How to add a subfloor ground moisture barrier?

[Chrismichael]

Hello,

I want to place black plastic polythene under my subfloor. The plastic needs to go on top of the ground to keep the moisture from effecting hardwood floors that we are planning to install. I have no idea if there are companies in Sydney that are able to do the installation? I've started laying one row but the space is quite tight and probably needs someone a bit smaller that has the patience to do the work. Any ideas how I can 'google' and find tradies / companies that can do the work? 

Link to a site in New Zealand that speaks to the works I need to do:
https://www.ecodesignadvisor.org.nz/resources/ground-moisture-barriers-guide-installation/

Thanks so much!

[EricL]

Hello @Chrismichael 

Thank you very much for providing that information. Let me tag @FrivolousPanda to make them aware of your recommendations.

Eric

[FrivolousPanda]

Hi Mitchell,

Regards to your idea of stapling the plastic to the joists, I have a double brick house with some brick vents on the external walls. If I stapled the plastic to the joists it would cover these vents up or at least prevent the air under the floorboards circulating with outside air.

I'm not sure if that is a good or bad  thing.

[MitchellMc]

I guess that depends on where the moisture is coming from that you want to exclude @FrivolousPanda. The air vents are to allow the area under the house to dry out, rather than the floorboards themselves. If you do a lot of wet mopping of the floorboards, it might not be a good idea to seal under them. However, moisture barriers come in one-way designs. So, moisture can't penetrate through them from underneath to reach the joists, but any moisture in the joists can penetrate out into the area under the house, allowing them to dry.

Mitchell