Our neighborhood review board is encouraging us to ballast the whole thing

Why?

Are roof leaks part of the "mountain modern" style??

They feel a TPO roof looks unfinished. It will be a commercial grade roof but can anyone see a benefit to ballast that we are not understanding or 6" parapet?

The difference between .05/12 and 1/12 is 1/2" per foot. Neither will be a good option in a snow prone region if you ask me.

Look around nearby for local examples, talk to local builders, roofing contractors and even a TPO manufacturer's rep for advice. Snow loads can vary significantly due to elevation in the same subdivision.

FYI - no expertise required to be on the neighborhood review board.

We had some similar struggles. More here: https://amodernmountainhome.com/2020/08/06/hoas-and-flat-roofs/

Can anyone see this roof? Anything over 1/4 on 12 is acceptable for TPO.

IMO 2/12 is as low as I would go whhere snow load is an issue we have a shingled 2/12 roof in a S. B.C. where we can get snow loads that actually need to be shovelled off the roof we are planning to do a metal roof next time.

That seems a very strange request, to suggest a ballasted roof, probably by someone who is not familiar with types of roofing. Maybe they are not aware that there will be a fascia, and a ballasted gravel stop may in fact be more prominent than a TPO edge detail. Then suggesting a parapet sounds like they initially may not want to see the roof slope expressed on the (rake) elevations, as a parapet will hide the slope.

A TPO is more expensive. A TPO to most looks cleaner from above, if that is a concern with neighbors up higher on the hill. In my experience, it is always a request to "upgrade" to TPO, not the other way around.

People in UT have been very successful over the last decade using TPO on flat roof designs even with the snow load. I agree the TPO looks cleaner from above but they see it as unfinished so are asking us to basically compromise the integrity of the roof so that it is aesthetically pleasing to the one homeowner above us who by the way has a TPO roof but got approved before they changed the design rules!

Unfortunately these are not just random homeowners on the board. They work for the development but really have little to no roofing experience. I'm out of my mind though and don't want to be stuck with a disaster after the fact. While a ballast roof on a full flat roof is fine, a ballast roof on a 1/12 slope is a terrible idea in a Utah climate. And doing half ballast and the 1/12 with a parapet seems even more ridiculous. So we are gathering as much data as possible to present and I was hoping someone on here with knowledge would chime in. thank you!

And we would have loved to do a flat metal roof on these flat roofs but that is not an option. in UT at least you get no warranty with a metal roof on anyting less that 2/12.

That's a great idea to reach out to the TPO manufacturer to get their perspective on ballast on a 1/12.

The parapet they said would hide the TPO if we chose not to do ballast. Seriously our architect couldn't believe they even suggested that. A huge plane of roof was really going to be hidden by a 6" parapet?!? nonsense. And from our understanding isn't a parapet even more inclined for clogs and frozen drains?

Hi there! I know I'M late to reply here but funny enough we are building in utah too. We have a combo of metal sloped and flat roofs (flat roofs are about 1600 sq feet) and we need to do ballast roof for those flat areas, per the HOA. There was an error on the builder's part adn they forgot to include the cost of putting gravel on the roof. Even without the cost of gravel, just the flat roof (minus stones) came in at $35K for 1666 sq feet. That's about $21/square feet or $27/square feet if you include cost to put stones on the roof. Does this sound normal to anyone??? Our metal roof is about $9/sq feet and we have about 6700 sq feet of that and that came to $65K.

And while I'm asking here, I looked at the invoices from months ago and the roofer's invoices say "installation of ballast roof" but again, there was no application of gravel/stones from this roofer. We are having our landscaper do that part since the roofer does not apply the stones. I find it odd that their invoices say "installation of ballast roof" but all they did was apply the Dens deck, insulation, and EPDM.

Littlemansion are you building in the park city/heber area? Who is your builder out of curiosity? Ballast should include stones.  We are just starting our build in heber.   I'll have to look at our bid for our flat since we are all flat. We were told flat was a lot cheaper than metal which was a first that something we were actually wanting was the cheaper route... that's a significant difference and I'm curious why. 





 route route...

Littlemansion, that flat roof price seems incredibly high unless there was a lot a detailing at penetrations, skylites and such. Make sure the ballast is a rounded gravel that won't break down due to freeze/thaw. Granite is good. I've seen limestone break into sharp pieces and cause holes in roof.

Hi @lar32, I probably shouldn't publicly cite the builder in this forum but we are building in a dev't/club in the same area. The flat roofs are definitely less expensive based on all this post-construction research I've been doing. Something seems to have "went wrong" to say it kindly. A ballast roof means you have to put stones/gravel/pavers on top of the EPDM and the invoices say "installation of a ballast roof" but all we got was a rubber membrane roof. We're currently digging deeper into this. Coincidentally, the invoices that mention "ballast roof" went missing and were never sent to us but we were billed for a "ballast roof". One tip that I can give you is there are lots of diff stones you can use and they vary in price so ask your builder for the least expensive. I tried following you on houzz so that perhaps I can msg you privately - i rarely use this forum so i'll try to reach out in case you have any other questions or post here and happy to help! Another thing - a flat ballast roof is less expensive but in the long run, if you ever have a leak/tear in the membrane, it will be a very costly repair process so make sure they do it right!

@lar32, Would you be able to tell me what your cost was for your flat roof and the sq footage? I emailed 2 roofers in the area in hopes that they can provide an estimate but not sure they'll pull through. This would be incredibly helpful!

A ballasted roof has to be initially designed for in the structure, as there is significant weight added. No roofer I've ever come across would forego themselves installing the ballast, yet still provide a warranty. And a ballasted roof has no mechanical fastening to the structure, so they would not stop at the membrane and consider the job finished. Something is wrong. As far as cost, a ballasted roof would probably require a commercial contractor, where prices will be higher per unit to have them come down to a 1600sf residential roof instead of a 10,000+ sized footprint that typically have ballasted roofs.

If someone other than yourself changed the EPDM to fully adhered (since maybe they specified using 60mil anyway) then that has to be reconciled with the cost, roof detailing, and HOA.

3onthetree, thank you very much for your insight/advice. I looked at the roofer's bid/contract and it says:

"Ballast Roof":

-Install tapered installation, 1/2" dens deck, 60mil EPDM, install 24 gauge drip metal, parapet cap metal"

At this time, I don't know what's holding down the EPDM - not sure if it's fully adhered or just laying freely (if that's such a thing) but I'm getting clarification from the builder on what it exactly looks like and how it was constructed.

Based on what I copy/pasted above in bold, did I essentially get a Flat Rubber Membrane Roof? And for $35K for 1666 sq feet? All I know is I didnt not change anything including the EPDM to fully adhered. The architect laid out plans on how to lay down the roofing elements for the flat ballast roof and all I know is the order in which they laid down those components changed but I think EPDM is what's on the very top as of now. And now I am paying an extra +$13K on top of he $35K for a landscaper company to lay down filter fabric and stones on top of EPDM. That's $48K total I"m paying for a true ballast roof for a small portion of my house

Littlemansion, is there a way to private message on houzz?  I just followed you but am unclear if there is a way to message. I agree a lot of this discussion would be better off this public string.

Unfortunately we are supposed to have our driveway being dug out next week so we are just at the beginning stages and our quote isn't broken down into great detail but our whole house is 6500 sf but the bid isn't broken down by sf.  Our builder just sends the plans to his roofer and gets a quote.  Heaven knows how close it will be to what we actually pay.   

Because we have a 1/12 slope on half and .50/12 on the other half we are unable to use metal but refused to ballast the 1/12.  Our hoa is also very strict but for our roof is not requiring ballast after we fought it.   Because even at a 1/12 pitch snow would cause the gravel to move.  We researched our flat roof system a lot so feel pretty educated on best practices which was important building in the utah climate. 








 6500  sf

So a differentiation with the bid was not defined for "ballasted roof" ("single ply membrane ballasted roof" or "built-up membrane ballasted roof"), but you say was in the architectural details and specs, and the structure accounted up to another 25lbs/sf? For either, the ballast is an integral part of the system. The manufacturer of the EPDM should have specific installation instructions for their warranty that concerns the ballast, so technically if the roofer didn't follow those, they are in breach. However, there needs to be a reconciliation between the architect's details, specs, the bids, and what the G.C. requested in his sub's bids and why he did not account for complying with the architect's details (switched the order around???).

With the DensDeck used though, that tells me that they adhered the EPDM to it. Otherwise it would be installed right over the polyiso (unless there is some brand I'm not aware of their details). But that also means that there are very specific guidelines in how the polyiso and DensDeck were fastened, you can't just switch willy-nilly between ballasted and open membrane.

For 1600sf, the $35K seems high, and the $13K too. On the ballast, my math says its about 20yards worth of gravel on the light side (1600sf @ 4" thick = 20cuyd), and I'd use $50/cuyd for the gravel.

FWIW there are single-ply ballasted systems that go up to 2:12, no concern for movement from snow.

https://www.houzz.com/settingsAdvanced

hi @lar32, try going here and adjusting settings. this might work for PM'ing.

@3onthetree, thanks again for this. i think i need to have some conversations this wk (sadly all this is post-construction so i'm not sure what recourse i have). and thank you for the cost insight on stones. the cost of the stones isn't really high - they said it's the labor that is the bulk the cost of shoveling/spreading out gravel across the flat roof.

Three on the tree, you are correct technically you can ballast up to 2/12 but you will not be able to find anyone or any discussion of anyone ever doing it on a 1/12 or greater pitched roof on a custom home.  The gravel would end up in our gutters after a year or two.   The heavier the gravel the more risk to the roof for tears as it eventually moves. Not to mention at some point there will be a roof leak and moving that gravel is expensive and can make finding leaks very difficult.
Little mansion i updated my settings but you have to update yours to allow me to send you a message.   It doesn't give me an option to email you!  Being that you have completed your build in the same area,  i would love to be able to compare notes as we go through this… if you are open to that.   Thank you!



 that.   Thank

Will the single-ply membrane be installed over the roof deck or over the insulation?

In my experience, low-sloped ballasted roofs have internal drains rather than gutters so the entire perimeter of the roof is level. Scuppers would be provided for overflow protection.

The architect's plans have the EPDM (membrane) under the insulation (so over the deck) but i'm pretty sure the builder put the membrane on top of the insulation. theree is zero pitch/slope so we have no drains. The water would just run off the edges of the roof. They did mention scupperes so we do that those installed.

The thing I'm trying to understand is the contract/bid says "Ballast Roof" but after they were done , the buildeer said they forgot to include the actual ballast (stones) and the application of it in the Construction Estimate. Doesn't a "ballast roof" definitely mean a roof covered w/ stones or graveel?

Dens Deck is not recommended by the manufactrer for ballasted roofing systems.

The only part of the contractor's "description" (it's not a specification) that suggests the roofing system might be ballasted is the title, "Ballast Roof".

The "description" suggests Dens Deck was intended to be installed on top of the insulation as a "recovery board" providing the typical base to which a single-ply roofing membrane is mechanically attached or fully adhered. This is not a ballasted system. Also, the board for this kind of installation is Dens Deck Prime.

Your architect should have written the roofing specification.

https://www.buildsite.com/pdf/carlislesyntec/DensDeck-DensDeck-Prime-Roof-Board-Summary-Brochure-229162.pdf

I would have a big concern with snow load on your flat roofs. Is your currently designed structure sized to handle the dead load from a constant snow pack throughout the winter?

A roof should never be perfectly flat; no roofing system is designed to be under water. The typical slope of a low-slope, single-ply membrane roofing system is 1/4" per foot.

In the western mountains, because of the dry air, hot sun and low air pressure, sublimation (skipping of the water phase) occurs so the snow loads are relatively transient and snow just seems to disappear. However, short term storm and drifting loads must be accommodated especially for shaded roofs.

@Norwood Architects, It's 1600 sq feet of flat roof compared to about 6000 of sloped meetal roof so it's not the bulk of the home. The architectural plans say ballast roof so I am assuming the home is structrually sound and can take the snowload.

@res2architect you're right - maybe there IS a very slight pitch but it is being called out as a flat roof in plans.. I also just looked at old photos and i see Dexcell being used under the EPDM. Is that the same as Dens Deck? I looked at Dens Deck installation guidelines and you are absolutely right - they are not reco'd for ballast roofs. But maybe Dexcell is and that's why they used that instead?

@lar32 I just messaged you earlier, let see if this works :)

National Gypsum's DEXcell and Georgia-Pacific's Dens Deck are both fiberglass mat covered gypsum underlayment/recovery boards. Other products are made with the same brandnames so its difficuilt to compare them without more information.

From your description of the work it appears you have a fully adhered membrane instead of a ballasted system.

@res2architect That's unfortunate because both my Construction Estimate and the Roofer's Invoices (and the Architect's plans) all say "Ballast Roof". Would you say $35K for 1666 sq feet for a fully adhered membrane roof is high? That's $21/square feet...compared to my METAL roof which is $9.20/sq feet and that cost me $66K for 6700 square feet.