‘R’ you greener than a medieval mason?
Which building do you think has better insulating properties: a stone house from 1000 years ago, or a relatively recent 1970’s office building? Although there have been huge advances in technology, surprisingly, or maybe it’s not so much of a surprise, the building of 1000 years ago typically performed better in terms of insulation.
A couple of weeks ago, I attended the symposium on Energy Efficiency, Insulation and Historic Building Envelopes by the Association for Preservation Technology. The day started out with an interesting comparison of R values in buildings through time. R value is a measure of thermal resistance used in the building industry – it tells you how well insulated a wall (or window or roof or anything) is. More formally, Wikipedia defines it as “the ratio of the temperature difference across an insulator and the heat flow per unit area through it.” But what you need to know is really the bigger the R value number, the better its insulating effectiveness.
A stone building from 1000 years ago could be estimated at R2. With changing methods of construction, R values increased up until the late 19th century, to around R8 for a 2′ thick masonry wall building with single glazed windows. Then there was a huge decrease with curtain wall construction, to around R1.5 for a single glazed 1970’s building. (You’ve probably noticed how the cold seems to come in right at the windows in your home so perhaps it is not surprising that a building which had just a huge window at the exterior would be pretty badly insulated!) Now with better (thermally broken) glazed curtain walls, R values may be in the range of R2 (about the same as 1000 years ago, still better than the 1970’s). Not that we should propose to build everything as though it were the year 1010, but it does make you aware that historic buildings with traditional masonry construction can be as “green” as new construction, even without considering embodied energy.
If you are building a new home, or thinking about adding insulation in your walls or attic, R values can be calculated for different wall systems, with and without different types and thicknesses of insulation, which allows a comparison of different strategies. There are calculators online that can help with these calculations.