Convert poor cold roof to warm roof with annoying pipe

[glennpierce]

Hi

I have an old flat roof work room where half of it was converted quickly into a bathroom (no vapour barrier or adequate ventilation). 
Although I see no issues with damp in the bathroom below I am now I am converting the other side of this workroom into a office and wanted to have a warm roof to correct any possible issues with the bathroom side. The felt needs replacing anyhow.

 

I have tried to get a few local roofers to give quotes but they all ghost me after viewing. I think the issue is the 
soil stack show in the image here 

 

I suspect they don't want to be hassled with it.

 

The large soil pipe leading to the back goes directly into the upstairs bathroom for the toilet and so can't really be moved.

 

Does anyone have suggestions for how to deal with this ? Ideally I would like to stick with the warm roof to solve the issues above even if it meant just going up to the front of the pipe and keeping that area as is (re felted or grp).

Looks are not that important as its not a visible area.

 

Thanks for any advoce

[PeterW]

Why not rip the felt off, build a new low sloping (ie 10° Angle) roof and then insulate, board and GRP that as a new surface overall. It would hide the junction which is probably your biggest issue, and also then make the roof penetration easier. 

[glennpierce]

24 minutes ago, PeterW said:

Why not rip the felt off, build a new low sloping (ie 10° Angle) roof and then insulate, board and GRP that as a new surface overall. It would hide the junction which is probably your biggest issue, and also then make the roof penetration easier. 

That would be good. Unfortunately the roof is a little more complicated. (I didn't want to complicate things)

 

There is a image here that shows how it wraps around the house. I think it made be hard to do a sloped roof around that.

 

Thanks

[Dave Jones]

looks like you have scope for build height which you are going to need.

 

The soil pipe isnt an issue really, ok you are going to lose a little performance but no more than current.

 

The build up needs to be:

 

rip it all off to expose joists. 

OSB 12/18 mm covering.

now the bit you have to get right. A decent vapour barrier (not plastic sheet) such as Alutrix, it needs to seal against all 4 walls front and back so there is zero air flow from inside the rooms into the roof. bring it ip 300mm tight around the soil pipe (there are videos showing how to do this detail.

Insulate, look at kingspan thermataper to save having to use firring strips. it comes glass backed ready to bond edpm too.

thermally broken mushrooms to pin it all down.

covering with edpm or whatever takes your fancy.

 

get the VCL wrong it will fill with water and black mould in no time. Have a look at steve the roofer on youtube he gets called out to so called warm roofls less than a year old with missing VCL that are black with mould and have to ripped out.

[glennpierce]

Would I need something like 47mm x 100mm Sawn Timber Treated for the left edge to provide an upstand for the vapour barrier and keep the insulation contained ? Thanks

[Dave Jones]

you want the vapour barrier going down onto the internal walls not up.

[Mr Punter]

45 minutes ago, Dave Jones said:

you want the vapour barrier going down onto the internal walls not up.

 

Really?  I normally see joists, osb, firrings, OSB, vapour barrier, insulation, osb, waterproofing.  How would you lap the vb around the joist ends or wall ledger if it is lapped down?

[Dave Jones]

2 hours ago, Mr Punter said:

 

Really?  I normally see joists, osb, firrings, OSB, vapour barrier, insulation, osb, waterproofing.  How would you lap the vb around the joist ends or wall ledger if it is lapped down?

 

the goal is to airtight the story below obviously. If you have a parapet wall then you can lap up but have to take account of cold bridging. It's hard to get a warm roof correct.