Can you use underfloor insulation for a ceiling?

[mervb]

Can I use foam under floor foam insulation for the ceiling of my garage.

[EricL]

Hello @mervb

Welcome to the Bunnings Workshop community. It's wonderful to have you join us, and thank you for sharing your question about underfloor insulation being used for the ceiling.

The quick answer is yes, however, it will not provide the same kind of insulation as a dedicated foam ceiling insulation. But before we go any further, would you be able to show us which floor foam insulation you're planning to use? We just want to know what type you'll be using so that we can give you a comprehensive recommendation.

In general ceiling insulation tends to be much thicker and has a higher "R" value than floor insulation. Whereas floor insulation is shaped to go between the floor studs and tends to be narrower than the ceiling insulation and has a lower "R" value.

The "R" value generally refers to the thickness of the insulation. The higher the number the thicker the insulation is.

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

Eric

[mervb]

Thanks for that. I don't have enough leftover to do the job that way now. Instead I plan to use foam board. Thanks

[EricL]

Hello @mervb

Thanks for posting that photo of the roof you're trying to insulate. It must get awfully hot in the summertime, I suggest using Ametalin 1500mm x 30m SilverSark xR HD Extra R-value Reflective Roof and Wall Insulation. It's specifically designed for metal roofs and creates a reflective barrier against radiating heat, however, you'll need to make a timber frame in order to install it.  

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

Eric

[EricL]

Hello @mervb 

Just a friendly reminder that if you are in NZ, I'm afraid the Ametalin product is not available to you as an option. Instead, I recommend using standard foam insulation for your roof.

Eric

Important note for our New Zealand readers:

The New Zealand Ministry of Business, Innovation and Employment (MBIE) issued a ban on the use of foil insulation in July 2016. The ban applies to the installation and/or repair of foil insulation in residential buildings. More information is available here: Foil insulation ban | Building Performance.

[mervb]

Eric, thanks for the tip, but building a cieling structure without putting holes in the roof or heavy cross beams would be quite expensive. I cheched out your suggested insulation this morning and it seems to be most suitable, howevef, I have a large quantity of magnetic hooks which I'm planing to glue (with something like JB weld) to the undersde on the metal roof (magnetic so the hook is held in place while resin setting). From these hooks I plan to hang a foamboard false ceiling  ... hope that makes sense ... the hooks can support some lightweight ceiling lights. 😆