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renovation questions: insulation / airtightness / MHRV

  • 16-03-2012 5:41pm
    Registered Users Posts: 1,372 ✭✭✭


    I'm currently working with an architect to plan the renovation of a 1960's house.

    It needs a lot of work - new windows/insulation/heating system etc - it has cavity blocks, suspended timber floor, single glazed windows.

    I'm trying to weigh off how much effort it's worth going to to get the house airtight and well insulated - I'd like to put in a MHRV unit as I've experienced how well they work at keeping the air fresh and dry.

    What type of things should I be looking at particularly in relation to
    - insulating the ground floor (apparently it's a big job, is it necessary?)
    - making sure the walls are airtight ?

    I'm not necessarily looking for Passive House type levels of airtightness but I do want to aim for a reasonable BER (and cost). My architect hasn't previously specified a domestic MHRV so I'm trying to get information together for him (including recommended suppliers).

    Any information and suggestions you have will be gratefully accepted...


  • Moderators, Home & Garden Moderators Posts: 10,133 Mod ✭✭✭✭BryanF

    insualting and air-tightness of the suspended ground floor, is not that big a job, and is worth doing. If your architect is not familiar with air-tightness or MVHR bring in an air-tightness specialist/ someone familiar with the detailing required. there are some strange misconceptions out-there at moment regarding 'passive levels' and there cost - imo if your not willing to achieve the best of air-tightness levels consider mechanical ventilation without the heat recovery. the airtightness Limit value in a retro-fit passive house is n50 ≤ 1.0 h , if your doing the amount of work you suggest, why not aim for these levels..

  • Registered Users Posts: 586 ✭✭✭Wally Runs

    OP we did this with 1970 cavity block; air tightness, internal insulation, MHRV, underfloor heating (suspended wooden floor), new windows etc. Home went from G+++++ to B1. Now much of the advice came from the various suppliers who were very willing to work with contractors. I would have to dig around to find the details as it was 3 years ago now. If you are in or near Dublin try the upcoming energy show?

  • Registered Users Posts: 1,372 ✭✭✭silverside

    Thank you both.

    @Wally Runs, thanks - it's good to hear practical experiences, if you can recall any of the info it would be great if you could share it?

    The Energy Show you mentioned does look interesting, although it doesn't seem aimed at private individuals.

  • Registered Users Posts: 586 ✭✭✭Wally Runs

    OP I will do on the stuff. You can drop in to the Energy Show, use your work as reason? See if you can get your QS or Arch to come with you (promise them a cup of tea). I assume you are in Dublin. You really just want to see what is available. Get some ideas. I have a spare pass if all else fails.

  • Registered Users Posts: 34 suttonca2597

    Renovating a 1970's house at present and installing a mhrv and just had air tightness test done today before slabbing begins.

    We had to strip back old plaster board from majority of external walls but basically what we did to save on having to fit an air tight membrane around the whole envelope was to plaster skim any unplastered walls (any already plastered were fine) and place a membrane only on the ceiling, sealing up to the membrane with the skim on the walls.

    We also taped very carefully using air tight tapes and mastics around all windows, pipes, etc going through external walls.

    We used a gypsum hard coat on the walls but I'm told sand and cement would be just fine. If the walls are already plastered you can just fill in any problem areas/ holes.

    We are now going to put a 92.5mm insulated plasterboard on the walls.

    The air tightness test result was 3.5 m3/m2/hr which is very good and will only get better after the slabs are up and walls are skimmed.

    The guy doing the test said less than 5 m3/m2/hr is best when installing a mhrv.

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  • Moderators, Home & Garden Moderators Posts: 10,133 Mod ✭✭✭✭BryanF

    The guy doing the test said less than 5 m3/m2/hr is best when installing a mhrv.
    less than 5 is crap
    less than 3 is ok
    less than 2 is great
    less than 1 is best