# Roof Insulation on roof with just slates



## dingdong (1 Jul 2010)

Hi 

I have bought a 1940s redbrick house, which needs refurbishment, the attic, space is big and would like to convert.

My question is , the roof has no insulation, and only slates applied with morter - ( no felt or plastic sheeting, how can i best insulate this from leaks, without removing slates, which will be expensive job. 

 The roof slates are in good condition,and secure


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## RKQ (2 Jul 2010)

Traditional methods of insulation will be fine.
You could run high density foil board (Kingspan, Xthratherm etc) between the rafters. Leave a 50mm air gap between the back of the slate & the top of the insulation.

There are foams available with IAB Certification, that are airtight or breathable. These foams claim to hold loose slate in place & claim to be ideal for your type of roof.

Re-slating is expensive - labour, new slate, scaffold etc, but it is worth considering. Especially if you wish to convert your attic as I assume you will then be installing roof lights for light & means of escape in your conversion.


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## Superman (2 Jul 2010)

RKQ said:


> There are foams available with IAB Certification, that are airtight or breathable. These foams claim to hold loose slate in place & claim to be ideal for your type of roof.


There are significant problems with these.  They force water to the roof timbers and cause interstitial condensation at these points - i.e. they will rot your roof timbers.
They are a non-breathable form of construction - presumably the existing roof consists of lime parging on the underside of the slate. 
Also by sticking all slates together, they make any repairs to slates difficult/impossible. So it reduces the overall lifespan of the roof.

The best way IMO is your other suggestion.
i.e.screw 50mm timber battens/blocks just inside the rafters (to keep insulation away from underside of the slate).  Then stick Rafterloc or similar between the rafters as far as the underside of the rafter.  Then finish off with a vapour control layer/foil backed plasterboard. 
Ensure adequate ventilation of the roof space by ensuring 25mm continuous equivalent ventilation at the soffit/fascia and including roof vents/ridge vents.

I'm not sure there is an easy way to install any form of roofing membrane/felt on the outside of the insulation unfortunately.


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## dingdong (2 Jul 2010)

Thanks for your opinion, superman, is your opinion from actual experience.

 I saw on the web people recomending BIO Foam Spray Insulation, you spray roof timbers and slates. everyone seems to saying differnt things.

When i look at underside of slate , you can see morter is that what you mean?


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## onq (4 Jul 2010)

On an older property that was built before cavity wall technology or  drained external leaves and roofing felt, you would be well advised to  seek specialist advice.

Its easy to do stupid things, to such a building 


 starting with raking out the old lime mortar and replacing it with  cement mortar,
 moving on to sealing up the chimneys and making the windows airtight to  stop draughts
 progressing then to insulating the inside of the external walls to stop  them getting damp.
 etc., etc.

All the sealing and prevention of ventilation stops the movement of water vapour through the structure and spaces of older houses while reducing the amount of heat passing through the structure can lead to a build up of water vapour in the masonry itself, increasing the rate of heat loss further water retention and leading to an unhealthy environment and increased chance of forst damage.

The amount of damage well-meaning amateurs can do to an old building is  considerable - take competent professional advice and watch those attic  services in particular.

ONQ

  [broken link removed]

  All advice on AAM is remote from the situation and cannot be relied   upon                                   as a defence or support - in and   of     itself  -         should       legal        action    be        taken.
  Competent legal and building professionals should be asked to advise in                                     Real Life with rights to inspect and      issue         reports    on     the         matters    at       hand.


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## RKQ (5 Jul 2010)

RKQ said:


> There are foams available with *IAB Certification*, that are airtight or breathable. These foams claim to hold loose slate in place & claim to be ideal for your type of roof.


 
Personally I prefer traditional methods of insulating a roof, as described in my post above. I would advise the OP to seek professional advice, specific to their roof.

Any foam spray used, should be installed as outlined in its Irish Aggr Board Certificate. If the foam isn't certified with a IAB Cert then don't use it. There are a number of foams on the market.


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## dingdong (5 Jul 2010)

Thanks for your comments, anyone recomend someone who could would have experience with this or would be good.


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## JohnJay (5 Mar 2013)

so any further developments on this since 2010?

I too have an old slate roof without felt. Ive insulated my attic as much as i can without loosing it for storage space. I'm thinking about spray insulation for the roof, but I read different opinions on it regarding wet root/dry rot etc. Some companies say they spray directly on to slates. Others install a tray and spray on to this. Which is the best way? Or dont do it at all?


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## lowCO2design (6 Mar 2013)

JohnJay said:


> Some companies say they spray directly on to slates.


find me the iab certification thats states this ?


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## JohnJay (6 Mar 2013)

lowCO2design said:


> find me the iab certification thats states this ?



Certification for all methods seem a bit vague to be honest. I think I would be a bit worried about the direct-on-slates option alright. And my jury is still out on the other method!


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## lowCO2design (10 Mar 2013)

JohnJay said:


> And my jury is still out on the other method!


can you elaborate ?


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## JohnJay (10 Mar 2013)

lowCO2design said:


> can you elaborate ?



I'm just a bit weary about the whole process. I can see how it would work well on a new build, but my 100 year old roof was not designed for this kind (or any kind) of insulation. Is it good to subject these old roofs (and old houses) to near air-tight treatment? Are these materials around long enough for us to know the long-term effects?


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## lowCO2design (10 Mar 2013)

JohnJay said:


> I'm just a bit weary about the whole process. I can see how it would work well on a new build, but my 100 year old roof was not designed for this kind (or any kind) of insulation. Is it good to subject these old roofs (and old houses) to near air-tight treatment?


no 





> Are these materials around long enough for us to know the long-term effects?


no there not, and there not suitable for what you require

i would get an arch tech/ surveyor to review a specify the insulation and ventilation of structure required, probably using natural materials from: http://www.ecologicalbuildingsystems.com/ (or similar Irish material supplier, no connection btw)

see here for the building science:
http://www.conservationphysics.org/

and here of the draft retro-fitting guidelines: 
http://www.nsainep.ie/Home/Index?Co...ack=.gmp_2820860.gde_2820860_member_220846087S.R.54: Code of practice — Methodology for the  energy efficient retrofit of existing domestic dwellings is now out for  public comment. 

and here for a great Scottish conservation document: 
http://www.changeworks.org.uk/uploads/83096-EnergyHeritage_online1.pdf


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