How to add insulation question to a small house?

Question

hi there - we gave bought a very small house in the country - 69sq. The exterior is corrugated iron sheets and the interior is plaster sheets. I dont expect there is insulation. I plan to add floor to ceiling vertical panel boards (sort of ship lap style i think). I am wondering if there is an insulation solution that i could add to the walls before i panel that will not reduce the size of each room too much - they are tiny. Does anyone have any ideas or hacks for this - i understand this may not be best / common practice but wondering if there is an alternative to dismantling the current structure - given i will be adding another layer anyhow. Any ideas or hacks would be really appreciated.

MitchellMc · Answer

Insulation is something many DIYers can do @KPD, but it really depends on the situation. If you have easy access, like open wall cavities during a renovation or a roof space, then installing insulation batts is generally quite manageable with basic tools and careful handling. It mostly involves measuring, cutting to fit, and placing the batts snugly between studs or joists without compressing them.

Where it becomes more difficult is in finished walls, like in your case. Retrofitting insulation into enclosed cavities without removing wall linings can be tricky and is often better suited to professionals, especially if you’re considering blown-in insulation. There are also important considerations like moisture control, ventilation, and making sure the insulation is installed correctly to actually perform as intended.

Safety is another factor to keep in mind. You’ll want to use appropriate PPE like gloves, long sleeves, eye protection, and a mask, particularly with fibreglass products. And as mentioned earlier, always check for asbestos before disturbing any older wall or ceiling linings.

So yes, DIY insulation is definitely possible in the right scenario, but for closed walls or more complex setups, getting a professional involved is often the safer and more effective option.

Mitchell

KPD · Answer

That is really helpful and thank you. I will check out the resources. Is insulation something that DIYers can do generally? :-)

MitchellMc · Answer

HI @KPD,

There isn’t really a thin insulation product that will make a noticeable difference in a setup like yours. Most insulation works by trapping air, which requires thickness, so anything only a few millimetres to around 10 mm thick will have very limited impact on keeping heat in during winter or out during summer, especially with corrugated iron cladding, which transfers heat quite easily. While products like foilboard panels do exist and can be installed under your new wall panelling, they’re not typically designed to go over existing wall linings and their performance is modest compared to proper cavity insulation.

The most effective solution is still to remove the internal wall sheeting and install bulk insulation, such as fibreglass or polyester batts, into the wall cavity before relining or adding your panels. That’s what will give you a meaningful improvement in comfort. If you’re trying to avoid removing the walls sheets, a compromise would be blown-in insulation, where small holes are drilled and insulation is pumped into the cavity. This can provide decent coverage without full demolition, though results depend on how well the cavities can be filled.

Before doing any drilling, cutting, or fixing into existing wall sheets, it’s important to check whether they contain asbestos, as this was commonly used in older homes. Even small disturbances like drilling can be hazardous if asbestos is present, so testing first is strongly recommended.

For anyone in New Zealand, foil-based insulation products are prohibited from use.

Here are some helpful guides: How to insulate walls, How to top up your roof insulation and Everything you need to know about insulation. Also, here's another guide on How to winter-proof your home. Apart from having adequate insulation, heat can be lost through gaps and sealing them can improve the home's overall ability to retain heat. In some situations, you might see more improvement from sealing gaps, than you would by adding insulation.

Please let me know if you have any questions.

Mitchell