Flat roof replacement dilemma!

Hi guys,
I sure hope I can get some professional advice on flat roof replacement here, as I have delayed a decision far too long. Your input would be much appreciated!

I inherited a mid-century home with a very slightly pitched roof that was originally tar-and-gravel, now EPDM. There is also a free-standing flat roof garage with Mod-Bit roofing, and a small studio house on the property that is half EPDM, half Mod-Bit. All need replacement roofing, but especially the main home, where I’ve had leaks.

After online research, consulting with a number of roofers, and observing what has held up best here over the years, I wanted to go with torch-down Mod-Bit. The roof on the free-standing garage and half the studio house are Mod-Bit, torchdown I think, and these have held up best for the longest time. However it seems torchdown is rarely available for residential anymore due to insurance costs of flammability.

The roofer I was most inclined towards hiring switched from agreeing with my choice of Mod-Bit to recommending silicon. That was like opening a whole new chapter. I think his reasoning was cost, and the fact that with silicon the old roof would not need to be stripped off and could easily be attached to guttering, as well as easily repaired over the years if needed. I’d take his advice, as the price is the best too, but still have reservations…

I am not sure the old roof on the main house should not be stripped off. I’m concerned about possible rotted decking, as I have leaks. Plus, silicon does not seem to have the longevity of Mod-Bit. And it’s white, which could stain due to overhanging trees. A dark color silicon is available, but at an added cost, raising the cost to be in range of Mod-Bit.

It’s really Mod-Bit versus silicon at this point. My neighbors have had bad experiences with TPO. And my EPDM roofing has not held up as well as the Mod-Bit.

Obviously cost is a consideration, too, with 3 structures to roof here. I can’t afford a wrong decision.

So I’m wondering what you guys think of silicon. I’m still more inclined towards tried-and-true Mod-Bit, but if I can’t get torchdown, would adhesive applied Mod-Bit offer the same durability and longevity?

It’s raining here right now and I’m listening to drips with the sickening feeling my roof/ceiling/beams/home are all going to cave in before I’m able to make a decision. Thank you so much for any advice that can help!

ps…if it makes a difference, I’m in the middle of the midwest here, seasonal hot and cold temperatures, plenty of rain.

You really need to tear it all off, remove damaged deck, and stay away from silicone. Your roof has too many questions and too much water in it. I would suggest a fully adhered 60 mil EPDM, but that is the system I use regularly. Finding a good roofer is what matters, you’re paying for the labor, the material cost is secondary.


Darkthirty gave you good advice. Properly installed 060 EPDM has a good 30 to 40yr life.

What state are you in?

Residential with tree over-hang and debris?
Torch-down is the most bullet proof if they know what their doing.

The roofer that agreed and then tried to switch to silicone wont know what their doing.

Silicone on top of TPO??


“IF they know what they’re doing”

Thank you! I’m no expert, but from what I’ve seen torchdown Mod-Bit seems most long-lasting and durable. The silicon would be over EPDM, though, by the way. Not TPO.

To be fair, the EPDM I have now is probably very old. I’m not sure how old. I inherited the place and do not know when my parents last put on a new roof. If there have been leaks, is it best to do a full tear off so as not to capture moisture in the decking?

Most roofers I talked with did not think the decking was rotted as they did not sense soft spots when walking over the roof. But there have been carpenter ants falling down from the ceiling. And the house is mid-century “post and beam”…there are only a few inches of roof and decking above the wood plank ceiling.

Regardless of what system you use, don’t coat it, vet your roofer, and tear it off.

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With 3 roofs to replace (plus renovating the little studio house)…I’ve got tons of expenses. I think full tear-off meant replacing the faccia, and the price just about doubles. So when a roofer tells me full tear-off is not necessary, it makes my heart sing! But I need to do right by this house. It was my dad’s baby.

Info from a core sample: “Core Sample - you have your EPDM membrane, then below that you have 2.5” of ISO board, then you have your tongue and groove ceiling inside/next.”

Square footage has been estimated between 2200 - 2400 square feet (estimates have varied.)

To get objective input locally, possibly from a roofing retiree, someone who could actually look at the roof without profit interest, is there such a thing as roofing associations?

Unless you have union carpenters ants, they’re busy. Repair the what you can and tear off the main house with the ants. I’ve seen them colonize EXP, so you might get lucky if they’re nesting in the Iso. What state are you in?

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Could there be partial tear-off where needed? Looking through my bids, most have been TPO. Some do Mod-Bit, but I’m not seeing torch-down. I realize torch-down is complicated by fire hazards and insurance coverage. In your opinion, are torchdown seams significantly more sturdy than adhesive?

Mod bit is torch down. 2 types - SBS is usually hot mopped, APP is torched. I’m certified in TPO but won’t install it due to what I see on repairs. What it comes down to is finding a roofer that has pride in his work. You pay the painter top dollar and buy $35 a gallon paint. Flooring and carpet is all pricey, furniture isn’t cheap. Hire a cheap roofer that’s willing to cut corners and install seconds to save you money, and the paint, floor, furniture is ruined AND you still need a roof… With 2 layers of roof, water and ants falling out of the ceiling there is no way I would do your roof without a tear off. I don’t think any manufacturer will warranty a system with those conditions. Edit: Sorry if I come off a little harsh, but you’re making yourself a perfect target for a con man that will promise you anything til he’s got all your money.


If we were giving you a proposal we would likely recommend a full year off and 3 ply torch applied modified, one ply mechanically fastened ventilated base sheet, one ply smooth, one ply granular cap sheet.


With any roof system, the qualified installer is the key to long term performance. There are many options as you have heard, here are my two cents:
-TPO, has long term performance issues, not to mention is very slick when wet if you have to get up there. Definitely no.
-Silicon can be a good restoration product to prolong the life of a decent roof, but as with all coatings the manufacturers specs will say “existing roof must be inspected and all Wet roofing and insulation must be removed and replaced prior to coating installation”. Your roofs are too small for this and wouldn’t make sense. A huge factory with a limited budget might consider this to buy some time to deal with the expense of a major replacement.
-EPDM is a very good roof if properly installed; however, as with TPO and other single ply membranes, locations with trees / brush in our area are prone to squirrels, raccoons, rodents, and other varments chewing threw and burrowing into it.
-I would agree with others above that the ceramic granular surfaced modified bitumen would be the best, most durable choice for your application. I would prefer the 3 ply system using the mechanically attached vented base sheet with an intermediate ply of smooth SBS smooth and the granular cap sheet both adhered with SBS adhesive and all seams hot air welded. (Torches scare me on homes, too much wood and can’t guarantee the installer is careful). You can also get the granular cap sheet in several colors with various manufacturers. This is a very good system, however, it requires that the installer installs, terminates, and seals all perimeter and vertical flashings properly. It takes a little more skill and effort but will lead to long term performance.

I would suggest that whichever way you go, that you have the installer provide a roof plan and detail drawings for all flashings, a minimum contractor’s two year labor and material warranty in writing, and references for roofs installed 5 years or older. If a contractor provides resistance to these items I would continue to look for a quality installer elsewhere.

Sorry for the long narrative, but one last thing, you may find a qualified affordable contractor; however, “you get what you pay for” is very true in the roofing industry… Good luck!


Torch prices in my area are set to skyrocket this year. Friend of mine with 0 claims went from 14k for insurance to 35 with worse coverage.
Probably why your seeing bids for tpo

Been told by a tech that membrane splitting in the field is still common with TPO.


Insurance won’t cover the contractor if they burn your house down while torching over wood deck, and they would have to pay for it out of pocket. At least that is true here.

Mod bit can be installed with hot asphalt, torch, cold adhesive, or self adhering. You can also cold adhere the rolls and hot air weld the seams.

Silicon is not a roof, it is a coating. Anyone who tries to sell it as a roof is misleading you or misinformed.

You should go mod bit but you must also be careful about mechanically fastening the roof. If your deck is also the ceiling inside I have seen a lot of mistakes where screws or nails go thru and stick out inside.

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I am very excited to see so much positive response for Mod-Bit! It has taken almost a year to get to this much of a decision, and I am so relieved to finally make some progress.

The roofer I have most contact with has suggested tear-off and replacement with Mod-Bit, with EPDM lining the gutter. However, he said there would have to be a 1/2 inch to 2 inch metal lip over the outside metal fascia. This could look weird, I don’t know. The alternative would be replacing the metal fascia altogether, which would add to costs.

I do need to do something soon. There’s a drip over my dining room table and we haven’t had a significant rain in a week : (

The metal lip will fine as long as the color matches well. Nothing to worry about.

Find a different guy you can’t merge those two products and expect that marriage to last…it sounds like you have a Yankee gutter also. 2 ply torch down,use GAF rubber-oid . Do your homework.Rush strip? mechanically fastened? , primed ? smooth then granular cap✓ done right 30-50 years of life possible roof maintenance is easy and lasting and should be done every couple of years