John Downie and his wife are planning to build a house in Ontario, and instead of choosing a conventional wall system they are considering poured concrete exterior walls that are insulated on the outside.
Downie likes the “solidity” of concrete and recalls a comment from former GBA editor Martin Holladay that a poured concrete wall is functionally the same as a wall built with insulating concrete forms (ICFs, pictured above).
Otherwise the house looks fairly straightforward: between 1200 and 1800 sq. ft. over a single story with polished concrete floors, high ceilings, and a gable roof. Heating and cooling would be with a minisplit heat pump.
“I bought a book on ICFs 20 years ago and am still intrigued,” Downie writes in a Q&A post. “I fear, however, that they are the 3D printer of the building world—the wall of the future and always will be…
“To make a short story long, I am wondering if a conventionally poured concrete wall with sufficient external [extruded polystyrene] XPS only would be functional, or would insulation be required on the inside as well.”
Our topic for today’s Q&A Spotlight: Is Downie onto something, or should he look for another way to build his house?
It will work, but…
Although Downie’s proposed wall will be “perfectly functional from an energy efficiency standpoint” without any interior insulation, Brendan Albano writes, it carries an environmental price tag.
“If you are concerned about your environmental impacts in addition to your energy use, it is best to minimize the use of concrete in our project to only the areas where there are no reasonable alternatives,” Albano says. “Concrete is great for foundations, retaining walls, etc., but unless you have very unusual requirements for your home, probably not the necessary for your walls.”