Not too long ago I was at a lecture given by a well-known futurist who proudly described (to a room full of heritage professionals) how he insulated his 200 year old home with seven inches of polyurethane foam. The room shook from all the eyeballs rolling. It is a complex issue; we all want to insulate, but a little heat leaking through a masonry wall drives the moisture out. If you insulate too much, freeze-thaw cycles can destroy a wall in a few years. Nobody is quite certain how much insulation is safe, what all the factors affecting it are, and what kind of insulation to use.
Now Ken Levenson and his team at 475 High Performance Building Supply, have written a book about the subject. Ken, an architect by training, is not a fan of foam insulation, and has many in the industry foaming at the mouth with his statements like:
Foam plastic insulation dominates high-performance and green construction today, a clear victory of the power of chemical company marketing over common sense. First used in buildings as roof insulation, now it too often metastasizes around our entire building enclosure.
He instead favors cellulose glass or mineral wool, which have their own sets of issues. It's all very controversial; over at Green Building Advisor, Scott Gibson reviews the book and writes:
Some recommendations in the book, such as those on insulating exterior walls, probably won't be accepted by all building scientists. The book distributed by 475 recommends insulating thick brick walls on the interior with cellulose or fiberglass insulation — a controversial method. When asked about this approach, building scientist John Straube said, "I have qualms."
I really admire John Straube; he is the author of another bible about the topic, High Performance Building Enclosures, which I consulted on my recent house renovation. Straube is a foam fan; in an earlier article on the subject in Green Building advisor, he is quoted: “One thing about spray foam: it does a really good job or air-tightening, as well as some water tightening.”
As I said, it's complicated. Martin Holladay gives a really good overview of the problems in his post Insulating Old Brick Buildings, but Ken Levenson and his team have done an important contribution to the discussion with their book, which you can download for free here.
This is a book for professionals; don't try this at home without consulting one as there are so many factors that affect how a wall is going to react. But it will help keep people from ruining buildings. It's big at 186 meg, but worth the wait on the old AOL dialup.