Flat roof - reroofing needed? Material and roofer recommendations (South London)

[DanRobertsB]

Hi

I suspect this roof needs insulating and re-roofing, given condensation issues. We may replace the skylights at the same time. Any advice greatly appreciated - anything from what material would be good (bitumen felt, EDPM, single ply uPVC, etc), to who you'd recommend, general tips, etc. 

Details:

 

Trapezoid ground flat roof over two bathrooms, c. 9.1m x 2m (at the wide end) and 1m (at the narrow end), adjoining a masonry parapet wall and a cold roof (just a timber wall). 

Construction date unknown, probably 1982-4, but possibly as late as 2000.

It appears to be unvented (unless they’re behind the fascia?).  

Roof appears to be solid underfoot, but condensation/mould issues suggests it needs attention. Both bathrooms ceilings were showing signs of peeling/mould/condensation etc around the skylights (see here). In Aug 2022, the upstands/skylights were re-flashbanded and both bathrooms ceilings decorated. Both have deteriorated a far bit since, but it’s much worse in the smaller bathroom, with clear evidence of water issues (seemingly condensation; rust on metal angle edges, etc)). This is despite very limited use (shower not used; bath used max once a week) in that smaller bathroom, so presumably interstitial condensation and/or roof leak, rather than humidity. It’s a bit odd that it’s only affecting one of the two bathrooms (the one used least) when it’s the same roof. 

In both rooms, on the opposite (far) side of the room to the shower (so a far way away), there’s a humidstat extractor fan and a window with a trickle vent. It may be advisable to install a further humidistat extractor fan directly over the showers and vent them directly out the roof with a (mushroom cowling). I have suitable fans to install (and can get them installed, though imagine you’d need to do at least the finishing etc on the roof side. 

I’m guessing it’d be best to: add a VCL and 150mm PIR, and refinish on top; probably put in new skylights; improve detailing etc where it joins the walls.  

There are three existing polycarbonate skylights (400x400mm externally, 600x600mm internally), with upstands. If insulating and re-roofing, can these be sensibly be re-used? I suspect there’s sense in switching them out for new 600x600 double- or possibly triple-glazed flat roof units e.g. Velux CFU 060060 0020Q, with Velux curved glass top unit ISU 060060 1093 and extension kerbs (unless cheaper/better to build these e.g. from OSB) ZCU 060060 0015. It might be that one or two of these should be electronically humidity controlled with rain sensors (e.g. Velux CVU 060060 0220Q, with humidity control unit). Open to alternative product suggestions, etc. 

Depending on cost and if it can take the weight, we might also be open to a green roof.