[RE-wrenches] PV and Roof Flammability

[Matt Lafferty]

Hi Joel,

Trying to compare HVAC equipment to PV in a roof covering flammability
discussion is about the same as the proverbial apples to oranges. They are
profoundly different. I will even go out on a limb and say the the PV
industry lobbyists are probably foaming at the mouth more than HVAC
lobbyists. Go to SPI and then go to the next national SMACNA or ASHRAE
convention to see the difference.

Deciding to study the effects of putting PV over roof coverings, and not do
the same for HVAC equipment, didn't have squat to do with lobbyists.

Let's start with the differences:

First and foremost, the amount of roof covering that is covered by PV is far
greater than HVAC equipment. Think in terms of 25-100X, or infinity. In
flush-mounted systems, the PV is mounted close to the surface of the roof
covering. HVAC equipment is enclosed in a steel cabinet and generally does
NOT sit over the roof-covering due to curb-mounting. I see these differences
as the primary ones.

We should all want to know how spreading PV across many contiguous square
feet of roof affects the flammability of the roof covering. Good or bad, we
should want to know. If putting PV over the top of a roof covering decreases
the effective fire resistance of that roof covering by an unacceptable
amount, maybe we shouldn't just throw it up there willy nilly. If we find
that some application is bad for protecting the structure and people in it,
we need to address that. If we find that it doesn't cause any negative
effects, we want to know that.

If we don't address it, sooner or later installations are simply gonna stop
on a Public Saftey issue. If we don't address it, when (not if) there is a
fire with human casualties, and the roof beneath the PV is involved, the
lawyers are gonna insist the PV is at least partly to blame. If you don't
have a valid study, you don't have a defense. I say be proactive.

The question has been around since before I got into PV. I know that some
comp shingles get brittle because they are under an array and some don't.
I've seen many aging low-profile flush-mounted rooftop PV systems at this
point, and there is a distinct difference in the weathering of some
materials. Because the PV is over them. Specifically because the PV is over
them. Although I haven't tracked hard data on this, my unscientific
observation is that arrays mounted farther away from the roof have less
adverse effects on the roof covering. 

I haven't bought the standard solar industry line that "your roof will last
longer because the solar shades it". I believe it's true in some cases and
patently false in others. But I don't know how to identify which brands and
models of shingles have which characteristics. Particularly if the material
is 5 or 10 years old already. And, if I don't know, then I sure ain't gonna
expect the salesperson to know, much less care.

It's always been in the back of my mind whether or not the PV affects the
ACTUAL flammability of the roof covering. And not just when they are both
new. What happens over time? Does the flammability change with age? My
instinct is that it likely does in some and does not in others. But which
ones? Are they the same ones that get brittle?

>From a big-picture view, I'm glad somebody is at least studying this and
reporting on it. I'm glad that it's not just the roofing industry, or worse,
UL on their own. I'm glad that folks from the Solar ABC's are involved.

I haven't read this whole interim report yet, but I will. The Exec Summary
was encouraging and disappointing at the same time. Nevertheless, these
findings will affect the way we build stuff going forward. And they should!


Some module or rack manufacturer is gonna have to come up with a convection
enhancement that minimizes gassing and gas stagnation beneath the modules,
for instance. Or maybe we find that simply installing at least X number of
inches off the roof surface has no negative affect on the roof covering. Or
maybe we find that PV simply should not be installed above certain roof
covering products at all. And learn how to identify them, inform building
owners of the situation, recommend a solution, and move on. 

For all kinds of reasons, PV isn't right for every roof. Shade, orientation,
structural deficiencies, roof type or condition, owner-is-a-jerk... All
kinds of reasons.

I'm not afraid to find out the truth in this matter. I want to know. I hope
that the rabid solar lobbyists don't somehow block or marginalize
responsible efforts to study and understand the issue.

$0.02001 

Solar Janitor

-----Original Message-----
From: Joel Davidson
Sent: Wednesday, September 22, 2010 7:12 PM
To: RE-wrenches
Subject: [RE-wrenches] PV and Roof Flammability

Wrenches,

See http://www.solarabcs.org/flammability/ and the report at
http://www.solarabcs.org/flammability/Flammability_Interimreport.pdf

Is there any flammability difference between PV equipment on a roof and HVAC
or air handling equipment on a roof? My concern is whether PV is being
singled out as a flammability concern while other more established
industries with more powerful lobbyists are not.

Joel Davidson