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Posted on Jan 14, 2015 in Green Building

Bridging the Gap

True or false: “The higher the R-value, the better insulated the home.”

It’s a common misconception, but this statement is not always true.

R-value measures a materials’ resistance to heat transfer so R-value certainly affects how well the home is insulated but it is definitely not the only factor.  A high R-value is great, but that number is based on a controlled environment free from wind and air pressure changes.  The number loses meaning during air pressure changes, with the wind pushing air through the house.  Fiberglass batt insulation has a high R-value in a 2×6 wall (R-19), but has a lot of air gaps that allow exterior air to filter into the house.  Foam insulation (R-6 per inch thickness) is a superior product at eliminating air transfer, but is also the most costly form of insulation.  So a 2×6 wall of fiberglass batt insulation (R-19) in reality does not perform nearly as well as a 2×4 wall of open cell spray foam (R-18) or blown fiberglass (R-16).

In Urban North, we are going to present a balanced approach with installing blown-fiberglass insulation into the walls, with a solid barrier of 1” rigid foam around the exterior walls of the house.  This 1” rigid foam carries R-5 rating, and will provide the air barrier to boost the efficiency of the R-21 rating the wall will have.  The ceilings and roof lines will also have a balance of insulation materials to continue the higher efficiency of the building envelope.

Another benefit of the 1” rigid foam insulation is that it also helps evenly insulation both the insulated spaces as well as all of the wood framing members.  Conditioned air loss between the wood framing members is called “thermal bridging”, and means there is a gap in the structure or insulation that is allowing heat to escape from the home therefore increasing your utility bill. The rigid foam wrap around the exterior should help to prevent some of the heat loss shown in this photo of typical new home construction:

[Image Source: http://www2.buildinggreen.com/article/thermal-bridging]

[Image Source: http://www2.buildinggreen.com/article/thermal-bridging]

[GreenBuildingAdvisor.com]