McCracken

I thought cold roof was insulation in joists , assuming you don't have vaulted ceiling

what would you recommend instead? I was thinking HRV will deal with humidity, Izoperm was for create airtight.

Looking at IZOPERM PLUS to the rafters for vapour and airtightness. I'm going to install a HRV, its only 2 rooms btw. Tyvek Supro above.

Apols, warm roof..

I'm doing one per side to the front, enclosed and covered with fibre glass. its a cold roof.. as in 100mm insulation between 6x 2 rafters. I have run DPC down the side of parapet behind the battening for the valley and continued it up and over the block work behind the OSB.. and now Im thinking will condensation be a problem. Overthinking is a speciality with me.. prob a thing with most DIY'ers

of course, water resistant. I'm using DPC to separate from outer block assuming that it becomes more water resistant.

I'm cladding a parapet with OSB3, and was planning on running DPC up and over between it and the blockwork to keep it dry. Parapet will get fibre glass. I know OSB is waterproof, but I had some DPC left over and threw it in. Does anyone foresee any problems with that? Is it the done thing?

Smaller size would defo help , but as you say.. not sure about quality. I suppose you know what you're getting with Velux, plus I've already purchased. Might just see how it goes

I have a really tight Velux install between a hip and the jack board of a valley.. the window will literally be sitting above the jack board with the flashing down approx 100mm into the a 200mm valley. It has been mentioned that I may have a problem if it snows? Anyone foresee any other issues with this? Also one of the top corners is going to go tight to a ridge tile, so I am going to have to cut the top of the flashing to fit under the ridge tile on the hip. Again , prob not the best idea but does anyone think its an absolute No no . Doesn't help that the flashing is so tall on the top . I don't have an option to move the window, and its the smallest Velux I could get CK 01.

Thanks Mark

I should say I'm trying the least fall possible as I have roof windows to fit on a hip without much room for manoeuvre

I'm currently building a valley against a parapet to deal with rain water drainage, could anybody give me an idea on what fall I should have on a 10 metre valley coming off a pitched roof? I have been using 1/80, but even that looks excessive.

My worry is more that it was just one block sitting up, and wouldn't bond through DPC, but it actually seems sturdy.

hoping to avoid coping and do it with fibre glass across top with overhang on the out side. any thoughts on DPC at that height?

the rational given was to stop moisture coming down through the top thro the block. As I said, I'm not too comfortable with blocks sitting on plastic up there, and I reckon the fibre glass will do the same. No cavity tray, just DPC at ground level, 155mm up from deck. Prob a bit late for that now. Its 100mm cavity with 80mm PIR. I've not closed with a block, so sealing with insulation and a bit of DPC. I've 6x 2 rafters coming down onto wall plate, so will be creating a valley with OSB and fibre glass.