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  • Susie

Add insulation without pulling apart the walls

We all know that older houses are always colder and draughtier. But at what point can you say enough is enough to both the wintry draught that hits you in the face when you wake up, and to losing that expensive warmth the minute you turn off the heating supply?

As we approached our second winter in our weatherboard 1910 villa here in New Zealand, the original rooms at the front were already significantly colder. Having drilled some holes in the wall to have a look-see, we knew why they were so cold - because there was a big old gap of NOTHING!

Our walls have plasterboard (also known as GIB here in NZ, Gyprock in Oz and drywall in the US) facing into the room, which sat in front of the original wall. This original wall is actually made up of horizontal wooden boards. These are called 'sarking' in the UK/NZ, or shiplap in the US. Then there's a gap, before the external weatherboards, with not a smidgen of insulation in sight.

In the 1900s, walls were built from horizontal wood planks (sarking in the UK/NZ, or shiplap in the US) that were often put in place wet. A thin hessian 'scrim' sat in front, then lining paper

This is because it used to be monumentally disruptive to retrofit insulation. It would require removal of the glued-on plasterboard, then cutting out every third sarking plank and scooching batt insulation blindly into place, before replacing the sarking, adding new plasterboard, then plastering or re-lining, then painting. PHEW! Or waiting until the external weatherboards need replacing but either way, huge job! No wonder it's often neglected.

But now there is an alternative. It's called 'blown-in insulation' and it's exactly what it says on the can. They drill regular holes in your walls, blow in loose insulation until it's packed tightly, fill the holes, check there are no gaps with thermal imaging, and leave you to re-decorate. Two large rooms took my guys 4 hours work. They were very tidy too.

Of course, it still needs attention afterwards. Our lounge was left with 97 holes to sand, fill, prime and re-paint. It's still a pain in the backside, but this brings it to a level the home renovator/decorator (like me!) can deal with. I've managed to return the room to its former glory in 4 or 5 days, and most of that was waiting, not working - i.e. drying time for putty and paint.

You might prefer them to drill through your external walls, but as we have weatherboards, I felt this might open us up to the possibility of leaks. (They can drill through any type of external wall) Plus our house is on a slope so not all the walls would be accessible without scaffolding, and external painting is too professional a job for a home renovator like me.

Retrofitting insulation in Auckland requires council permission, but will add value as details go on your property file. Your installer will prepare/submit the forms which take under 3 weeks for approval. Council take a fee of course, but the installer self-certifies on completion

There were two areas that I researched heavily. Human health and house health.

This insulation is a mineral wool and formaldehyde-free. No carcinogens. No toxins. It's water repellant, and CodeMark certified in NZ to be used in old houses with or without building paper.

We do not have building paper in those rooms. Cynics might argue that we've changed the integrity of the house, and we'll face issues in the future, but my research would entirely disagree.

Obviously, the cost of this may be prohibitive for some, but we chose to spend money here because 1) we are total believers in insulation, 2) we did lots of research on all our options, 3) we had quotes to insulate the traditional way which were much more expensive and time-consuming than this, 4) we knew it was going to be a dramatic difference as we were going from no insulation to complete insulation, 5) these spaces matter to us as one is the master bed and the other is our everyday lounge.

So, the big question - has it changed anything? YES, DRAMATICALLY! The rooms have a totally different feel to them now. Both thermal and sound are vastly improved. Cocoon-like even. We didn't think the sound would change as much as it did, but we can barely hear outside noise now, despite having single-glazing.

In fact, this insulation had to combat lots of draughts to be effective: 1) 4 double-hung timber sash windows (lots of air gaps) 2) old plate glass that is only 3mm thick 3) 3.4m high ceilings 4) an original cast iron fireplace with a damper that doesn't quite shut 5) and currently the original floorboards are exposed which are hardly air-tight (although we do have underfloor insulation) 6) there's a big gap under the door from when there was carpet.

Despite all this, the improvement feels as much as 8-10 degrees in my opinion. Better still, once the heating is on, (did you spot the radiator? How very English) the room warms up way faster and then retains that heat very well. Imagine how warm it'll be once all the reno jobs are done!

Here in NZ, retrofitting double glazing is crazy expensive, so be sure to look into insulating beforehand. We no longer feel the need to get double glazing. I'm amazed to be saying that.

And suddenly, we're more in love with that part of our old house.

Note to self: 1) I have not entirely mastered the art of filling and sanding holes. I can still see a few rings around some holes after 3 rounds of filling, but you have to know where to look. My husband kindly claims to see none. 2) The blue wall colour is stunning but does show every imperfection of the wall. 3) dogs are no help when decorating.

Our installer was Harley Turner from Insulmax in Auckland. You can find out more at (This is not a sponsored post, we just thoroughly recommend them!)

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