough all ready. There is an issue with ventilation as I need to vent the cold roof where the roofs meet.

 Would it be possible to re profile the existing roof some how, big firring strips?  The truth is I am at a loss how to proceed. 

 

Thanks in advance any ideas would be appreciated.

 

[Mr Punter]

Remove the bottom row of tiles and fix a board to this.  Run the roof covering up the board under the tiles.

 

Ideally your flat roof insulation should be going on top of the rafters so you may need to strip 2 rows of tiles.

[David R]

Mr Punter thanks for the quick reply.

 

You are correct the insulation ideally would be going on top of the rafters. The design is for a cold roof with the insulation between the rafters. The roof was to be a walk on roof, but plans changed. I could change the roof to a warm roof come to think of it.

 

What I am trying to get my head round is, how do I refit the gutter and vent the cold roof or do I not fit the gutter and allow the existing roof to drain on to the flat roof?

 

Answering my own question, if it was a warm roof with the insulation on top it would not need venting. 

 

Good man, I should have asked you earlier, I was loosing sleep over this.

 

 

 

 

 

[ETC]

It currently doesn’t look like you could ventilate the flat roof anyway so doing a warm roof is the answer. Insulation above the flat roof joists - no need to ventilate the flat roof. As the previous poster said take a couple of rows of the bottom of the existing roof and take the flat roof covering up the slope of the roof minimum 150mm vertically - standard flat roof detail. Don’t forget to install tile vents to the existing roof at low level.

[David R]

ETC.  

 

Thank you, tile vents are a good idea,  plus a 150mm up stand. The person who put the rafters in ignored the fact that it needed venting.

 

 The roof will be getting stripped and  a dry ridge system fitted as well.  The original roof is a bit rough, loads of birds nests under the tiles, ancient fiber board under the felt and rotting battens.

 

I intend pushing the boat out by using Aultrix 600 vapour barrier.   I will be very glad when I have got this build water tight.