Mixing PVC and Antifreeze???

Why use antifreeeze???

Maybe fill the pipes with fine dry sand (block paving sand) instead?

Less messy when it leaks (yes when, not if). Cheap, easy to handle, non toxic, kids can play with it when you are done.

Del

Dam' sight easier to use fluid (and don't tell me dry sand is fluid - try syphoning it!)

Hang on there....

Unless this is a flat roof...in which case filling with a liquid will still be a pain because of air locks.

It would be easy enough to fill the 'vertically sloping' sections with sand, this would fulfill the objective of making the structure heavy. The fine dry sand that is sold for sweeping onto block paving to fill the interstices does flow quite nicely down hill.

I still think filling it with liquid is an accident waiting to happen...after all why is the tarp' there in the first place? To keep liquid out...

Del

Del,

I have taken into account the possibility of entrapped air; and taken steps to prevent entrapment or expansion/contraction adverse effects. Here's a description to give you a better picture. The roof is not steeply pitched and comprises two sets of gabled surfaces over an el-shaped structure. Taking one roof section (the other being similar), imagine 5 equally spaced, 3/4-inch-dia (roof-slope-following) "verticals" descending on both sides of the ridge. At the ridge, the verticals are each joined by an angle fitting to form a saddle arrangement--the verticals, in effect, hanging from either side of the ridge. Between the verticals are arrayed and joined 3 parallel rows of laterals, also equally spaced. Provisions for filling are installed near the ridge for each array (and on both sides of the saddled arrays). Also, near the ridge is provided a second, open, pluggable fitting to permit displaced air to escape during filling. I will probably also drill the plugs to afford air to escape and re-enter the array under various temperature (expand contract) conditions. No matter where the liquid is added, it will flow to the bottom and fill the laterals, with the liquid level working its way upward (filling the verticals and laterals in between), displacing air towards the ridge. At the fill end, between each of the lateral rows, I have also incorporated pluggable openings (fittings) into the vertical. By leaving a plug removed at a particular level (from the bottom) I can preselect the liquid level in the array; when the liquid (water and antifreeze solution) level reaches the open fitting, water will begin to flow out, telling me to cease filling. Because of the saddle arrangement, I do not expect to have to fill above the first, possibly the second, tier. The weight of pipe and liquid at the bottom on both sides of the ridge will tend to force the array downward on both sides of the ridge, thus "pinning" the array, and the underlying tarp, to the roof surface. The piping array will be laid over the tarp so that any leakage--which I don't expect--will simply run off on top of the tarp - just like rain. It was just this possibility--leakage--that led me to prefer alcohol rather than ethylene glycol as an antifreeze--against the equally remote possibility of ingestion of the antifreeze by critters. Additionally, it is wind that is a major concern, since a stiff breeze will tend both to rip out grommets in any tarp, as well as to lift/move the tarp, vertically and laterally, off the roof. The piping array will provide hold-down weight distributed over the entire tarp, not just the edges, preventing wind from "flowing" under the tarp across the entire roof slope. In addition, I anticipate that the piping will disrupt any laminar flow over the roof and tarp, this causing turbulence, and thus minimizing aerodynamic, vertical lifting of the tarp. Additionally, ropes will be stretched across the pipe array and fastened (with shock cords) to rake/leave edges. Finally, blocks will be positioned to support the laterals at the bottom of the verticals--thus counteracting any lateral pipe deformation under the weight of the liquid.

Hope this makes clearer how I hope things to work.

Sounds like a good gust of wind and you will have a fine parasail. Tie the tarp down.

Yes I'll be doing do that, too.

Speaking of sails, it was just the other day, when I had the tarp temporarily tied (no pipe grid yet) that the day decided to be a stiffly breezy one. I went outside to check on it...and to find the leeward edge to the tarp still fastened, but the windward edge being lifted straight up into the air. I had threaded a length of 1/4" poly rope, through the grommets, around the entire perimeter of the quite large tarp; and spiced the rope ends to form a continuous loop. (Leaving slack in the rope, the idea was to be able to hook the rope at various places and to distribute loading of the grommets--to permit limited flexing and shifting of the tarp--hopefully to prevent tear outs.) Towards windward (abaft on the roof you might say), that rope had been secured by ball cord to a former (former : because antenna and tarp could not coexist) antenna-guy eye screw eye.

Now, as the tarp was attempting to be blown away by the wind, the only thing that stayed anchored (that didn't slip out from under sandbags and blocks) was (in addition to [formerly windward but now] leeward roof edge fastenings) that rope, holding fast towards windward. So, as the (now) sail tarp was carried on the wind, it followed the path of least resistance, sliding by its grommets before the wind until, when I went out and looked up to check, it had taken on all the aspects and appearance of one huge, and deeply bowed, spinnaker--as if driving a lone yacht practicing for regatta. I wondered aloud to spouse as to what the impression must be with motorists passing by on the highway; whether non-land lubbers driving into the wind might not wonder whether it was this...prairie house ship, and not they, which was actually making forward progress.

So you see, that is why I think it necessary to have redundancy of "tie down": not only ropes, but also ropes tied over weighted pipes distributed over the entire sai...er, tarp.

Just thought you'd be amused.

Why don't you join CR4? Pick an avatar, you don't have to tell anyone where you live, and there's no spam to speak of. You seem to enjoy interfacing with members, why not join. You could be useful in our plans to dominate the World!

Will probably do so but right now dealing with some problem with computer and biopod, trying to reinstall office because of some degraded files. So I'm holding to status quo til I get these problems worked out. But I do appreciate the invite. Interacting here is a pleasant experience and so much to learn, too.

HydroP

Use a 50/50 mix of antifreeze and water and it should not harm the PVC pipe.Just make sure to clean and prime the fittings before gluing.Do not use piping that has deep scratches,for they will become an eventual failure point, due to creating stress risers.

I recommend a environmentally friendly antifreeze,such as propylene glycol based, as is used in campers . It is harmless to pets and other animals that may happen to lap up a spill. Propylene Glycol is used in foods, such as Vanilla extract, among others so it is benign.

Use common sense to eliminate large air pockets, but leave a little head room for expansion and contraction due to temperature changes.

Good Luck!

Thanks. I hope I won't need it again this winter.

I thought propylene glycol was definitely not safe for pets, especially cat! Could you expound on this point, please.

I think so, too. I considered sand, and it wouldn't be too much problem dropping it down the slant pipes; its getting across the laterals that makes sand a non-starter--that and lugging 60 pound bags up the ladder with a bad knee. With fluid it's only a funnel and jug, and a water hose to finish filling to the desired level.

But thanks for the idea.

Ta, nice to get a reply, so many just don't bother.

Good point about the weight....

Mind, I don't think you would need to fill the laterals?

Del

Possibly not, but once it's done it has to stay done. I am hoping to get as equally widespread distribution of "hold-down" on the tarp as possible. The idea is that any lifting that does occur will be contained/localized and not transferred across the tarp. If laterals were left "unweighted" there would be a path--a path of lift or of inflation--extending all the way from the bottom to the ridge. Since this is thin-walled pvc, I can envision that any such lifting between weighted verticals might cause those verticals to shift as the intermediate laterals were bowed upward. If this repeated many times the entire array could eventually shift. So, if I tried it out with sand, and later had to convert, I would have a real problem on my hands trying to evacuate or flush sand before going with liquid. So I see it as better to go with the full package the first time...so I can forget about it (more or less) 'til next summer.

Thanks again.

Just remember that antifreeze is intensely toxic to dogs and especially cats. The most danger is that it tastes good to cats, so they go for it. About two teaspoons are lethal. So, if you have any dogs or kitties around that you care about, make sure it doesn't leak.

On the other hand, might I suggest using salt brine. What's the problem with that? Or, if that doesn't fit your fancy, why not use cheap (and I mean really cheap) vodka? It won't freeze, and you can get it at your local grocery store. If that still doesn't float your boat, what about just installing a few strategically placed freeze plugs?

I mean, talk about making a tempest in a teapot!!!

HI Vermin,

It's also a great fungicide--kills dry rot almost instantaneously--suppose that's why it's in paints--even penetrates right through cured paint into the substrate wood.

Yes,I do have pets and wild fauna around--that's one reason I was tending towards alcohol as a liquid antifreeze.

Funny you mention vodka...when checking auto parts stores I did not find any clerk who had ever heard of alcohol as an antifreeze; or knew about antifreeze windshield/screen washer solution. It all became clearer when I describe it as vodka. Now, one problem with rotgut vodka is that it's never more than 80-proof. So I'd be buying the water as well--at alcohol price. But then again, it might--no, would be--certainly the easiest to find. Salt's a possibility; but I wonder about encrustation.

Brine is used in skating rinks to freeze the water to ice. I have never had a bottle of vodka in my freezer that ever disassociated. Pretty much, when water and ethyl alcohol are mixed, they stay mixed!!!

I have never had a bottle of vodka in my freezer that ever disassociated. Pretty much, when water and ethyl alcohol are mixed, they stay mixed!!!

--vermin

I never had vodka in my freezer--period. But the point is well taken: alcohol-water solutions are best dissociated by swallowing!!

Brine is used in skating rinks to freeze the water to ice.

--ibid.

??? Not, unfreeze ice to water?? Is this sumkinda bay area nano-techno-phenomenon?

hydro

Oh yes, freeze plugs.

Maybe a silicon wafer cemented over a hole in the pipe?

Since I'm not that far (over the coastal range) from your location, I don't anticipate that hard a freeze.

Add some rubbing alcohol to your windshield washer solution. If the methyl alcohol don't effect it. Isopropyl shouldn't either.

ethylene glycol is poison if it leaks and something drinks it. Brine will work and is cheep too.

Brad

RV water system antifreeze. It is used in PVC pipes all the time.

Or pool antifreeze, whichever you can find cheaper. They are both propylene glycol which is non-toxic. They even put it in cheap ice cream, yum.

Jag, RCapper,

Thanks to you both. I've seen the animal-friendly antifreeze/coolant in auto parts stores. Seems like it was rather pricey compared to regular (classic ) engine coolant/antifreeze. I like the pool antifreeze idea as well. As to comparative prices--including that of brine, as mentioned by Brad--I suppose the "cheapest" will depend in part on how close they can be found--how much gas to bring one home. I'll have to do some calling around.

About that RV water system, I'm not too familiar with RV systems, so need some clarification. By RV water system antifreeze, is this an expendable...possibly potable? Or something else? Or are you saying I might find "full strength" antifreeze (of the alcohol type) at an RV supply business? Thanks again.

Hydro.

Recreational vehicle (RV) water system antifreeze is available at Walmart, Pep Boys, Auto Zone, etc.

Jag, thanks, will check it out.

Correction: I mistakenly attributed brine to Brad; I should have said, Vermin. Sorry about that.

Uh... Exactly where is that emoticon placing that light bulb?

Thanks, Brad. I take it from your and other posts that either alcohol or glycols will not interact with pvc or pvc weld solvent; and that rubbing alcohol can be mixed with methyl alcohol (in the washer solution). Your post also brought to mind one source I forgot to check--Home Depot--for alcohols in larger than medicinal-sized containers.

Another thing I didn't think of before is whether any type of alcohol will remain in solution or tend to stratify--possibly become concentrated at the top--when mixed in water and left standing, undisturbed.

Hydro...

Hello Hydro,

Another thing I didn't think of before is whether any type of alcohol will remain in solution or tend to stratify--possibly become concentrated at the top--when mixed in water and left standing, undisturbed.

The meths or glycol antifreeze dissolves in the water.

The only time they separate out, is if you did not use enough antifreeze, and the system freezes - at the freeze point, the water freezes first, generally bursting the pipes, leaving the antifreeze as liquid....

Thanks for that clarification, Sparks.... Guess I'll need to go ahead with calculating system volume as another post-er asked about. Fortunately, my locale makes hard freezing quite unlikely. The last deep freeze here was in 1990 as I recall, and that was a once in century event.

To any degree that the liquid solution is expose to air, which, if any, will evaporate faster? The water solute or antifreeze solvent. If the former, then the solution should become more concentrated over time. Correct? Other wise it might be necessary to "recharge" periodically? Or is that a non-happener?

Hydrophobic - why not register on CR4?

What I.D. & total length of pipe to you intend to use? Is it transparent?

John,

Not transparent, but if you're thinking about how to fill to a certain level, I described that in another post above. As to the volume of the "grid," I've been so busy tracking weather forecasts and putting the system together that I haven't had time to calculate... Soon as I get the totals I'll post again.

Thanks.

Hydro...

Yes, am considering enrollment. Appreciate the invite.

If it's not transparent, that's another mark against dry fill.

Only takes 2 minutes to register !

Thanks, and thanks. Looks like I miss-anticipated your question about transparency.

Time to retire now but one question--a little off topic. In this country (U.S.) the town of Reading, and the Railroad (the real one and the Monopoly one), is pronounced, "Redding." What about there? Just curious.

Definitely "Redding"! Used to be spelt like that on old maps etc.

We don't have Reading on the Monopoly board.

Obviously. Doubtless your Monopoly doesn't have Pennsylvania, Baltimore & Ohio, and (that other one whose name escapes...) railroad companies either. But, what railways does your monopoly have?

Here's data on the pipe array:

Cumulative pipe length: 3365 (+about 10) feet

Nominal pipe dia.: 3/4-inch

Approx. connector volume: 12-12.6 CI

Pipe pressure class: 200psi

Kings Cross, Marylebone, Fenchurch St. and Liverpool St. (all stations in London).

Oops? About those pipe measurements...

"Cumulative pipe length: 3365 (+about 10) feet

"Nominal pipe dia.: 3/4-inch

"Approx. connector volume: 12-12.6 CI

"Pipe pressure class: 200psi"

...I should have said, pipe length: 3365...inches, not feet!

Glad I caught the blunder before someone got an idea I might be posting from a penitentiary.

Why do you have about 2⁄3 miles of pipe on you house?!

See above.

And below.

...I should have said, pipe length: 3365...inches, not feet!

Okay?

Okay.

HydroP

Woof!!! Thanks for that clarification!

Why don't you just put a big block of concrete on top of it and just forget all this business about PVC pipe?

I did, several in fact. And a few dozen sand bags. It didn't work. My house is situated in fairly open countryside. Not much, not anything, to break the winds when they blow in from the ocean. Another reason is that I have already procured the pipes, fittings supplies, done the planning, assembled the grids and (tonight) completed installation....just in time for badly needed rains over night. So it will get its first test.

When the pipe is not longer needed, I am considering breaking the grid down into truck transportable sub grids and offering the whole shebang for purchase by a roofing contractor. The way the weather is here (Mediterranean climate: hot, dry summers, cool, very wet winters) roofers are in constant need of ways to keep water out of work in progress. If that doesn't work out, the pipe will probably go underground for lawn and beds irrigation.

you should call an RV dealer and inquire about their antifreeze for the fresh water system , as it is nontoxic. Use to work at davis rv in lubbock tx , this is the way I would go

Thanks rdavis. Are you a Red Raider rooter? I used to live all around Lubbock, but Davis RV would be a bit too far to drive now. Fortunately, there is a big RV outlet in Davis, Calif, not too far from here. I'll give them a call.

hydro

Party college!!! Woo hoo!!! Tip that cow!!!

I have seen dry fine sand suggested and quickly poo-pooed as not viable.

Well in a number of industries they do transfer dry powders into and through pipes by using compressed air. So as long as you don't need a 100% fill you can pretty much fill everything to a decent level with selective venting and good air flow. All with the sand, compressor and you firmly on the ground most of the time. Just change which pipes you fill to and which you vent from back to your feed hopper.

As to the brine suggestion - unless you are situated in a salt marsh it is just one step less toxic than antifreeze - no immediate pet deaths but you will pretty much exterminate a lot of plant life and do some nice structural damage as well when you get your leaks. salt and roofing nails don't play well together. Also the environmental watchdogs may get a sniff of what you are up to or even worse, after something goes foobar. Play safe know your environment.

Leaks were mentioned. If you fill with sand and do not completely fill or have a bad seal, any residual moisture left in or humidity intrusion through a leak may condense and wet the sand. Emptying wet sand could be fun to watch but not to do. Leave a space at the top of the sand and insert a desiccant bag.

Mention was made of the cost of antifreeze (RV style, which is considered potable). It was also stated that there hasn't been a hard freeze in years. You do not have to use full strength antifreeze. Even if you dilute to about 25F and the temperature goes to 20F overnight, the mixture will get sort of slushy but not freeze solid. If there is any minor expansion, it will flow into any air spaces.

You have correctly anticipated my thinking about the antifreeze: I only need protection sufficient to deal with sort term cold snaps--probably I would want protection down to about 25F--just in case.

I'm not quite clear about that dessicant bag thing. Would this go inside a 3/4" pipe on top of sand? Or was it to be used somehow as part of evacuating wet sand? (Just for what it's worth...since the pipes are now filled with liquid.)

After filling with sand, leave an air space and, stuff in the desiccant bag.

Hi, thrudd. Thanks for your input. Please understand that I did not mean to poo-poo the sand idea; I can certainly see its plusses. It's only that since the installation had already been partially completed when I asked the question, and because I was and am "under the gun" in terms of weather conditions/forecast, I really did not have the luxury of the (let's call it) additional logistic that would be required to plan and implement sand filling of the pipes--this in addition to reasons I've already stated, plus not wanting to walk on poly tarp on a pitched roof...for fear of slipping/falling and/or damaging the tarp. Since this is a household project I do not think the "industrial" approach you described is something I could manage in short order.

Now here is a status for you and the others. Two nights ago I competed most of the piping assembly, positioned it, and tied off. The next morning--with winds and gusts of between 10 to 20 MPH--was to be the initial test. As it turned out, the the test was part success, part failure. The unweighted grid on one roof--it was tied across with cordage and weighted along the edges--kept its position with only moderate movement of the tarp. On the other roof--held by a separate pipe grid--also not yet filled/weighted--and not yet fully tied because of the odd shape of the roof and because the tarp overlies a valley--the wind caused the tarp to balloon up under the pipe grid until eventually--just before the weather moderated, the grid slid off tarp and roof, landing on one edge on the ground in front of and leaning against the house. The tarp itself shifted quite a lot but did not blow off. Today, after some rigging with ropes I was able to hoist the entire grid back up, and re-positon it over the tarp after re-straightening the tarp. I also completed installation of water ports at various positions on the grid, connected the hose, and slowly filled both ridges up to the ridge. No leakage whatsoever was detected--this in spite of the previous incident and hoisting. I also added more ropes stretched across the breadth of roof and across the grids, and also added more blocks and sandbags along the tarp perimeter to block out air underneath. Tomorrow afternoon the "system" will get its next test, as two days of rain are forecast along with a brief period of winds up to 20mph. I fully expect that with the added weight and added ropes and weights the tarp should stay in place this time. BTW, even with the mishap the tarp did pass as far as shedding all water, with none getting underneath.

Also, as to antifreeze, I inquired at depot, etc, about swimming pool antifreeze and RV water system antifreeze. I found that these are not available in the store locally, but RV antifreeze is available by online mail order. This means of buying such a product I am not inclined to do, at least before more looking for a local supplier. Depot did have denatured methanol but I am leary of using that because of its toxicity and drain time, even greatly diluted.

As to salt, I did consider the consequence of draining salt water onto the lawn in terms of damage to grass and plants; however, it seems you have looked at the bigger picture. For the time being, and since there is not a freeze in the forecast for the next week or so, it will be just water. After the next test and any modifications required, I will then revisit draining, adding an antifreeze agent, and refilling.

If and when an opportunity arises, I will attempt to take and post a photo.

Once again, thanks for helping out; and thanks to everyone for your help thus far.

Hydro

Go to Wal Mart and get some RV antifreeze for plumbing. It is bio degradable, non toxic and cheap....

Aaron

Hello Aaron,

Your answer brings to mind several questions...in part due to my unfamiliarity with RV mechanical systems.

First, you mention "plumbing." Would it be correct to say this is in reference to flexible tubing of some kind? I find it difficult to envision that RVs would be fitted with rigid piping, unless, perhaps, plastic piping.

How exactly is this non-toxic RV antifreeze applied? To the outside of the plumbing or holding tank(s) (say, in a jacket surrounding the actual water "piping" or tank)? In tubing inside the holding tank (like a radiator)? In solution with the stored water itself? With only shower &or dish &or flush water? Or with drinking/cooking faucet water as well?

What is the chemically or physically active ingredient of RV plumbing antifreeze? Is it consumed/depleted during use (as in drank or drained away)?

As to where I might find it (and this might have something to do with its chemical makeup), I went to Depot on recommendation by other responders only to find that it was not available--except from Depot's Web site. Store personnel could not offer any explanation for this, but I have seen before how, because of state gov't regulation, products available in other states sometimes are not available "off the shelf" in Calif. Or they can only be distributed by "approved" sellers, which might not include general retail places like Home Depot or WalMart. So it might be that Arizona and other states' WalMarts have it, but not Calif. WalMarts. Or, if the RV antifreeze is a drinkable alcohol the state might restrict it (because it's not denatured) for fear of untaxed consumption, or of competition with licensed beverage sellers.

But, since people do have RVs in this state, and it does freeze in the mountains where RVs might go, it seems that RV antifreeze ought to be available somewhere in in this Calif. city.

The purpose of RV antifreeze is to protect residual water in sink, shower and toilet traps from freezing and cracking the plumbing. Usually when preparing the vehicle for storage during cold weather, a little is poured in each fixture. After removing most of the water from holding tanks, it is added and run through all water lines, pumps and water heaters

Nothing exceeds an overwrought question like a concise and to-the-point answer. Maybe it should be called, "RV storage antifreeze!?" Thanks for painting the correct description, Jag.

HydroP

You ain't seen overwrought till you check out the "Bath Breaking Technique" thread.

I have used it in my RV and a mobile home that was winterized. The RV had PVC and Polybutyl(?) plumbing the mobile had all PVC. It is put in the holding tanks and drains. It catches in the goosenecks. It can be used straight or mixed to keep them from freezing. Check this link out for one type of antifreeze : http://www.peakantifreeze.com/rvmarine.htm There is also a material data sheet available. You can check with any RV parts supplier as well as big box outlets. There are probably many makers of the stuff so I am sure the exact composition and safety may vary. But with our federal laws and the patriot act, material data safety sheets must be made available to give you the info you need.

Thanks, hope this helps...

Aaron

Finding no antifreeze in California wouldn't be surprising.

Finding none in Quebec would be a different story!

http://www.coleparmer.com/techinfo/chemcomp.asp might prove useful in this and other areas.

PW,

What a great reference tool. It will certainly go in my favorites file.

Thanks.

PS to all. Sorry it took a while to get back...weather here and tarp on the roof have kept me quite preoccupied. I think I said something about posting pics. I try now in my next post and we'll all see the....results so far.

We are looking forward to your pictures, particularly the one of you on the roof, during a torrential downpour and thunderstorm.

Kind Regards....

No chance of that...me in a downpour that is.

Here's a followup on what has transpired with the PVC pipe grid tarp hold-down system. As it turned out, time ran out before I could find an antifreeze solution to purchase. So when the rain, wind, and "cold" weather arrived I decided to go with plain water (filling the pipes to capacity) and hope for the best; I also figured that if it got cold enough that pipe rupture did occur, with diligence I might be able to get a patch on it before thawing and draining.

As it turned out, temps in December (typically Calif's coldest month if it's going to have an unusually cold month) only got cold enough to put a thin glaze on puddles, not hard or long enough to cause freeze damage to the pipes. So, barring any unexpected weather it looks like antifreeze will prove to have been unnecessary after all.

As to whether or not the piping grid was "overkill"--whether, as some suggested, simple edge tying or weighting with blocks would have "done the trick"--it now appear that "the results are in." In going with the hold-down pipe grid idea, I had "calculated" from experience that prevailing winds of 25-30 mph and less, and spring-time gusts up to about 50 mph, were unlikely to be exceeded. As it turned out, and before any "before" photo's could be shot, a massive series of (freak) Pacific storms moved across Calif. just over a week ago; blame it on La Nina, we were told by the weather folks. With the second storm system to come ashore of that series, came prevailing winds of 40 mph and above, hurricane force gusts, and inch+ per-hour rains - a storm so large it took over 12 hours for the worst to pass. Extensive, severe damage was incurred over much of the Calif (and NW) coasts and Calif. inland valleys. (Mountain elevations to the east encountered 100MPH prevailing winds and as much as 12 feet of snow over a couple of days.) The composite pictures below, taken a few days after the storm, tells the tale of how effective the water-weighted piping grid proved to be.

The first pic shows both, where the grid was in use (on the main house in the foreground), and where only edge tying, weighting, and lashing over with ropes was employed (on the garage in the background).

Notice that there was some displacement of the piping grid on the right and some slippage of the tarp; on the left the grid and tarp remained almost unmoved. Two sand filled pipes which had been laid in the valley to retard ballooning slipped to the bottom. It is certain the big house tarp, as a unit or in pieces, would have been blown to parts unknown but for the grid. The tarp in general sustained minor damage in a few places at roof edges and peak, but nothing which can't be readily repaired. In contrast, the garage in the background, where tarps were only tied/lashed and weighted, shows (and doesn't show) extensive tarp movement, and damage up to total destruction.

The pic below shows the garage roof tarp damage more clearly (at least those tarps which weren't blown, along with sand bags and blocks, completely off the garage).

At the far left can be seen where blasting by wind and horizontal rain reduced a tarp to shreds. At the right one tarp has been pushed into a gutter area, another was greatly displaced, and its grommets ripped out. A tarp originally covering the ridge is hanging, unseen from the far end of the garage. In the background at right is a reverse image of the scene in the previous picture. The comparative effectiveness of the pipe grid is clearly seen.

Finally, another view of the house tarp and grid, shot from beyond the ridge at background center of the 2nd image, shows the extent of displacement of the pipe grid in closer detail. The pipe grid was displaced only about eight or so inches

laterally, the tarp between zero and about 24 inches. Aside from water weighting and blocks, the grid was held down by two cords stretched and fastened across breadth of the roof. Had time permitted to tie the grid at the corners, shifting could probably have been totally prevented; so that will need to be done before the next storm. About 20 minutes is all that was required to realign the pipe array and tarp to the correct position.

Conclusion: Given the rare and unexpected storm intensity, I am satisfied that the pipe grid met, and even exceeded, expectations.

What will I do with all that pipe once summer arrives and the re-roof is completed, you ask? Since it is not schedule 40, I had planned that it might be salvaged for use, downstream of valves, in a planned lawn irrigation sprinkler installation. Alternatively, if it can be cut down into pick-up truck transportable modules that can be reassembled, and with plenty of pics demonstrating performance in extreme weather, there's a good chance that mine or another roofing contractor might be interested in purchasing.

I'll conclude now by thanking everyone for your interest and helpful suggestions. It's been a kick--except for the going up and down a ladder and dodging the weather part.

Down the street, an old 1 story industrial building is being converted into a church. As I drive by, I see various parts of work. There was a nasty storm brewing the other day, and they covered the entire open roof with a layer of black PVC. I'm not sure how they got it to all fit on so well - no concrete blocks and no PVC pipe. I think what they used were PVC sheets used for rail cars. They're huge!

It's going to be a church! God works in mysterious ways ...

(Sorry - meant to flag this as OT, but can't go back).

Naturally, if the roof is open then there are virtually unlimited points to secure the tarp--from beneath--using "pinch" clamps (such as EZGrabits) or even staples. It being a church, one might assume water (shedding) was the "least problem" because of steep pitch(??). As to wind, it would--seems to me--depend on: mil thickness; number of tie points; and (I'm winging it here) the better ability to neutralize pressure differentials (lift) owing to attachment to open-top building(?). I, too, saw such a (in this case, clear) PVC sheet--perhaps 1/3-acre or more!--used as ground cover over prepared soil at a construction site here. (One also sees PVC used frequently in the central valley as ground cover over crop fields--in particular, strawberries--to hold in moisture (save on irrigation); maintain soil warmth; and promote germination.) The tarp at the construction site did not stay down completely, to the apparent consternation of the guys walking around in waders after the storm, scratching their hard hats. (Undoubtedly, we are referring to one and the same storm event--but I understand that the bay area received the greater brunt in some locales.)

I considered PVC myself, both clear and black (which is usually cheaper). I found plastic sheeting in thicknesses up to 11 mil (where 4 mil is standard heavy duty). With PVC it's thickness that gives strength and tear resistance; with tarp its both thickness (to lesser degree than sheeting) and imbedded reinforcement. A major PVC sheeting disadvantage--given that both sheeting and tarp must realistically be considered as a disposable, one-time-use items--that "decided" me on tarp was the recent restriction in PVC availability and, with it, the much-increased price--even higher when clamping costs are included--even higher than my expense for the PVC piping grid. There was also the problem with how one person would be able to handle, hoist and spread the significantly greater weight of thick PVC sheeting.

You did not say but, were you able to observe that "church" after the storm passed? How well did the open-roof covering hold up?

Just one point, when it comes to strawberries, "I think" they use the tarps during fumigation. Before strawberries are planted on a commercial scale, they nuke the heck out of the field with really nasty poison gas.