roof pipe insulation

My sister's house has water pipes on the roof. Though this is Florida (Gainesville), it gets cold enough that they need some protection. We've tried every kind of pipe insulation we can find in the big box stores, and it all falls apart quickly in the sunlight, even the highest quality stuff. I'm looking for ideas.
The pipes carry water for a water/air heat-exchange heat pump. It's almost always running when the outside temperature is below freezing, and combined with the fact that an extremely cold night might get down to, oh, 12F every 20 years or so, we're not worried about what happens under normal conditions. The worry is what happens when electrical power goes out, or if the unit malfunctions. The pipes are PVC and I figure that, unprotected, they could freeze to breaking in an hour or two. It hasn't happened yet, but the worry remains.
There are two parallel pipes, 1" diameter IIRC (or close), about 5" apart, total length from eaves to unit about 40'. (Once they turn under the eaves, I have little worry about freezing.) They are about 1-1/2" above the roof surface (held up by bits of 2x4). There are three right angles. Where the pipes reach the unit, they have a short distance that's farther above the roof, but that's another problem.
Option 1: I figure if I had some light weight 8" PVC pipe, I could rip it into two halves, spray a little foam insulation on the inside, and make a sort of Quonset hut over the pair of pipes. I haven't found reasonably light weight PVC pipe, and the normal stuff in that size is expensive and probably pretty difficult to cut.
Option 2: I could maybe do a similar thing with 3" or 4" PVC pipe -- rip it, spray foam insulation, and put it on top of one pipe before the foam sets. This would not protect the bottom of the pipe, but might be sufficient. Or glue some strips of foam board to the bottom ... the latter would eventually deteriorate in the sunlight, but would be fairly easy to replace.
Option 3: I could use 8" diameter metal ducting, split, as in Option 1 above. That's expensive, hard to cut lengthwise, and probably would rust.
Option 4: I could make a plywood box to go over the pipes, and line it with foam insulation board. But I would have to use PT plywood, and I've only seen that in 3/4" thickness. Heavy and expensive. I really only need 1/4".
Option 5: I could do a similar thing to Option 4 with PT lumber. Have not compared cost with PT plywood, but seems to have the same disadvantages otherwise.
Any ideas?
Edward
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On Monday, November 10, 2014 2:51:37 PM UTC-5, Edward Reid wrote:

Since the water is apparently in a closed loop for a heat exchanger, is it possible to use antifreeze to solve the freezing problem? I would think you'd want it insulated against heat loss, but you did say that you were not concerned about normal operation, just freezing.
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Edward:
Have you tried fiberglass or foam ASJ (All Service Jacket)?
http://tinyurl.com/jvrafjy
ASJ is a stiff fiberglass or foam insulation that's covered with a metallic radiant reflecting coating and then a white paper. It's called "All Service" because it's used for hot water heating pipes, air conditioning ducts, refrigeration piping, basically every kind of pipe you'd need to insulate. Normally, it's not used for outdoor installations, but I'm thinking you could have some sheet metal bent into an upside down channel to keep the rain and Sun off the insulation, and screw the flanges of that channel down to pieces of 2X4 material every 8 feet or so. (Would that stay down in a hurricane?)
Just phone up any heating contractor in your area, and find out who sells insulation for hot water heating systems. Whomever sells that will no doubt carry fiberglass All Service Jacket.
PS: Metal is the most opaque material known to man. You can stop more light (and any other kind of electro magnetic radiation) with aluminum foil than you can with any other material of equivalent thickness. The solution to your sunlight problem is to put metal between the Sun and your insulated piping. I expect any sheet metal shop could bend some sheet metal into a channel of sorts for you that you could put over the piping to protect it from the Sun. If you have a flange bent on each side, you could then screw the flanges down to the 2X4 supports that hold the pipes off the roof.
--
nestork


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On 11/10/2014 11:51 AM, Edward Reid wrote:

I have used the Big-Box-Store foam pipe insulation on pipes and tubing going to my heat pump. As you say, it fell apart after a year or so.
When I had the unit serviced a couple of years ago, I asked the service guy to replace the foam insulation. Their foam tube insulation is UV protected, so it lasts for years. And it has!
Find a heating/ AC contractor and get some foam insulation from their stock. It will do the trick.
The box store insulation is meant for insulation inside the house or under the house pipes.
Paul
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Thanks all ... sounds like Paul's idea is the best, I'll try to get some of that UV-protected insulation.
Bob: I would not trust any sticky adhesive on a roof in Florida.
trader_4: The water is not in a closed loop. It's the heat source/sink for the heat pump. Water is pumped from the ground (by a pump that was once, but is no longer, the source of water for the house), runs through the pipe on the roof to the heat exchanger, gives (winter) or receives (summer) heat to the refrigerant fluid, runs back via the parallel pipe, and goes to sprinklers in the yard.
http://en.wikipedia.org/wiki/Heat_pump#Water_source_heat_pumps_.28WSHP.29
nestork: sounds like a good idea if I can't get the UV-resistant stuff that Paul mentions. I should be able to create the shield using aluminum flashing, no? It might blow off in a hurricane, but those come in the summer, leaving time for repairs before freezing weather.
The hurricane season of 2004 dumped huge amounts of rain in the area. Power was still out on a clear, still night a couple of days after Jeanne passed over when a huge hickory tree, roots probably weakened from nearby trees toppling earlier in the season, fell on the carport. Took several months and a $75,000 insurance payment to rebuild. In the house at the time were my mom and my other sister. (Our parents built the house in 1956. Mom died in 2009. First sister now lives in the house.) Had the tree fallen 45 degrees counterclockwise from the direction it did, it would have completely destroyed the house and might have killed one or both of them.
OK, end of digression.
Edward
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In typed:

First, if the existing pipes are PVC, I think that exposure to sunlight may cause the pipes to deteriorate, so covering them in some way is probably a good idea anyway.
Another option that may help a little in terms of tolerating freezing may be to change those PVC pipes to PEX, but PEX also needs to be protected from sunlight (even more so than PVC, I think).
My vote for the insulation part would be to just build a 3-sided wood cover (probably just plywood) that goes over the pipes. Put some type of roof coating over the box to protect the wood -- maybe regular roof coating (black), or if that is a bad idea in Florida maybe aluminum roof coating.
I would not insulate the pipes themselves. I anything, I would put insulation on the inside surfaces of the wood box, but no insulation between the roof and the pipes. I would want the heat from inside the house to be able to come up through the roof and into the box where the pipes are located. I would not want the pipes insulated from the roof or the inside of the house.
I think this would probably be the cheapest and easiest approach, and my guess is that it will work.
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In typed:

P.S. Another thought that I had is, If it is cold enough outside for the roof pipes to freeze, won't the water lines that are inside the heat-exchange heat pump also freeze? You would have to figure out how to insulate them in addition to the pipes on the roof.
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Project is complete for now, though certainly subject to future reevaluation and modification. Some pics (including some redundant ones) at
http://paleo.org/albums/pipeinsulation
The flashing should provide adequate sun protection for the pipe insulation. Whether the flashing is adequately secured remains to be seen. Loose edges do tend to catch wind.
TomR, PVC is generally not susceptible to sunlight damage. When people say sunlight damages plastic, that's a very general statement, as plastics vary enormously. Polyethylene tends to be the worst in this respect, but my personal observation is that even PE varies a lot.
Yes, there are potential concerns about pipes in the heat exchanger freezing. At least it's in a box, albeit a metal box. The pipes there are soft metal and so not as prone to damage from minor freezing as the PVC. The system did partially freeze once, several years ago. It was my fault too -- I was visiting and for reasons now forgotten turned the heat off at the thermostat late one evening and forgot to turn it back on. Luckily the freeze was mild, but when we turned it back on in the morning it ran for a few seconds (known because we observed that the sprinklers taking the cooled output water ran) and stopped. I spent quite a while trying to warm the PVC pipes, assuming that was the blockage location. Finally I opened the box with the heat exchanger, put a hair dryer in there running, and in less than half an hour the system was running again. My interpretation is that there was slush in the pipes which moved to the heat exchanger and clogged the smaller passages there. No permanent damage. Anyway, if I decide that area needs more protection, I could put some insulation board inside that box -- it's a solid metal box with a good lid held on by screws, and IIRC there's room inside for some foam board.
I don't think I mentioned before that the roof is SPF, so only insignificant amounts of heat can reach the pipes from below. That's the problem with some of my plans, and with TomR's suggestion.
You'll observe lots of problems with the SPF roof, and I commented on it on one of the photos. The original (1956) roof was BUR (aka tar and gravel) and had a couple of bad leaks which we had been unable to find or fix. My mom was planning on adding the SPF both to fix those leaks and to add insulation (previously none) when the summer of 2004 came, with heavy rains and winds from hurricanes Charley, Frances, and Jeanne. Several trees, mostly water oaks, fell to the east and northeast of the house, but none hit the house. On a quiet evening a day or two after Jeanne passed (electricity not yet restored), a huge hickory tree, perhaps 30" DBH, at the northeast corner of the main house fell to the WNW, totally destroying the carport though leaving two cars under the carport undamaged. It took several months to get the damaged areas reconstructed, and the SPF went on afterward. Unfortunately the roofing contractor failed to correct the ponding, as you can see in the photos -- the puddles you see in the photos are in the same places that I remember them from 50+ years ago. And there's lots of major bubbles in the surface, some just under the final coating and some between layers of the foam, another sign of incompetence.
Well, I digress. The deed is done. Now to observe ...
Edward
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