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Wall Insulation

March 13, 2018

There are lots of good ways to insulate a house wall. They each have some benefits and some drawbacks and you pick the pros and cons that best suit your project.

 

It got more involved in 2016 when Manitoba adopted changes to the National Building Code, Part 9.36 which deals with the energy efficiency of houses. You can get into some complicated calculations and tradeoffs but for most new houses there's no need to go there.

 

The Manitoba Building Code now requires an EFFECTIVE R-value of 15.9 in house walls above ground. The person who draws the plans for your new house will list all the stuff in the walls and how much of an insulation value each one has. So, for example, a wall with vinyl siding, housewrap, OSB sheathing, studs 16” on centre with fiberglass batts between them, vapour barrier, and painted drywall looks like this on your construction drawing details:

 

exterior air film - R 0.68

vinyl siding - R 0.62

weather resistant barrier - R 0.0

7/16” OSB - R 0.61

2x6 studwall 16” o.c. c/w R-20 fiberglass batt insulation - R 13.79

vapour barrier sealed at edges and penetrations - R 0.0

1/2” drywall - R 0.45

interior paint surface - R 0.0

interior air film - R 0.68

assembly thermal performance - R 16.83

 

The little stuff adds up and it all counts.

 

There are some shortcut documents to help. The City of Brandon has a good one which goes into some of the more complex tradeoff calculations that you can use for tall walls or houses with lots of windows.

 

http://www.brandon.ca/images/pdf/Building_Safety/Energy_Efficiency_Pamphlet_2016_8_22.pdf

 

If you have the patience or you end up in a disagreement with your designer, builder, or inspector about whether things will work out the way you want, go to the source at the National Research Council for the numbers that nobody argues with.

 

http://www.nrcan.gc.ca/energy/efficiency/housing/new-homes/energy-star/14176#a51d

 

It's worth noting that all those numbers are metric. To convert the Imperial R-value numbers to metric RSI value, divide by 5.678. Multiply by 5.678 to go from RSI to R-value.

 

When these changes first came out people got excited about the idea that framing 2x6 walls with 16” stud spacing wasn't allowed, but that's only true if your builder uses a stucco exterior. If you use vinyl, wood, or composite siding you're fine. List the components of your wall and add them up. If you're over 15.9 for a wall that's up to 10' tall it should be good to go.

 

 

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