help in understanding my roof set up

Steveshouse · 31 Jan 2014

Hi

My dormer bungalow was built in 1960 and my roof set up is a space in the roof split into 2 rooms by a supporting wall with a dormer to the side.

There are access doors either side going to the eaves which are vented at the soffits
There is a small air gap i think immediately under the tiles, then felt, then insulation, all on top of the rafters

There is no lnsulation in the rafters or in the stud walls that make up the bedrooms there is however iinsulation between the joists of the ceilings below.

I would appreciate advice from someone on what type of roof (warm or cold) I actually have and would I be causing any problems if I was to insulate all the upper stud walls and ceilings with insulation and insulated plasterboard

Your help would be greatly appreciated

Thanks
Steve

Jameswren · 31 Jan 2014

it's a cold roof.

You can insulate between the rafters but you need some ventilation by creating a gap between the new ceiling and underside of the roof covering.

Steveshouse · 31 Jan 2014

Hi and thanks for replying

Because of the access to the roof above the upper ceilings am I ok to insulate from the inside - for the rafters I can reach in the eaves would putting insulating board under the rafter thus maintaining an air gap be ok

Thanks

Steveshouse · 31 Jan 2014

Im a bit confused about the insulation above the rafters if you said I have a cold roof - what purpose does this insulation have?

noseall · 1 Feb 2014

Steveshouse said:
Im a bit confused about the insulation above the rafters if you said I have a cold roof - what purpose does this insulation have?

It will only ever be classed as a warm roof if you remove all the roof tiles and battens and insulate on TOP of the rafters.

Everything else is classed as a cold roof.

A cold roof does not mean that the loft dormer is cold, rather that the rafter timbers themselves remain cold or as cold as the temp's outside. It's all about condensation, ventilation and dew points.

Steveshouse · 1 Feb 2014

Hi noseall

Thanks for the reply

I am with you on most points my main concern is condensation if I change any elements that might affect temp and dew points

I am not looking to insulate the eaves only all the room walls and ceiling In the roof space.

Because the insulation is on TOP of the rafters im confused as you have said I have a cold roof and a roof can only be classed as warm if on top of rafters,

I know I will make the roof colder by insulating the rooms and this will cause temp to drop but will it lead to any problems in the future.

Thanks
Steve

jeds · 1 Feb 2014

What you are describing is a warm roof - not a cold roof. This wouldn't have been original to the house. Must have been retro-fitted at some time. What thickness of insulation do you have above the rafters?

Steveshouse · 1 Feb 2014

The insulation above the rafters is very thin. It is a semi detached and I have checked if it was continuous through both roofs and it would appear to be from what I can see through the small hole above the party wall in the roof space.

The roof space is not closed in respect of the wind coming in at the soffits, you can see through the vents in the soffits to the street and the downstairs rooms ceilings have insulation above?

Thanks
Steve

jeds · 1 Feb 2014

Sounds like half an attempt at a warm roof. You'd be better off doing the roof before the walls. I'd just ignore the daft bit of insulation above. Provide a ventilation gap and fit new insulation between and under rafters.

Steveshouse · 1 Feb 2014

Thanks I was confused by the insulation on top of the rafters and everything else open to the elements.

So If I ignore the eaves for now and insulate all the upper room ceilings and stud walls including dormer I can come back to the roof space later and work out if I want to make it warm or leave it cold? Which would be for storage only.

Will making the eaves colder by insulating have any consequences?

Thanks
Steve

jeds · 1 Feb 2014

Yes you could do that. I think the warm roof part is a bit of a misnomer really. Insulation over rafters is technically a 'warm' roof but if it's only a thin layer it isn't really adding much. Insulating between and under rafters (in order to upgrade your loft rooms) converts your roof back to a cold roof. As long as you include ventilation that won't be a problem except you'll be effectively abandoning the existing warm layer - the daft thin layer. I don't see an alternative to that though. Just one of those things.

Steveshouse · 1 Feb 2014

Thanks jeds

I will crack on and insulate all upper rooms

Sorry one other thing I am insulating the dormer roof at present and the gap along the rafters varies between 95-100 mm which means when I insert 50mm insulation board the air gap will be 45-50 mm is this considered acceptable?

Thanks
Steve

Cabbyfan · 2 Feb 2014

I have pretty much the same situation. My bungalow has a dormer conversion but there is no insulation directly under the roof rafters.

The actual rafters are only 70mm deep so BC have advised 30 or 40mm air space directly under the tiles & flashing then using celotex or similar to the flush part of the rafter. Then to add additional insulation using 50mm or whatever I like fitted horizontally spanning the rafters. There will be a membrane between the airgap and first layer of insulation.

At the moment all it has is a thin layer of yellow wool sat between the ceiling joists and the stud work that forms the room has half inch thick sheets of polystyrene randomly nailed to the reverse side of the stud work lol.

The flat roof is felt and isn't very well insulated either.

It's going to cost be a bit in insulation !

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Steveshouse · 2 Feb 2014

Ditto on costs
Thanks for the reply I'll go with what's I've got.

Steveshouse · 4 Feb 2014

Hi again
I broke through the plasterboard in one of my upper rooms with the intention of installing insulation over the whole loft space then sealing it again and that will be that...

I was pleasantly surprised to see how much space there was up there and not that cold. With a better understanding of the loft set up - insulated above the rafters equals warm roof if the insulation is of an ok thickness, thanks to previous posts here.

I was wondering what I would need to do to keep this for storage after creating a permanent opening and at an ok temperature whilst stopping heat escape from the rooms below. Do I need to put in any measures to avoid condensation?

Your help is much appreciated

Steve

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help in understanding my roof set up

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