How to add underfloor insulation?

edechalain

Hi to all,

I live in a slightly elevated home .

The cold from the earth underneath comes right through the floorboards and tiles/carpets.

I am contemplating installing styrofoam sheets under the floorboards. Is this the best and easiest

option or is there a better recommended method to insulate the floor from the bare earth beneath.

Thanks for any advice.

Eric

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Comments

EricL

Hello @edechalain

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

Polystyrene insulation is one of the easiest underfloor insulation products you can install. It's trimmable and it does not need adhesives or special fittings to install. Once you have the polystyrene in place my only other suggestion is to cover the bottom with builder's plastic. This will prevent any condensation from forming on the surface of the polystyrene.

Here are some handy step-by-step guides that show you the different types of insulation.:

I also suggest having a look at these discussions:

Please remember to wear appropriate clothing and personal protection such as gloves, goggles and a dust mask when installing the polystyrene.

Please note it might be necessary to engage a registered installer to complete this work. If in doubt, consult your local building authority before starting.

If you need further assistance, please let us know.

Eric

Oddjobs_Lucy

https://www.workshop.bunnings.com.au/discussion/comment/27580#Comment_27580

Hi Everyone,

I'm also facing the same issue. Another pertinent question I have is, given that there is just the floorboards between the interior and underneath the house, is there anything that needs to be installed between the floorboard and the insulation? I ask because, say I spill something on the floor - usually it will spill straight through and into the bare earth under the house. If there is insulation in place, how do I protect the insulation from taking on the spill/moisture from above?

Thanks in advance!

Best,

Lucy

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/88197#Comment_88197

Hi @Oddjobs_Lucy,

Most underfloor insulation products—whether it’s bulk insulation like polyester batts or rigid foam boards—are designed to be installed snugly between the floor joists, leaving the floorboards above as they are. There’s usually no additional layer needed between the insulation and the floorboards.

However, if liquid regularly finds its way between your floorboards, the best solution would be to seal the gaps between boards from above. This helps stop drafts, moisture, and dirt from getting through and also makes cleaning easier indoors. If you plan on sanding and refinishing your floorboards, it’s a great time to seal them up.

Realistically, since insulation doesn't significantly decompose with moisture, occasional minor spills shouldn’t cause long-term issues unless they’re frequent and left uncleaned. The only other option would be to install sarking under the floor before the insulation. However, the spill will hit the sarking and sit there or run into the timber joists, which isn't a good scenario.

Please let me know if you have any questions.

Mitchell

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