Some spray foam contractors write contracts with vague language. Example: “spray apply elastomeric top coat to roof.” This contract doesn’t mention what type of material is being used, what rate; or what the ending thickness of the material will be. Most manufactures use formulations (especially for acrylic coatings) which are 50% solids by volume. Translated, this means that one gallon of coating will yield 8 dry mils (one mil = one thousandths of an inch) of coating.
Make sure that your spray foam contractor is using the material you were presented with in the brochure. A reputable spray foam contractor will probe the spray foam they apply in order to ensure that they are applying the correct thickness and you are getting what you paid for.
A one inch minimum of spray foam was developed by the SPFA (governing body over spray foam) and should be only applied over a smooth surface. Since spray foam contractors’ foam thicknesses will vary ¼” from highs to lows, you need to make sure the spray foam thickness is never less than one inch. Along the same lines, a 1 ½” minimum is required over an irregular surface and 2″ minimum is needed to stop condensation in roof applications.
Be careful with contractors who use long warranty years to sell contracts. This makes you believe, the longer the warranty the better which therefore entices you to buy. The standard warranty from coating companies is 10 years. Therefore, this is the standard warranty you should find on spray foam contractors’ contracts. Warranties of greater length have more coating applied to the roofs, or the contractor has proven to be a master applicator with that roof coating company.
A standard 10 year warranty will be around 30 dry mils of coating on the roof, + or – this amount depending on manufacture. Therefore, longer warranties will have greater thicknesses. Usually, another 10 mills of coating will yield another 5 years, or a total of 15 years. Very few contractors, if any, offer greater than 15 year warranties. Warranties in excess or greater than 10 years, with minimal thickness of coating, are considered to be the most risky.
Remember, if it’s too good to be true, it probably is.