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Saturday, January 16, 2021

Episode 9 — Polyethy-lean-to

This video is very long. There is an extra bit of video after the credits of how the final project behaves in high wind though, so it isn't quite as long as the time stamp would have you believe. There are Chapters embedded into it so you can easily skip to the next section if you feel you have see enough of me drilling holes. Each Chapter has it's own section in the blog as well if you want to find the details on one particular step.

The most concise details are in the spreadsheet I made. Click the links below for a PDF you can save with links you can click to go to the vendor websites, or access a spreadsheet in Google Sheets.

PDF Bill of Materials with Hotlinks

Google Drive Spreadsheet Bill of Materials with Hotlinks


Back in August I started thinking about how much nicer it would be to work on Ally Mo if I wasn't so pressured by the weather. If there was some kind of roof over it then I could take out the windows and not have to rush to get something in the hole. I could have lots of fresh air during the disgusting part of removing all the mouse infested cabinets and paneling and insulation. And it could provide shade. On a cool winter day it would stay cool enough for me to work in full PPE.


  1. Aesthetic - It needs to look nice. I need something to boost my confidence and make me want to work on the project
  2. Cost - It should cost less per square foot than a comparable ready-made canopy kit or else I'll feel dumb for having these high aesthetic standards at the cost of a lot of extra work

Research and Development

I did some research looking at photos of midcentury carports to see what they had going on.

V shaped supports. Nice, but I don't know if that's going to work for me.

I found some interesting tropical structures

Eventually I stumbled into the farming sector and learned about caterpillar tunnels and hoop houses

Tunnel Vision Hoops Caterpillar Tunnel

I started considering what I could do with these readily available components and techniques. What if I could lift that up and tilt it over? That might look interesting. I did a very basic elevation drawing (I currently lack any explanation for why I chose these line colors) to verify I had the scale right in my mind. 
I don't really trust drawings though. I need to see things in place. So I bought a couple 10' lengths of 1" conduit to play with, see how bendy it is. I got it in roughly the right place with a couple of ladders so I could stand back and take it in.

I liked the curve of the 20' of 1" pipe so I decided to move forward. I made a spreadsheet with a bill of materials and got an idea of what I was looking at for cost. I figured it was going to be around $700 minimum. I allowed as how I would assess how flimsy it was and may have to buy more lumber to shore it up. 

How does this compare to kits I could buy? If it was going to cost a lot more per square foot how would I rationalize not doing it the easy way? The cheapest Harbor Freight carport tent thing is $99 for 10' x 20'. I'll call that $100/200 sq feet = $0.50 per square foot. That's cheap.

The Shelter Logic version that used to come in different sizes is $349.99. It's only available in 10'x20' right now, January 2021. But from the reviews I see they used to make them big enough for an RV. The reviews complain that the covers only last a year. Anyway, ignoring that it's too small for Ally Mo, the price per square foot is $1.75/ square f

My early spreadsheet made it look like I would be spending $1.20/sq ft. That's in between. Of course neither of those are big enough to even cover my project. What about one that is big enough? I found a 15' x 40' gable end canopy 8' tall, which Ally Mo would fit in, as long as I didn't want to get on the roof. But it was over $2964.76 for 600 square feet, or $4.94 per square foot

There's an Arrow brand RV canopy that's 14' x 47' x 14' for $5399.99. So the math on that is $5400/658 sq ft = $8.20 per square foot. 

These numbers made me feel pretty good about my plan. It would be good value. Also I need to work on my trailer. I can't have those posts so close to the side and have the roof right up against an 8' canopy. That would be all kinds of in the way. Not to mention guy ropes all over the place. I decided to commit to the PVC hooped based project.

Material Acquisition

The big challenge was going to be getting the long materials. I hurried out and bought 10 foot long pressure treated 4x4s in August because I'd heard on the Fine Homebuilding Podcast that there were shortages. There was still plenty of stock at Home Depot in Tallahassee. I asked them if they'd had unusual demand on pressure treated because everybody was stuck at home and wanted to build a deck. They said no, people weren't buying it more than normal, but that logging crews stopped harvesting trees during the initial shutdown in March so they weren't getting their normal shipments. But they still had plenty from before the pandemic.

I couldn't find any place that would deliver 20' PVC pipe to Beachton, but I did find a Lowe's on the far side of Tallahassee that stocked it. I wanted to buy the long pipe and 12' pressure treated 2x4s at the same time since I had to tie all that on the roof rack. I needed to not dawdle because of the rapidly rising prices on building materials due to increased demand and limited supply. One day in early September my car battery died. I got it started with my battery charger and drove straight to the Auto Zone and bought a new battery. Then I went across town to Lowe's and loaded up my car. I had a man help me lift the materials up there and then I tied it on. I was not keen to get on I-10 with it, but it was fine. I guess all that experience tying on kayaks was worthwhile. I had to get my Aunt June to come help me lift it off or risk damaging my car. Fortunately she was nearby. Thanks, June!

Alternative to White Schedule 40 PVC:

I'm going to have to paint this pipe because ultraviolet radiation will discolor it and make it brittle. If the manufacturer adds only 2% of carbon black to the PVC formula it makes it resistant to sun damage (citation). I'm guessing that's why conduit is gray. If you can get hold of some 20' conduit you could avoid painting it. I found it on Lowe's website, but there's a large minimum order that didn't work for me. Also I wanted white for aesthetic reasons. If you were doing a shade fabric lean-to gray might look neat.
Schedule 80 PVC Pipe, UV Resistant

I didn't want to use 10' lengths pushed together in the middle. I don't have any evidence it wouldn't work, but it just seemed inelegant.I worried that the joint would make a discontinuity in the sweep of the line. It would also be a heavy spot that could unbalance the whole thing.  I wanted a smooth curve. 

The key to my plan was this aluminum channel that farmers use to hold the edges of the polyethylene. I looked online and found lots of sources. I even found a place 80 miles away in Central Georgia that manufactures the stuff, Atlas Greenhouse. I called them up about coming over there to pick up materials in person. But we were in the middle of a pandemic and I didn't think it was a great idea. I decided to just have it shipped from a place that had some other stuff I wanted, Advancing Alternatives. Here's my shopping cart.
I wanted to get this stuff in my hands before I started building anything. Like a 20' long pipe, I needed to see how bendy it was going to be. I am going to have to make this 36 feet long. Can it handle it? 
I want to use this as a purlin

What's a Purlin?

Purlins are the part of the roof that runs perpendicular to the rafters. You don't get them in houses that much because they put sheathing right on top of the rafters instead. But my house has purlins. It's 2x4s I screwed across the rafters and then I attached my metal roof to them. For my lean-to the plastic pipe hoops will be like joists or rafters and this channel will be where I attach the plastic, so that makes it a purlin. My shed doesn't even have rafters, it only has purlins. They're 30' long steel members with a C shape profile. They attach right to the end walls and the corrugated steel goes on top. The industrial metal is actually a structural component, not just a cladding. Even the polyethylene in this project has some structural importance. It's like the paper on a balsa wood model airplane.

In the video I moved pretty fast over the other profile I used. It looks like this.
Since I would be screwing these to a 2x4 I wasn't that worried about how stiff they were. These are also incredibly common. I found them on Tunnel Vision Hoops, who also offers the double channelBootstrap Farmer, and Farm Plastic Supply. I bought them from Advancing Alternatives because I could get the quantity I needed without going over. I also liked that they used stainless steel for the spring wire instead of a PVC coating.

The polyethylene itself I decided to get from Farm Plastic Supply, along with ABS clamps to hold the ends. I went with 55% opaque plastic because it's freaking hot here and most of what I need to do is inside the trailer anyway. The extra light wouldn't help me see.

Now that I have everything built and tested I may be able to get away with 16' wide plastic next time and it would be $88 instead of $96. Seems like it's worth $8 to have plenty of slack though.

Some of the expensive stuff I had to buy was fasteners. People seem to just gloss over them when they're talking about a project but I find them to be one of the most expensive line items. The 4" long 1/4" Spax construction screws I wanted to screw the tie beam to the side of the shed cost $6.98 for a box of 12. That's $0.58 each. I bought $15 worth of them and had 2 leftover. I bought $20 worth of Deckmate screws to fasten the pressure treated lumber together. I can't get over how expensive those things are. I didn't even have enough. I had to scrounge some more out of my stash in the shed. I also used a lot of galvanized collated nails for my nail gun, but I already had those leftover from a box I bought about 30 years ago. Ultimately I spent $55 on fasteners for this project.

Placing End Posts

I decided not to be too fussy about my post placement. I could have put up batter boards or measured diagonals and all that, but why? It's going to have an entirely flexible roof. So what if it's a couple inches off one way or another? I just measured 16 feet from the corner of the shed and eyeballed a straight line. I dug a hole, placed a post, carefully packing the soil in lifts, and got on with my life. 

Shed Repair

I had to finish fixing the shed before I could attach the lean-to. I patched it up back in 2005 when I first moved back to Beachton but the flashing on the end was so damaged I threw it away. I finally measured the other doorway and did a drawing and had new stuff made. Here's what I started with in 2005

I took out the overhead power feed and replaced the studs in the corner back in 2005. And then since Brenna and I ran underground power in June I got the lights working again. Just put a switch on the same old wiring from the 8' fluorescent fixtures. They came right on. You can hear them humming in one of the clips in the video where I forgot to turn them off when filming at night.

Middle Posts

Once the two end posts were set then the placement of the middle two is actually pretty important. If they aren't in a straight line then the whole thing will look wavy and awful. Fortunately that's not what I screwed up on the second one. I used  string to be sure it was in a line with the other posts, I just marked the spot wrong and the spacing between them isn't even. I didn't double check it before I dug the post hole. My bad.

Cap Beam

I started out putting a single 2x4 between the posts. The shed is 36' long so with 3 spaces 12' long it comes out just about right. Once I subtract the thickness of the actual posts it leaves a little extra to cut off. I wanted to see how much the structure would move with this scenario, figuring I could double it up if it seems sketchy.

My Most Valuable Skill

I figured out I made a mistake on the post by the back door of Ally Mo when I was putting the 2x4s in between. I rationalized that it wouldn't really matter as long as the line was straight. It will only be viewed from one end on an angle so it's going to look fine anyway.

How Flimsy Is This?

I shot some slo mo video of how the posts and beam move when I push on it. It's pretty wobbly. There's more footage of how it moves after I doubled up the 2x4s in the part where I hammered on the straps.

Prescribed Fire

My aunt was burning the woods down the hill to the southwest of my house one day and it made it all smokey. It was a nice segue to talk about a possible drawback of a polyethylene roof at my house. Falling embers could melt holes in it. The plastic has to be replaced every couple of years anyway, so maybe it's not that big a deal. Something to think about though.

Full Scale Planning

Even though I did some drawings to figure out how to build this thing I still had some working out to do with how to space the hoops out. I need the holes to line up with the high ribs of the shed, but I also need the screws to go through the high ribs where the panels overlap. So I can't have a hole there. Then there's the ends of the boards to deal with. They need to fall between mounting points and hoop holes. And hopefully not come too close to either one. I decided on a kind of odd arrangement that worked out like this. 

° 4 ° 4 ° 3° 3° 3°2°3 °3 °3 ° 4 ° 4 °

The numbers are feet. The ends of the boards were in there somewhere. I had some 8', 10', and 12' lumber. I didn't cut any of it ahead of time, keeping the pressure treated ends intact.

Farmers use huge hoop spacing like 5 feet apart. I had to buy my pipe bundled up in groups of 5 so I figured I might as well use 12 of them.

I clamped a broom handle to the post and used a ladder to hold the other end while I got the one end in place. Then I climbed up and used a protractor to determine how to angle my holes. I didn't take a picture of measuring the other side. It was 20°.

40° Hoop Holes

1" PVC pipe has an outside diameter of 1 3/8". I had a 1 3/8" spade bit so I started out with that to see how it would go. It didn't go great. It kept knocking the spindle out of the drill press.

I made a few test holes and considered leaving part of the board at the bottom of the hole as a stop. I decided against this and just drilled all the holes clean through.

I made a special trip to Home Depot to get some alternatives for making the holes. I settled on a hole saw. They were out of the one I wanted and I had to buy a lot of extra stuff, but in hindsight I bought the wrong extra stuff and I had regrets.

I wanted this for $12.37

But I got this 1 3/8" hole saw for $10.47

and this quick change arbor for $21.47
I also bought a longer bit

But the big fat part at the back hit the wood and got pushed up out of the notches in the hole saw so it overtightened on the arbor. I finished the job with it anyway. 

A half round wood rasp was pretty vital too. Here's a link if you don't have one. I already had one so it's not in my Bill of Materials.

20° Hoop Holes

Slightly different technique for these ones. No chisel work.

Check Hoop Holes

I put the first tie beam section on the shed and clamped the 2x4 cap with a 20° hole in it up on the top of the posts to be sure I was doing everything in the right direction and to be sure the angles worked. Stuck a 20' pipe in. Looks good. Climbed up and checked the height over the Spartan. It comes to about my chin, which means I can work under there just fine.

Put up Tie Beam

Steve came to hold the end of the tie beam while I drilled the holes and put the screws in. He shot a few video clips with my phone from the other ladder. I almost forgot. 

I'm including painting the tie beam in this chapter. It was easy with the holes already painted. My superpower is knowing exactly how much paint to put in my paint pot.

Double the Cap Beam

I doubled the 2x4s between the posts with a lot of galvanized nails. 

Screw on 20° Drilled Cap

Then I screwed the 2x4s on top with the 20° holes drilled in them. I had to plane the beam a bit to get it all tight. I used $10 worth of 2 1/2" Deckmate screws and some 3" ones too for going into the tops of the posts.


I didn't go into this part that much in the video because it's kind of a matter of personal preference. I just used the lumber I had on hand. It is important to use lag bolts and not just screws though. I used screws to hold it all together while I took it apart and marked and cut and set my posts but then I added big ol 1/4" bolts at the end. Here's what my braces look like. I used a piece of HardiTrim for that shelf. I had it leftover from when I rebuilt my outdoor shower. The angle bracket on the front of the post is what backs up the hole for the first hoop joist. Stops it falling through.


This step was probably totally overkill, but straps are pretty cheap. In fact they would've been free if I'd realized I already had some in the shed, but I bought new ones anyway. I couldn't find the receipt for them because I paid with cash so it didn't go into my email as normal. They were about a dollar. The box of nails about $7. I can't find them on the Home Depot website.

Straps like this always remind me of Taylor Huddleston. When we were building June's little garden house we strapped the rigid frame to the joists. June was helping by nailing the straps under the house. Taylor went to inspect her work. She was only putting nails in about every 3rd hole. He asked her why. "They didn't put the holes in it to reduce the weight!"

I also put nailing plates across the joints in the 2x4s on top. Totally ridiculous I know. But I wanted to attempt an editing trick to make it look instantly nailed. It didn't really work because outdoors. I need controlled lighting for that.


The cap beam between my posts is a bit wobbly because of the joint at the post. I could have bolted a 2x4 to each side across the post but I thought that would look shitty. So I just bolted on a wee piece of steel just because I had it. The lag bolts were also in my stash. If I'd braced all four posts it wouldn't have mattered. In fact it probably still doesn't matter. The flexibility of that structure has not entered my mind once in the month or so since I finished it. The loading on it is really minuscule. The top structure is light and wind doesn't seem to do much to it.

Prepare the Pipes

I cut the bell ends off all 12 pipes at a 40° angle. I didn't bother with the angle on the other end since that would require me to match the axis of the cut on the two ends. That seemed way too easy to screw up. I guess I could use the writing on the pipe, but it just isn't worth it.

I washed the pipes with water just because there were dusty from being in the shed, then I cleaned them with acetone to sort of give the surface some tooth for the paint. For paint I used Gripper primer. It is just a regular water cleanup acrylic paint.

A lot of the farmer websites sell a white felt tape to put on the pipes to prevent wear and heat from damaging the polyethylene prematurely. I wasn't sure I'd be able to get that on easily because my structure is kind of high. Also it is expensive. But if the polyethylene fails over the pipes I may consider adding it when I buy new polyethylene. It's $15.99 for 45 feet. It would cost me $64 to put felt tape on all the pipes, far more than the pipes themselves cost. 

My paint roller came from Zoro. It's only $14.99, but you have to get roller covers too and there's shipping. 

Paint the Post Side/Wire Channel

I painted this side of the structure on Thanksgiving morning under the threat of rain. I was partway done when it started to rain. I quickly covered the unpainted part with visqueen. In about 10 minutes it stopped and I uncovered it and finished painting. Then later when I drove over to have pie with Brenna I was astonished that the highway was soaking wet! It POURED all around me, but right at my house, nothing. Lucky!

Brenna and I put the aluminum channel on the side when the sun was setting and almost forgot entirely about filming it. I handed Brenna my phone and got a few seconds of video. It is pretty straight forward. I predrilled the aluminum then used roof screws because that's all I could find. I should have gotten screws specifically for this.

Purlin It All Together

I meant to order screws from McMaster to hold the conduit clamps to the purlins but I forgot. So I had to buy them at Home Depot at the last minute. It was a painful and expensive purchase. I decided #12 was the best fit. Those only come in stainless steel. The right size is #12 Stainless Steel Panhead Screw 3/4" long with #12 stainless steel nuts. A nut driver is very handy for working on these.

I had to put the conduit clamps on the 6' lengths of purlin first because when I rivet on the plates the end of the groove is covered up.

You could still rivet these together if you don't have buck rivets. You could just use pop rivets.

Belly Pan

I did do some work on the actual trailer in this episode. I took off the belly pan. In 1949 they used this asphalt impregnated product with aluminum channels holding it up. They seem to have put an off white color mineral wool or rock wool insulation with a kraft paper backing over the steel frame before they put the plywood floor down, sort of like how my dad did the roof of my shed. The mice and rats had completely separated the fluffy stuff from the backing. 
Packrats carried my avatar into the belly of Ally Mo. It was on a corrugated plastic sign I had made at Vistaprint that said "Longleaf Conservation Area"

This is a detail of the drain from the roll-down window

Really high quality screws in this trailer. I just unscrewed them! Heads intact.

In 1951 they used pink fiberglass insulation. They must have run out of the scraps they used to make the channel too because they used sheet aluminum screwed directly to the steel frame. 
Detail from removing the belly pan from Ally Min, 1951 Spartan.

But Ally Mo had these nice aluminum channels under there and I intended to use them. I extracted them and then pieced them together and riveted them until I had a 36 foot piece stiff enough for Brenna and I to carry it.

I measured my spacing for the hoops (see above) and drilled holes on either side for cable ties. I tried a regular twist bit but it didn't work great. The tapered bit worked the best. At the ends I let the cable tie go around the end of the metal and over the hoop.

Drill holes at the hoop joist locations

Make the holes big enough and spaced properly for your cable ties

I added a second cable tie over the first. There was still room in the hole!

Putting up the Purlin

I cut a dozen foot long pieces of conduit and stuck them in my holes in the tie beam and then Brenna and I lifted the double channel purlin up there. Then I pulled the short pieces of conduit out and put them through the conduit clamps so it was all lined up and ready for the next nice day.

Hoop Day

This was a fun day. The hoops went up very easily. Brenna declared it very satisfying. It was just like a dance. It was everything I dreamed it could be.

We were on the next to the last hoop when I remembered Brenna was in the color guard in high school. I asked her to show me her skills. Then we finished the job.

Polyethylene Day

This was a hard day. I exhausted myself. It was a lot of getting up and down. But I got the sheet of plastic on the hoops. Just watch it.

I never really went into detail in how I laced the purlin to the wall. I had the roll of rope and I sort of made lark's head knots around the tie beam. I made a loop then put the whole spool of rope through it. I did that on either side of the screw holding the 2x4 to the wall. You're really supposed to have plastic in both of these channels. They use it for roll-up sides. And then you put the clips on top of the plastic. I just got this kind because I needed the structural properties.

Last Day

I did some final adjustments and added an art.

Weather Tests

I captured some time lapse footage of wind and rain to see how the polyethy-lean-to performs. It seems to perform quite well. 


Thanks for watching/reading. I'm now going to get to work making things to sell so I can buy some plexiglass and weather stripping. Go buck yourself.


This episode features my niece Brenna Tomlinson who drove up from Tampa for Thanksgiving. Because of the pandemic there was no family gathering. Brenna and I worked on the polyethy-lean-to instead. It thought it was great fun and I didn't miss the feast in the least.

Also I had help from Steve Leacock who drove out to Beachton on short notice two times. Once to help me put the tie beam on the side of the shed, and then on Polyethylene Day when I over exerted myself and lacked the strength to squeeze the ABS clamps on to hold the polyethylene to the ends of my structure.

And I had help from my Aunt June in September who drove over in the farm truck to help me take the long materials off the roof rack of my Honda.

Thank you Brenna, Steve, and June!