How to add insulation to cathedral ceiling?

Question

Hi there, I am wanting to insulate the living and kitchen area in this open plan unit. It gets very hot in summer in the Lismore NSW area. HOW CAN I INSTALL INSULATION  from the inside? The roof is made of concrete tiles so not an option to do it from the rooftop.

Kaeren27 · Answer

thanks very much Jacob! That’s sounds like a great solution!

JacobZ · Answer

Hi @Kaeren27,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Since your rafters and beams are exposed, you’ve actually got a good opportunity to install insulation from the inside. You can fit insulation directly between the rafters.

A common option is standard glasswool batts such as Earthwool. These are designed and sized to fit between rafters. They provide solid thermal performance, and are a cost-effective way to reduce heat coming through the roof. For your area, you’d generally be looking at something around R3.5 to R4.0 in the ceiling to help manage summer heat. Make sure the batts are installed snugly with no gaps, and you can use insulation strapping to hold them securely in place between the rafters.

Another option is rigid foam insulation like Foilboard. It is easy to cut to size and can be installed neatly between the rafters using the Foilboard Flexifast Fasteners. Check out the Cathedral or Skillion Ceiling page for further information. The installation guide can be found in the downloads tab.

If you’re after a cleaner, more finished look and even better performance, you could also install insulation between the rafters and then add a plasterboard ceiling underneath. This creates a sealed cavity which improves efficiency and gives you a smooth ceiling finish.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

A note for our New Zealand readers - The use of foil faced insulation has been banned in New Zealand.