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Low slope EPDM or TPO?

I am going to have to reroof 3 squares of low slope roof on my home.

My plan is to fit a cool roof to keep cool in summer, plus 0.5" deck and two layers of lapped 2" of polyiso under for winter warmth.


I have a choice of white EPDM, or white TPO.

Also there is light gray TPO and that would match the smoke gray EcoStar Majestic Slate (in our Product Guide) on the tie in roof which is tempting. But the light gray drops the reflectivity from .75 for white to .45. I'm on Long Island the heat isn't that strong, but no point heating the roof needlessly.

I see there are two TPO membranes in the product guide (one Dow one Firestone).


1) What's the plus and minuses of EPDM vs TPO.
2) For TPO peel and stick, or applied adhesive?

TPO is more slippery - bad for falling, good for cleaning.
TPO is available in light gray if I go for looks (but it is not visible from ground level).

I see a lot of comparisons being made around the net, but usually by those with a vested interest.

Asked by Mark Bartosik
Posted Jul 18, 2009 12:33 AM ET

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15 Answers

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1.

I've been working with EPDM for many years and have had such great success with it I can't imagine going with another product. We lay brick floors on it all the time and even did one roof with a Koi pond on it and have used it to create landscape ponds and to make weatherstripping for barn doors. The only down side I see is that the powder they dust it with at the factory can be a skin irritant and the left overs seem to walk out of the back of the storage van as employees cut off scraps for chicken shed roofs and firewood piles etc. The ability to get cured and uncured seaming tape is a big advantage for me. I've lined wooden gutters with the stuff and formed the outlet flashings with the stretchy uncured stuff held in place with copper collars. Amazingly versatile.

That said I have no experience with the TPO and had I started with that I might be singing it's praises today.

Answered by Michael Chandler
Posted Jul 18, 2009 3:46 PM ET

2.

my roofer prefers sarnafil over TPO and EPDM having used all three single ply membranes. from lifecycle perspective of TPO and EPDM research i've done has TPO coming out on tops, but my roofers concern is more with durability and risk of puncture and for that he picks sarnafil (sp?) over the others which also comes in light colours for solar reflectance. for rainwater harvesting of flat/low slope roof, non bitumen roofing is highly preferable hence torch-on not a good solution if looking to harvest, and why wouldn't you :0

Answered by Allison Ashcroft
Posted Jul 28, 2009 5:00 PM ET

3.

Allison, thanks for that - Sarnafil
I'm going to call their local rep tomorrow!
They have pictures of their roofs up to 33 years old. That's the sort of durability I'm after. They even have in nice light reflective colors!

I'm going to be installing some solar peal and stick laminates on this, and really want this roof to last. I'm mostly concerned with longevity and durability (which go hand-in-hand).

My only reservations are getting an installer for only 3 sq, and it being a PVC based product (e.g. plastizer leaching into rain water). It looks just like TPO to install - with a heat gun.

If I had to choose between TPO and EPDM what makes TPO come out top for you?

Answered by Mark Bartosik
Posted Jul 28, 2009 11:28 PM ET

4.

I have to jump in here to discuss Sarnafil product. If this is a Sarnafil PVC membrane, DO NOT use butyl adhesive thin-film solar laminates (like Uni-Solar). The PVC material counteracts with the butyl and will turn it to paste, your panels will delaminate and you'll be very upset.

My recommendation is to go with Firestone Eco-White EPDM, which has a nice reflective surface and is very durable, especially when using the membrane as a substrate for thin-film PV. We have a research project on our office building in Manhattan, Kansas that is testing the membrane tolerances of 9 different roof systems, including PVC, TPO, black EPDM, white EPDM, metal, and a new white mod. bit. membrane made by Derbigum. Don't forget that all PV modules generate heat and can cause the laminate panels (especially those with a thin sheet metal layer like Uni-Solar) to expand and contract as they warm up and cool down, so you want to use a roofing membrane that provides durability and flexibility, which is why I like the Eco-White EPDM. You can visit our website at www.diamondsolarmonitor.com and www.diamondsolarsolutions.com to learn more. Also, if you haven't already moved forward with this project, call me and we can discuss.

Answered by Marc Cameron
Posted Dec 9, 2009 12:14 PM ET

5.

Marc I have already installed this.
In the end I chose to use an 80 mil white TPO.
Unisolar have qualified the Firestone (actually branded as GenFlex), and at the time of ordering materials they had completed testing on Johns Manville TPO, which is what I went with because a smaller roll length was available 10 ft wide.
I spoke with Unisolar in Germany (they are easier to get on phone than in USA) and they too warned about non approved substrates like Sarnafil.

Answered by Mark Bartosik
Posted Dec 9, 2009 12:41 PM ET

6.

Mark,
Great choice with the 80 mil TPO, which has the durability necessary to withstand the pressures created by the expansion and contraction of the PV laminates on the substrate. As a roofing contractor and a solar installer/distributor, I have installed on 45 mil TPO and on 60 mil TPO and I have never been totally satisfied with the results. The only real concern right now about TPO is its ability to withstand temperatures of greater than 150 degrees. We have thermocouples installed on our system here in Manhattan, KS that measure the temperature of different roofing membrane with PV installed on top. So far, we've not seen temperatures higher than 160 degrees, and fortunately they don't stay at that temperature very long. For the purpose of maintenance, I would suggest that you regularly inspect the PV panels and keep them good and clean. Just curious, what type of inverter are you using? Sunny Boy? PV Powered? How is your system performing? Are you satisfied? Please respond. If you're interested in some of the temperature readings coming off these panels and membranes, you can visit this website where we have the data streaming live. http://www.sri-engineering.com/mrca/. Unfortunately we have about 12 inches of snow on the ground and roofs, so it won't be of much interest, but check back when the sun is shining to see what's going on. PS - SOOOOOOO glad you didn't go with PVC and I bet you are too.

Answered by Marc Cameron
Posted Dec 10, 2009 12:44 PM ET

7.

Marc, I used Unisolar PVL-124 and Enphase M190 inverters. Be careful some PVL versions like 144 I think may push the high side voltage of these inverters. This is not a manufacture certified configuration.

The configuration is 2 PVL-124 in parallel for each M190 inverter.
I only have 4 laminates (and two inverters) -- all I could fit in the unshared space.

Since your concern is largely temperature and stress on membrane, here are the details of attachment...

I laid the 4 PLV-124 side-by-side without a gap, which maybe I should have left for expansion. But the width is still only a quarter of the length. I have seen installations with groups of PVL with no gap and installations with a gap. The install manual does not specify.

I fully adhered the TPO membrane to 3.75" of polyiso board (I preferred this over mechanical fastening).

I've been crazy busy and have not yet wired in the inverters and metering so I cannot say anything about output yet (I have 3 other solar systems on the house so I can compare).

- Mark

Answered by Mark Bartosik
Posted Dec 11, 2009 10:27 PM ET

8.

I just started to read these threads and thought of a great solution for any membrane or mod bit. roof application. It is a BIPV product called CoolPly that is manufactured by SolarFrameWorks. You can work with TPO, PVC, EPDM, and even mod bit using crystalline modules so you can maximize your kWh on a constricted roof. The CoolPly can be designed from a 0-20 degree tilt angle and it supports any crystalline module out in the market today. If you want more kW for your roof use Crystalline!!!!!!

Answered by Joe Patrykus
Posted Dec 21, 2009 5:28 PM ET

9.

Mark - I think that it would be a great idea for you to regularly inspect your uni-solar panels given that you haven't left any space between the panels. I would guess that you're aware, but the uni-solar panels have a very thin layer of stainless steel on the bottom, just above the butyl adhesive. This causes the panels to expand and contract with heat. With no space b/w the panels, you'll want to make sure to inspect the panels regularly to ensure that you're not running into any adhesion problems along the long edges.

Answered by Marc Cameron
Posted Jan 26, 2010 1:23 PM ET

10.

I trust the the TPO over the EPDM due to the weldability verses the gluing. In low-slope or ponding areas I feel the better choice is TPO.

Answered by gambler_iam
Posted Feb 1, 2011 3:55 PM ET

11.

I went with the TPO, and I am very pleased with it.
I don't have data for it, but in summer the room is also now cooler

Answered by Mark Bartosik
Posted Feb 1, 2011 4:57 PM ET

12.

I've also had long term great success with EPDM. Going forward, however, I won't use anything that is black, because we need to reject that heat back out to space. Is there white or paintable EPDM?

TPO sounds OK.

As you probably know, the low cost solution is torch-down modified bituthane, NOT ok if there is the slightest bit of ponding. It can be painted silver, which isn't as good as white. I don't know if the white stuff is compatible with modified.

Answered by Kevin Dickson, MSME
Posted Feb 1, 2011 5:47 PM ET

13.

Great info everyone, I have used glue down 60 mil Firestone in the past with PT floating deck over. Makes a nice deck over boathouse. Glad top see Firestone has a white product. What one of all these products is OK for using as the actual surface to walk on for a deck on top boathouse, any of them? Not that we would but sometimes customers like indoor outdoor carpet on their decks.

Will use this soon, Firestone Eco-White EPDM, with the walked on area covered.

Answered by aj builder, Upstate NY Zone 6a
Posted Feb 1, 2011 8:12 PM ET

14.

The TPO that I have is 80 mil and is fine for ocassional walking.
Some manufacturers have EPDM walkway mats, I have only seen black and gray, I didn't see anything in white.

Answered by Mark Bartosik
Posted Feb 1, 2011 9:01 PM ET

15.

Have you considered a liquid-applied PMMA roof membrane. You can get it in bright white, it is self-terminating, and it is extremely durable. You can even make it more durable buy adding a traffic surface to it. Matter of fact, liquid-applied PMMA were origianlly used as a waterproof traffic coating.

Michael H. Lichy
mlichy2@lichy.com
RC Lichy & Associates, Inc.
www.lichy.com
Roofing and Waterproofing Consultants

Answered by Michael Lichy
Posted Mar 6, 2011 12:58 AM ET

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