General roofing questions for my self-build

[BartW]

Hi,

We are starting on the timber frame on Monday, and technically in three weeks time I should be in a position to take over and start working on my roofs and facades.

 

After my recent dilemmas with hybrid / cold / warm roofs, I decided I was going to stick to warm roofs on both flat and pitched.

 

All roofs are to achieve 0.15u Value, so 150mm PIR has been selected. All flat roofs will be GRP, and pitched will be Cedral Thrutone Blue-Black slate tiles.

 

I have a few questions, however:

- should frame the insulation on all flat roofs with a 6"x2"?

- I am going to use Twistfix nails / screws to secure the PIR insulation on the pitched roof. I had the calculations done, and worked out I need 12 screws per sq m. Do I still need a stop batten on the bottom of the pitched roof? If so, do I just stand a 6"x2" upright, or do I need to install 3no layers flat?

- do I lap the VCL on the flat roof (below the insulation) with anything? Or just run an excess and ensure it is continuous across the roof?

- as above, but breather tyvek membrane

- I want a hidden gutter on the pitched roof. I found a design that achieves exactly what I am after on Cedral Website. Can anyone suggest a technical detail for this? Should I build a gutter box out of OSB, then lap extended GRP flashing up the pitched roof? It should in theory then sit below the Tyvek wrap, or should it? Link here: https://www.cedral.world/en-gb/roofing/projects/scrabo-clachan---ireland/193252/

- do I just use a dry verge trim from Cedral to finish off the pitched roof? Adjacent facade beneath said side will be charred timber.

- the flat roof adjoins the pitched roof. Should I just use the GRP "A trims"? If so, how do I nicely detail the junction? Or should I have some bespoke A trims made out of pressed aluminium for consistent looks? 

 

I know may of these questions are down to aesthetics, and quite frankly it has been doing my head in, as the concept I am working on is rather uncommon...

 

 

Can anyone help, or even better, has done something similar, and can offer advice please?

 

PS. I designed the house myself. Did all my drawings. Read all Building Regs, TRADA, and NHBC documents, and it has been a very steep learning curve full of pitfalls (that I am sure to still discover, and most probably pay for), but I am trying to stay positive, and motivated that one day I will be able to say it was my brainchild from concept to finishing.

 

Many thanks!

Bart