Various roof failures, including asphalt shingle blow-off, and premature curling and cracking, has led homeowners to look for more reliable and durable solutions. As such, people often start asking about metal roofing.
Metal roofing continues to be more and more popular, despite its initial cost, because people are getting tired of having roofs that fail much before their warranties expire. The metal product offerings come in a dizzying variety of materials, appearances, textures, colours, and performance. How does one wade through all the sales claims and marketing hype to decide which options are truly the best for you? It helps to remember that there is no product invented by humans that is truly perfect in every circumstance. So the exercise is to find the product whose weaknesses are minimized in your particular circumstances, and whose strong points are fully delivered. It should not be a surprise that proper preparation and installation play a very big role in the final quality of the result. So let’s examine a selection of products and discuss how their weak (and strong) points should be considered in your selection process.
Closed cell-spray foam used as insulation, has been on the market since about 1979, and has gone through a number of evolutionary steps. The product is a solid plastic, formed by the chemical reaction of two primary components: an “A” side which is isocyanate, and a “B” side which is usually a mixture of oils, stabilizers, fire retardants, blowing agents, and colouring agents. The reaction is exothermic (ie, generates a lot of heat), and the materials form a solid within seconds. The blowing agents are the compounds which produce the low-conductivity gas that forms the bubbles in the foam, and thereby form the primary insulation.
When applied to a minimum thickness of 50mm (slightly under 2 inches), the material acts as insulation, vapour barrier, and an air barrier. Newly-installed foam has R-values of R-6 to R-7.5 per inch, but this diminishes to about R-5 per inch over time as the insulating gas dissipates. Compared to other insulation products like fiberglass bat or mineral wool bats, the product has more insulating value per inch, and resists the loss of heating value that sometimes occurs with loose insulation due to air convection with extreme temperature differences.
The ability to prevent air and vapor movement is generally a good thing, except in situations where moisture can enter a wood structure, and then cannot get out. Therefore the short answer to the question in the header is “spray foam is good when PROPERLY installed, and BAD when installed in inappropriate places or in an incorrect manner. There are also issues of the impact on the environment, and potential impact on the health of the people living in the homes where the product is used. The rest of the post touches on some aspects that inform whether the installation is good or not.