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Thickness of Ground Floor Insulation for UFH?

  • 02-11-2021 6:22pm
    Registered Users Posts: 15 PC00123424

    Have been advised to go for 150mm PIR rigid board for ground floor insulation on the raft. Wondering if there are any possible options to go for less thick, maybe 100mm or 75, or is 150mm PIR correct?



  • Moderators, Home & Garden Moderators, Science, Health & Environment Moderators Posts: 16,291 Mod ✭✭✭✭ DOCARCH

    I doubt 75mm or 100mm will give you the right u-value? For refurb I'd be going for 125mm and for new build 150mm.

  • Registered Users Posts: 15 PC00123424


  • Registered Users Posts: 2,146 ✭✭✭ Yellow_Fern

    There are materials that will allow you to go thinner than PIR but they are very rarely used due to cost

  • Registered Users Posts: 808 ✭✭✭ monseiur

    If new build go for 150mm - but if you have central heating pipes and other service ducts criss crossing the slab, instead of one board 150mm thick go for 2 boards 60mm and 90mm. The 60mm board will be cut to fit between pipes etc and the 90mm will go on top with staggered joints etc. - a much better job.


  • Registered Users Posts: 15 PC00123424

    Thanks for your replies. No central heating pipes or much else of anything else down there so in this case think we'll stick with the single 150mm thickness board.

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  • Registered Users Posts: 1,074 ✭✭✭ Roger Mellie Man on the Telly

    For UFH you must achieve a maximum u-value of 0.15W/m2K to achieve prima facie compliance with Building Regulations.

    To determine the thickness of your chosen insulation type, you need to carry out a floor U-value calculation using the perimeter / area ratio for your particular design.