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Penta's Raising the Roof on a Retrofit

by Joe Wedge

Roof Retrofit

A recent roof retrofit project on a cabin in Lake of the woods provides a perfect example of where ½ lb  open cell foam can be used to accelerate a project schedule and generate significant savings for an owner.

The client had a vaulted ceiling that had frequent condensation problems and ice damming due to a poorly installed or compromised polyethylene (poly) air / vapour barrier.

The solution proposed was to use spray foam insulation to create a proper air barrier and upgrade the insulation

The cabin was a finished building and removing the interior ceiling would have been far too disruptive.  The decision was made to remove the roof and sheathing and attack the project from the exterior.

The cavity depth was 10” which allowed for lots of room to add insulation.

Roof Retrofit Remove the roof to insulate

The next hurdle was how to complete the insulation work and avoid any damages to the interior from rain.

Penta suggested using open cell foam since there was an existing poly vapour barrier.  Although obviously not sealed enough to act as an air barrier to keep air from entering the cavity, any building science guru knows that poly does not have to be continuous to act as an effective vapour barrier.

Open celled foam is not a vapour barrier by definition but it is an excellent air barrier. 

Given these existing conditions by adding 10” of open celled foam the owner would get a roof assembly with a very efficient R37 insulation and also an excellent air barrier.

The other benefit of open celled foam is that it can be installed in one lift in one pass.  This allowed the Penta crew to complete the work in one day which allowed the contractor to sheath and shingle the roof right behind making sure that the building was weather tight with no risk of damage from rain.

In order to install R37 of 2 lb density closed cell foam would have required the application in maximum 4” passes per day which could have been a problem for the unfinished and unsealed roof.

The part that the owner really liked was that the open celled foam cost 40% less than the closed cell option saving the owner over $3000.

Open cell, ½ lb foam is an excellent product for certain applications and this certainly was one of these scenarios.


spray foam in the roof


So if you are looking for a solution to an insulation problem, contact us and we can help you. We have seen it all.

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