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Spray Foam Insulation in roof rafters - closed cell. Any issues?

  • 14-03-2022 6:08pm
    Registered Users Posts: 11 elcummino

    We have spray foam insulation in our attic. Just bought the house and the surveyor mentioned that he would remove the spray foam as it may cause rot to the timbers down the track. Its closed cell foam, reasonably hard though with a bit of force you can pick at it. It's sprayed all over the roof and rafters, directly onto the felt.

    There's no vent card used. Though there is defo air circulating in the attic - so I think there is a vent somewhere.

    Spray foam installers have mixed views on it. One said to remove it straight away, another said it should be grand as long as air is circulating. Has anyone else ever got any advice on it or had issues with closed cell foam on their roof or in their attic?


  • Registered Users Posts: 290 ✭✭ Biker1

    Doesn't matter if it is open or closed cell a 50mm air gap must be maintained between it and the felt. It is in plain language on the cert.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    Spray foam may cause problems in the attic.

    The Building Regulations (BR) 2019 require Ventilation of the roof void of a domestic dwelling. 

    The minimum ventilation requirement are set out in Technical Guidance Document (TGD) ‘F’ Ventilation. - here is the Diagram 11- Ventilation of Roof Voids, from this document- which shows the minimum requirements 

    If what you plan to do is not shown here, then do not construct it, as it will not be in Compliance with the Building Regulations. 

    Fresh air is wonderful for building materials. Timber with a little extra moisture and lack of ventilation will enable Dry Rot to flourish.

    The Building Regulations have 5 purposes, 3 of which are as follows:- Health, Welfare and Safety of persons.

  • Registered Users Posts: 11 elcummino

    Thanks all. I think the foam was sprayed more than 10 years ago - apparently before the building regulations and need for a cert. That's part of the problem, in buying the house we have no idea if regulations were met. Assume they were not. But don't know if this necessarily means there is a problem with it or a need to remove it

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    The Building Regulations became active on 1 June 1992.

    Remove the insulation.

  • Registered Users Posts: 11 elcummino

    Thanks C Eastwood.

    I may be wrong, but I don't think the regulations on spray foam was added until very recently?

    Even if it is against todays regulations, does that necessarily mean it will be problematic?

    Any advice on how to remove it?

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  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    Here is a copy of the Building Regulations Diagrams for the ventilation of Roofs voids of domestic Dwellings, which are in place since June 1992.

    Diagram D shows a 50 mm air ventilation cavity between the top of the insulation and the underside of the felt/ membrane.

    Spray foam cannot achieve this.

    The Building Regulations have 5 purposes - 3 are the Health Welfare and Safety of persons.

    I would not worry about it not being in compliance with the Building Regulations. If there is any ingress of rainwater or a build up of condensation, on the felt / membrane above the spray foam - then the timbers of the roof may be damaged by Wet Rot or Dry Rot.

    I do not know how to remove the foam. I would phone a number of reputable Insulation Company - and ask them what is the correct way to remove the sprayed foam. You may get a solution from them.

    I think that the spray foam will be bonded to the underside of the roofing felt/ membrane, and if you will damage this membrane (which is on top of the rafters and under the slate/tiling battens) by removing the foam, - then I would leave the foam in place. Do not damage this felt/ membrane.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood

  • Registered Users Posts: 2,272 ✭✭✭ Yellow_Fern

    Hypothetically, if the person had a fully breathable underlay and counter battons, would the spray foam be tolerable?

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood

    Yellow Fern.

    I am not expert on Spray Insulation. Closed cell foam means that each one of the millions of tiny air pockets are not connected to any of the adjoining cells. Therefore it is not porous, and is impervious, and therefore fluids cannot pass through it.

    it will be chemically bonded to the underside of the underlay. The battens and counter battens will be above the underlay and will be well vented and will never have any problems.

    If it were my house, I would not remove the Spray Form, because I have a reservation - that to remove the foam will cause irreparable damage to the underlay.

    because the foam is impervious, interstitial condensation (condensation within a material) cannot occur. Therefore it is only moisture from ingress of rainwater (under the Tiles /slates) can cause Rot in the timbers. If the underlay is fixed in place in accordance with Manufactures Instructions no rainwater should be able to get near the timbers. If any rainwater gets in it will only be in a few areas.

    Leave the foam in place.

  • Registered Users Posts: 290 ✭✭ Biker1

    Yes, if counter battened above the membrane and over fascia ventilator used then rafters can be full filled with any insulation. You will still need a vapour barrier/airtight membrane on the warm side so no real benefit in using spray foam and I would recommend mineral wool with a thermal conductivity of 0.034w/mk.

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  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    I agree.

    Mineral wool is perfect for thermal insulation.

  • Registered Users Posts: 11 elcummino

    Thanks for this.

    It feels like the best bet is to just leave it rather than risk damage to the felt.

    The roof is in good order so I am not too concerned of ingress of rain water, but Imight buy a moisture meter reader and put it into the timber rafters to get an idea if any damage has been done.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood

    Can you put up a photo of the rafters and spray foam.

    in an attic the roof timbers will be approx 16% (+ /- 2%) Moisture Content.

    I don’t think that the Moisture Meter will be of any benefit to you. If there is any ingress of rainwater in one part of the roof- using the Moisture Meter on the underside of the rafters would be like trying to find a needle in a haystack.

  • Registered Users Posts: 11 elcummino

    These photos OK

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    Photos perfect. your roof looks perfect.

    do not bother with a Moisture Meter.

    you will reck your entire roof by interfering with the spray foam. Do not allow anyone to try to remove the foam.

    the roof is at a very high pitch, approx 40 degrees which is good. Therefore rainwater may not be blown up between the tiles/slates in very windy weather.

    The purpose of the roof membrane is to prevent rainwater which is blown up under the tiles/slates from falling down on to the ceiling.

    because of the high pitch, any rainwater blown up under the tiles/ slates in high winds will fall on to the felt/ roof membrane, and run rapidly down the membrane and out in to the gutters.

    if there is no damage to the membrane and if the membrane is well sagged between the rafters then it will be almost impossible for and rainwater to get near the rafters

    the roof is perfect- leave it alone.

    It appears from the photos that there is no ventilation from outside to the Attic void. You can check if there is ventilation by going up in to the attic and check if there is any draughts coming in to the attic from the wind on very windy days

    there is approx 100 insulation on the ceiling. If the attic void is ventilatilated /draughty, then add 200mm insulation on top of the existing ceiling insulation

    you need to check you attic in damp weather to ensure that surface condensation is not occurring on the underside-inner face of the Spray Foam, if this occurs you will need to provide ventilation of the attic void.

    Kind Regards

  • Registered Users Posts: 561 ✭✭✭ Kingkong


    I have a new build and looking to convert the attic now. Roof has trusts in it for conversion. I was keen on getting the attic insulated with spray foam as I thought it was superior finish. However after reading this I am uncertain.

    What is the position on the best method for attic insultation assuming cost is secondary to quality and durability.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    I would never recommend Spray Foam to any of my clients.

    Your attic void must be ventilated to prevent condensation occurring on the underside of the roof membrane.

    See the Building Regulations Diagrams above in relation to Ventilation of roofs.

    It is expensive to heat the volume of air in your house in order to have a good warm environment in the house. Therefore the best upper insulation of the house is to install 300 mm of insulation on top of the ceiling, in the attic void.

    I do not understand why people use spray insulation foam on the underside of the roof membrane. Apart from all the problems it causes, it blocks ventilation, and if there is no insulation on the ceiling slabs - you must now heat the huge volume of air in the attic void, which will be warmer than your house because heat will rise. Eventually the heat in the attic will escape by Conduction through the Spray Foam insulation.

    Why do this when you are very rarely in your attic.

    Spend the money on a good holiday 😂

    The muppets selling the Spray Foam Insulation are excellent Sales People. 10/10.

  • Registered Users Posts: 11 elcummino

    Thanks so much C Eastwood for all your insight and advice on this.

    Really helpful and has put my mind somewhat at ease.


  • Registered Users Posts: 2,579 ✭✭✭ Casati

    I used spray in a new build and it was a great job, as well as providing excellent insulation it also was fantastic for air tightness. As the other poster said you need the 50mm gap which can be achieved with cardboard insert.

    Having said that my house was a dormer but if your building a standard two story and the attic isn’t liveable then mineral insultation is a lot cheaper and easier plus will ensure air floor of roof timbers

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    Thanks for your kind words.

    Kind Regards


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  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    and you get a very large extra volume of air to heat in the attic

  • Registered Users Posts: 4,695 ✭✭✭ budhabob

    Hey folks, we are looking at external insulation, PV Solar and an attic conversion in the not too distant future. We have a mid terraced c.70 year old house.

    WRT the attic, given that we are going to convert it (cut roof construction, great height etc), what should we be specifying for the insulation of the rafters. Also, will having the insulation in place cause any difficulties with Solar fitting?

    Thanks in advance, very useful thread.

  • Registered Users Posts: 751 ✭✭✭ C. Eastwood


    If you Google roof insulation Ireland and phone or email the Insulation manufactures, one of their technical people will give you advice and necessary drawing details. They are very helpful.