The word, in certain construction circles, is that open-cell spray foam insulation is bad for roofs and dangerous to work with and around. Tales of workers falling through rotted roofs blamed on the product have been circulating for sometime, and deserve some investigation. Truthfully, as with any product, how you use open-cell spray foam insulation determines safety and how well it performs. The four most important factors to keep in mind are as follows: 1) A vapor retarder must be used in cold climates. 2) The attic must be sealed airtight. 3) The relative humidity and temperature must be monitored with an alarm or sensor. 4) Conditioning the attic air is key.
Read the full aticle here: Does Open-Cell Spray Foam Really Rot Roofs? | GreenBuildingAdvisor.com