Need to choose flat roof option's raining inside

I bought a 40 yr old flat roof house 5 yrs ago. the BUR was overlayed with Mod.Bit. in 1990. in 99, a white thermoflex? paint was applied…i have added coats over last 4 years. it is leaking in my living room and under the roof drain that is above my hallway. Roof is 2 tiered and 2,500 sqft. 4 roofers have looked at it. 2 want to go over existing roof with 1" insulation and either TPO or Mod.Bit…both at about $13k. 2 others want to tear off and start from plywood with 1" insulation and TPO. One bid for this is $21k, the other is not in yet. $21k includes some drainwork and working around a roof top A/C…and is from a respected 50 year roofer that i have been refered to as a flat roof expert. **i want to know if price sound right and if solution of tear off and tpo sounds good. **I live in W.PA. and current roof has good draining…a few tiny ponds and 1 deep one near drain.

Can’t comment on the price too much as it varies from region to region.

I like the 50 yr roofer’s solution of tearing off and fixing everything.
I think that you will get much better results from it.
If the roof has been leaking the existing insulation is most likely shot, as is some of the decking.
The $8K price difference is in line with a full tear off as opposed to roofing over.
Ask him if he does Sarnifil or IB.
TPO is the “cheap” flat roof, that doesn’t mean that it isn’t good though.
I do think that the Sarnifil or IB systems will last much longer.
Properly flashing the ac unit and addressing the drain should be part of all the bids.

Perhaps RoofBoss will chime in, he knows flat roofs far better than I.

Personally, if given the choice between TPO and APP (torch applied) mod bit I would pick the mod bit every time.

Axiom, I was weened on flat roofing in the same Union as RoofBoss, but would defer to his more extensive and lengthy background. but you pretty much hit the nail on the head with all of your comments.

You can’t fix wet decking and insulation with a re-roof.

A tear-off, unfortunately is your only long term solution, otherwise, you will be experiencing even more problems in the not too distant future.

I consistently hear nothing but good praises for the IB Roof System, although I have never installed it.

Drains, flashings and the perimeter edge details will be the most critical areas, so what does the specifications state how he wil treat these areas.

Since he is the preferred and referred expert and the price for the Correctly specified job is not too much more, percentage wise, that wopuld be the more prudent contractor decision to use.


Thank you for the feedback. 50 yr Roofer originally suggested a black roof (i can’t remember what he called it…it wasn’t mod.bit) but i asked about tpo as other roofers suggested it was more flexible. he indicated it was similar to what he was planning to use and could work well and priced job with that…he wants to use a .48mil tpo.
so i am now convinced a tear off will be best and the only remaining question is …will .48 mil work. roofer says he can get a .6 or .7 but that it is not in stock and will take time to get. given my indoor rain, he said he can bump me into schedule this coming week…and i am afraid to wait for .7 delivery.
By the way, some trees around house but i only ever have to remove leafs once a year, if that.

Any advice on tpo and tpo thickness? hoping it will last for 15 + yrs.

Tpo has been out for a while now and I would feel comfortable saying that 15 years isn’t a problem if its installed correctly. In fact if you used the thicker membrane (80 mil) 30 year warranty’s can be had.
With the ib membrane a residential ndl warranty is available where as with the tpo most of the time its a material only warranty due to the manufactures only offering commercial ndl warranty’s.
If water sits on the roof then single plys the way to go an asphalt roof doesn’t like water sitting on it.

Bornaroofer…when you say
"If water sits on the roof then single plys the way to go an asphalt roof doesn’t like water sitting on it."
are you saying that tpo is a single ply and that mod.bit is an asphalt? i am not familiar with the exact composition of materials and your advice is really appreciated.

Yes tpo is a single ply and modbit is asphalt.
Asphalt degrades quicker when water sits on it. Ponding water doesn’t really affect tpo, epdm, pvc ect…
Not to say that ponding is good in any case.

Modified Bitumen is an asphaltic based petroleum product which contains plasticizers to to lend to it’s flexibility.

I t can get applied, the APP version, with a hot air or open flame torch. The SBS version gets applied with an appropriate adhesive.

Ponding water on either of those materials voids the warranty.

Attention to correcting deflected deck sheathing and a possibility of adding a tapered insulation to create positive drainage would extend the useful life of Any roof system applies.

A properly designed tapered insulation would induce the water flowage off of the roof as efficiently as possible, which may be the 1/4" per inch version or the 1/8" per foot variety of pre-cut insulation systems.

Man roofers claim a modified bitumen roof falls into the “Single Ply” family, which is technically true, but not what the term single ply was intended to portray. In that definition, instead of a 3-4 ply roof system, a one ply mopping of felt paper would then be considered a single ply roof.

The Black membrane he originally proposed may have been an EPDM Rubber Roof system. A fully adhered EPDM is a very good system too.


i appreciate all the advice…i am definitely going with a re-roof…just trying to figure if tpo is ok and thickness. i will be asking a couple roofers additional info.
any feedback on ib is appreciated…cost vs. tpo would probably be one of most important guestimates that i am looking for.

Mod bit,
3 ply = Base sheet + smooth mod bit + granulated mod bit cap sheet = multiple plys, a very good roof.

2 ply = Base sheet + cap sheet = multiple plys, a good roof.

I don’t see how it could be considered a single ply system.

I can’t ever recommend torching directly to the deck which would technically make it a single ply system.

it does not sound like you have a simple roof.
dittto etr.


heres my two bits worth.
both thermo plastics and modified bitumin systems are great. the catch is figuring out how well the installer you pick can install it. my advise here is ask questions. alot of questions. experience with the product.references(at least 5). do you fell comfortable with the answers you get. my advise will ALWAYS be to tear it off and start new. then any flaw can be detected and rectified.dont be afraid to ask any question you may have. after all YOU are footing the bill here. is this a tree limb fall zone? what roof will hold up better? how can we eliminate ponding water @ minimal costs? these are just a few of the ?'s needed to be asked. if you do your research you’ll get a good roof that will last a long time. i have seen mod bit roofs last 25 yrs.ive seen tpo roofs that are 10 yrs and still perform and look fine. make a decision on what will get YOU the best bang for YOUR bucks.
hope i helped :slight_smile:

“2 want to go over existing roof with 1” insulation and either TPO or Mod.Bit…"

That would make it a 3rd roof - is that even allowed by your code? Michigan code, as an example, allows 2 roofs max; otherwise tearoff is a must. Correct me if I’m wrong on this please. I do think that a TPO or Single ply definetely counts as another roof and isnt looked at as a paint coating which doesnt count as a roof.

Make sure you check through your entire roof deck design. Your house is old and prior to the '70’s many flat roofs had condensation problems
due to misunderstanding of ventilation and insulation. That 1" of insulation might be too thin, depending on your climate and other factors. Alot of roofers, especially flat roofers it seems, are still stuck in the 70’s and continue tearoff/reroof without a care to correcting faulty design.

Especially in P.A.(pensyltucky)lol

good to read ya roofboss.
aint read ya in a while.


I am a little bias…but I would say go with a PVC single ply. TPO’s have been around a long time HOWEVER their formulation has changed. Alot of companies have added more chalk and less UV stabilizers (chalk is cheaper). Any of you seen a TPO with a powdered looking coat?

A PVC roof will last longer than a TPO roof. Of course that depends upon the quality of the install and the product. If you get a great Mod roof its going last as long as a PVC roof.

There are several Manufactures that sell only to certified installers. I would look up in your area if their are any Certified Sarnafil Installers. Sarnafil (40 year company) has a true .48 mil roof (most other companies membranes are “nominal” which means the thickness could vary 10% so a .48 mil could effectively be .44 mil.

Another added bonus is PVC/TPO are white…they will reflect alot of UV rays (sarnafil is 86%)…energy savings. Sarnafil can also be 100% recycled at the end of its life (25-35+ years) Thinker the membrane the longer it will last.

If you have any questions or comments feel free to email me.