Ask the Architect

The problem of a hot roof


Q. I read your column on insulating attics and putting foam insulation in the roof rafters, and completely disagree with the method, because it forms a much bigger problem — a hot roof. Most people don’t know what a hot roof is, but not ventilating the bottom side of the roof can cause failure of the roof shingles and even the roofing plywood, which can buckle in high heat. You should not be recommending this to people. It is just wrong.

A. Your observation and explanation of a “hot roof” points out a true dilemma in the construction industry. Before I write a column, I research every angle of the pros and cons, best practices and codes, rules and regulations, and I encourage you to do the same. Misinformation starts with not taking the time to fully investigate the subject, and I urge you to do some more investigation before reaching your conclusions, in this case about hot roofs.
While it’s true that the damage you describe is happening, like everything, there is a time and a place for applying specific methods, and material installation is usually part of a system with chain-reaction results, good or bad. The sources for my column, which are extensive, originated from a need, and whether you appreciate it or not, start with a long chain of command, from the federal government down to the state you live in, and down to the local municipality. Along the way, several hundred private and public institutions, from manufacturers to universities, jumped on the bandwagon, and the band became a full-blown orchestra.
The term “hot roof” is a bit misleading, and conjures up thoughts of frying-pan-like heating of the roof. That’s an exaggeration. Studies using sophisticated sensors, computers and applied physics have shown that many regions, from warm climates to cold, benefit from insulating directly under the roof, as a system, and actually enclosing the attic space, unvented. Temperature fluctuations varied by less than 10 degrees when the attic became part of the “conditioned” space of the home, meaning that the attic was treated like any other room in the dwelling, resisting the heat or cold, just like the walls do.
Because of the complete barrier under the plywood below your shingles, the only extreme effect on your shingles is the extreme sunlight, which, if the shingles are installed to the manufacturer’s specifications, they are made to resist, and do so very well in most cases. The benefits include having a better vapor barrier at the roof, a more stable and temperature-resistant system and less chance of heat from the attic in the winter causing the formation of ice dams, which lead to shingle damage, water penetration and collapse in extreme circumstances. So before you dismiss the idea of this type of insulation system, please investigate online at one of the many sites or read the published reports from Canada to Florida. Before doing work on homes, please do your homework. Good luck!

© 2023 Monte Leeper. Readers are encouraged to send questions to, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.