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Insulating old house

  • 22-03-2022 12:45pm
    Registered Users Posts: 2,206 ✭✭✭ Girly Gal

    Hi all,

    Looking for some advice on insulating an old single story house. The house is 70 years old, high pitched roof, single leaf wall (concrete & stone) construction. The house currently has no insulation, ceilings also need replacing. The house has a solid fuel range central heating system, which will remain. External wall insulation is not an option.

    Keeping the above in mind what's the best value for money way to insulate the attic and rooms; materials & methods, etc. Any advice appreciated.


  • Registered Users Posts: 733 ✭✭✭ bemak

    Common topic on here. If the walls are built predominantly of stone you'll need to apply a breathable insulation internally like an insulating lime render or hemp. There are many voices proclaiming which works better so you'll have to decide on what the best option is for you. I looked into hemp recently and if you have enough room to apply it to the internal face of the external walls it looks to be a very good product. Any breathable solutions require a lot of prep (if the walls are stone internally). You need to take off the internal render before applying any of the products mentioned. You're wasting your time otherwise in my opinion. A lot of people would have put up insulated slabs onto stonework and they'd swear by it but it's just a problem waiting to happen.

    If the walls are blockwork internally you could look at slabbing it with insulation backed plasterboard. I would leave a cavity behind between the slabs and the walls to allow air to circulate. You'll need to add vents to assist with this also.

    The quick win is the attic insulation. Just make sure the roofspace is well ventilated to avoid condensation etc.

    Floors are trickier. It's very costly to put in a new slab and I often wonder if the cost is worth it considering the improvement in performance.

    Good windows, installed properly to avoid draughts will also improve the perceived comfort levels.

    If the walls are stone on the outside, I'd consider putting in a french drain to help take the water away from the base of the walls.

    Good rainwater goods are vital if you want to avoid water ingress.

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

    Girly gal.

    If the house is 70 years old, then in was built in the mid 50’s. At that time in Ireland most houses in urban areas were constructed with solid concrete block walls, with a Damp Proof Course at floor level.

    Please post photos of the stonework.

    Is there any rising dampness or ingress of rainwater apparent in the walls. This damp will present in the form of Efflorescent Salts causing the paint to lift off the wall. This is a problem.

    Black/ olive colour mould growth on the paintwork on the wall is Condensation Mould Growth. This is not a problem.

    Please post photos.

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


    How do you propose to create a cavity between the walls and the proposed insulation, for air to circulate.

  • Registered Users Posts: 733 ✭✭✭ bemak

    Battens on the wall to create a cavity between the wall face and the plasterboard. It's more for an air gap than air circulation. Maybe I wasn't explaining properly. Cavity can be used to run services too.

  • Registered Users Posts: 2,771 ✭✭✭ Ginger83

    We renovated an old limestone building and what we did was build stud partition walls inside. We put rigid insulation in the partition walls and left a gap between them and the original stone walls. When the roof was replaced vents in the soffit allows air to circulate. The downside was we lost a few inches of room space but house is very warm.

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

    We do not know for certain if there is rising dampness or ingress of rainwater in these 70 year old walls

    Battens on the wall on a 70 year old concrete block/ stone wall in a house may possibly end up with Dry Rot.

    If the battens are at 400 mm centres, then Ventilation will be required at the top and bottom at every 400 mm to vent each of the individual cavies created by each pair of battens.

    No Construction Professional with Professional Indemnity Insurance would specify or certify this.

  • Registered Users Posts: 733 ✭✭✭ bemak

    i would always put dpc between the battens and wall to reduce the risk of rot as much as possible.

    the battens needn't be continuous either so you don't necessarily need to vent every cavity.

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

    Most timber is contaminated with Dry Roy spores.

    Dry Rot (Serpula lacrymans) needs Timber, lack of fresh air, and 22% Moisture Content (MC) to germinate.

    Moisture is highly intelligent and will evaporate from the wall in to the cavities between the battens and vertical DPC. It will increase the Relative Humidity in the cavity and increase the MC of the timber from 16% to above 22% and the Dry Rot spores will germinate

    Your Specification is an absolute no no.

    Persons without knowledge (or a little knowledge) of Building Science, should retain a Building Surveyor.

  • Registered Users Posts: 2,206 ✭✭✭ Girly Gal

    Thanks for all the replies, there is no rainwater or moisture ingress on most of the house apart from 1 room which I think is caused by the window in that room. There is some black/ olive mould in another room -how do we get rid of this so it doesn't return?

    The stonewalls are not exposed- they are plastered outside (replastered about 15 years ago) and a rough render finish internally (when house originally built) - don't know what material used.

    Regarding attic insulation what's the best type to get and what thickness should we install.

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

    Girly gal

    The black / olive mould growth is Condensation Mould growth. Wash it off with water and household bleach 3 water to 1 bleach.

    The walls should be checked by a construction professional with a Moisture Meter to ensure that there is no rising damp or ingress of rainwater or any form of dampness.

    if the internal face of the walls are dry , then you can apply /fix Insulated slabs to the inner face of the walls.

    if the walls are solid walls, then to comply with the Building Regulations you need to achieve a maximum U Value 0.35 W/m2/degree C/ hr.

    the present solid walls will have a U Value of approx 2.1 W/m2/degreeC. So you will be reducing the current heat loss down to approx 1/6 of what it is now

    you could use Kingspan Kooltherm K118 Insulated Plasterboard with 52.5 mm insulation fixed with adhesive and nylon mushroom fixings

    if you use metal mushroom fixings,- because the solid wall will be a cold bridge - condensation mould growth may appear on the 3 mm plaster skim over the tops of the metal fixings

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


    if there is dampness on the inner face of the external walls caused by rising damp, it needs to be investigated to reduce or stop it if possible.

    if it is caused by ingress of rainwater then that should be investigated and stopped.

    A new floor could be installed. Kept approx 70 mm from the walls below floor level, to form a cavity between the edges of the 150 mm floor and external walls.

    The DPM /Radon is brought up the side perimeter of the concrete floor and folded on to the to the top surface of the floor.

    Construct a metal Stud Partition on top of a DPC on top of the DPM/Radon. This can be a 100 or 150 metal Stud Partition, which is approx minimum of 50 mm away (cavity) from the external walls, to be fitted in accordance with the manufactures instructions.

    This cavity between the external wall and Stud partition must be adequately ventilated in accordance with the Building Regulations.

    Fit approved Insulation in to the metal stud partition in accordance with the manufactures instructions, Fit Services etc. and fix Airtightness membrane, and fix plasterboard slabs and apply skim of plaster.

    There will also be a need to attend to many other details of items of works.

    Any damp - don’t use timber. ☹️☹️☹️

  • Registered Users Posts: 733 ✭✭✭ bemak

    Ya I actually used metal studs 25mm off an existing wall on my own house, worked great. The purpose was for better acoustic separation so there was a different spec on the PB etc. But it would be a similar idea to what you're saying there.

    Every house is different and you really need to consider the overall approach first rather than looking at everything as individual problems.

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

    Yes bemak, every house is totally different.

    For many past projects, I advised the clients to demolish the old house and construct a new building.

  • Registered Users Posts: 733 ✭✭✭ bemak

    Definitely better value for money. Seems a shame though in a lot of instances

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

    Very old houses were built in different eras with different requirements etc.

    Most were not constructed to get the best benefits of the Sun or views

    Carrying out major changes to old houses, has a lot of unknowns and is usually unquantifiable by Quantity Surveyor etc and is very expensive.

    The Layout and room sizes are not suitable for todays housing needs.

    in many cases it is best to demolish them and construct a new building to the Clients design, because they are making their biggest investment.

  • Registered Users Posts: 2,206 ✭✭✭ Girly Gal

    Thanks for the replies, alot of good advice about the walls, will likely go down the metal stud wall with cavity route as described above. We definitely won't be knocking the house as we are happy with the layout and can't afford a rebuild even if we wanted to. Regarding the attic insulation what's the best option/method here?

  • Registered Users Posts: 290 ✭✭ Biker1

    You would be advised to get a condensation risk analysis carried out based on the proposed insulation build-up. I'm sure you don't want mould build up in your building fabric and eventually making it's way inside.

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

    Girly gal.

    You are a good decision maker, and that is all that is required for these refurbishment works

    Dont waste money on carrying out any Condensation risk analysis.

    Insulate the Attic with 300 mm of rolls of attic insulation.

    Ensure adequate ventilation of the attic to prevent surface condensation. In winter time this condensation will be visible on the underside of the felt/ membrane. If it’s not visible there then the attic is adequately ventilated.

    Phone or email the Irish Insulation manufactures for advice. They give excellent advice to comply with the Building Regulations, and will give you detailed information to print off, etc.

    Enjoy the renovations works.

  • Registered Users Posts: 2,206 ✭✭✭ Girly Gal

    Thanks for all the advice. In relation to the Irish Insulation manufacturers, are you talking about insulation manufacturers in general or is there a specific company or organisation called Irish Insulation manufacturers- I 've googled and it lists different insulation manufacturers.

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

    Any of the Irish Insulation companies have Technical persons to provide help by phone or email.

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