Ah the good ol’ Irish cavity wall…

Ah, that ol’ staple of Irish construction – the blockwork cavity wall.

Still very much in use and prevalent and even still being used in certified Passivhaus construction.

Let’s have a little look back in history to see where we’ve come in what is a relatively short time…

Here’s one of the first cavity walls I’d have experience of in the UK with a brick & block cavity wall; zero insulation in cavity. Interesting too for just the 2″ of quilt at ceiling level.


Special thanks to GLC Good Practice Details 1979 – u value = 1.56W/m2K

Skip forward to when we were building our house in 2004 and current standard was 100mm cavity with 40mm Aerobord in cavity: u value = 0.49 W/m2K.

We thought we were doing well with 60mm high density insulation within a 100mm cavity; u value = 0.27W/m2K

We did this house in 2007 with additional internal drylining, u value = 0.19 W/m2K (first airtight construction we did btw with pro clima airtightness membrane on battens with airtightness test):

Sligo House

We then did this house in 2008 with a 150mm cavity, u value = 0.20 W/m2K ( pro clima airtightnesss tapes/membranes on masonry openings & ceilings )

Blower door test

Blower door test on 150mm cavity wall

Special thanks to Donal Gilroy at gilroyenergy.ie for the airtightness tests (photo is of his blower door assembly)

And this year we’ve been working on the first wider cavity walls at 200mm and beyond (u value = 0.16 W/m2K) which throws up all sorts of problems structurally and finishing in relation to cills, lintels, dpc’s…

As I’ve said before, I still believe we need to move away from the ubiquitous cavity wall; it’s reached it’s limit and we still need to go further. This can only be done with an adequately trained work force and a knowledgeable client base.

For further reading Joseph Little has written some excellent papers on this topic HERE

18 thoughts on “Ah the good ol’ Irish cavity wall…

  1. 50 or 75mm cavities with little or no insulation, became 100mm cavity with at least 50mm insulation, or fully filled… and as you say Mark, we are now going wider and wider, giving ourselves some interesting structural issues. I think the more airtight and thermally insulated we go, the more we will be looking at cladding type solutions rather than traditional construction methods.

    When I look back at my early (Mid 1980’s) hand drawn construction details (though they live in a tube out of reach most of the time) and compare them with the CAD drawings completed more recently, the differences are perhaps subtle to the untrained eye, but very interesting to those of us in the know!

    Loft insulation, once considered adequate at 100mm (or less!) laid between the ceiling joists is now laid between and over them (even under when an insulated plasterboard is used) to seemingly ever increasing depths, making walking through the loft more like a blindfolded moon walk requiring adequate H&S signage to warn you of the fragile ceiling below, between the joists you can no longer see!

    Closing the cavity at the top and below windows with a block or a brick and a bit of black plastic DPC… now we use a thermally insulated cavity closer such as Thermabate etc.

    Steel Lintels, once hollow, now packed with insulation.

    Concrete cantilevers and pieces of steel passing through the external envelope… now weird & wonderful ways to do the same but without a thermal bridge… all costing more of course!

    I remember at college I was told that there was no heat loss through the floor, only it’s perimeter… well, that seems to have gone out the window so to speak with the amount of insulation we put under a screed or slab these days… though P/A calculations do still support the theory in the main…

    And pressurisation… that was something we did to aircraft wasn’t it???

  2. I’m 47 (ish), loosing count of the years and have no reason to try and find out for sure… πŸ™‚

    Just flicked through my (almost antique) 1983 Eighth Impression of Chudley’s Construction Technology Volume 1 (First Impression was in 1973) and am shuddering (with cold and damp) at the construction details in there… which I remember copying and getting good marks for…

    Compare them with the warm cosy feeling that the details in my Chudley & Green Building Coinstruction Handbook (Ironically the Eighth Edition…) dated 2010 convey…

  3. I am still torn. About to build a new house and have been looking at timber frame for all the usual reasons. But ….
    Will it structural integrity of the house still be as good as using block/ concrete/poroton in 25 years time. The sharp intake of breath from those I speak to (OK, traditional Irish menfolk) when I say timber has raised genuine concerns. I have read loads about how many centuries humans have built timber frame dwellings but these days with airtight membranes, vapour barriers and all the other new technology sealing the walls, are we sure that my house will not develop some sort of rot in the timber frames in 25 years time (when I’m in my 80s!) and not in a position to afford an extensive re-build. Please convince me because I do like the timber frame approach for all the usual reasons.

    Or should I use Poroton or similar?

      1. Thanks for the reply but unfortunately it is still not the type of re-assurance I am after. My question, and I have been asking this for some months now, is can I be assured that my timber frame house will last as long as a block built house? That it will not fall down around my ears in 25 or 30 years time. And I don’t seem to be able to get any re-assurance on this, even from timber frame manufacturers.

          1. Marks

            Thanks once again for taking the time to reply. I looked at the link and you know, that is an oak frame house in Clare. And , as I said in my initial post here I know there are houses that were built centuries ago of timber frame but these are not modern softwood framed houses that have all the timber sealed behind multiple layers of material that stop the owner keeping an eye on what is going on (I have a timber classic cruiser nearly 50 years old and it is because I can get access to all parts that I can keep an eye on the timber and ensure I deal with any degradation before it gets too advanced). You are right of course, there are lots of timber frame houses over 25 years old, but not are all doing brilliantly (and I know of one couple who would never live in a timber frame house again because of the problems they had with their previous house). Although I would like to use timber frame, I still have not been able get the evidence or assurance (or insurance!) that will guarantee that such a method will last as well as traditional old cavity wall.

            That’s all I’m trying to find out. And maybe I won’t be able to get a definitive answer. But should I gamble with such a major part of my life, my home?

          2. I don’t think you’ll get a definitive answer; but there are stacks of softwood timber houses that are performing very well. I think there’s a big difference between a developer-built timber frame house and those that made on a more individual basis; especially now with current levels of insulation and airtightness.

            Bear in mind also that you need to consider the economics and available work-force and as I said this still leans towards the prevalence of blockwork cavity walls.

            Hope this helps


  4. If I was building my own house again, I would not use “traditional” construction. I would choose between timber or lightweight steel framing and err towards off site fabrication as much as possible. A few years ago, I would not have said the same thing…

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