Replacing "Pitched" roof with GRP and question regarding ventillation when roof is 13-14 degrees?

[TacticalBrick]

Hi, first post here, I'm hopefully looking for some advise to make sure I'm not being taken for a ride and to find out if there's any other options other than what I've found.

 

I've had a multitude of issues with the roof around my extension since I moved here in 2017. It was extended by the previous owners and the pitch of the roof is between 13 and 14 degrees with flat tiles that are meant to be for 17.5 degrees and above (or so a multitude of roofers have informed me).

 

Since we moved in we've had various leaks and there's paint touch ups on the ceiling in other places, so the previous owners must have known.  I've spent thousands on it on the last 5 years including refelting sections and installing additional underfelt collars around the 6 Keylite windows (which are also only rated for 15 degrees). 

 

 

Right now, we occasionally get a small 50mm spot that appears downhill of a skylight and that's about it, however it was much worse in that area. Weirdly since the last roofer came around to take a look and lifted a tile to show me the "capillary action" caused by the wrong tiles and put it back again, it's much better. However, I feel it's only a matter of time before everything goes wrong.

 

I initially went down the route of getting quotes for a re-roof to rip everything off, then renew everything except for replacing with Marley Mendip 12.5 tiles. However, when a roofer was meant to start work, he realised the additional height would probably stop an upstairs window opening as it'd raise the hip joint too much:

 

 

We've also got a section of flat roof that joins this roof, just to add further complexity as it's already quite close to it's respective window:

 

 

I've therefor been advised to go down the GRP fibreglass roof and boy those quotes go from one extreme to the other.  Approx £5,800 to £25,000 to do 63m2 (the latter quote the guy also quote £21,000 to re-roof using the 12.5 tiles, so I think that's likely taking the mick).

 

Another option that was suggested was to just re-roof, use the same tiles and fit Klober Permo Extreme felt, but that feels like just hiding the issue? Although, if it's the better option over fibreglass, I'd go for it.

 

I found a few companies from the Confederation of Roofing Contractors who quoted around the £7k mark to do GRP. They said it'd need to be done as a cold roof as there's no room to sufficiently insulate over the roof joists (not that there's any insulation in certain parts of the roof, but that's another story...), which makes sense due to the location of the windows. However, both of them have said that they would just:

 

• Fill the joists to the top with celotex / rigid insulation
• Fill gaps with expanding foam
• Fit T&G boards
• Tape the boards
• Fit all the fancy angled pieces into the mortar at that abutments
• GRP it all.

 

I'd read quite a bit about GRP before they came over, so I was concerned about ventillation (I even spoke to planning control to confirm my understanding that there must be at least a 50mm air gap for cross flow above the insulation and under the boarding). However, neither roofer said it'd be an issue which seemed odd, especially when they're so well reviewed and can offer insurance backed guarantees.

 

They both also said they'd just go around the current windows with the fibreglass and there'd be no issues with the pitch of those windows either.

 

So my questions really are:

 

• Is the ventillation required? I assume so, because otherwise warm air from my house is going to rise up through the spotlights/plasterboard, find a way through somewhere and condense
  • If yes, why are the roofers so well reviewed if they're not bothering to follow regs, because surely it'll go wrong?
• What ventillation options are there for abutments at the current pitch? I assume that soffit vents are all that'd be required at the soffits, but there needs to be something at the top for cross flow
• How can they build up around the windows with GRP and guarantee no leaks?
• Should I even go down the GRP route considering the above, or should I look at the Klober Permo Extreme or just re-roof with normal felt and hope it lasts?

 

(Apologies if any terminology is wrong or needs correcting.)

Edited January 19, 2023 by TacticalBrick

[Jacob]

Escandella do a 10 deg interlocking tile called planum ive used on my house. And I have samples of 2 other tiles that go to 10.