Stone/Brick walls and insulation

Just putting this out there to see if anyone has come across it before.

Our home is built from stone and brick. It has a cavity between the two, but it's very irregular as you would expect, and the cavity is completely bridged at any external door or window.

We've been replacing windows as we renovate, and are using double glazed/argon/low-e units where possible. Some are without argon, but lets not cry about that :)

So, now we have some unrenovated rooms with new high efficiency glazing, but with uninsulated walls. Using my Jaycar QM7221 Infrared thermometer, I can now see that on a cold day, those walls are 4 to 5 degrees colder than the surface of the window (you actually don't need the thermometer, you can feel the difference with your hand) This results in the heating running hard and having limited effect, so I'm starting to dream up ways of getting insulated external walls.

To date, 3 different approaches have been proposed:

1) Apply insulation to the cavity. Either beanbag balls, fibre, or expanding foam.

Not that happy eith this because I'm not convinced it will work as well as the sellers say. It might work ok for a standard brick cavity, but we don't have that.

2) Apply Insulation to the external faces of the building.

This has become a quite popular method overseas, and it does have advantages by keeping a large thermal mass inside the building. Unfortunately, it also completely changes the look of the place, and both SWMBO and I couldn't stomach that. I do think this is the best technical solution though. If our place looked like rubbish outside, I'd do it.

3) Insulate the walls internally.

This is starting to look like my preferred option. There are a number of suggested methods, but the one I am currently liking is using an expanded poly board which is RFL coated on both sides called foilboard. One of the fitting methods calls for a batten on the wall, foilboard on top of that, followed by another batten and then plasterboard. I'm thinking that the airgap between the wall and the board will be good for moisture control, and the double air gaps along with the poly board will give quite good R rating, bringing the house upto or above minimum suggested rating. The RFL will be an added benefit in summer when the wall heats up (as it does).

Downsides are that the window reveals go from 200mm to 270mm or thereabouts, the rooms will require redecorating, (cornice, plaster, architraves, paint etc) and of course, expense. Redecorating is not a biggie for us, as all of the effected areas have not yet been renovated and are currently in their worn 1970's grandeur.

When we do this, it has to be done right because I'm not doing it again. :no: Do it once, do it right.

All comments and alternate suggestions welcome.

woodbe.


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