How to ventilate insulated roof? (Ed.)

[PeteMars]

(Edited)
The question is:
"Want to ensure airflow over Kingspan. Roofer was, I think, skimping throughout, and didn't add rafter trays which I've just discovered are a thing, and it's too late to install now from inside attic. So I'm thinking to gently poke a 25mm pipe down over each board to ensure the separation remains. Will this work?"



Roofer did new felt battons and tiles, to our 1930s house, and added 50mm Kingspan between rafters over the load bearing eaves (sloped ceiling in bedroom) at my request.

Roofer did not add soffit ventilation, only ridge. I've learned that this was wrong, and that breathable felt is not (as he claimed) adequate for intake, and so I've bought 25 lap vents to install myself.



Ill see how it all performs over next year before attempting to DIY install vents in soffits.

 

[PeteMars]

Photos:

 

[noseall]

(Edited)
The question is:
"Want to ensure airflow over Kingspan. Roofer was, I think, skimping throughout, and didn't add rafter trays which I've just discovered are a thing, and it's too late to install now from inside attic. So I'm thinking to gently poke a 25mm pipe down over each board to ensure the separation remains. Will this work?"



Roofer did new felt battons and tiles, to our 1930s house, and added 50mm Kingspan between rafters over the load bearing eaves (sloped ceiling in bedroom) at my request.

View attachment 342230

View attachment 342232

Roofer did not add soffit ventilation, only ridge. I've learned that this was wrong, and that breathable felt is not (as he claimed) adequate for intake, and so I've bought 25 lap vents to install myself.



Ill see how it all performs over next year before attempting to DIY install vents in soffits.

We always supplement our breathable membrane with additional OFV's (over-fascia vents), as I'm well aware of the limitations of even the best breathable membranes.
Your eaves (raked ceiling) protection is admirable, but short on a wee bit of thought. Whilst 50mm should have worked in practice i.e. 75mm rafter = 50mm insulation + 25mm air gap, it doesn't work in practice, owing to probably a lot of bulky plaster snots (lath & plaster) forcing the air gap to lessen.
As is often the case, it's better to rip the rake down internally and insulate between AND across the rafters. We are now adding knock-on timbers to 75mm deep rafters in order to use the correct thickness insulation and still achieve an air gap.

 

[PeteMars]

You are right about the snotty top surface of the ceiling! Well, it seemed worth a shot whilst tiles were being replaced, and for very little additional cost. Regarding lowering the 'rake' this sounds like something I'd consider doing when getting the artex ceilings upgraded, but that won't be for another year or so... so I'm just trying to avoid any mould for next winter... so I guess you're saying it's probably not worth even buying some cheap plastic pipe to act as a spacer?
Out of interest what are the OFVs and are they a DIY job?

 

[noseall]

Out of interest what are the OFVs and are they a DIY job?

Over-fascia vents. Absolute boon. It sometimes means reducing the existing fascia board to make them work.

 

[PeteMars]

It looks to be beyond my skillset to install these but thanks for bringing them to my attention