Super_Paulie

I'll see how I feel about it, 125mm, 140mm something like that. No harm in going longer if I can get em.

correct. Yeah i'll crack on tonight, insulation washers and 100mm screws. Its just to hold it until my battens are up, at which point i'll fix the battens in place with 125mm screws.

i suppose i would have said "75mm PIR over rafters, 75mm in rafters" in that order if i was going for a hybrid/incorrect setup, thought the order made it clear. Anyways, lets move on, its a debate i didnt intend, i was just after opinions on PIR orientation as per the title. Cheers guys

Yep, marked them all up on the wall so I'm good to go ✌️

Will do. I've already done my between rafter work, foamed and taped. Last thing to do is the overboard/underboard and that's all my insulation finished. BC described it as overboard and suggested horizontal, however I guess it's underboard and vertical now...!

Might be the wrong word to use but thought the above made it obvious. I have my answer anyways, cheers.

My question was in regards to the orientation of the second pir layer, horizontal or vertical. There is no insulation above the air gap. Tiles-batten-membrane-gap-pir-pir-batten-board. Pretty standard install. I guess it makes me feel good. At least as good as a roof can 🤷🏼‍♂️. Don't think I've wasted any money so far.

It's all in hand Gus, it's too late for the dramatic! Cold roof, breathable membrane, 50mm gap, 75mm PIR in rafters, 75mm over rafters, service void with batten, board.

My rear pitched roof (cold) has 75mm PIR between the rafters and I'm going with 75mm overboard. It works out a lot easier (due to velux positions amongst other things) if I overboard with the boards long edge on the vertical, which is against what I'm seeing in most instances where the second layer of PIR is 90° to the rafters. I assume it's ok to do this and BC won't get upset? I'll be battening afterwards for my service gap.

looks ok to my non-drainage eyes. But if it stinks still then yeah its not ideal. But thats a £500 job tops surely.

at first glance i thought not terrible, not great. But on a closer inspection, its god awful. Id be tearing that down if it was me im afraid. How come the courses line up one side but not the other, makes no sense. Time for a little shrub in a pot at that point to hide the join i think.

I haven't fired it all up yet as I'm still at the insulation stage in my roof. I assume it'll be ok but it was a steep learning curve and @Nickfromwales and @JohnMo helped loads amongst other forum members, all very helpful. I didn't even know what a buffer tank was until they helped me out, now it's obvious it would have been required in the way I want to do things. I've tested the electronics and valves and its all good to go in the near future, but it was stressful and confusing at first. I'll draw it all out at some point for future reference but attached is how it's all controlled. Zone valves and buffer are at the upstairs/loft.

It was an annoying situation all round and if I could go back I'd just get one from a store that I could return. Hasn't leaked though, but looks a bit silly with a tap stuck on top.

To close this, I went 120mm PIR between the joists, 120mm PIR on top of that, both angled to provide the ventilation void and span the cavity. Then I threw 100mm of wool over the top just because I had it. So 240mm PIR and 100mm wool, which is surely excessive. Got a cold bridge on the underside of the joists and the beam but I'll look at that when it comes to ceiling time.

Yeah, potentially. I was planning on not doing that so that the heat from downstairs will transfer upwards, however I'm not at that stage yet and it could well be the way to go. I guess I'll add in 120mm PIR between the extension roof joists, put in 200mm wool over the top of that, foam and tape and move on. Seems about all I can do here.

Not unless I do the entire ground floor... it might be a possibility depending on my ceiling height, could very well end up lowering it to meet the main steel which we are leaving exposed. Could happen, but not sure.

It's about as continuous as I can get it! I can get the pir in the small roof space over the cavity of the main wall. I guess the only place I can't is where the header joist is up against the steel beam. I'm open to any suggestions with this, although I'm hoping to do the job today so any great ideas would be welcome.

Looking at it now I'm at home, I could potentially put 120mm in the 70mm joists and just have the PIR heigher then the joist top. I'd just angle the pir on the end to cover the cavity. Then I can lie as much wool as I can over the top of that? Can also add 50mm directly to the block wall above the joist.

i just got my crayons out. So basically, can i go with option B is I suppose what im asking, i just dont know if 2 airtight layers with a void inbetween is such a good idea or not. Obviously the more insulation the better, think BC wanted 300mm if going the wool only route.

morning fella. No, this roof is totally separate to the porch and canopy section. It has the original brick wall at the house side and is block on the new gable side. Im well versed with FM330 and its a hell of a product, i used that when foaming the joins on my rear extension before cutting back and taping. So this roof is separate to all the others. It has no vents but i have used wedges so i can see daylight between the membrane and the eaves tray every foot along its length, so it has "air in". Would insulating this in this way be acceptable, im not so sure. PIR foamed and taped in the rafters, fibreglass in the void the PIR foamed and taped into the joists? I worry that any moisture could get trapped in this "inbetween section" or am i worrying about nothing? As the ceiling level will be flush with the rest of the house i need this section to be well insulated as its within the envelope. Cheers fella.

Yeah it's tricky. I was thinking, 50mm between the rafters (red), made airtight. 75mm between the joists, airtight again (green). Then just fill the void "triangle" in-between with as much wool as I can (blue). Any issues with that?

Job done, thanks for the input ✌️

Hi guys. The pitched roof of my extension at the front of the property needs insulation. What's the preferred buildup, see attached. The ceiling/plasterboard is to go flat straight across so that leaves the void above. Would it be best to use 50mm PIR between the rafters (leaving room for ventilation), wool in the void, then PIR between the joists to finish or is this overkill? Or PIR between the joists with 200mm wool layed over the top for sound/heat retention? Any thoughts would be most welcome.

yeah sorry the photo doesnt show that it is hipped very clearly. So a few soffit vents on the left and right of the porch will surrfice? Wont be too difficult id imagine, cheers!

sorry, yeah the canopy above the bay window. This is currently "open" underneath as i havent added any soffits yet. There is an osb divider that separates the porch and the bay window roofs, so i could open that up so the airflow can pass all the way through as you say extreme L to extreme R. As it stands there are no vents in the porch roof and it is a separate entity to the bay roof. As there are no vents on the porch side, i could add some quite easily. Im not sure what the builder intended by not putting vents in he did on the rear pitched roof. I would obviously have had to add a ceiling into the porch so what he intended i have no idea.