Explain flat roofs to me
September 3, 2021 8:48 AM Subscribe
I own a townhouse with a flat roof that needs to be redone. The options I see include SBS/modified bitumen, liquid membranes, EPDM, and TPO, but here in NYC, almost nobody does EPDM or TPO on residential roofs! I want to learn more about why this is and how opinionated I should be about these different systems.
I am looking for a long-lasting and energy-efficient roof. My main concerns about the SBS systems that I see are, first of all, that it is on the thick/heavy side meaning that in 10 years I'll have to pay someone $$$ to pull it all off and replace it, and second of all, that many of the most durable systems come only in black and can't be easily painted white/silver, and will thus trap a lot of heat. The liquid systems seem cheap and easy to apply, and are very reflective, but seem significantly less durable.
So much of the NYC residential construction industry is built on decades' worth of "this is how we've always done it", so I don't want to just blindly follow what the contractors suggest. If there is a better way, I want to do it! I am very willing to pay 2x the cost today for a 2x length warranty especially if it solves my issues above. On the other hand, I don't want to hire someone to install a kind of roof that they don't usually do, since the chances are that they'll do a bad job if they'll even agree to do it at all...and maybe there's a reason they don't use them as much?
Thanks!
I am looking for a long-lasting and energy-efficient roof. My main concerns about the SBS systems that I see are, first of all, that it is on the thick/heavy side meaning that in 10 years I'll have to pay someone $$$ to pull it all off and replace it, and second of all, that many of the most durable systems come only in black and can't be easily painted white/silver, and will thus trap a lot of heat. The liquid systems seem cheap and easy to apply, and are very reflective, but seem significantly less durable.
So much of the NYC residential construction industry is built on decades' worth of "this is how we've always done it", so I don't want to just blindly follow what the contractors suggest. If there is a better way, I want to do it! I am very willing to pay 2x the cost today for a 2x length warranty especially if it solves my issues above. On the other hand, I don't want to hire someone to install a kind of roof that they don't usually do, since the chances are that they'll do a bad job if they'll even agree to do it at all...and maybe there's a reason they don't use them as much?
Thanks!
Best answer: A few notes... Since my building just did this and I have roofers above me right now.
1. There is no need to pull off a flat roof every 10 years unless you have major water issues, in my building we went 40 years between layers (yes layers! If you don't have major damage you can just slap a new layer of roof on, for obvious reasons this doesn't seem to last as long as a brand new roof, but can certainly be a valid fix.)
2. SBS comes in white, and that appears to standard in NYC.
3. Getting a warrantee for over 20 years was neigh impossible, for a fresh layer we got quotes a 15 year warrantee, for a full roof replacement (our decking had rotted out partially and is being replaced) we got a 20 year warrantee.
4. Decide on your access to the roof and if you need to adjust that, we kept our heavy roof hatch because we don't want people to have casual access on our roof. (Obviously it's fine for fire-safety, isn't considered an emergency exit for our building, but YMMV)
5. Torch down roofing isn't allowed in Manhattan anymore (since the 1990's!) for residential buildings (it's using a blowtorch to apply tar, and most buildings still have wood decking so it's a huge fire risk), so if anyone tried to sell you that ask questions. (Not sure if that's the BUR system referred to above)
Cost varied tremendously, our high and low were separated by 80k, and listed out the same work, insurance coverage etc. Talk to your neighbors, get at least 4 different quotes and compare proposed contracts to make sure nothing obvious is missing. Also consider if there's any landmark stuff involved, that will complicate this unless you are doing an emergency repair (and it's still complicated). DM if you have questions, I was the point person for this project for my building.
posted by larthegreat at 10:59 AM on September 3, 2021
1. There is no need to pull off a flat roof every 10 years unless you have major water issues, in my building we went 40 years between layers (yes layers! If you don't have major damage you can just slap a new layer of roof on, for obvious reasons this doesn't seem to last as long as a brand new roof, but can certainly be a valid fix.)
2. SBS comes in white, and that appears to standard in NYC.
3. Getting a warrantee for over 20 years was neigh impossible, for a fresh layer we got quotes a 15 year warrantee, for a full roof replacement (our decking had rotted out partially and is being replaced) we got a 20 year warrantee.
4. Decide on your access to the roof and if you need to adjust that, we kept our heavy roof hatch because we don't want people to have casual access on our roof. (Obviously it's fine for fire-safety, isn't considered an emergency exit for our building, but YMMV)
5. Torch down roofing isn't allowed in Manhattan anymore (since the 1990's!) for residential buildings (it's using a blowtorch to apply tar, and most buildings still have wood decking so it's a huge fire risk), so if anyone tried to sell you that ask questions. (Not sure if that's the BUR system referred to above)
Cost varied tremendously, our high and low were separated by 80k, and listed out the same work, insurance coverage etc. Talk to your neighbors, get at least 4 different quotes and compare proposed contracts to make sure nothing obvious is missing. Also consider if there's any landmark stuff involved, that will complicate this unless you are doing an emergency repair (and it's still complicated). DM if you have questions, I was the point person for this project for my building.
posted by larthegreat at 10:59 AM on September 3, 2021
Best answer: My uncle is a union roofer, and I’ve been involved in a lot of institutional flat roof installations that are intended to last forever.
I once asked my uncle what the most durable flat roof, and he recommended a 5 layer SBS roof. That’s really expensive, so at work we install 3 layer SBS, in the most reflective white finish available. I prefer the integrated white finish over coatings, but it’s more expensive so I’ve had roofers try to skip it and hope I don’t notice. SBS (here) is typically only available from the higher quality roofers, is more forgiving of installation errors, highly durable, and somewhat self-healing. It’s heavy and expensive due to the labor. It easily lasts 20 plus years.
For my own house, he recommended heavier weight EPDM. It requires more skill and isn’t redundant layers. But it’s lightweight, fast to install, reliable if installed well, and easy to patch. TPO is similar but I’ve heard it stiffens and becomes less repairable. The EPDM has been surprisingly resilient to punctures but it is a risk. Also lasts 15-20+ years.
Other roof thoughts you didn’t ask for:
- add as much insulation board as you can. It will make a huge difference and is much better than attic insulation because it’s a blanket on the outside.
- make sure the roof slopes correctly to the drains. You can use sloped insulation board for this. You don’t want water ponding anywhere.
- Have a backup drain overflow.
- the vast majority of leaks, like really almost all of them, are at joints. That’s the most important workmanship.
- clean your drains regularly
posted by sepviva at 7:24 PM on September 3, 2021 [1 favorite]
I once asked my uncle what the most durable flat roof, and he recommended a 5 layer SBS roof. That’s really expensive, so at work we install 3 layer SBS, in the most reflective white finish available. I prefer the integrated white finish over coatings, but it’s more expensive so I’ve had roofers try to skip it and hope I don’t notice. SBS (here) is typically only available from the higher quality roofers, is more forgiving of installation errors, highly durable, and somewhat self-healing. It’s heavy and expensive due to the labor. It easily lasts 20 plus years.
For my own house, he recommended heavier weight EPDM. It requires more skill and isn’t redundant layers. But it’s lightweight, fast to install, reliable if installed well, and easy to patch. TPO is similar but I’ve heard it stiffens and becomes less repairable. The EPDM has been surprisingly resilient to punctures but it is a risk. Also lasts 15-20+ years.
Other roof thoughts you didn’t ask for:
- add as much insulation board as you can. It will make a huge difference and is much better than attic insulation because it’s a blanket on the outside.
- make sure the roof slopes correctly to the drains. You can use sloped insulation board for this. You don’t want water ponding anywhere.
- Have a backup drain overflow.
- the vast majority of leaks, like really almost all of them, are at joints. That’s the most important workmanship.
- clean your drains regularly
posted by sepviva at 7:24 PM on September 3, 2021 [1 favorite]
Response by poster: Turns out I just had to ask for white SBS??? Thanks all!
posted by goingonit at 10:35 PM on September 5, 2021
posted by goingonit at 10:35 PM on September 5, 2021
This thread is closed to new comments.
...incidentally, experience in Chicago has shown that pretty much any roof system (including SBS) can be reflective-painted with good success, so the color alone probably shouldn't dissuade you (e.g.; Karnak 28 can be applied to cold-applied SBS that's cured for >30 days, or BUR that's weathered for >180 days, or metal that's weathered for 30 days, etc. etc.).
posted by aramaic at 9:15 AM on September 3, 2021 [1 favorite]