A small greenhouse is a structure under 100 square feet, designed to extend the growing season beyond natural weather limitations. Building one yourself offers significant cost savings compared to purchasing a prefabricated unit. This DIY approach allows you to personalize dimensions and features to fit a specific space and need. This guide covers the practical steps of planning and constructing a growing environment.
Pre-Construction Planning and Site Selection
The structure’s performance depends heavily on initial placement. Orienting the longest side toward the south in the Northern Hemisphere maximizes light capture, beneficial during winter. The chosen area must also be level to ensure the frame is square and stable.
A slight natural grade away from the perimeter promotes good drainage and prevents water accumulation. Standing water can lead to structural damage or excessive humidity. Consider the proximity to utility connections, especially water for irrigation and electricity for temperature regulation. Running utilities over long distances adds complexity and cost.
Before purchasing parts, the structure’s type must be finalized, such as a lean-to attached to a south-facing wall or a small freestanding unit. This decision dictates the required dimensions and material quantity. Determining the size and style early ensures efficient material selection and construction.
Essential Materials and Structural Choices
The structural integrity depends heavily on the framing material selected. Treated lumber, such as pressure-treated pine, provides a durable frame that resists moisture and decay. While strong, lumber requires more precise cutting and joining than other options.
Alternatively, metal conduit offers a lighter profile with high strength for creating curved hoop-style structures. PVC piping is the least expensive option and is easy to assemble. However, PVC frames are less resistant to high winds and can degrade due to UV exposure, often requiring periodic replacement.
The material choice should balance the initial project cost with longevity and resilience.
The choice of covering, known as glazing, determines light transmission and insulation value. Polyethylene film is the most cost-effective solution, providing good light diffusion but typically lasting only two to four years before needing replacement.
For a more permanent structure, rigid polycarbonate panels offer superior impact resistance and insulation. Polycarbonate panels achieve high insulation values due to their twin-wall or triple-wall construction, which traps air. These panels have a lifespan of ten years or more, minimizing heat loss compared to single-pane glass.
Step-by-Step Assembly
Construction begins with preparing the site and firmly anchoring the base. The perimeter frame, typically made of treated lumber or concrete blocks, must be secured directly to the ground using heavy-duty anchors or ground screws. Failure to anchor the structure properly makes it susceptible to damage during severe weather events.
Once the foundation is secure, the vertical uprights and horizontal supports are erected and squared. Use a large carpenter’s square and diagonal measurements to ensure all corners are 90 degrees. Misalignment will complicate the attachment of rigid glazing panels and compromise structural stability.
For structures utilizing metal conduit or PVC, the hoops are bent according to a template and secured to the base rail. Consistent spacing between each hoop is necessary to distribute the load evenly and prevent the covering material from sagging. Uneven spacing can create pockets where snow or water might accumulate.
Attaching the covering requires careful attention to sealing the entire envelope. Polyethylene film should be pulled taut across the frame, then secured using specialized wiggle wire channel systems or wooden batten strips to prevent flapping. This tight application minimizes stress points and reduces heat loss through air gaps.
Rigid polycarbonate or glass panels are fitted precisely into the frame, ensuring a slight overlap or the use of silicone sealant at all joints. Proper sealing is paramount to maintaining a warm, humid environment and preventing cold air infiltration. Any gap allows internal heat to escape.
The final steps involve installing the access door and ventilation openings. The door frame must swing freely without binding, and vents should be positioned near the roof apex. Securing heavy-duty hinges and latches keeps the door sealed against drafts and prevents accidental opening.
Managing the Internal Climate
Maintaining plant health requires precise management of air circulation and temperature. Ventilation prevents rapid overheating, which occurs even on cool, sunny days. Passive ventilation relies on thermal buoyancy, where hot air escapes through high vents while cooler air is drawn in through low side vents.
For structures exceeding 50 square feet, active ventilation using exhaust fans may be necessary. Fans should replace the total volume of air inside at least once per minute. This exchange prevents fungal spores and excessive heat, which damage plant tissues.
During cold periods, strategies mitigate heat loss. Placing large, dark water barrels inside absorbs solar radiation during the day. The water slowly releases stored heat back into the air overnight, buffering temperature fluctuations. Small electric heaters provide supplemental heat.
Regulating humidity is important for plant physiology. Low humidity causes excessive transpiration, and high humidity encourages disease. Misting the plants or dampening the floor surface increases moisture content during dry winter months.