A greenhouse is a wonderful thing. Stepping into a bright, warm greenhouse when it is cold outside is like stepping into a gardening haven, regardless of the time of year. The air is fresh, earthy, warm and moist. It urges one to plant and grow things immediately, no matter what month it may be. It lifts the spirits, making the hopes and dreams of the gardener spring eternal.

If you wish to experience this gardening phenomenon, prepare to step into your own greenhouse. Believe it or not, you can build one yourself using ordinary materials.

Commercial greenhouse framing kits can be prohibitively expensive. A relatively inexpensive, economical and logical alternative solution may be to build one from scratch. This project in it's simplest form involves building simple trusses, setting them up, framing the end walls in, and covering the greenhouse with UV protected plastic or other translucent sheeting. In addition to building materials, you will need some carpentry tools, basic carpentry skills and a design.

Design and other considerations.

A greenhouse can be built with ordinary straight wall framing, as an "A-frame", or other variations, for example, hip roofs that look like a common rural barn. Each style has it's disadvantages. A straight wall is standard stud framing. Stability and snow load on the roof can be a problem with roofs with inadequate pitch, which is also a common problem with an ordinary "hoop" style greenhouse. An "A-frame" structure is built with two walls leaning in sharply, forming an "A" and is a strong design, but unless the "A" is very tall, floor space close to the wall may be low and difficult to access.
There is a more efficient design, called a "lean-wall", my personal favourite. The two longest walls lean in marginally, supporting the roof. Interestingly, if you would like a greenhouse built onto the south wall of your house, a half "lean-wall" truss can also be used as an attractive greenhouse or sun space structure.
A lean wall truss can be built as a full truss, using several to create a strong, efficient and free-standing structure.

A lean-wall, free-standing design that is 24' long by 12' wide is constructed of 9* simple standing trusses spaced 3' apart. ( *Yes, 8x3 does equal 24', but remember to add a truss for the end!)

That dimension allows room for two 24' x4' beds for growing things, hanging flowering pots, a central 4' wide walkway, a double sink and potting table. There is plenty of room for pot and peat storage and an area for a heater. In this greenhouse, we do garden "on the ground" in prepared, heavily mulched beds, but the space could easily be converted from growing beds to the "screened table and flats used by commercial greenhouses.

Heavy snow slides easily off of the roof, compacts along the leaning walls and creates a snowbank that help insulate the greenhouse With minimal wall leaning of the side walls, all floor space is usable. At -10C, with bright sunlight, it is often 20C or warmer in the greenhouse.

The lean-wall framing consists of pre-fabricated, simple trusses built on site. A minimum of material is used, and this design can be made smaller, bigger or taller if desired by simply increasing or decreasing the length of the framing members. The secret is to build each of the simple trusses exactly the same.

For your project, do take advantage of available standard material lengths and minimize both expense and cutting. Two 12' 2x6's will build one truss that has a 12' span, the width at the base, and a 6' high wall. If the top of the wall is "leaned in" one foot, the height of the peak will be approximately 9' high. Assembled with standard gussets made of plywood, or pressed steel truss plates or steel nailing "gang plates" available at most building centers and simple lumber collar tie, an individual truss is very strong, economical, effective and simple to build. After assembly, several trusses are stood up, aligned and fastened on a double 2x6 plate much like a regular wall is, and then tied together and braced diagonally for rigidity.
Consider using 10' x 2x4's to build the trusses if you want a greenhouse with a 10' width and 5' high exterior wall, but use 2' spacing between the trusses.

Remember that the larger the greenhouse is, the greater volume of air is heated by the sun, and the warmer the ground remains, which is perfect for an unheated greenhouse. Similarly, if you wish to go to the expense of having your greenhouse heated, a larger greenhouse will also require more fuel to heat when there is no sunlight.

The Site
The greenhouse site should be relatively level, well-drained, and not overly shaded by large trees or buildings. The best orientation to maximize the amount of sunlight entering the greenhouse is north-south for a lean-wall design, but orientation is optional. Potentially excessive shading, however, should be avoided. A southern or south- eastern exposure is best in most cases.

Materials

Note: Materials for the whole project are not listed, since they can be highly variable, depending on the size of the project you choose, the cost, availability and the glazing chosen for the structure you choose to build. This project may be built with recycled dimensioned material if it is in good solid condition. For the smaller structures, 2x4 dimensioned lumber is satisfactory.

The number of trusses and the spacing (3' maximum) will determine the length of the greenhouse. Draw a little plan prior to starting, to simplify your project and calculate your material requirements.

To build -*ONE*- full TRUSS that is 12' wide you will need:

2- 12' x 2x6" Cut in half, each 12' length makes one side of the truss.
" Plywood to make gussets. (Alternatively, use metal gang truss plates, two for each side of each joint. Metal truss plates are easily obtainable at your building supply center.
Fasteners - Choose 1-1/4" galvanized roofing nails for gussets, or use anodized screws
Build A Truss !

*For truss layout, work on solid, level ground and use temporary support blocking for convenience as for any carpentry project.
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1. Lay 2 six-foot 2x6's on their sides, parallel and 12' apart (outside dimension) with the bottom, or "foot" of each resting on a supporting plank or 2x4.
2. Measure diagonally across to ensure they are exactly parallel.
3. Tack the "foot end" temporarily to the support temporarily with one single nail.
4. Move the "top end" of each of the sides in, or toward each other a distance of 12".
5. Add the "peak". Overlay 6' x 2x6's at the top end to form the "peak". Establish the angles at the peak, at the foot of the wall, and the hip angle where the wall member meets the roof. Verify the layout is symmetrical by measuring carefully diagonally.
6. Using a straight rule, Mark the angles required to butt the truss side member and roof member together correctly. Remember, you want a vertical cut line on the "peak" on both roof members, and a wedge must be trimmed off of the "feet" to enable them to sit flat on the plate when installed.
7. Cut the angles for one side member, and one roof member with a skill saw. Transfer the angles to the opposite side using the first as a template, or use a bevel square. Both sides should now be identical when compared, and both peak members should be identical. Lay all four truss components on the ground and check the fit of the angles. You can now see the shape of the truss and adjust or modify it if you wish. Verify the angles and cuts with a bevel square to ensure accuracy and a satisfactory fit.
8. *Hint: Prior to assembling the first truss, if the angles are exact, use the actual members of the first truss as templates to lay out the angles and lengths for all of the remaining trusses to minimize error.

9. Form a truss. Toe-nail the 4 truss components tightly together using spiral nails.

10. Make a cardboard template for the joints at the peak and heel and cut plywood gusset plates to fit. To draw the template, follow the outside of the roof profile for 16" on both sides of the joint, but "short-cut" the inside, making the gussets sub triangular. Cut cut off the sharp points.
11. Nail the gussets on with no less than a dozen nails on each side of the joint. If the nails come through, you will clinch them on the other side. ( Alternatively, install commercially available steel pressed truss plates or metal gang plates. Using support blocking underneath the truss, hammer the plates on tightly or nail them as specified using 1-1/4" galvanized roofing nails. DO remember to install metal truss plates on BOTH sides of the truss.
12. (*NOTE: For the two end trusses, if you use plywood gussets, place gussets only on ONE side to maintain a flush surface. If you use flat metal truss plates, however, install them on both sides of all trusses.

13. Fit and install a 1"x4" or 1"x6" collar across the truss just above the roof heel joint gusset. Nail securely with 2-1/2" Ardox (spiraled) nails or screws. Clinch any exposed nails, and install gussets or gang plates on the other side.

You now have one truss completed. Build as many trusses as you require. (The number of trusses is determined by the length of the greenhouse required, and by whether you are using 2' or 3' spacing between the trusses)

Rasp or sand the outside corners of the joints to ensure they are not sharp to avoid snagging the plastic and stain or paint the trusses as desired.

Set up the Greenhouse

Lay out plates to match truss dimensions. To construct plates, use timbers or pressure-treated 2x6 lumber, staggering any joints for strength. Set them on bricks and level the plates, installing equivalent end plates at the same time. Measure diagonally to ensure the foundation is square.
Lay out the truss plan carefully on the plates 2' or 3' on center, starting from the same end.

*Hint: Set up a scaffold inside the foundation at one end to make raising the trusses easier.

1. Raise the first truss at the end with any plywood gussets facing IN and install a temporary brace on the truss.

2. Plumb and brace the truss into position, and toe-nail the feet securely to both plates with 3" spiral nails or equivalent. Commercial metal brackets may also be used.
3. Install a long diagonal brace from inside the wall down to the plate.
4. Tack a short, temporary 1x4"strap just above the hip of the truss to steady the second and subsequent trusses as you stand and align them.
5. Raise all subsequent trusses, plumbing them carefully, nailing them securely to the plates, and install strapping and the diagonal brace on each of them as you go.
6. Install the last truss with any plywood gusset plates facing IN .
7. Install permanent 1x4 dimensioned lumber as strapping to tie the trusses together both immediately below and above the roof/wall joint. Notching out the trusses to accept the strapping is optional, but will make a smoother roof if you are installing plastic. Alternatively, install the strapping INSIDE the truss. Install a second set of strapping similarly, on either side of the peak.
8. Ensure you install diagonal bracing on both sides, from both ends of the structure, from the top of the end truss wall, and down toward the middle of the plate for maximum strength
9. Power sand or plane the peak and hip joints on the strapping to ensure there are no sharp fragments or corners on the trusses if you are using 6 mil UV plastic glazing.
10. Frame the end walls in, allowing for a doorway as desired. Keep all framing flush on the outside by notching 2x4 framing and fitting it to the truss from the inside.
11. Install fibreglass or other glazing. To install 6 or 10 mil "UV-protected greenhouse plastic" that is designed to resist sun damage, fasten a full-length 2x4 to the plastic sheet on one side prior to pulling the sheeting up and over the structure. Allow extra length for rolling it up and tensioning. Use caution when installing the plastic to avoid tearing or perforating the plastic.
12. Draw the plastic smoothly over the and staple it into place. Install a similar 2x4 on the other side. The weight of the 2x4's will hold the plastic taut.
* Note: Alternatively, commercial fastening systems are available for this purpose, consisting of a metal channel installed with "zig-zag" wire insert that fits into the channel to tension and hold the plastic in place.
13. Install the end plastic sheeting, plastic or Fiberglas sheets and fasten into place using the recommended system.

If you have only used staples to secure the plastic, install lath strips on the studs or other methods to secure the plastic on the end walls .
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Lay out the walkway in the greenhouse using a thick layer of wood chips gravel, old brick, paverrs, or other materials of your choice. Use 2x4, timbers, or other edging to establish growing beds if desired.

Set up benches, install a heater and don't forget ventilation. A window casing can be framed into the end walls or into the roof as desired . Install a permanent water line or use a garden hose for water. A couple of barrels of water will gather heat during the day and keep the greenhouse warmer at night.

Be creative . Bring in the potting table and plant stuff. Enjoy your new greenhouse, after all, you built it right from scratch. If the sun is shining, it's probably already warm and dreamy in there !