Tarps vs. Shade cloth for flat roof structure

[uncle sticky]

So I'm building a 20 x 20 shade structure. Using 1" conduit, metal corners. I'll have four corners, plus four t-intersections with down poles. All will be secured by putting rebar into the ground at an angle to create tension, then sliding the posts over that. Additionally, I'll be using trucker straps and all junctions, with l brackets and big lag screws to crank the structure down tight.

Question is, if I use a heavy duty 20 by 20 silver tarp attached with bungie balls, will that create too much of a sail? I figure that shade cloth lets more wind through, but it's also at least twice the cost.

[Canoe]

20x20 is a fair amount of sail to have without a way for wind pressure to get in/out.

One "theme" in such shade structures seems to be to make them out of a series of smaller panels. In this case, 4 panels of 10x10. Even if using tarp instead of the more pressure friendly shade cloth, you've got minor gaps between the panels for pressure to equalize.

Have you found photos of such a structure using the same size poles covering the same area?

[Just_Joe]

We were new to EMT structures last year but we had a 20x20 tarp in the middle of our 20x50 structure and didn't have any problems. Last year.

.... crank the structure down tight....

Don't turn your ropes/ratchet straps into banjo strings. A little tension is fine. A lot will pull the entire top. You almost need to have a person on the other end, tightening in tandem with you to keep everything square.

[Roundabout]

IMHO, As long as you are just creating a flat roof with no walls, your design will work just fine as long as your tarp is stretched tight. If you decide to put on a wall or walls, the wind dynamics will change and more engineering will be required.

[trilobyte]

I've never had trouble with bigger tarps, I do 20x20 and 20x30 pretty regularly. I recommend building the frame first, adjust your position and then anchor it, then attach the roof tarp and finally any side tarps. The key to success, IMO, is to get some help when setting up the roof tarp. And wait until the wind dies down.

Start on the windward side (where the wind is coming from). Bungee up the corner (don't loop around a bunch of times), and then once at the 10' mark (where your vertical pole is at). With a person at each corner, have the other helpers push the tarp across to the other side, and then get a bungee into the other corners. Then pop a bungee into where the other vertical posts are at.. the slight tension should help you get it centered a bit. Then go back to the windward side and bungee all the grommets, if there's slack then go twice around, otherwise just once. Repeat the process on the opposite side, then get the other two sides.

We also do angled side tarps, which provides both additional shade but a much better wind break. On an angle, and instead of fighting the wind it just goes up and over your structure. We do silver on silver heavy duty UV for the roof (maximum shade/protection), and then white for the sides. Slightly less energy efficient than the silver, but it keeps the place from feeling like some kind of cave.

In recent years we've also dabbled in aluminet. I love the stuff, but a) it's spendy and b) doesn't block raindrops. This year, our major structures will be 3 20x30 with tarps (for kitchen and tents) around a 30x40 central courtyard (covered by 2 20x30 piece of aluminet), and a separate 20x30 with aluminet.

[MacGlenver]

Trilobyte -- that's a 20x20 flat EMT shade structure? Hmmm -- nice. We're going EMT for the first time this year and have several 20x20 tarps that we were considering cutting down to 10x10 for wind load protection. Sounds like this is unnecessary... that will save us a ton of work (both in setup, cost of more poles/fittings, and cutting up tarps)...

If you're feeling really nice, dont suppose you have a link to a definitive pricing/design guide for these? Ok ok I'll go look

[FIGJAM]

With the big El Niño year it may be a good idea to bring a few center poles just for when it rains.

A longer piece of EMT with a plastic bowl on top would do it.

[MacGlenver]

Yeah, good call. If that happens, I think we'll have some spare EMT from our other shade (see below) and if we need more height we can just stick something under them (like a person's head or a cooler or something).

We're also planning to do some 30x30 aluminet with vertical supports & spreaders like so for some more bulk shade (2 or 3 of these). Any commentary welcome - havent seen anyone being dissuaded from such a design yet...

With the big El Niño year it may be a good idea to bring a few center poles just for when it rains.

A longer piece of EMT with a plastic bowl on top would do it.

[MacGlenver]

Realized that the guys that sell EMT shade structures conveniently put a parts list. Nice. http://wpstore.formandreform.com/produc ... arly-burn/

[trilobyte]

Figgy, if you're worried about the effects of El Nino in August/September, you may have been sitting out in the sun too long. I'm pretty sure that when the effect is prominent, it starts in mid to late fall and continues into late spring.

MacGlenver, yeah I've done a few of the little 20x20's, but generally go with the 20x30's for my core structures. I strongly recommend that you do not cut down your tarps, if you do, that'll result in a tarp that's more susceptible to tearing under heavy load (as in during really high wind). 20x20 is a walk in the park, just have patience and wait til the wind dies down. Murphy's law says it'll kick up a bit as soon as you touch the big tarp, and impatience will tempt you to want to just put it up already. If it's windy bust out the Bailey's, and maybe an old shoe...

[media]

[MacGlenver]

Thx man. Old Gregg -- *sheds tear*. The camp decided to change the theme this year! We are now Dr. Placebo's Snake Oil Emporium. At least we didnt go with Cat camp, which was the early suggestion *shoots self*. Actually think this will be a decent theme tho, thankfully.

As for cutting tarps, yeah, glad we dont have to go that route. Since I'm new to building the EMT stuff, I realize upon further planning that going with a 20x20 wont save me on EMT, cause I still have to support the center (right?), so i'll still have a 10x10 matrix of EMT, but the 20 foot tarp will just rest on top of some of it... I was convinced of this a minute ago, but as I type this, i wonder if I can skip some poles and just stretch the tarp across the whole span (ie. only build the edge poles and leave the center empty...)?

Figgy, if you're worried about the effects of El Nino in August/September, you may have been sitting out in the sun too long. I'm pretty sure that when the effect is prominent, it starts in mid to late fall and continues into late spring.

MacGlenver, yeah I've done a few of the little 20x20's, but generally go with the 20x30's for my core structures. I strongly recommend that you do not cut down your tarps, if you do, that'll result in a tarp that's more susceptible to tearing under heavy load (as in during really high wind). 20x20 is a walk in the park, just have patience and wait til the wind dies down. Murphy's law says it'll kick up a bit as soon as you touch the big tarp, and impatience will tempt you to want to just put it up already. If it's windy bust out the Bailey's, and maybe an old shoe...

[FIGJAM]

I hope you're right about the playa Trilo, but 60 yrs. experience say they start in mid July here, and with the strongest El Niño on record building up, It could get real interesting on the playa.

If we can get on it at all!!!

[SageV]

I strongly recommend that you do not cut down your tarps, if you do, that'll result in a tarp that's more susceptible to tearing under heavy load (as in during really high wind). 20x20 is a walk in the park, just have patience and wait til the wind dies down. Murphy's law says it'll kick up a bit as soon as you touch the big tarp, and impatience will tempt you to want to just put it up already.

+1 that, that IMHO is why surplus parachutes go in and out of vogue as shade cloth depending how windy the playa was the previous year. Not everyone makes that connection between wind and parachutes until their 30' dome starts slowly creeping outside the playa. Another reason bent rebar is your friend.

IMHO, industrial tarps, with bolt roping in the hem, a stitched hem, and reinforced corners are good for the playa. Mine have survived some hellacious playa windstorms and relatively cheap if you get together with some other burners to buy them by the case. Caveat emptor, the China made ones are not uniform.

[skippy3k]

I know others said they didn't have trouble last year, but my 20x16 single tarp gave me fits the whole week. Sure, it didn't sail away, but I watched it balloon up far too many times for me to be comfortable. I'm going with a 20x20 EMT structure this year and four 10x10 tarps or at least two 10x20 tarps.

[MacGlenver]

Trilo -- any opinion on the feedback above? Sounds like a 20x20 tarp is no biggie for you, but do you get the billowing effect like was mentioned above? Is that where you say "just chill and wait for wind to die"?

Also, any thoughts on whether one should do a grid of 10x10 EMT even if their tarp is gonna be 20x20, or could one just do a 20x20 square of EMT with nothing in the center? Would seem to be less structurally sound, but not sure.

Last question -- footpad or no foodpad? Will it sink much? I wouldnt think it'd sink enough to matter.

20x20 is a walk in the park, just have patience and wait til the wind dies down.

[Roundabout]

IMHO, Yes, keep a 10x10' EMT grid. A 20' length to unsupported tarp will v likely sag, and this can possibly create problems in high wind and certainly will create a problem in the event of rain.

Here is the EMT shade structure that I am building for our camp this year.

[GreyCoyote]

I hope you're right about the playa Trilo, but 60 yrs. experience say they start in mid July here, and with the strongest El Niño on record building up, It could get real interesting on the playa.

If we can get on it at all!!!

^^^ +100 to this. ^^£

Shit happens. The guy who thinks he can predict the weather is usually the guy trying to explain why his theory failed.

The playa is completely capricious. If you are looking for rhyme or reason, fuggetaboutit!

[skippy3k]

Last question -- footpad or no foodpad? Will it sink much? I wouldnt think it'd sink enough to matter.

I strongly recommend footpads. I lag bolt mine down and they aren't going anywhere. It then only becomes a matter of what will fail first in high winds; the bungees holding the tarps, or have the poles pull out of the footpads. The poles are held into the footpads by eyebolts serving the purpose of set screws. I've replaced mine with bolts that I can quickly tighten using a cordless drill, but that only eases setup and teardown...it's doesn't really add much to overall strength. I've been kicking the idea around of drilling an actual hole in the poles and have the set screw/bolts go into the hole. That would lock the poles into place, preventing them from pulling back out. But I think if not done exactly right, it would create just enough play to have the poles rattle within the footpads, since they no longer have the pressure of the set screws/bolts holding them tight.

Has anyone else done this?

[Roundabout]

I put a 2 link chain on the lag screw and run rope through it and over the top poles and then cinch it tight with a trucker's knot. That keeps everything firm to the ground.

[Soliton]

FWIW, After reading many posts on this board, I decided to go with a 20 X 20, flat-topped 1" EMT structure this year (first time on Playa).
Some notes:
1. The Chinese-made tarps (silver/white, sold as "heavy duty") really didn't look all that heavy duty to me once they arrived. I'd suggest American-made and spend a few extra $$ if you can.
2. The center is all 10 X 10 tarps, and I am adding 10X12 tarps on all 4 sides (at a 45 degree angle) to minimize wind load forces. Also adding folded 12X12 tarps at 3 corners with an extra rope and tie-down point (1st timer's overkill... )
3. From my reading in a few places, foot pads are advised.
4. I'm using 3/8" rope for all tie-downs, including on all nine center posts (to lag bolts/chain links). That way there is no reliance on the eyebolts clamping the EMT at all. I liked the fish-tape idea, but didn't relish the mess that I thought the 'prelubrication' that comes with it might make.
5. The vertical EMT posts will be shortened to provide an 8' ceiling. Even that seems awfully long and skinny as a compression load member.

Being a Virgin, I have absolutely no idea how well or easy this thing is going to be to set up, or how durable it will be on-Playa, but it does represent a distillation of some really good comments found on this board. While going solo this year, I liked the expandability of these types of structures, allowing me to invite others in future years if things go well.

Best,
Soliton

[Popeye]

FWIW, After reading many posts on this board, I decided to go with a 20 X 20, flat-topped 1" EMT structure this year (first time on Playa).

4. I'm using 3/8" rope for all tie-downs, including on all nine center posts (to lag bolts/chain links). That way there is no reliance on the eyebolts clamping the EMT at all. I liked the fish-tape idea, but didn't relish the mess that I thought the 'prelubrication' that comes with it might make.

Best,
Soliton

Sounds good, but all rope is not created equal. Look for something with a certified load rating, most hardware store rope is crap, you might find what you need at a marine dealer. Poly is weak and moopy. Nylon might be ok but remember it stretches which can be good or bad. Perhaps the best idea is straps. A little more expensive but strong and easy to use.

[Roundabout]

2. Also adding folded 12X12 tarps at 3 corners with an extra rope and tie-down point (1st timer's overkill...
5. The vertical EMT posts will be shortened to provide an 8' ceiling. Even that seems awfully long and skinny as a compression load member.

No need to do the corners. In fact it will probably work against you. Besides, the corners make great entrances.
I do my vertical EMT posts at 7'3". That way I can reach up and make adjustments without having to get a stool. YMMV
As to angled side walls, I would suggest using dynamic rigging (zig zag paracord like a boat sail) instead of the static rigging that is bungee balls. Those walls have to withstand a lot of wind pressure, and the dynamic rigging spreads out the load among the grommets. Also, it is easier to raise the wall in moderate wind when you use dynamic rigging. On the ground side, I use 2x3 or 2x4 sections of lumber between the lag screw head and the tarp grommet to spread the load (some consider this to be overkill).

[Soliton]

Roundabout,--

As to angled side walls, I would suggest using dynamic rigging (zig zag paracord like a boat sail) instead of the static rigging that is bungee balls. Those walls have to withstand a lot of wind pressure, and the dynamic rigging spreads out the load among the grommets. Also, it is easier to raise the wall in moderate wind when you use dynamic rigging. On the ground side, I use 2x3 or 2x4 sections of lumber between the lag screw head and the tarp grommet to spread the load (some consider this to be overkill).

Great idea about the dynamic rigging! Hadn't thought of that...
The rope I purchased was indeed from a marine dealer, and is braided polyester. I had thought that if I melt the ends, there shouldn't be much of a moop/fraying issue. Polyester is supposed to have relatively little stretch, and somewhere I read that that some other types of rope commonly used are too stretchy for good guy-lines (paracord, for instance was mentioned as being too flexible). Haven't practiced tying knots with it yet, however...

8' ceilings will require I bring a ladder. There is a balance of being too low (hot ceiling and air layer at head level) and too high (poor wind load handling). Comments from others on ideal ceiling height? I haven't purchased or cut EMT yet, so have flexibility on ultimate ceiling height.

I like the idea of wood blocks to distribute the load at the tarp grommets, but that would be a lot of blocks (~40 for my structure) or extra long lumber to haul. Will have to think about that.

Thanks for the comments!

[Popeye]

If you already have poly you might as well use it. Strands will break easily where they rub so you might want to check that before you use it again. On the plus side it is fairly easy to splice, pick up a fid for a dollar or two and you can loop it through grommetts etc. or splice two ropes together without knotting. Really easy after you do it once.

[Roundabout]

Great idea about the dynamic rigging! Hadn't thought of that...
The rope I purchased is braided polyester. Polyester is supposed to have relatively little stretch, and somewhere I read that that some other types of rope commonly used are too stretchy for good guy-lines (paracord, for instance was mentioned as being too flexible). Haven't practiced tying knots with it yet, however...

I like the idea of wood blocks to distribute the load at the tarp grommets, but that would be a lot of blocks (~40 for my structure) or extra long lumber to haul. Will have to think about that.

The stretchiness of paracord is beneficial for dynamic rigging. I suspect that you won't get as much benefit from dynamic rigging using polyester. I do agree, however, that polyester is the better rope for guy lines. If you get paracord, be sure it is rated at 550. It's very inexpensive and comes in a zillion colors on eBay. It's also easy to tie off with a simple clove hitch.

If you do decide to use the wood blocks, I use 2x3s which are very inexpensive around here. I cut them into approx 15" sections and pre-drill a hole for the lag screw. They bundle up into a pretty compact area.

[motskyroonmatick]

I use tennis balls for my foot pads and rebar protectors. They work well, store well and are cut easily with a sharp utility knife. I usually cut the appropriate sized opening on the makers mark so it is easy to find. I just got 50 tennis balls used for under the price of 30 new on of that on line auction place. It's good to reuse!

[fernley1]

On mine 20×20 flat shade structure, I use 1 20x20 heavy duty silver tarp. To help prevent ballooning, I use ratchet straps over the top, making a cross acrossed the tarp. Last year during the rain storm, I used my shovel handle to lift up on the tarp to remove the pooled water, it was sagging pretty bad when I woke up.

[inventory]

8' ceilings will require I bring a ladder. There is a balance of being too low (hot ceiling and air layer at head level) and too high (poor wind load handling). Comments from others on ideal ceiling height?

8 foot height for our (extremely similar) structure worked well for us. A 5'6" person standing on a milk crate can reach the top bar for tightening set screws / lacing paracord for running rigging. If your intended installer is likely to break a milk crate, other more solid (yet still non-ladder) items could be found. Even a stepstool should work.

Protip: for running rigging it can be a help to bungee in the four corners to get the tarp centered & held while you lace. This only works in low wind though.

[MacGlenver]

I put a 2 link chain on the lag screw and run rope through it and over the top poles and then cinch it tight with a trucker's knot. That keeps everything firm to the ground.

This is exactly what I was thinking/hoping to do. This will be stronger than a footpad/set screw by far. Thanks for validating my thinking.

[MacGlenver]

On mine 20×20 flat shade structure, I use 1 20x20 heavy duty silver tarp. To help prevent ballooning, I use ratchet straps over the top, making a cross acrossed the tarp. Last year during the rain storm, I used my shovel handle to lift up on the tarp to remove the pooled water, it was sagging pretty bad when I woke up.

Any opinions on this suggestion? So far Trilo has said 20x20 is no big deal (just chill when it starts ballooning), and this seems like a good safety measure. Any words of caution, or do you think its fine?