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Spray foam insulation in attic

  • 14-07-2022 12:34pm
    Registered Users Posts: 2,922 ✭✭✭ Shelga

    Hi all- I’ve just gotten a quote for €1480 to put spray foam insulation in my mid-terrace house attic. The guy said that you need to get 200mm thickness to avail of a grant, but that this is a waste of time and 100mm is sufficient.

    I’ve read some previous threads here but am still quite clueless- does anyone know if this sounds reasonable? It’s a small house but the upstairs rooms are freezing in winter, and if this would make any noticeable difference I’d probably go for it. I’m not looking for perfection.


  • Registered Users Posts: 117 ✭✭ GalwayMan74

    Don't get it done.

    Its a disaster.

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

    Is it a normal pitch roof or do you have rooms in the Roof space (Dormers etc.)

    If its a standard attic space, seal all the holes in the ceilings to stop draughts. Heat loss by Convection.

    Fit 300 mm fibreglass insulation on top of the ceiling. To reduce Heat Loss by Conduction.

    An uninsulated ceiling in a pitched roof will have a U Value of approx 2.1 watts/m.sq/degreeC/hr.

    300 mm of good quality Insulation laid on top of the ceiling ( between ceiling joists and above) will give a U Value of approx 0.16 Watts/m.sq/degreeC/hr.

    This reduces the heat loss through the Ceiling to 1/13th of the present heat loss. This is a fantastic saving.

    If all the draughts through the ceilings are not completely blocked, you will still have a lot of heat loss by Convection.

    I do not approve of Spray-foam between the rafters.

    Fresh air by ventilation is very important to the timbers in the Attic Area.

  • Registered Users Posts: 694 ✭✭✭ CreadanLady

    Do not do it. It is a crazy practice.

    Roof timbers need to breath and encasing them in foam insulation stifles that ventilation. Any moisture that somehow might penetrate the roof covering will lodge and will not dry out properly and you could end up with rot. And because it is then hidden you will have no way of knowing until very serious damage has been caused.

    Whats more, if you are selling the house, a surveyor will not be able to evaluate the condition of the roof timbers. Even worse, they might even be very caustions and consider the possibility that you deliberately spray foamed the roof in order to hide a known rot or other issue with the roof timbers.

    Stay away from it. do no do it. Pay no heed to the salesmen who are offering it, they are only trying to get business and they don't give a toss about any issues. A lot of these fellas would be nearly half glorified travellers anyway.

    The MFV Creadan Lady is a mussel dredger from Dunmore East.

  • Registered Users Posts: 6,648 ✭✭✭ furiousox


    CPL 593H

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


    Brilliant Advice.

    If there is no felt/ breather membrane in the roof, the expanding foam may cause slates to me lifted.

    The Felt / breather membrane must be well sagged between the rafters to form a gutter to allow any rainwater to flow down the membrane below the battens, and in to the gutters. The expanding foam will lift up the underly membrane and eliminate this gutter. Therefore any ingress of rainwater in very strong winds cannot flow under the battens and will cause many problems.

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  • Registered Users Posts: 3,691 ✭✭✭ spaceHopper

    honestly, 300mm of fiber glass insulation is easy to fit or get fitted, and makes a huge difference. I'd also look at fitting insulated board to the wall 100mm ideally but if it's a small house 50mm. Check around the existing window frames for drafts often they are not fitted correctly and you get drafts at the edges. If you insulate the wall internally it's easy to fix then.

  • Registered Users Posts: 290 ✭✭ kildarejohn

    Just to add to all the negative comments about spray foam insulation, there are also health & safety issues, The foam emits fumes as it cures, and if you are sensitive e.g. asthmatic, this could be an issue. Also not great for fire safety, you would need to check spec to see it meets fire resistance standards required by Building Regulations.

  • Registered Users Posts: 694 ✭✭✭ CreadanLady

    Beware also that these salesmen are full to the eyeballs with plámás and will try to bamboozle with sh!the talk if you question is suitability. I'd estimate that most of them are chancers.

    10 or 15 years ago they were probably tarmacing driveways and putting up bad gutters.

    Now they've moved on to spray foam because it's easy. They just stick their head into the attic and let loose with a nozzle. I bet too that a lot of them only do the bits you can see and leave big gaps in more inaccessible areas.

    The MFV Creadan Lady is a mussel dredger from Dunmore East.