Alright, you have me here. I don’t come around as much anymore, because there is seldom something new and interesting to talk about.
As for this poster. First of all, a TPO should be fine so long as it is installed to meet local/state wind uplift loss prevention. If you are in S. Florida, you probably have to meet FM I-120 requirements for commercial buildings, but I’m not sure about residetial. A local roofing contractor or consultant should be able to talk to you about acceptable systems for your area. For what it is worth, I’m in Houston, so I’m sure we have similar weather.
It should also be pointed out that like some others have mentioned, the TPO membrane has not been out as long as built-up roofs, and mod. bits. Still, that does not mean it isn’t a good membrane, but it is a single-ply membrane nonetheless. That is where the redundancy of a built-up roof makes it a tougher roof system. In the end, there are positives to both systems, just make sure it is the right one for you not just because it is the right one for the contractor. You’ll find some contractors are strictly single-ply roofers, and there are built-up roofers that won’t touch single-ply systems.
Now, if you have decided to go with the built-up roof system with a modified bitumen cap sheet, you are always better off adding the additional ply. In fact, a base, 3 plies of Type IV felt, and a modified bitumen cap sheet is even better. In your case, I’m guessing the base is going to be nailed to plywood roof deck or mopped onto roof board insulation. Over top the base you should go ahead with the 2-plies of Type IV felts, and install a modified bitumen cap sheet. The only question remaining is what type of modified bitumen membrane, and how to install the membrane. There is the SBS modified bitumen, which generally is a mopped on product, though there are some torch-grade SBS products. Then there is the APP modified bitumen membranes, and they are typically torch-applied or cold-applied. I like the APP’s better than the SBS’s, though I suspect the contractor was planning on using an SBS. If that is the case, the main problem I have with SBS membranes is the end lap shrinkage and granule loss. So, after 2, 3, 5 years or so, before the membrane starts to lose too many granules, you can have the roof coated with and Aluminum Coating to help extend the SBS membrane’s service-life. Narturally, there are several white colored urethane and acrylic coatings, but some of those get expensive and you only want to apply the Aluminum Coating for the reflective qualities and to help bond the granules to the membrane.
If you have any more questions, just hunt me down. Apparently, if you leave me a private message, I get an email notification.