Another article about the air tight and vapour behaviour performance of spray foam insulation
As you´ve might noticed by reading through prodomo Ireland´s blog, I have written some articles about spray foam insulation in the past already.
The reason why I want to write another post is the fact, that I currently have to deal with a rising amount of enquiries in regards to the air tightness of spray foam insulation again.
And it seems that nothing has changed over the years - most of the spray foam installers do still praise their products as air tight without requiring and additional air tightness strategy.
To make it short and simple - if you want to go with spray foam insulation, please ask your prefered installer for the NSAI cert prior the installation. The certs of all NSAI registered spray foam products (e.g. Icynene, Lapolla, Biofoam, e:zero or Walltite) do contain detailed installation details.
In all cases, it´s clearly pointed out that a vapour control layer is required/ recommended.
What is the difference between a vapour control layer and an air tightness layer?
Honestly speaking, nothing in the most cases. A vapour control layer does always act as an air tightness layer, because vapour is conveyed through the air.
Why do I require a vapour control layer for spray foam insulation?
Because the open cell spray foam, as used for insulation in dwellings, can absorb vapour and could lead to condensation issues in the building structure.
Why is sprayfoam mostly claimed as air tight?
In my oppinion for marketing purposes only. It puts saving into the clients mind, by having no need for an additional air tightness strategy.
As coming from my own air tightness testing experience, spray foam insulation as the sole air tightness layer is never as air tight as insulation strategies (even spray foam) with an additional air tightness layer.
Overall, please bear in mind that spray foam insulation requires a vapour control strategy.
Another interesting aspect of spray foam insulation was highlighted recently in an article of the Passive House Plus magazine: