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Insulating external walls of 1930s cottage

  • 04-02-2022 3:52pm
    Registered Users Posts: 4 Pman


    Should I insulate the inside face or external face . Is there much of a difference regarding heat retention ? The wall is stone rubble and mortar.

    Thanks for all opinions.


  • Registered Users Posts: 4,401 ✭✭✭ Gusser09

    Ewi is the best insulation solution available. Heat retention is savage. I have it. Heating house for 400 quid a year.

  • Registered Users Posts: 3,638 ✭✭✭ washman3

    Ewi + External wall insulation. Can you elaborate more about your type of house.? ie age, wall type, floor/ceiling insulation? What heat source are you using? Thanks.

  • Registered Users Posts: 746 ✭✭✭ bemak

    Rubble stone walls need to be able to breathe so if you wanted to do this properly you would be looking at removing the existing render as it's likely to be sand and cement and replace it with lime render externally and insulating lime render or hemp or similar breathable material internally. On top of that you should install perimeter drainage to help prevent water runoff from being soaked up at the base of the walls. New rainwater goods would be essential too. That's probably the best thing to do but it is expensive.

    One thing you could omit from the above is the removal of the external sand and cement render. You could accept this, make sure it's in good shape but you're relying then on the walls drying to the inside. Which they should do eventually.

    Looking at doing this for a project myself at the moment and I'll probably go with the latter solution for now. It still gives me the option to remove the external render in the future should I still experience problems.

    I've seen people use EWI in similar situations. I'm not sure about it. You have a lot of wall to heat before it hits the insulation. EWI doesn't rectify dampness in the wall either. In fact, it will probably make things worse in that regard

  • Registered Users Posts: 290 ✭✭ kildarejohn

    As Bemak noted, rubble stone walls need to be able to breath. Therefore it is important to use BREATHABLE external wall insulation, e.g. Rockwool, and not PU foam insulations which are not breathable. Beamal's points on drainage are important. Also note that while the main EWI should be Rockwool, the bottom 300mm or so needs to be polystyrene foam as the Rockwool would allow rising damp to rise in the walls as it would bridge the damp proof course (if any). Above based on personal experience.

    As Bemak says "you have a lot of wall to heat before you hit the insulation". But this is not a bad thing - it is "Thermal Mass" - this means your house may take a longer time to heat up, but it also stays warmer for longer and maintains an even temperature

  • Registered Users Posts: 4,401 ✭✭✭ Gusser09

    Hi Apologies for delay in getting back to you.

    Age - 1985 3 bed Semi D.

    No floor insulation.

    Attic was insulated when EWI was done. Was pointless doing the EWI without the Attic getting done.

    Heating - Kero.

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  • Registered Users Posts: 3,638 ✭✭✭ washman3