Warm or Cold Roof

[Twin Dad]

I am looking to create a room in the loft (Velux conversion) but want/need replace the roof covering before I do so - the bituminous felt is getting old/brittle, has slipped in places and has been shredded by birds around the valleys and eaves.

A warm roof looks like a more elegant solution with the added bonus of some extra head-height. It does however mean I'll likely need planning for the increase in ridge height due to the build up of insulation and counter batons etc. Is the warm roof the best way to go, or is it over complicating things? Is there likely to be a significant cost difference between a warm roof and traditional insulation between/under the batons?

Thanks in advance.

 

[^woody^]

Planning would be required to alter roof height, and normally not granted

References to warm and cold roofs tend to relate to flat roofs.

Options for loft conversions are vented or unvented, and will require insulation between and below the rafters regardless.

 

[Twin Dad]

Thanks Woody I am aware of the planning requirement but that aside, I'm interested on what is the better solution from a cost and performance perspective. I assume a warm roof is unvented and cold the vented?

Why would a warm/unvented pitched roof need additional insulation between & underneath the rafters if there is already a continuous layer over the rafters?

I'm looking at something like this if it makes it clearer.

What is the Difference Between a Warm Pitched Roof and a Cold Pitched Roof?

Find out the difference between warm pitched roofs and cold pitched roofs and the different ways of creating them.

www.kingspan.com

 

[noseall]

Thanks Woody I am aware of the planning requirement but that aside, I'm interested on what is the better solution from a cost and performance perspective. I assume a warm roof is unvented and cold the vented?

Why would a warm/unvented pitched roof need additional insulation between & underneath the rafters if there is already a continuous layer over the rafters?

I'm looking at something like this if it makes it clearer.

What is the Difference Between a Warm Pitched Roof and a Cold Pitched Roof?

Find out the difference between warm pitched roofs and cold pitched roofs and the different ways of creating them.

www.kingspan.com

That diagram image is a cold (pitched) roof.

One wouldn't normally opt for a warm system on a pitched roof because they are easily ventilated and it can add problems to roofs where additional height above the rafters is an issue.

 

[Twin Dad]

That diagram image is a cold (pitched) roof.

One wouldn't normally opt for a warm system on a pitched roof because they are easily ventilated and it can add problems to roofs where additional height above the rafters is an issue.

Thanks for that. Yes, the diagram is of a cold roof but the description refers to a warm roof build up as being the best suited to the UK climate. Lazy link from me I'm afraid. Better illustration below with this manufacturer stating it is often chosen for re-roofing as it performs better.

I'm sensing that whilst the theory says that whilst retrofitting a warm roof is better when it comes to practice those who are doing it day to day seem to prefer the traditional approach?

Insulating a pitched roof above the rafters: warm roof insulation - Mannok Insulation

Insulating a pitched roof above the rafters is the common method chosen for new builds and re-roofing existing detached buildings as it provides superior thermal performance for the building. Insulating the roof above the rafters is known as warm roof insulation as the rafters are brought into...

www.mannokbuild.com

 

[noseall]

I'm sensing that whilst the theory says that whilst retrofitting a warm roof is better when it comes to practice those who are doing it day to day seem to prefer the traditional approach?

Not especially no.

Flatties = warm roof because they are difficult to vent.

Pitched = cold roof because they are a lot less difficult to vent.

Doing ANYTHING retrospectively to any roof will require design, with a view to which is the best/most economical way to insulate/ventilate. You need to look at the eaves, membrane type, ridge, planning issues etc before launching into your renovation job.

 

[Twin Dad]

Not especially no.

Flatties = warm roof because they are difficult to vent.

Pitched = cold roof because they are a lot less difficult to vent.

Doing ANYTHING retrospectively to any roof will require design, with a view to which is the best/most economical way to insulate/ventilate. You need to look at the eaves, membrane type, ridge, planning issues etc before launching into your renovation job.

Thanks. That is exactly where my head is at. The ridge will be higher (planning). I guess I would likely also have deeper soffits and some sort of facia at the side to mitigate the extra roof depth.
The roof needs recovering anyway and I'll be adding a room in the roof. Trying to gauge if improved performance of the warm roof is worth the extra hassle. Probably it is not. Probably won't get through planning in the conservation area I live in anyway

 

[noseall]

Trying to gauge if improved performance of the warm roof is worth the extra hassle. Probably it is not. Probably won't get through planning in the conservation area I live in anyway

The only real benefit of warm v's cold regards say a room in a roof (in view of the fact that venting is not a problem) would be height issues internally and that the cold method will reduce that further. Otherwise I can't see the point of the faff in opting for a warm pitched rafter roof.

 

[Twin Dad]

The only real benefit of warm v's cold regards say a room in a roof (in view of the fact that venting is not a problem) would be height issues internally and that the cold method will reduce that further. Otherwise I can't see the point of the faff in opting for a warm pitched rafter roof.

Thanks. I had always thought the cold roof was still compromised in some way. Perhaps not.

 

[noseall]

Thanks. I had always thought the cold roof was still compromised in some way. Perhaps not.

The performance of the insulation works the same. It's the issues dealing with the water vapour (venting) that become contentious with any design. Whether that be location of vents, light fittings compromising VCL's, issues with bulky overly thick insulation etc.

 

[noseall]

Planning would be required to alter roof height, and normally not granted

err...?

Raising the (ridge) height of the existing roof isn't surely?

Yes, a whole one or two extra storeys.

Enjoy

https://www.planningportal.co.uk/pe...storeys-extending-upwards/planning-permission

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