Journal · 2026.07 · 11 min

Retrofitting an Old Greenhouse — What to Watch For

Taiwan has a large stock of greenhouses in service for ten or twenty years and more. As energy gets pricier, labour scarcer, and weather more extreme, growers are asking: retrofit the old house, or tear it down and rebuild? The answer turns on three things — structure, energy, and operation — most of which are only clear from the engineering side.

By Chen Chien-Wei · Principal & Design Director, Hwa-Nan Greenhouse Design Co., Ltd.

Published 07/2026 · Last updated 31 July 2026

Retrofitting an Old Greenhouse — What to Watch For

Ask most people about “upgrading a greenhouse” and the first thought is a new climate computer, supplemental lighting, smart gear. But what really decides whether an old house is worth retrofitting was never the equipment — it’s the frame nobody wants to climb up and inspect: how far the corrosion has gone, whether the foundation has settled, whether drainage can hold a downpour, whether it still meets current wind standards. Yes to those and a retrofit makes sense; no, and the newest equipment is just bolted to a shell that won’t last.

Whether an old house is worth retrofitting — and how to do it without wasting money — comes down to structural loads, corrosion, drainage, wind resistance and regulation. Below, the things to watch for before a retrofit are organised into three gates — structure, energy and operation — with practical references from U.S. university agricultural-extension centres.

STRUCTURE FIRST

Gate One: Assess the Structure Before Swapping Equipment

The first step of any retrofit is always to assess structural integrity. A sound frame and foundation can usually support modern upgrades, making a retrofit viable; conversely, if the structure has reached the end of its life, bolting on new equipment just spends money on a shell that won’t last. Before retrofitting, confirm at least the following:

Corrosion and material ageing: check for steel corrosion, degraded galvanising, and loose joints or ground anchors — the most direct indicator of “retrofit” versus “replace.”
Whether the structure can carry new loads: energy curtains, supplemental lighting, fans, even solar panels all add load to frame and foundation and must be recalculated, not simply hung on.
Ridge height and truss spacing: roof height and truss spacing directly affect airflow and whether new equipment can be installed cleanly — the most common built-in limit of older houses.
Foundation and floor: whether the fixed foundation and drainage floor are still intact bears directly on later wind and flood performance.

Corrosion and degraded galvanising are the most direct clues to whether an old house should be retrofitted or replaced — structural assessment always comes before swapping equipment.

“A greenhouse that is paid for is a greenhouse that is ready to be replaced.”
— A.J. Both, Rutgers University

Rutgers University greenhouse engineer A.J. Both cautions against assuming “the best greenhouse is one that is paid for” — an old, inefficient house burns money simply by operating. So before deciding to retrofit or rebuild, run a thorough economic analysis of the structure’s efficiency rather than going on instinct.

AUDIT BEFORE YOU BUY

Gate Two: Audit Energy and Equipment First

Michigan State University (MSU) Extension advises doing an energy audit before retrofitting: list the quantity, sizes, annual run-times, and age of existing fans and circulation fans, plus lighting fixture counts, types, wattages, and daily hours, then flag the items you want to upgrade. UMass Extension notes the typical energy split of a greenhouse — about 75% for heating, 15% for electricity, 10% for vehicles — meaning resources should go first where the savings are largest.

~15%

Heating energy saved with an infrared/anti-condensate (IR/AC) inner film — payback about 2–3 months (UMass)

20–40%

Winter heating cost saved with an energy curtain — which also shades and cools in summer

~20%

Total energy use that can be saved just by cleaning fan blades and safety screens (Penn State)

SIX RETROFITS WORTH DOING

Gate Three: Six Retrofits Worth Doing

1. Ventilation — the most cost-effective first move

Adding roll-up sides, roof vents, and ridge ventilation to an old house is usually the simplest, most cost-effective retrofit; aged vent rubber grows brittle and leaks, so switching to more durable EPDM lets openings seal properly.

2. Covering and insulation together

Add double poly to an old structure with an IR/AC inner layer for about 15% heating savings; switching side and end walls to twin-wall polycarbonate keeps heat in and cuts re-covering labour.

3. Energy and shade curtains

An energy curtain saves 20–40% on winter heating and shades and cools in summer — an upgrade with a relatively clear return.

4. Stop air leaks

Weatherstrip doors, vents, and fan openings, and add door closers; small as it seems, this is where heat and money quietly leak away.

5. Upgrade mechanical and electrical efficiency

Choose standard-compliant fans with a Ventilation Efficiency Ratio above 15 and premium-efficiency motors, and replace on-off thermostats with computerised controls — smarter and cheaper to run.

6. Reinforcement and drainage — not optional in Taiwan

Use the retrofit to re-evaluate wind resistance, reinforce covering attachment, and add roof gutters and perimeter ditches — the most overlooked yet most critical part of retrofitting an old house in Taiwan.

Openings on the building’s flanks — side windows, roll-up sides and tilting glass — let hot air escape up top while cooler air is drawn in below, creating natural convection. Natural ventilation uses no electricity and no fans, making it the most cost-effective first step for cooling, dehumidifying and cutting disease and running costs in an old greenhouse.

EXTRA NOTES FOR TAIWAN

Extra Notes for Retrofits in Taiwan

Re-check wind resistance: old houses often fail current wind standards; a retrofit should re-evaluate wind pressure and the attachment of covering and end walls.
Drainage and flooding: roof gutters, perimeter ditches, and site levels must be reviewed together so the house doesn’t still flood after retrofit.
Added loads: energy curtains, lighting, and solar all add weight to frame and foundation and must be recalculated, not forced on.
Regulation and permitted use: changes to structure or floor area may trigger building-permit and agricultural-facility permitted-use rules.
Subsidy reimbursement: disaster-resilient facility subsidies carry specific spec and procedural requirements — confirm eligibility before planning the retrofit.
Construction interface and downtime: phase the work and avoid the growing season to minimise the hit to operations.

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