SF low slope modified bitumen roof (some questions)

Hi dear all, this is my first posting. How are y’all doing?

We have a family house in San Francisco. The whole house is mostly built with concrete long time ago. My mother-in-law replaced the roof about 8-10 years ago (modified bitumen). There was a rain storm couple of months ago and we were traveling outside of the country for a while. When we got back we noticed some water leaking into the house. We went up to the roof and found out the outlet (scupper) were clogged with leaves, and the water must be trapped on the roof for a while thus caused the water leaking into the house (see photos at picturetrail.com/sf4roof)

We talked to about 5-7 roofing companies, some suggest some repair ($900 - $1800) would do it, but they can’t guarantee the repair will totally fix the water leaking problem. The others suggest to replace the whole roof as they noticed some (very few) blisters, and the current jack opening (the scupper) are too smaller, and could cause the water to back-flow. Over the years my mother-in-law hired some roofers to do some patches here and there on the roof. One roofer did a quick fix by pouring some kind of “tar” over the modified bitumen around the chimney area to prevent water leaking (see photos).

Here are my questions:

  1. Given the current condition, one roofer proposed to put in another layer (one ply) of bitumen OVER the existing layer. Is this a recommended way to do it? I think the base of the roof should be concrete, but still, should I be concerned about the weight? The other 3-4 roofers all proposed to take out the existing modified bitumen material then put up the new one. What’s the pros and cons of these two different ways?

  2. Some roofers recommended using “copper” scupper instead of “sheet metal” scupper. Some said that you have to replace the scupper whenever you replace the whole roof (every 10 to 15 years?), so why bother to use the more expensive “copper” scupper. Any thoughts or comments about this? What’s the advantage of using a copper one instead of the more generic “sheet metal” (zinc?) one?

  3. For the weather of SF (mild weather, temperature usually 55 - 70 degrees through out the year), is it worth to consider “rubber” type of roof, such as the “IB roof system” (ibroof.com)? I can’t seem to be able to find any roofer in SF that would install “IB Roof system” though.

  4. One roofer gave us two price estimate for replacing the roof. With one ply of modified bitumen he would charge $5000, and with 3 ply of modified bitumen he would charge $8400. Is the 3 ply option a better one? Thoughts or comments?

Thanks again!

maybe consider rubberbond fleeceback. environmentally sound resistant to uv rays and tough.cold applied , no mess and no fuss. wont crack either.

I wouldnt trust any of those contractors to do my roof. I dont think that They are being honest.
They will put on a roof that is not as good as the one you already have.

Your material has not started to deteriorate at all.
Fix the one leak and be done with it.

Yes, you are going to have other leaks to fix.
But You own a swimming pool for a roof.
It happens.

i havent seen pics but whatever you do, make shure they tear out scupper hole and metal scupper and make it as big as they can when putting it back. that hole is the key to your roof not leaking. it must be as big as it can and as free from obstruction as it can.
also if you have a collectorhead , on the outside, the top of it must be a couple inches lower than the bottom of your scupper hole. ive seen so many collectorheads back up and leak back through scupper because they were install to high.

good luck.

gweedo

[quote=“gweedo”]i havent seen pics but whatever you do, make shure they tear out scupper hole and metal scupper and make it as big as they can when putting it back. that hole is the key to your roof not leaking. it must be as big as it can and as free from obstruction as it can.
also if you have a collectorhead , on the outside, the top of it must be a couple inches lower than the bottom of your scupper hole. ive seen so many collectorheads back up and leak back through scupper because they were install to high.

good luck.

gweedo[/quote]

Good stuff…Good info.

Is this the type of roofing that is self-adhesive, and apply without torch-down process?

[quote=“roof-lover”]

[quote=“gweedo”]i havent seen pics but whatever you do, make shure they tear out scupper hole and metal scupper and make it as big as they can when putting it back. that hole is the key to your roof not leaking. it must be as big as it can and as free from obstruction as it can.
also if you have a collectorhead , on the outside, the top of it must be a couple inches lower than the bottom of your scupper hole. ive seen so many collectorheads back up and leak back through scupper because they were install to high.

good luck.

gweedo[/quote]

Good stuff…Good info.[/quote]

I second that. At least 4-6 roofers said the same thing. Thanks!

Why not make the necessary repairs to the mod. bit. roof, enlarge the scupper, and then put a coating on it? Your roof didn’t look too bad, so you could make it go from something like this:

To something like this:

As for why to use copper, it is more malleable and can be soldered without worrying about the metal rusting. In the end, it probably won’t matter which one you use, though copper is better. Zinc is even better than copper, but it cost even more. I suspect you meant galvanized, which has a zinc coating.

Oh yeah, for what it is worth the product used to coat the modified bitumen was Firestone’s AcyrliTop PC-100.

thanks for the compliments guys.
roof-lover , good to have rain in florida again huh?
looks good cerb.
good to see you posting more.

gweedo.

yeah, also good useful info.
Thankyou, i’m going to look into that.
Im very interested in specific quality products to install over granulated modified bitumen
or smooth for that matter.

[quote=“roof-lover”]

yeah, also good useful info.
Thankyou, i’m going to look into that.
Im very interested in specific quality products to install over granulated modified bitumen
or smooth for that matter.[/quote]

If you want a good coating/roof-system that you can get a 10-year warranty on, look into HydroStop.

for granulated asphalt roof sistems:AcryliTop PC-100 and Acryli Bace Coat. Firestone item number w56rac6501(light gray),w56rac6550(white),W56fac6570(tan),and acrylic base coat w70racacbs(yellow).Good luck :slight_smile:

[quote=“Cerberus”]Why not make the necessary repairs to the mod. bit. roof, enlarge the scupper, and then put a coating on it? Your roof didn’t look too bad.
[/quote]

Thanks Cerberus! A professional waterproofing and roofing consultant (who usually only do “commercial building” but due to some special connection, also came to look at the roof), also commented the same thing. Some quick questions:

  1. By the way do you know what kind of coating we should be using? I assume that Firestone’s AcyrliTop PC-100 is the coating material that you recommended? Can this type of coating be applied to “granular” type of mod.bit. roof? Also how would this type of coating compare to some type of elastomeric roof coating (I take that the AcyrliTop PC-100 is not elastomeric based?) See:

lexiscoatings.com/modified-b … of-repair/

  1. Also, another roofer commented that among all the mod.bit. roof, “Dibiten” (www.dibiten.com) is the best. Thoughts or comments about this? Does the “thickness” of the mod. bit. matters by the way? Would one ply be good enough or should we apply for 2 ply? Thoughts?

  2. Some roofers commented that for the granular surfaced mod.bit. roof, it would be more difficult to “repair” it in the future, while the “smooth” surfaced mod.bit. roof would be easier to be repaired in the future. However, for smooth surfaced roof, we will have to apply a coating at the end of the process so that it can be UV-proof, but the granular surfaced does not need the coating. In general is this true? Any comments on this? What’s the pros and cons of using “smooth” surface mod. bit. v.s. “granular” type of mod. bit. on such a low-slope roof?

Thanks so much for all the great comments. Great discussions so far and you guys are the best!

By the way, anyone know anything about “cold tar process” here? How would this “cold tar” process compare to the “coating” process? Thanks!

Thanks Cerberus! A professional waterproofing and roofing consultant (who usually only do “commercial building” but due to some special connection, also came to look at the roof), also commented the same thing. Some quick questions:

  1. By the way do you know what kind of coating we should be using? I assume that Firestone’s AcyrliTop PC-100 is the coating material that you recommended? Can this type of coating be applied to “granular” type of mod.bit. roof? Also how would this type of coating compare to some type of elastomeric roof coating (I take that the AcyrliTop PC-100 is not elastomeric based?) See:

lexiscoatings.com/modified-b … of-repair/

  1. Also, another roofer commented that among all the mod.bit. roof, “Dibiten” (www.dibiten.com) is the best. Thoughts or comments about this? Does the “thickness” of the mod. bit. matters by the way? Would one ply be good enough or should we apply for 2 ply? Thoughts?

  2. Some roofers commented that for the granular surfaced mod.bit. roof, it would be more difficult to “repair” it in the future, while the “smooth” surfaced mod.bit. roof would be easier to be repaired in the future. However, for smooth surfaced roof, we will have to apply a coating at the end of the process so that it can be UV-proof, but the granular surfaced does not need the coating. In general is this true? Any comments on this? What’s the pros and cons of using “smooth” surface mod. bit. v.s. “granular” type of mod. bit. on such a low-slope roof?

Thanks so much for all the great comments. Great discussions so far and you guys are the best![/quote]

  1. Firestone is just one of many coatings. The HydroStop is pretty good too, but pricey. The advantage of HydroStop is that it stands up to ponded water. Of course, if you have good drainage an acrylic base like Firestones product is a good choice. The acrylics don’t stand up to ponding as well as urethanes (more expensive), but they should perform well on your roof from what I’ve seen. Any bad areas that start to peel in 3 years or so can then be coated in those areas only with a urethane.

  2. I haven’t dealt with Dibiten in years, and actually thought Dibiten USA went under. Anyway, it is just one of several mod. bits. out there that perform as desired. However, if you decide to go with a new mod. bit. roof I would certainly recommend an APP modified membrane over the SBS modified. Besides, why are you going to reroof if you can repair and coat what you have?

  3. If you are going to go with a smooth-surfaced membrane it should be something like DerbiBrite by Performance Roof Systems. Otherwise, stay with the granule-surfaced mod. bits., because smooth-surfaced mod. bit. membranes require re-coating periodically to protect them from the sun; plus you add to the cost of the job to install the roof, and then apply a coating.

  4. Stay away from cold process if you are talking about a waterproofing coating. If you are talking about cold-applied mod. bits. that is different, but you still want your laps heat-fused with a torch or hot-air gun.

I did some googling and found this:

barrettroofs.com/products/ra … index.html

I think this is probably what the other roofer was referring to as “cold tar” process…