Vapour Permeability Test

I recently conducted a backyard building science experiment with some pliable membranes. I was introduced to this test when I attended building science training in Denver with Construction Instruction.

The test involves filling a vessel with a prescribed amount of water, (in this case 125ml) and sealing the lid with the pliable membrane in place as the cover. I used clear plastic containers with lockable, sealed rim lids. I cut a hole in the lid, stretched the pliable membrane over the hole, then locked the lid to the container for an airtight seal.

The pliable membranes tested are:

  1. Thermakraft Covertek 407.
  2. Bradford Enviroseal Proctorwrap – residential walls.
  3. Bradford Enviroseal Proctorwrap – roof sarking.
  4. Polyweave foil.

125ml of water was added to each container on 3rd August 2019. The containers were stored inside a conditioned room with the air temperate 16 – 20 degrees Celcius and a Relative Humidity of 33-40.

The attached video shows the change in water level after 25 days. The three vapour permeable membranes have lost a fair amount of water. The poor old container on the right with the polyweave foil membrane still has 125ml of water in it, (no measurable water loss).

I will keep monitoring these containers over the coming months to see how long it takes for them to completely dry out.

Click here to learn why vapour permeability is important.







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