Roof Insulation on a old stone property?

[up4it]

I am in the process of buying a detached stone house that was built around 100 years ago.
The house has a very large open attic with very large roof timbers and a slate roof in good condition but has ZERO insulation! :shock:
I have had the timbers checked out and they are in good condition.

Can anyone advise me of the best way to insulate the roof without causing any future problems with trapped condensation, rot, fungus, etc..
As I would like to create two new rooms in the attic space and would ideally like to keep the old beams exposed to give extra character to the rooms and maintain the character of the house.

I had in mind something along the following:-
Kingspan leaving a 2 inch gap behind for air circulation, with foil insulation over the top of that and then cover it with plaster board leaving the large beams exposed.
But am open to suggestions!

Thanks for any responses in advance! 8)

I have uploaded a photo showing the attic roof as it is now...

 

[AMc]

I had in mind something along the following:-
Kingspan leaving a 2 inch gap behind for air circulation, with foil insulation over the top of that and then cover it with plaster board leaving the large beams exposed.
But am open to suggestions!

Doesn't sound like a bad idea but you'll need to check it meets building regs. requirements for thermal performance. Kingspan etc. usually have PDF files of their recommended installation methods which can be used to gain approval.
Personally I wouldn't bother with the foil blanket (expensive and contentious) but go with a layer of solid foam board insulation foamed to seal the joints with the timbers and alumninium taped at board to board joints, then cross boarded with insulated plasterboard and skimmed.
You could also use rockwool/sheepswool insulation, hemp boards and limeplaster which will be vapour permeable a.k.a. breathable but you'll need more depth to achieve the same thermal performance and may find it impossible to keep the beams on show.
Finally I would definitely use some "wool" type insulation over the ceiling below to reduce draughts and also take a look at sound insulation to reduced noise in the rooms below.

 

[Flyfisher]

Welcome to the forum.

Is the house listed? If it is, you may not have to worry about meeting an absolute thermal performance. Otherwise, I agree with AMc's point about the challenge of sealing between the timbers and minimising the depth of the air-gap/insulation/plasterboard to allow the timbers to remain visible.

Another option would be to insulate the roof from the outside of the rafters, although I appreciate this may not be appealing if the existing roof is in very good order.

There are pros and cons for both approaches.

 

[up4it]

AMc: Thanks for the Kingspan recommended installation PDF file suggestion. I will definitely look into that! 8)

 

[up4it]

FlyFisher: Thanks for the response.

No, the house is not listed. As for the roof, it is big and in very good condition.

 

[agbagb]

From the picture it looks like you dont have roofing membrane so the ventilation should be good although you might a vented ridge or vent slates adding. I would fill in between the rafters leaving a 25mm gap so with a 3" rafter use 50mm Kingspan/celotex. Under the rafters horizontally with as thick as you need for Building Regs possibly 50mm (or for your own comfort and bills) . This layer should form a vapour barrier if well sealed with the foil tape. Then plaster board up to it. Some info on how I did mine http://roomuptop.blogspot.co.uk/2008_03_01_archive.html

The super quilt stuff doesn't give a real thickness advantage because you are supoosed to have air gaps both sides.
If it's the original roof it might be ready for renewing soon. When you do a, breathable membrane should be used so the vent gap is still sufficient. Good luck with it.

 

[middi]

An air gap of at least 25mm is required between a breatheable , stretched, membrane, and the insulation. A breatheable membrane in tight contact with surfaces defeats the object.

If you already have a breatheable membrane under the roof tiles, by using insulation that is pushed between the rafters but taking care to retain the air gap you will be fine. Small battens nailed to the inner sides of the rafters and plasterboards screwed on to these will solve your problem.
The amount, type and efficiency of insulation is restricted to the depth of your rafters.
In an ideal world the roof should be stripped, Thick, modern insulation sheets spanned across the outer face of the rafters and then finished with counterbattens, breath. membrane, battens and then tiles

In your case compromise is the order of the day ( as long as a reasonably good insulating factor is achieved)

Middi

 

[stuart45]

Putting up the insulation on top is a good method. Iv'e just built an extension at home using that method, although it is a bit tricky getting the fixings through the counter battens and 120mm of insulation into the rafters.

 

[up4it]

agbagb: Thanks for your blog. It has some good info for me such as the insulated plasterboard tip.

For anyone interested here are some links I found as a result...

Kooltherm K17 Insulated Plasterboard Link:-
http://www.kingspaninsulation.co.uk/Products/Kooltherm/Kooltherm-K17-Insulated-Plasterboard/Overview.aspx

PDF Download showing how to install it:-
http://www.kingspaninsulation.co.uk/getattachment/633e1bad-b13e-43ef-a4a4-4b1789667cd6/Kooltherm-K17-Insulated-Plasterboard.aspx

 

[up4it]

Some prices I found:-

Kingspan Kooltherm K17 Insulated Plasterboard 37.5mm 2400mm x 1200mm Board
37.5 mm insulated dry-lining plasterboard for plaster dab/adhesive bonding
Our Price: £47.58 (£39.65 exc VAT)

Kingspan Kooltherm K17 Insulated Plasterboard 62.5mm 2400mm x 1200mm Board
62.5 mm insulated dry-lining plasterboard for plaster dab/adhesive bonding
Our Price: £59.34 (£49.45 exc VAT)

Link Here:-
http://www.kingspandirect.com/category-s/94.htm

 

[up4it]

Has anyone used any cheaper equivalent products other than Kingspan? eg Celotex, etc..

I need to do some shopping around to compare products & prices.

 

[AMc]

Cheaper than Kingspan? no, I used a combination of Kingspan and Ecotherm - Ecotherm was my builders preference IIRC it was slightly more effective thickness for thickness (better U value).
I sourced mine from Sheffield Insulations but got healthy discounts because my builder is also a major underfloor heating installer and buys a lot of insulation. When Ecotherm wasn't available then we used Kingspan.

There is a seconds outlet for Kingspan etc. I've never used them but have seen them recommended
http://www.secondsandco.co.uk/Products.html

I would strongly advise you to install the best performing material, in the deepest thickness possible with the greatest possible attention to installation detail. Insulation will pay back it's cost in savings for years and years but the installation costs are virtually the same for doing a quick bodge with cheap materials or fitting the best materials in the most careful way possible. Well fitted insulation will make those rooms comfortable in summer and cheap to heat in winter, rushed gappy installation and you'll be hot in summer and pouring money into the sky in winter.

Good luck!

 

[stuart45]

Has anyone used any cheaper equivalent products other than Kingspan? eg Celotex, etc..

I need to do some shopping around to compare products & prices.

You could try Recticel insulation, or aandainsulation for Celotex seconds.