HOW TO BUILD A 100 SQUARE FOOT WOOD FRAME SOLEXX GREENHOUSE
Below you will find working drawings for the greenhouse. Click on the PDF files one at a time and print them out on regular 8 1/2 by 11 printer paper.
Feel free print out and share any of these drawings and ideas with anyone who might benefit from them. Does this project give you any ideas? If so please share your thoughts and ideas in the “Comments” box at the bottom of this page. There is an email box at the bottom of the home page if email is your thing.
This qualifies as a shed and does not need a building permit in most areas. In San Bernardino county the following conditions must be met to avoid pulling a permit.
- It must be less than 120 sq feet. (It is only 96 sq feet)
- It may not have a permanent foundation.
- It must be at least 15 feet from all other structures
- It can not be hooked up to any utilities
If you meat these criteria then it is considered personal property and will not count to raise your real estate property tax. Each county has different rules so check with your local building department before you start this project.
HOW TO BUILD THE STRUCTURE
Cost effective (not cheapest)
Qualify as a shed and not require a building permit in most jurisdictions
Be able to stand up to severe winds and weather
Be put together with screws and bolts so it can be disassembled and moved
Use normal DIY materials so it can be built by anyone
Support all types of hydroponic, and soil growing methods
Lend itself to all types of off grid thermal mass temperature controls
Have plenty of simple ventilation
Lend itself to photovoltaic solar-powered fans, pumps, lighting and control systems
Once built it should last for many years without maintenance
When completed, it provides high output with a small investment of time and money
This greenhouse should make a significant contribution to food self-sufficiency
What is different about this structure?: This monocoque structure uses the outer skin (in this case, Solexx) to provide much of its strength. Since Solexx has so much rigidly, tensile strength, and compressive strength it does not need cross braces. All of the lateral support comes from the Solexx. No cross braces block sunlight and omits the cost of cross-brace material. For this reason use 5mm Solexx and stick with it for this design, as it will not work with other material.
No sunlight comes through the north wall so install a normal wood frame. This saves money. It allows you to use an off-the-shelf high quality exterior door. It provides a secure location to mount louvers, windows and heaters. This greenhouse must be oriented true north and south, and not magnetic north and south because of differences in location. When you lay out the base, get it as close to true north as possible. The closer to true north it gets, the more efficient and productive the greenhouse will be. If you are building south of the equator then reverse the orientation.
Overheating is a major problem for any greenhouse. More southerly locations need more ventilation. The default design calls for five 24 by 24-inch vents around the bottom. There is one automatic Easy Flow louver above the door. This may or may not be enough. It is easy to add more vents if needed.
Step 1 – The base
Identify where you want the greenhouse to be, and level it. Then level an area at least 3 feet on all sides of it to provide a workspace. Level and clear areas north and south of the building site to set up work tables and saw horses.
Lay out the base with snap lines oriented to true north.
Dig four post holes near the corners.
Cut 4 x 4 treated lumber. The outside dimensions should be exactly 8 feet by 11 feet 10 inches. This leaves 1 inch on each side for the Solexx to overhang.
Pre-drill and bolt corners together with 7 inch lag bolts and washers. If you don’t pre-drill, the 4 by 4s might split.
Cut four fence posts 24 inches and pre-drill.
Bolt the fence posts 8 inches from the end of the 4 x 4s.
Using stakes and other temporary supports, position the base with the fence posts suspended in the holes.
Make sure the base is oriented due north and south. Level and square. Measure the diagonals to assure it is square. Make certain the base level in both axis are square. If the base level isn’t exactly right then all the rest of the project will be more difficult. Take time to get this starting point exactly right. When ready, pour the cement in the post holes and give it a couple of hours to dry. Put in enough Ready Mix Cement to assure that it stays rigidly in place.
Step 2 – Lay out and cut top and side reinforcements
Prepare 11 top corner reinforcements and 22 side corner reinforcements. Cut them from about 1-1/2 sheets of construction sheeting. I used 4 x 8 sheets, 7/16 inches thick (1 R 24 / 2F 16 / W 24) with exterior type adhesive. Lay them up according to the drawing and cut them out with a jigsaw. Use the first one cut as a template for all the others. Keep track of the one used as a template for use as a template to cut the arcs on the north wall, bulkhead structures, and south wall. I prefer painting all wood used in the structure before assembling. Select a high quality exterior to last in a warm, wet environment.
Step 3 – Build temporary floor
Frame in a temporary floor with two 2 x 4s, and a 7/16 thick, 4 x 8 piece of construction sheeting. Line it up with the south edge of the base. This will serve as a place to lay up the north wall and make a template for the five bulkheads ,and south wall. It is important that all the bulkheads and the north and south wall maintain the same profile. This is also a good time to set up saw horses and work tables nearby.
Step 3 – North wall
When laying out the north wall, mark out a template to use for the five bulkheads and south wall. maintain the same profile for all of the parts.
Find the midpoint of the south edge and drive in a small nail. Use a snap line and snap a line to the adjacent corners of the 7/16th construction sheeting. It will end up as a 90 degree angle angle at the top, and 45 degree angles for both sides.
The snap lines are the inside lines for the top 4 x 4s.
Finish laying out the rest of the framing for the 4 x 4s and 2 x 4s according to the following drawing.
Build the frame using 2-1/2 inch rust-proof screws.
Use the corner reinforcements as a guide to mark the 9 inch radius at the top and two sides.
The rough opening for the Easy Flow louver is 24-3/8 by 12-3/8.
The manufacturer of the door and window you buy can provide the rough opening information.
Paint the inside of the Easy Flow louver with same white paint used for the framing.
When I painted the outside of the north wall white, some of the over-spray got onto the temporary floor, which marked the outline. The outline was helpful in laying out the five bulkheads and south wall.
Cover the frame with a vapor barrier.
Put a clear bead of silicon sealer all the way around the outer edge of the north wall.
Screw on the siding using 1 inch rust-proof screws.
Trim with a jigsaw.
Tilt it up and brace it in place. Make sure it is plumbed.
Screw it to the base using 2-1/2 inch rust-proof screws.
Step 5 – Build bulkheads
This greenhouse has five bulkheads, each consisting of two posts, a west roof structure, and an east roof structure. There are two top braces and four side braces. One cross brace connects the corners. A temporary cross brace was added near the middle to help handle the other braces. All of these parts are cut from 2 x 4s.
Cut the ten posts 90 inches long.
Use the marking on the temporary floor to lay out and cut all the west and east structures
Use the corner and top braces to mark the arcs.
Use a jigsaw to cut the arcs.
Now is a good time to paint them all, at least two coats.
Assemble them one at a time using 1-½ “rust-proof screws.
Stand them up and lean them against the north wall.
Step 6 – Build the south wall
Use the markings on the temporary floor to lay out the south wall. Cut the Solexx and lay out the left and right sides. This leaves one seam that is vertical. The Solexx will overlap along the middle post. Stand the south wall up and line it up with the south edge of the base. Brace it and make sure it is vertical and square. Screw it to the base with 3 inch rust-proof screws and brace it in place.
Step 7 – Stand the bulkheads up
Mark the locations of the bulkheads on the base. The Solexx is 49-½ inches wide not 48 inches as you might expect. This is done so the Solexx will overlap. Overlapping provides strength and makes a good seal. Measure from the north edge of the base 48-½ inches and mark the base. That is where the outer edge of the Solexx will go. Measure from the south edge of the base 48- ½ inches and mark the base then back toward the south measure the width of a 2 x 4 and mark it.
Count the bulkheads from the north wall. The bulkhead closest to the north wall is the #1 bulkhead. Measure and mark the locations of the #2 and #4 bulkheads first. Then split the difference and mark the locations of the #1, #3, and #5 bulkheads half way between #2 and #4.
Once the locations are marked stand the bulkheads up starting with the #5 and working north.
Start at the south wall and stand the bulkheads up and secure them to the base with 3 inch rust-proof screws.
Step 8 – put the Solexx on.
Cut the Solexx into two 300 inch, and one 328 inch sheets. Make sure all the ends are square. The 300-inch sheets will not completely go all the way over the top and reach the opposite bottom of the wall. This allows a space to frame in 24-inch vents on two of the panels. The 328-inch panel will go all the way from the bottom of the east wall to the bottom of the west wall.
This was hard to do. As it turned out, the bulkheads and the north and south walls were not flat. Start with one of the 300- inch sheets of Solexx. Lay it along the edge of the #2 bulkhead. It overlaps the whole 2 x 4. Screw it into the bulkhead with rust-proof 1-inch screws. Don’t use fender washers yet. Put the screws in so that they are snug. Put eye bolts into the bulkhead and have a helper pull one way, while you pull the another way with ropes to force the #2 bulkhead to line up with the Solexx. Don’t cut the Solexx to make it fit. Shove and push as necessary to get the bulkhead to line up with the edge of the Solexx. Work in one direction so it doesn’t trap a wrinkle. The Solexx overlaps the edge of the north wall. Don’t worry about the #1 bulkhead yet. Again wrestle, push and shove the north wall so it is flat and the Solexx overlaps. Again don’t cut the Solexx to make it fit. Force the north wall into alignment. Work in one direction so it doesn’t trap a wrinkle. Use one inch rust-proof screws with fender washers 3 inches on center to secure the Solexx to the north wall. The #2 bulkhead and the north wall took a lot of pushing and shoving to get them to line up. The #1 bulkhead was easy to line up. Screw the #1 bulkhead in place with 1 inch rust-proof screws and fender washers 1 foot on center.
Don’t rest a ladder on top of the structure until the north wall, #1 and #2 bulkheads are screwed into place. Put ladders outside the north wall and adjacent to the #2 bulkhead. Work over the sides. The structure might not be strong enough to support the weight until then.
The location of the vents are a personal preference and will be different for different climates. This greenhouse has one 24 inch by 24 inch vent on the bottom of the first Solexx panel to the west side, and two 24 x 24- inch vents on the the east side panel.
The southernmost panel has no vents and the Solexx goes all the way from the base of the west wall to the base of the east wall.
The next two panels lined up easily. They overlap at the #4 bulkhead. Screw them into place with 1-inch rust-proof screws and Fender washers 6 inches on center. The Solexx overlaps the south wall about 1 inch.
Step 9 – Finish it
Hang the door and window and frame in the vents.
Caulk it like crazy.
Make the floor with either paving stones, gravel, or simply leave it dirt.
This concludes the step-by-step instructions to build the structure.
This little greenhouse should provide years of trouble-free service.
A couple of years ago my wife, Rita, and I were at Chena Hot Springs, Alaska. I spotted a couple of grizzled old Vietnam vets, and struck up a conversation with them. Both were long-time Alaska residents and both were experienced in building greenhouses for the harsh climates with 70 mile per hour winds and temperatures 50 below. They had tried many different greenhouse designs and materials and had settled on a material called Solexx. Both said that they would never build a greenhouse with anything else. It turned out that Chena Hot Springs had two large Solexx greenhouses used to produce the greens served in their small hotel. I checked them out and was sold on Solexx.
Solexx is not like other greenhouse glazing. The structure is similar to corrugated cardboard. Instead of paper it was wite plastic. The sunlight was defused and surrounded the vegetables. The sunlight came at the plants form all angles and did not cast shadows so large plants blocked less light from small plants.