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If this looks like too much work – I did a much simpler door on the other end.
This weekend I finally got time to start on the doors for my 50 dollar greenhouse. The design that I came up with is light, strong, simple, and can be built easily and quickly using only a circular saw and a hand drill. I must admit that I did use a table saw to rip out the stock, and put it through a planer to accurately dimension it, but this was only a convenience, and isn’t at all necessary for a good result. This polytunnel door design can be built on a set of sawhorses out in the driveway, but it will be a lot easier if you get someone to help you hold things while you saw, drill and fasten parts together.
Needless to say you can seriously hurt yourself with power tools, and you should follow all applicable safety rules for the tools that you use. No kidding, a friend of mine lost an eye about a year ago because he wasn’t wearing safety glasses. Don’t make a mistake like that. Be Careful.
You will need enough 1×2 stock to make your door – two pieces to make the sides, and three pieces to make the top, bottom and middle brace. The dimensions of these pieces will be determined by the size of the door that you are making to fit your polytunnel hoop house. The sides need to be the same length as the finished height of your door while the top, bottom, and brace need to be 3 inches less than the width of the finished door.
Pre-drill holes before screwing the frame together. If you don’t pre-drill you will probably have problems with your wooden parts splitting when you drive the screws. Use a bit that’s just small enough to allow the screws to get a good bite. Try it on a scrap of wood first to make sure that you aren’t pre-drilling too loose or tight.
I used 3″ washer headed self drilling screws (I still had to pre-drill the holes though to prevent splitting) but any 3″ screw would work. If there’s a gap between the parts after you screw them together – back out the screw and re-drive it. There is no point in gluing these joints because glue doesn’t hold very well on end grain – trust me, don’t bother – the finished product will be very strong anyway if you follow the plan.
Your frame should look something like this after you screw it together.
Now drill a hole in each corner to thread the brace wires through.
Thread a loop of wire diagonally both ways and secure the ends by twisting them together, and then twisting the tags back around the main wires. I used galvanized electric fence wire for this, but you can get a similar product called “utility” wire at any hardware store or home improvement center. You can also use small rope/large string, but wire is really better because it isn’t as likely to stretch.
Clip the ends off and bend them neatly so that they won’t stick out and snag people, clothes, or greenhouse plastic. There has to be a better way to do this than I’ve done here. Gotta’ look into that.
Check your frame for square by measuring diagonally across the corners. If they aren’t about the same then tweak the frame a bit to get it pretty close to square. Although this is a pretty forgiving design and unless it’s really out of square it probably won’t matter much – within a quarter of an inch is great.
Now use some scraps of wood to tension the wires. You want them to be merely tight, but not like guitar strings – just without any slack. This will pull all of the joints together so that they aren’t likely to come apart or sag. Check for square again to make sure you haven’t torqued everything out of whack.
This is how the tensioners finish off. You may have notice that I’m a fan of this kind of device – I used it on my polytunnel greenhouse for the same reason that I’m using it here – It’s strong, light, easy, and it works.
Now glue triangles of plywood at each of the frame intersections – the corners, and at the cross brace. Notice the pencil marks to help keep the glue in bounds. Use a water proof glue like Titebond 3, and secure the connection with screws or nails. I used scraps of 1/2″ plywood for this, but anything from 1/4″ to 3/4″ sheet goods would work, or even solid wood, but lightness is a virtue so mind the weight. I used what I had.
You will be amazed at how strong and light this structure is. You can certainly use other sizes of lumber instead of 1×2 to make your doors – 1x3s would also work great for the sides, and 1×4 or 1x6s would be fine for the other parts. However, your door will be heavier (although it might be stronger), and you will probably have to recess the screws that hold it all together so that you get enough penetration for them to hold – or find some really long screws. You will of course have to adjust the measurements to work with your door size and the lumber that you use. Keep in mind that if your door is very heavy it might be more than your polytunnel greenhouse frame can support without some beefing up.
When I turned my frame over I discovered that some of my screws were just a tad too long, and they poked through the other side. This had to be fixed or it would cut the plastic covering and would probably cut me or someone else sooner or later.
Just a few strokes of a file on each screw takes care of this small issue.
Nice and flush.
Now for the Plastic – After building the greenhouse I discovered that condensation and rain will collect at the bottom of the plastic if it can, so don’t fold the plastic around the bottom of the door just staple it flush so that water can run out the bottom. On the sides and top leave a little extra to fold it around and double it up…
Plain old (recycled) loose pin interior door hinges are fine for this application – be sure and install them right side up though so that the pins don’t work loose and fall out. With regular gate hinges the pins would be attached instead of loose and you couldn’t remove the doors as easily (by tapping the hinge pins out) when the weather turns warm next summer.
Another recycled item. You could also use a cabinet knob, or just a piece of 2×2 for a handle, or even a strap of leather from an old belt.
Ready to go… Wouldn’t you like to explore that shop? I used to love the “Mister Wizzard” TV show when I was a kid, and my life is now complete that I have a shop like his. Now all I need is a box on the shelf labeled “Dinosaurs” – I always wondered what was in that box.
Because of insufficient foresight I have this “situation” that I had to deal with before I could hang my door. The door frame needs to be unobstructed all the way to the ground.
I took the quick and dirty route of shoring up the problem spot with plastic and a scrap of galvanized metal after trimming the wood off flush.
Now that you’re ready to hang the door put a scrap of lumber under the door first to space it off of the ground. Since my polytunnel greenhouse site slopes, I only needed to do this on the high side.
Now just set the door down on the spacer and screw it temporarily to the greenhouse in just the position that you want. Stand back and take a good look for obvious problems before you continue.
I made my door about an inch and a half wider than the door opening on the greenhouse and a couple of inches taller because I want the door to close against the greenhouse itself instead of using a door stop. If you have much snow you might want your doors to open in – think about what your needs are, and adjust the design to do what you want with the materials that you have readily available.
Now, hold a piece of lumber that will be the jamb right against the side of the door and mark about a quarter inch above the top of the door. Cut it off at this mark, and do the same thing on the other side. Then screw the two resultant side jambs securely to the greenhouse leaving about a quarter of an inch of space between the jambs and the door.
The 2x4s that I used for jambs are 1/4″ thicker than the actual door – this turned out to be a good combination because it left enough space between the door and the greenhouse for the door to open and close easily, but because the polytunnel plastic is a bit poofy there isn’t really much of a gap for air to leak through. Serendipity I guess. If you do have problem gaps you can weather strip with scraps of foam carpet pad (or even carpet) and your staple gun.
Once you’ve attached the jambs you can screw the hinges to them, and remove the temporary screws that have been holding the door in place. At this point the door should open and close easily – if it binds or rubs excessively, back up and adjust before you go on. A common error would be to make the space between the door and the jambs too tight.
Now cut a piece of lumber to use as the head jamb. I ripped an angle on mine so that it would shed water better. I stapled the strip of black plastic to the back before attaching the head jamb.
The strip that was ripped off is then attached to the front to extend the jamb and give an overhang so that rain won’t run over the door. You could actually accomplish the same thing by just using a 2×4 that lays flat for the head jamb and letting it stick out.
Then, just staple and trim the plastic strip thusly.
Add a simple turn bolt both inside and out and your door is finished. Almost finished – I shoveled a bit of dirt in to close up the gap under my door, and I will probably add a simple sweep to the bottom later. But for now it works great, and looks fine. It’s easy to open and close even with just one hand.
On the other end of the hoop house I did something much simpler – basically a well secured curtain.
Secure two or three pieces of string at the top of the door opening – these will be used to tie the curtain open when you have it rolled up in warm weather.
On both sides of the door opening apply two strips of wood leaving a gap between them.
Hang the curtain by wrapping the top of it around a stick and then screwing it to the greenhouse.
Put two or three turn bolts on each side
To fasten the curtain shut push a stick into the gap on the sides..
And secure it with the turn bolts.
And that’s it. It isn’t as convenient to open and close as a hinged door, but it gets the job done.
Now that the doors are up it gets pretty warm in the polytunnel on a sunny day even when it’s cold outside – I have the same problem with my cold frame. Next time I’ll give you the scoop on some really easy automatic vents that you can make for about $10 – $15. Subscribe to the DoorGarden RSS Feed and you’ll never miss a thing.
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