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Dormer insulation advice

  • 13-02-2023 10:40am
    Registered Users Posts: 4,478 ✭✭✭

    Hi All,

    Hoping to get some advice about what type of insulation I could be enquiring about for my dormer.

    We are currently planning a rear extension with an architect. Unsure when we would execute on it, maybe this year, maybe next year, maybe never! The insulation plan is slightly on hold until we decide to move on the extension to the ground floor. We would be extending the rear and considering external insulation on the sides and potentially front of house.

    However I think we could potentially target improving the fabric of the upstairs of the dormer now? This would allow us to then decorate and improve the finish of these rooms without worrying it would all be ripped apart again.

    I have attached a bad drawing of a slice of upstairs. Middle section is the room space. Triangle is the roof. Squiggly lines are where the insulation currently exists. The eaves are 'cold'. The sloped ceiling seems to be the major problem. When buying the house, the recommendation in survey was to apply insulated plasterboard here.

    Is this the best approach?

    Goal is to make as draughtproof as possible while retaining heat. I have seen options where the company removes the roof tiles and sprays foam between rafters. This is attractive as the work is external but not sure if it is better or worse than the insulated plasterboard approach?

    If anyone has used any companies to work on a dormer, appreciate recommendation via pm.




  • Registered Users Posts: 2,823 ✭✭✭MicktheMan

    Dormers are notorious for heat loss by convection aka air leakage aka draughts.

    Adding extra insulation does NOT address this. This fact is not well understood. Some of the best insulated houses suffer high heat loss due to air leakage / draughts because of this misunderstanding.

    Nobody can give you any meaningful advice in the absence of an on site air tightness / heat loss survey. Sure, we can guess and generalise what may be at play but without testing your house this is just futile. And without testing your house in your presence, you won't appreciate what is at play and where to target your efforts / money.

  • Registered Users Posts: 4,478 ✭✭✭wheres me jumpa


    Any recommended air tightness testers? I see companies specialising in just that. Will they call out specific works to be done based on the test?

  • Registered Users Posts: 2,823 ✭✭✭MicktheMan

    Location of your house would be useful 😉

    Could also try google with "heat loss survey" and your location.

  • Registered Users Posts: 4,478 ✭✭✭wheres me jumpa

    House is in Kilkenny if anyone has a recommendation.