How to add waterproof membrane under timber floor?

[Zawadi]

Hi community,
I'm looking to add insulation and moisture protection under a timber floor for a terrace house (ground level). The timber floor will go over joists that are suspended with a small cavity of around 400mm above a dirt floor.
As well as to improve the insulation, I'm looking to stop moisture and musty smells coming up through the floor. The solution I'm thinking of is to add a breathable waterproof membrane over the joists and create a bit of a hammock to hold the earthwool floorshield insulation. Pic attached of the kind of setup:

The product I'm looking at for the membrane is the Ametalin VapourTech Brane

It doesn't mention floor application, so I wanted to get some opinion on whether it would work for my situation?

Much appreciated.

[Jewelleryrescue · Accepted solution]

Hi @Zawadi 

That product will work great dont forget  to tape up the overlaps. and around the  peirs

I think a  staple gun would speed  up the process of  attaching it to the joists.

It is a moisture barrier and will support the batts  weight.

Food  for thought if you attched the membraine from underneath  of floor it would protect  timber joists as well if you  wish.

I would also  consider adding cross straping between the  joists to stop sagging of the batts out of the floor cavity.

Zenith 19mm x 700m Poly Pro Insulation Strapping

https://www.bunnings.com.au/zenith-19mm-x-700m-poly-pro-insulation-strapping_p0810984

I/N: 0810984

$48.25

[Jason]

Welcome to the Bunnings Workshop community @Zawadi. It's great to have you join us. Please don't hesitate to post anytime you need a hand or have a project to share. 

@Jewelleryrescue has provided fantastic advice as always. Typically our resident Bunnings D.I.Y. experts would also be more than happy to chime in however they are unexpectedly absent from the site. Hopefully they will be back soon. Feel free to let us know if you need anything further. 

Jason

[Zawadi]

Thank you @Jewelleryrescue, good advice about the strapping, I'll add that in. And interesting thought about going under the joists. That could work well especially with the strapping to help support the batts. Appreciated.

[EricL]

Hello @Zawadi 

If I recall correctly Ametalin has a dedicated product for flooring called - Ametalin 500mm x 60m SilverFloor Underfloor Insulation. It is a Heavy Duty, vapour permeable floor insulation, designed for use under floors with a sealed air space between flooring and enclosed sub-floor space. 

Double-sided reflective surfaces provide increased R-value to your floor system. 5 mm weep holes at 400mm intervals in the membrane structure allow water and water vapour to permeate through, preventing moisture build-up under flooring.

In regards to the Ametalin 1370mm x 30m VapourTech Brane VHP Vapour Permeable Wall Insulation. Allow me to double check with Ametalin just to make sure you can use it for underfloor applications.

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

If you need further assistance, please let us know.

Eric

[Zawadi]

Thanks @EricL, seems like another good option. Interesting reading about the electrocution risk and reason it is banned in NZ. I might stick to the other wall membrane for that reason.

[EricL]

Hello @Zawadi 

Thank you for your patience. I've just received information from Ametalin and they suggest using Ametalin 1350mm x 60m SilverWrap Micro-perforated MD Vapour Permeable Reflective Wall Insulation - 6... instead of the Ametalin 1370mm x 30m VapourTech Brane VHP Vapour Permeable Wall Insulation. The Ametalin VHP is not strong enough to last exposed and unprotected. They recommend installing the Ametalin SilverWrap foil side down.

If you need further assistance, please let us know.

Eric

[Andrey_B]

Hi Eric

I am going to use Ametalin suggestion. I can not understand why they recommend putting foil side down?  Will vapour coming from ground go through the Ametalin and make the insulation wet?

Thank you in advance 

Andrey

[EricL]

Hello @Andrey_B 

Welcome to the Bunnings Workshop community. It's sensational to have you join us. 

I believe that the foil side is a better material to be exposed to the moisture as it it will not soak the insulation. It will technically condensate on the surface and fall away, whereas insulation material will absorb the moisture instead of turning it away. 

Since it is the recommended installation procedure, I propose following the instructions given by the manufacturer.  

If you need further assistance, please let us know.

Eric

[Andrey_B]

Thank you Eric, It makes sense, I will install it this weekend )))