How to install insulation under a tin roof?

Hi,

I am currently renovating my kitchen, which involves enclosing the back porch to build the kitchen out into this space for more room.

Before the plasterer sheets the ceiling and exterior walls, I'd like to install the insulation myself to save money. I'd like advice on what type of insulation to use for the ceiling and walls. The kitchen is a straight kitchen which will run along an external wall (not shown in the photo).

The photos show the rafters of the old porch roof. I live in a 1960s weatherboard house in Tamworth (warm temperate climate with hot summers and cool winters).

The ceiling is insulated with bats (guessing from the 1980s) and there is no sarking or other lining. As a result I have some problems with mould forming occasionally on the roof (which I clean regularly)

How do you suggest I insulate this roof?

Regarding the walls, they are not framed up yet, but would like some advice on what to use for insulation there. At least in that instance I'll be able to install sarking.

Many thanks!

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EricL

Hello @javajive

My best advice when it comes to insulation is, the higher the "R" value the higher the insulation properties will be. But timber gap, insulation space and your budget all play a part in your choice of insulation to install. For example, if the gap between your rafters is 400mm then I would suggest using the Earthwool R4.0 195 x 430 x 1160mm 7.5m² Insulation Ceiling Batt - 15 Pack which covers an area of 7.5m2. It does not have the highest "R" value, but it fits snugly into your existing space.

The same rules apply to your wall, you may want to install the thickest insulation batt, but if there is limited space forcing larger pieces of batt becomes counter-productive.

Here are some handy step-by-step guides:

Please remember to wear personal protection such as disposable coveralls, gloves, goggles and a mask while installing insulation.

If you have any other questions we can help with, please let us know.

Eric

javajive

Thanks Eric, that's very useful information.

As you can see in the photo, there isn't much room between the valley of the roof and the underside of the joist - the picture shows it a bit smaller, I think it's more like 160mm total depth. Do you know if there are batts that will fit this space and still have an air gap of 20mm between the top of batt and the roof? I couldn't see anything on the Bunnings website.

Otherwise, is there another suitable alternative - eg foil boards so I can achieve the air space? Plasterboard will be applied directly underneath. My plan is also to install downlights (have already run the cabling). Would I just cut around the foil board for the lights?

Thank you.

MitchellMc

Hi @javajive,

Eric's reference of 400mm was between the rafters, not the depth required for insulation. With your required 20mm gap, you'd need a batt that was less than 140mm thick. You'd probably need to go for something like the Bradford R2.5 1160 x 430 x 140mm 9m2 Gold Ceiling Batts, which are 140mm thick. Alternatively, you could use wall batts in the ceiling, which are typically much thinner than ceiling insulation.

You could use Foilboard if you wished. You could cut the Foilboard for the lights, or my preference would be to position it higher up in the 140mm cavity so it doesn't need to be. The foil board is only 25mm thick, and although that is great when you have very little space, it doesn't perform as well as thicker insulation, such as the ceiling batts I've linked above.

A note to our New Zealand members: The use of foil insulation products is prohibited.

Please let me know if you have any questions.

Mitchell

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