Advice on roofing project

Lumen

I have a single pitch roof section over the hallway at the front of my house, tiled in cement tiles since it was built in the 80s.

It measures about 4.4m wide x 5.5m "long", running up at about 23.5 degrees from 2m to 4m height, flashed to vertical walls on the left and top, and topping a side wall to the right. So it's basically a 24m2 rectangle.

The purpose of this project is to:

• Replace ripped felt (how did it rip? dunno. birds?) which has caused occasional water ingress
• Insulate and air-tight the slope, since it's directly over my hallway and causes massive heat loss. I will be putting a layer of insulation boards on the inside too to deal with cold bridging, but that's for later.
• (Maybe) clean the moss off the tiles.

I want to:

• Remove and clean the tiles
• Remove the battens and felt (the felt is ripped and non-breathable, so needs to go).
• Fit PIR boards between the rafters, sealed with foam to get a good fit, and probably taped on the underside for air tightness.
• Fit new felt.
• Re-fit the battens.
• Re-fit the tiles.

I propose to do this with ladders, balance and a helper.

My roofing experience to date was doing (from scratch) a cedar shingle roof of similar area, pitch and height, which I managed on my own without falling off, but I've never done cement tiles.

Questions:

• How do I choose nails, in terms of length and material (alu vs galv), from https://www.goodwins.ie/galvanised-roofing-nails/c-3182.html ?
• Do I nail every tile?
• What are the odds of the battens being reusable? Should I just replace regardless?
• Am I right in thinking the felt will be kept in place by the battens and flashing and doesn't need stapling to the rafters?
• What type of gun foam is best for sealing around the edges of the boards? I've used https://www.goodwins.ie/products/soudafoam-window-door-sws-gun-foam-750ml-4017006.html?name=window%20foam&type=simple before on other air tightness jobs and it was fine.
• How much gap should I leave around the boards to fill with foam? 10mm?
• Any tips on shaving foam if I use too much? This Soudafoam stuff is quite flexible from what I recall so maybe that won't work. Should I foam from underneath or above? Maybe tape the boards on the underside before foaming from above?
• Instead of roofing felt I'm planning on using this windtight breather membrane because I have a roll of it left over. Bad idea? https://www.ecologicalbuildingsystems.com/product/solitex-fronta-quattro
• I'm planning on using 70mm PIR boards between the 115mm rafters, leaving 45mm for rafter ventilation before the membrane. With a breather membrane I think I can go a bit deeper e.g. to 80mm or even 100mm, but should I? There's going to be cold bridging with the rafters anyway so I'm not sure I'll gain much. https://www.goodwins.ie/products/xtratherm-polyiso-rigid-foam-insulation-70mm-2-4m-x-1-2m.html?filter_set%5B%5D=1413,1426
• Is it a good idea to clean the moss of the tiles (how?), or should I just spray them with moss killer and let nature (and my gutters) deal with it?

For the foam calcs the data sheets says "Linear yield FEICA TM1002: 21m" and TM1002 says "standard joint of 20mm width and 50mm depth" so that's 42m with a 10mm joint. I reckon I have around 110 linear metres so that would be three cans. So I guess I should buy four?

I guess I should put some temporary battens on the underside to retain the PIR boards until I've foamed them.

Any other tips?

Rows Grower

Buy new battens and treat them, make sure the tiles don't have asbestos in them.

Lumen

https://www.boards.ie/discussion/comment/122257762#Comment_122257762

I have a can of Protim 265, will that do?

How do I tell if the tiles have asbestos in them? If they do, or I can't tell, should I just wear a good mask while doing the work?

tabby aspreme

I doubt concrete tiles have asbestos in them, its slates that contain asbestos

10-10-20

How do I choose nails, in terms of length and material (alu vs galv)
Do I nail every tile?
What are the odds of the battens being reusable? Should I just replace regardless?

I have concrete tiles here and they have alu nails and are nailed every second row (as it's somewhat exposed). Less exposed can be every three and more exposed would be every row. Battens - just play it by eye but if you have water ingress at the felt then that's indicating that you have another issue such as wind-driven rain (tile overlap not enough?) or a run-off from further up which is routing rain over the felt. Find that cause.

Am I right in thinking the felt will be kept in place by the battens and flashing and doesn't need stapling to the rafters?
What type of gun foam is best for sealing around the edges of the boards? I've used https://www.goodwins.ie/products/soudafoam-window-door-sws-gun-foam-750ml-4017006.html?name=window%20foam&type=simple before on other air tightness jobs and it was fine.
How much gap should I leave around the boards to fill with foam? 10mm?

Felt is usually tacked down just to keep it in place but if you can do it without tacks/staples then do.
I've used that foam on windows - it's good as it supports movement afterwards. Not sure if there are other airtight foams out there, but price the cans up as they add-up to a considerable portion of the project. I'd go for a 5mm gap either side of the insulation and lay down two foam trails right at the joists, then push down the insulation and finish off by foaming the tops along the joist. Dry-fit all of the insulation first too just to ensure that it fits.

If you're cutting the boards with a hand-saw then do this indoors/garage as that dust is horrific in a garden and much easier to clean up in a sheltered spot. I'd go with 100mm if I could instead of 75mm. Or even top it all off with glass-wool.

Edit. You know what - I typed all of this above and then remembered that you said that you were insulating the slope (rafters) rather than the joists. I'd say that you should forget about insulating the slope and just do the joists over the ceiling instead. Much easier to do properly and will give you a more effective solution as you don''t need to be sending warmth into the void when you don't have to.

Lumen

You know what - I typed all of this above and then remembered that you said that you were insulating the slope (rafters) rather than the joists. I'd say that you should forget about insulating the slope and just do the joists over the ceiling instead. Much easier to do properly and will give you a more effective solution as you don''t need to be sending warmth into the void when you don't have to.

There are no joists, this is a vaulted roof over a hall.

Pictures for clarity, also showing the damaged old felt which I bodged with membrane previously. The ingress is caused by busted felt, but I'm not sure what busted the felt.

10-10-20

Ok, the photo helps. So how much of the underside do you have access to?

FrancieBrady

Felt looks like it might have been treated to a big builders size nine and just covered over?

Lumen

https://www.boards.ie/discussion/comment/122259946#Comment_122259946

The original plan was to insulate from the underside, but that proved not to be possible because of various awkward cross members - there would be too many gaps, a bit like the difference between internal and external wall insulation.

Hence going in from above, which also allows me to replace the felt.

The mad thing is that the water ingress only became apparent after I stripped off the T&G internal cladding, so it's quite possible as @FrancieBrady says that this felt has been busted for 35 years, and the occasional blown-in water ingress has been draining down the backside of the T&G and behind the plasterboard. LOL.

10-10-20

https://www.boards.ie/discussion/comment/122260147#Comment_122260147

I'd tack on battens to the underside and fit it that way (as you mentioned). That was the reason for my question about access.