What I find interesting through this thread of conversation, coming from one of those three manufacturers who are NOT well known to architects and being a well-known architectural rep in my own right (note the irony), is that there is virtually a complete oversight of evaluating a system as a whole. You can have a decent polyester ply or cap sheet, because you have movement, but set it in a straight hot asphalt type and you have essentially negated the effect of the polyester sheet. It is not appropriate to have a conversation about roofing systems that are not inclusive of an entire “system”. A roof system by my definition is one which encompasses building usage, deck type, insulation needs, ply sheets, asphalt types, flashing systems (a whole system in it’s own right) and details, surfacing and last but not least maintenance considerations.
I can tell you the relative differences between all of the sheets, and have in past postings on this site, but without due consideration to the system as a whole, such as rubberized or non-rubberized asphalts, you are not getting a true story. Unfortunately the MB industry, as a whole, has played a game of carriers, thickness and tensile strength without necessarily designing to the needs of the builing. Whatever happened to providing sound solutions? ASTM 2523 is the truest measure of this and was established by NIST–not a manufacturer like me. Every manufacturer’s sales reps (some come in the form of roofing contractors and/or consultants) know how to play the game to their advantage–much like architectural firms do through billing or design re-use gone new.
If you have an interest in non-biased information on what sheets to use where don’t hesitate to contact me. It really is too much information to post and some of it has been addressed pretty adequately above.
Bob the reason that you have consultative manufacturers in the marketplace is that they deliver a high-level of service to the owner and to the architect when applicable. When re-roofing considerations were not in vogue there were very few resources for owners to rely on, not to mention very few manufacturers or architects willing to take on the liability. I am glad to come from a manufacturer that works with a multitude of entites: architects, owners, consultants and contractors. It has always been my goal to work with those who are willing to work with me. If there is an architect involved in design process then they should be taken in to the process, just like the manufacturer should if that be the owner’s desire. I will say, to all of you, that if your manufacturers are not working with you and the owner in tandum it can lead to more change orders, and possible issues in the end. Whenever roofing is the principle concern all entitites should be involved from the beginning.