Greenhouse Construction Checklist

Orient the greenhouse with the long axis running east-west for maximum southern sun exposure (in the northern hemisphere). Choose a location that receives at least 6 hours of direct sunlight in winter, avoiding shade from buildings, fences, and evergreen trees. Site on level ground with good drainage and convenient access to a water supply and electrical service. Locate near the house for easy access in cold weather.

1. Use a compass or sun-tracking app to verify the planned orientation captures maximum southern exposure

2. Observe the site in winter (or use a solar pathfinder tool) to confirm at least 6 hours of direct sun

3. Verify the site is level or can be graded level without excessive cut/fill

4. Confirm water supply is within reasonable distance (garden hose reach or plumbing run)

5. Check that the location allows for future expansion if desired

- Orienting with the long axis north-south, which significantly reduces winter light

- Placing too close to deciduous trees that still cast shadow from branches even without leaves

- Choosing a low spot where cold air pools and frost damage is worse

- Siting too far from the house, reducing the likelihood of regular winter monitoring

Choose a foundation appropriate for the greenhouse size and permanence: a poured concrete slab (most durable, best for year-round use), pressure-treated wood frame on a compacted gravel pad (good compromise), or concrete blocks (budget option). The foundation must be perfectly level and anchored to resist wind uplift. For permanent greenhouses, install anchor bolts or ground anchors rated for local wind loads. Provide drainage through the foundation to prevent standing water inside.

1. Check level across the full foundation perimeter in both directions (within 1/4" tolerance)

2. Verify anchor bolts or ground anchors are installed at intervals specified by the greenhouse manufacturer

3. Confirm the foundation dimensions match the greenhouse footprint exactly

4. Check that drainage is provided (gravel floor, floor drains, or sloped slab to a drain)

5. For wood foundations, verify all lumber is pressure-treated and rated for ground contact

- Foundation not level, causing frame stress, poor door operation, and glazing panel gaps

- No wind anchoring, allowing lightweight greenhouses to lift or shift in storms

- Standing water inside from inadequate drainage, promoting root rot and algae growth

- Foundation too small or out of square, preventing proper frame assembly

Select frame material based on needs: aluminum (lightweight, low maintenance, will not rot or rust), galvanized steel (strongest, best for large spans and heavy snow loads), PVC pipe (budget-friendly for hoop houses, must be UV-rated), or wood (attractive, good insulator, requires maintenance). Assemble per manufacturer instructions, ensuring all connections are tight and square. Brace the frame against racking with diagonal bracing or cross-ties. Secure the frame to the foundation with appropriate hardware.

1. Verify all frame connections are tight with no play or movement at joints

2. Check that the frame is square by measuring diagonals at each bay (should be equal within 1/4")

3. Confirm the frame is plumb and level at all vertical members

4. Verify diagonal bracing is installed to prevent racking under wind load

5. Check that the frame is securely bolted to the foundation at all base plate locations

- Loose connections that allow frame movement, eventually cracking glazing panels

- Frame not square, making glazing installation difficult and leaving gaps

- Missing diagonal bracing, resulting in frame failure in high winds

- PVC frame not UV-rated, becoming brittle and failing within 2-3 years

Choose glazing based on climate and budget: polycarbonate twin-wall panels (best insulation at R-1.5+, lightweight, virtually unbreakable), single-layer polyethylene film (lowest cost, replace every 1-4 years), or tempered glass (best clarity and longevity, heaviest, most expensive). Install panels with the UV-protected side facing out. Seal all joints with appropriate glazing tape, silicone, or manufacturer-provided gaskets. Ensure proper thermal expansion gaps per manufacturer specifications.

1. Verify polycarbonate panels are installed with UV-protected side facing outward (usually marked)

2. Check that all panel joints are sealed with no visible gaps or openings

3. Confirm thermal expansion gaps are provided at panel edges per manufacturer specs (typically 1/8" per 4' of panel)

4. Verify panels are secured with proper fasteners and rubber washers to prevent cracking

5. Check from inside during daylight for any light leaks at joints that indicate incomplete sealing

- Installing polycarbonate panels upside down (UV coating on wrong side), leading to yellowing and degradation within 2 years

- No expansion gaps, causing panels to buckle in heat or crack in cold

- Using silicone caulk instead of proper glazing tape on polycarbonate, which degrades the plastic

- Overtightening fasteners, cracking panels at screw holes

Provide ventilation equal to at least 20% of the floor area. Use a combination of ridge vents (at the peak) and side or louvre vents (at the base) to create a natural stack effect where hot air exits at the top and cool air enters at the bottom. Install automatic vent openers (wax-cylinder type) on roof vents for hands-free temperature regulation. For larger greenhouses (over 200 sq ft), supplement with exhaust fans sized to exchange the full air volume every 1-2 minutes.

1. Calculate total vent area and verify it equals at least 20% of floor area

2. Confirm vents are positioned for proper airflow: intake low, exhaust high

3. Test automatic vent openers by warming them with a heat gun; they should begin opening at approximately 68-72F

4. For fan systems, verify fan CFM rating matches the greenhouse volume for 1-2 minute air exchange

5. Check that all vents open and close fully without binding or obstruction

- Insufficient vent area, causing temperatures to spike above 100F on sunny days and damaging plants

- Vents only on one side, creating dead air zones with poor circulation

- Automatic vent openers not calibrated, opening too late after temperatures are already damaging

- No intake vents to match exhaust, causing negative pressure that pulls air through gaps and stresses the glazing

Run a water supply line to the greenhouse with a frost-proof hose bib or shutoff valve inside. Install at least one hose bib for hand watering. For automated watering, install a drip irrigation system with a timer for consistent moisture delivery, or a misting system for seed starting and humidity-loving plants. Provide bench drainage into a gravel bed floor or floor drain to handle excess water. Use a backflow preventer on the supply line to protect the potable water system.

1. Verify the water supply line is properly connected with a shutoff valve accessible inside the greenhouse

2. Confirm a backflow preventer is installed on the water supply per local plumbing code

3. Test drip irrigation for uniform coverage by checking output at emitters across the system

4. Verify bench drainage routes water away from plant roots and into the gravel bed or drain

5. If a timer is installed, test programming through a full cycle to confirm proper on/off operation

- Water line not buried below frost depth, freezing and bursting in winter

- No backflow preventer, creating a cross-connection hazard with the potable water supply

- Drip emitters clogged from mineral deposits; install an inline filter to prevent this

- Overwatering from timer set too long, leading to root rot and fungal issues

Select a heating method based on climate severity and budget: electric space heaters (easiest to install, best for mild climates), propane or natural gas heaters (powerful, good for cold climates, must be vented), thermal mass heat sinks (water-filled barrels painted black absorb daytime heat and release it at night), or an insulated north wall (reduces heat loss). Install a thermostat to maintain minimum temperature (typically 40-50F for cool-season growing, 55-65F for warm-season crops). Ensure adequate air circulation with a small fan to prevent cold spots.

1. Verify the heater is sized for the greenhouse volume and the temperature differential needed (BTU calculator based on greenhouse size, glazing R-value, and coldest expected temperature)

2. Confirm the thermostat is positioned at plant height in the center of the greenhouse, away from direct sun or heat sources

3. For gas heaters, verify proper venting to the exterior to prevent ethylene gas buildup that damages plants

4. Test the heating system on a cold night and monitor temperatures at multiple points to check for cold spots

5. Verify electrical connections meet code requirements (dedicated circuit, GFCI if applicable)

- Heater undersized for the greenhouse volume, failing to maintain temperature on the coldest nights

- Unvented propane or gas heaters producing ethylene and carbon dioxide buildup that damages plants

- No air circulation fan, creating temperature stratification (warm at the peak, cold at the floor)

- Thermostat placed in direct sunlight, giving false high readings and not activating the heater when needed