Mechanically fastened TPO roof vs torch down modified

Let me start out by saying my background in flat roofing is predominately torch down modified bitumen roll roofing. Im bidding job where customer is using building for storage only-not looking to spend a lot of money. Roof right now is tar and modified could be applied directly for a good cheap roof I would say. Sometimes I worry about fire with this roof. I have experience with fully adhered TPO roofs. Since I would have to install new insulation and seeing as the customer is not wanting to spend a lot of money I am wondering if mechanically fastened TPO roof that is not glued down only screwed and heat welded on the seams is better then a torch down directly to the existing tar.
Any knowledgeable opinions appreciated

Not quite sure what you mean exactly. Do you mean installing tpo directly over top of an existing modified roof without adding an insulation board? If so, I don’t think that is a good idea. I have no evidence to back this up but I would be worried about the rough surface of the old roof wearing out the new tpo from the bottom due to expansion and contraction. I wouldn’t do a layover with a single ply roof without adding the insulation board.

[quote=“willy C”]Let me start out by saying my background in flat roofing is predominately torch down modified bitumen roll roofing. Im bidding job where customer is using building for storage only-not looking to spend a lot of money. Roof right now is tar and modified could be applied directly for a good cheap roof I would say. Sometimes I worry about fire with this roof. I have experience with fully adhered TPO roofs. Since I would have to install new insulation and seeing as the customer is not wanting to spend a lot of money I am wondering if mechanically fastened TPO roof that is not glued down only screwed and heat welded on the seams is better then a torch down directly to the existing tar.
Any knowledgeable opinions appreciated[/quote]

Modified is the best material for what you need to do.
IMO modified will outlast the TPO easily if it is properly applied and coated.

No way! I disagree. M/A TPO is the way to go! Cheaper, faster, & less seams! Use 12’ rolls & then you’ll only have a seam/lap every 12’!

Anybody out there using IB that much yet?

Modified. Last is strong and over just a good roof.

I’ve been using IB for six or seven years & it welds real nice & easy & comes in a lot of nice colors like Duradeck does. However, you cant just go to a supplier & get it! Its like Sarnafil is, you either have to pick it up or have it shipped! IB is from Oregon or Washington state, I don’t recall. Your best off to cover the area with 1/2’’ insul & put down say Genflex .045 TPO, get like 10’ or 12’ for ways less field seams to weld! They have pressure sensitive russ strip to run down the center of the sheet as well.

I use a slipsheet when installing over existing. It’s basically a glorified landscape fabric