Thanks for all the ideas/questions/responses…..I’ll give you more info (sorry, I didn’t offer it before as I simply thought you’d like to see how bad this roof was).
The WHOLE house was a self-build 11yrs ago and, although I knew my mate had bought it, I didn’t realise the original owner/builder had hardly lived in it himself. By all accounts he did the roof himself.
I’m a retired QS, have a background in construction, did spend a fair few years as a building surveyor and can also turn my hand to most practical jobs which is why I’ve ended up getting involved. He originally asked me to come and have a look and give an opinion and, due to subsequent crazy quotes and lack of roofers, I offered to do the work for him (together with another mate and him labouring).
It‘s quite a complicated roof too (see google earth photo below) and so not a simple case of stripping and replacing…..cuts, cuts, cuts and more bloody cuts…..why oh why did I offer to help
Anyway I digress…..the CLAY INTERLOCKING tiles are Sandtoft Cassius and their spec dictates, for the pitch of this house, a minimum gauge of 75mm. It was very quickly apparent that the gauge was incorrect (as it turns out on ALL bar one of the slopes) - Firstly, and unbelievably, because when viewed from up high on a ladder you could, in several places actually see the nail holes on the top of the tiles (I kid you not!!!!!!). From the ground nothing looked particularly amiss. Secondly, through simple measurement and calculation, it shows that the roofer was one course shy. Thirdly, having now stripped some of the slopes, we were able to check (via watermarks) what the actual vertical head-laps had been….although some were borderline 75mm, most were way out and often equated to something akin to 50mm.
Even putting all of this aside for a mo, I’m still flummoxed by some of the more ‘questionable’ issues we have found like…1. First course on SOME slopes commenced at the very edge of the fascia with no attempt to overhang into the guttering. 2. Many instances of broken side-laps thus allowing any rainwater to immediately pass through to the membrane below (and so continually soaking certain areas of batten). 3. Poorly detailed GRP valley construction (in my opinion) which, debatably, would cause any water that works it way through the tiling to by-pass the valley itself and soak though to the underside membrane. 4. The valleys were all constructed unsupported - it appears that someone has walked up the centre of some and caused the fixing nails to be ‘ripped out’, meaning that one side of the valley was left somewhat unfixed (albeit held down with the weight of tiles above)…..this resulted in the finding of an enormous amount of ‘rubble’ underneath them when removed.
I’m still very surprised that the tanalised batten is so rotten…I’ve never seen anything this bad on such a young roof. It’s made me consider the potential limitations of treated timber in certain conditions.
I’ve got to keep reminding myself that the roof is only 11yrs old.
The daft part is that in other areas the original roofer has shown glimpses of roofing ’tricks’ indicating, perhaps, that he DID know what to do……it honestly is a head scratcher to work out WHY he did what he did.
In regard to exposure - Nowhere near the sea. It’s not that bad, in general, and seems that only two ‘faces’ take the worst of the weather and one of those has the correct gauge????? (and so we’re not touching it in the main areas). We’ve already complete the other and am now on a forth slope (loads of slopes, see photo). We’ve also agreed/decided to not do any work on some other slopes as these are not/have not caused any problems as yet.
In regard to ventilation - My mate wants rid of all cement mortar and so in addition to replacing the valleys (now also supported) we’re also converting the ridges to ventilated and will be adding soffit vents as I don’t think this current ‘lack of’ helped out his situation even though all of the membranes are breathable…..I’ve had a few conversations with some of the technical department boys for both the original membrane and new ridge kits and it’s actually been interesting to discuss the relative merits and issues with breathable felts and the need (perhaps) to add additional ventilation.
There’s probably more I can add but this’ll do for now.
