Air sealing the roof

Although I usually enjoy writing blog posts, this one doesn’t necessarily fall in the “fun” category. I am talking about my well intended roof insulation that required a partial do-over.

I did a very thorough job, starting with rock wool insulation between the roof joists, followed by four inch thick XPS foam board that we mounted under the roof joists and then airsealed with close cell spray foam. I subsequently discovered that my insulation assembly was upside-down and that I had created a cold roof deck. So I started the process of removing the carefully installed XPS insulation, which ultimately should be installed on top of the roof deck.

With the XPS insulation removed, I needed a new vapor permeable air seal. It needs to be vapor permeable to allow for seasonal drying of the roof assembly. Out of the handful of methods available, using half inch drywall in place of the XPS boards seemed to be the simplest and most reliable solution.

Once we had the drywall mounted under the roof joists, I made sure we mudded and taped it carefully to create an effective air barrier.

To seal the edges, I installed two by twos with a small gap that I filled and sealed with foam.

attic-33 attic-34

With my new air barrier in place, I started rebuilding the ceilings where needed and then I moved on to installing the ventilation duct work.

Related posts:

Do-over dilemma

Blower door test – after insulation

Double duty

Attic insulation – foam board component

Stuffing the attic – Part 2

Stuffing the attic – Part 1

Spatial challenge

Advancing on the attic

About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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