Kieran McCarthy: 'Our old home has a G BER even after it was upgraded'

Suspect ‘DIY’ wall insulation may conceal a whole host of problems
Kieran McCarthy: 'Our old home has a G BER even after it was upgraded'

A G rating is a pity because it suggests that you have lost some of the internal features whilst not benefiting from a dramatic improvement in energy efficiency.

Hi Kieran.

We have bought an older-era home in the country that the previous owners did some upgrade works on.

It’s pretty well insulated now in the attic, and most external walls have been slabbed with 50mm insulated plasterboard which appear to have been ‘stuck’ to the old walls, a mix of brick, block and some stone too.

I read that older stone walls should be allowed to ‘breathe” but that can’t happen in this case?

There is no sign of any mould or damp inside or outside at present, but we worry about the years ahead.

Should we remove this and replace it, or take our chances and leave it as is unless some issue manifests itself, which clearly would be our preference given the disruption and costs after only recently buying it.

It got a G BER when assessed for sale as the slabbing had been a DIY job and the BER assessor didn’t examine its depth, we were told. Thanks, Kieran.

Ann and Andrew

Ballyhooly, Cork

Hi Ann, Andrew,

Thank you for this question. So, you are the proud owners of an old country home which I am guessing is brimming with character and originality.

You mentioned that there has been some insulation added but that the house is still a G Ber.

This is a pity because it suggests that you have lost some of the internal features whilst not benefiting from a dramatic improvement in energy efficiency. So, what next for your home?

Firstly, as you are proposing to work on more than 25% of your external envelope (outer shell) of your home, you will need to comply with the relatively new NZEB regulations.

This broadly means that you will need to bring your entire home up to a B2 BER rating.

This will of course mean reviewing your heating system, external windows, airtightness and, of course, insulation, but let’s concentrate on the insulation for now.

Kieran McCarthy: 'Even though you can’t see any mould on these walls I would be very surprised if there aren’t significant issues buried in the fabric'
Kieran McCarthy: 'Even though you can’t see any mould on these walls I would be very surprised if there aren’t significant issues buried in the fabric'

The slight benefit in the fact that the inside faces of your external walls have been insulated already is that the features here have already been removed (so you haven’t had a chance to get emotionally attached to them!).

Even though you can’t see any mould on these walls I would be very surprised if there aren’t significant issues buried in the fabric of this ‘newly applied’ finish, given that this was applied in a handyman fashion.

The two key issues here are that the outside face of the insulation has not been allowed to breathe and the stonework of your building may also suffer from a lack of breathability too, though this is of lesser concern if the original lime render is still in place externally. Let me explain.

The outer face of your insulated plasterboard is where the dew point lies, ie where condensation occurs so there will be moisture sitting here. If this is not adequately ventilated you are trapping this moisture forever and you are promoting mould and fungal growth in this hidden area.

My second but lesser concern is that the stonework, where evident, on your external walls also needs to breathe but assuming you have the original lime render, which is itself breathable, in place externally, this is likely sufficient for the stonework.

The solution I would propose is to remove the insulated plasterboard and place a separation ‘stud’ framing on these walls and then to install a new insulated plasterboard slab with the required insulation thickness (as calculated by your BER Assessor).

You may opt for a high-density insulated slab here to provide a greater insulating value with a lesser thickness but you will need specialist advice here.

Check to ensure you have at least 300mm quilt insultation in your attic.
Check to ensure you have at least 300mm quilt insultation in your attic.

Now that you have a new ‘cavity’ between your insulation layer and your old wall you can ventilate this cavity to allow for a level of airflow to ventilate this area.

Given that you have stonework in place too, it would be good to ensure that your existing internal plaster layer is ideally breathable, as we mentioned earlier.

One other element I would look at is your attic. I know you mentioned that it has been well insulated but check to ensure you have at least 300mm quilt (assuming your top floor ceilings are flat).

Also, ensure that the previous owners maintained a level of ventilation for the roof timbers.

The reason I bring this up is that if the insulation here is less than this, you may still be losing a lot of heat through your roof, as well as your walls.

With these measures installed and aligned with the advice of your BER Assessor, you should have a dramatically improved home in terms of insulation and heat loss prevention.

This will help you keep heat in winter and of course, keep your home cool in those precious warm summer months.

Kieran McCarthy is a Building Engineer with KMC Homes, serving Cork and Limerick. He is also co-presenter of the RTÉ property show Cheap Irish Homes. Check out Kieran’s new podcast, Built Around You ‘dedicated to helping you build, renovate or upgrade your home’ released every Sunday night at 8pm on Apple Podcasts and Spotify and on the Built Around You Youtube channel. For more information or to take part in the podcast and share your home build story, follow Kieran on instagram @kierankmc

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