Increased R-value in foundation walls
Oct 22, 2013 / 5:00 am
Insulating your foundation wall is a very important step in being able to control and condition your basement/foundation.
Minimum code would be the equivalent of a 2x4 ‘frost wall’ with R12 Batt insulation in the cavities. However for minimal cost you can upgrade your wall and achieve a drastically higher R value as well as increase your moisture control.
By combining 1” XPS rigid insulation on the inside of your 2x4 wall with R13 Batt insulation you can increase the walls R value to parallel R18 because the thermal bridging of the framed wall is minimized, the overall improvement in R-value is R5.4 for one inch of R-5 insulation. Adding 1” of XPS results in an energy savings and will also reduce convective looping because the temperature gradient in the framed wall is less.
As mentioned the greatest benefit to adding 1” of XPS is arguably for moisture control and not thermal control. XPS controls the flow of water vapor from the concrete to the framed wall, both from vapor diffusion through the concrete and capillary wicking up the wall, reducing the relative humidity in the wall cavity. Small amounts of moisture (too small to drain) between the XPS and concrete is irrelevant because neither concrete or XPS is susceptible to moisture issues. The XPS must be well attached to the concrete foundation, and sealed, so air is not able to bypass the XPS insulation.
The XPS insulation will also increase the temperature of the condensation plane which would minimize the condensation of the increased interior relative humidity.
The construction of this type of wall system is not overly difficult, but with majority of wall systems great care should be taken with the air barrier that air is unable to get behind the XPS. This is typically accomplished with tape, caulking, spray foam or a combination of those products; however tape alone will not maintain a good air seal for the desired lifetime of the wall system.
Currently throughout the Okanagan, FortisBC is putting on an Energy Diet, where the cost of an energy evaluation to collect on these rebates has been drastically reduced from $300.00 to $60.00 and even less in some municipalities. Not only will you find out about your attic insulation but you will be given a detailed plan on everything you can do if you choose to, in order to make your home as energy efficient as possible, and what rebates are available for doing so!
To sign up for the Okanagan Energy Diet, click here.
Or call: 250-212-6484
Read more Think Globally Act Locally articles
- What is an Energy Efficiency Evaluation? Nov 30
- Energy efficient retrofits Nov 2
- Increased R-value in foundation walls Oct 22
- Importance of a well insulated attic Oct 5
- Okanagan Energy Diet: Part 2 Sep 21
- Okanagan Energy Diet: Part 1 Sep 7
- Importance of indoor air quality Jun 29
- Is your home energy efficient? May 29
(Click for RSS instructions.)