Re=roofing Built up roofs

[AustinScoobee]

Hi all. We are taking bids to reroof a low-slope (flat roof) and are looking at the new modified bitumens( 2 or 2 ply sys). There are lots of types, but all seem to mention that the base sheet be applied to clean dry wood decking.I defy anyone to get hot mopped tar off of our decking. You could likely get the old roll roofing off but the tar it was set in??! We are getting many varied ideas as to how to best re-roof it and wondered what was the norm?

So far we have,

1. Remove it as best as possible and screw down the base sheet, then the self adhesive 2nd sheet then Cap
2. Leave the roof as is and screw down the base sheet to it. then the

2nd self adhesive sheet then Cap

1. Hot mop OVER the old roof and apply base sheet. then the 2nd self adhesive sheet then Cap

1. screw down 1" rigid insulation, then use self ashesive base coat, then the 2nd self adhesive sheet then Cap

Any thoughts and ideas Every roofer to come out has a different idea!

G--

[tbasc]

Check the various manufacturer's web sites. If the specifics are not there, contact the tech department. They want to sell product and they do not want it to fail. The tech departments are usually very helpful. That's a good way to sort out the folks who will not support you after installation. TB

[bill allemann]

do you know that hot tar is on the sheathing, or is that just an assumption? On flat roofs, felt is applied first to sheathing with fasteners, then the hot tar process is done on top of the felt. If tar was applied directly to the decking, it was probably done by amateurs.

Bill

[<aemeijers]

Number 4. most closely resembles what I saw them do on the various 30-50 year old gravel-covered hot mop roofs on the monstrosity of a building complex I work at. (Hey, looking out the window watching them beat looking at my computer screen.) Rip off or scrape off what they could, apply another layer of plywood and/or rigid insulation board, put down a layer of some sort of blue membrane, and then a layer of beige membrane. Mop joints and flashing with a matching color sealer. No hot-tar buckets in evidence, and no gravel. Roof looks kinda funny to someone like me used to traditional methods, but seems to be holding up okay. (This building is 100+ years old, in this wing, so it has had multiple reroofs and remodels, most badly done, over the generations.)

aem sends...

[AustinScoobee]

Thanks Bill, No I dont know that it&#39;s mopped directly onto the tar. Its just 3 out of four roofers preferred to go right over the existing rather than pull it up, mentioning tar and PIA work. Everything on the building so far has been done to very good standards so I will now assume it was mopped over the appropriate paper first.

Since most of the roofers want to leave it there, should I suggest maybe adding 3/8plywood, then 1" insulation, right over it, would it cause problems? I will try to reach some manufacturers monday, thr Grace roofing membranes look really good, Thanks G

messagenews: [e-mail]...

[DanG]

If you cap the roof with ply or even pearl board, it is just about like starting out new. The big difference is the weight of the existing roof plus the new roof. If your structure can stand the load, go for it. No one likes tear off and there is a definite cost in time, money, and clean up/haul off to do the tear off. It is the right thing to do.

If you don&#39;t have 1/4"/ft fall now, you should strongly consider creating it in this re-roof. Modified bitumen is a great roof, but you want to make sure water doesn&#39;t stand on it.

[buffalobill]

[bill allemann]

do you know that hot tar is on the sheathing, or is that just an assumption? On flat roofs, felt is applied first to sheathing with fasteners, then the hot tar process is done on top of the felt. If tar was applied directly to the decking, it was probably done by amateurs.

Bill