Journal · 2026.07 · 6 min
Washing the Covering and Desilting the Gutters — the Maintenance Most Worth Scheduling
Once a greenhouse is up, cleaning is the first thing people skip. But a dirty covering loses light transmission, and a silted gutter turns every storm into leaks and standing water. Washing and desilting are really one maintenance routine — and going up to wash the roof is the best chance to catch a leak early.
One plum-rain season I got a call: a client’s multi-span house had flooded knee-deep overnight and the whole batch of propagation trays was soaked. Up on the roof, the structure was fine — the gutter was packed with half a year of rotting leaves. One unwashed drainage channel had drowned a whole house of seedlings. Once a greenhouse is up and the crop is in, cleaning is the first thing pushed to “when there’s time”; yet the covering and the gutters are exactly what decide whether a house works well and survives a typhoon — and they are really one routine: going up to wash the roof is also the moment to check drainage and leaks.
A Dirty Covering Loses Light First
A greenhouse’s appearance isn’t just about looks. Once the covering — film, twin-wall PC sheet, or glass — accumulates grime, the first casualty is light transmission, and light is the raw material of yield. In Taiwan’s heat and humidity, roofs are especially prone to a few things:
- Algae and moss: humidity plus dust quickly grows a green film on the roof and along the gutter edges.
- Dust and airborne grit: traffic and farm-road dust settle into a hazy film on the covering.
- Hard-water scale: hard irrigation or misting water leaves white deposits as it evaporates.
- Bird droppings, leaves and twigs: they block light and jam gutters and vent mechanisms.
The Gutter: The Most Overlooked, Most Critical Line
If the covering decides how much light comes in, the gutter decides how much water goes out. In a multi-span greenhouse the gutter is the valley between roofs, collecting rain off the whole roof and channelling it to the downpipes. When it silts up, the failure isn’t gradual — it hits on exactly the day you need it most, in the downpour of a typhoon or the plum-rain season.
- Leaves, algal sludge and silt build up, shrinking the flow section and slowing drainage.
- Water that can’t drain overflows the sides, straight into the house — ruining crops, materials and control gear.
- Standing water adds roof load, an extra burden on the structure and the outlets.
- Lingering water and damp accelerate corrosion of the gutter and its bolts, shortening structural life.
A Free Inspection While You Wash
This is the point Hwa-Nan most wants to stress: washing the roof isn’t only cleaning — it’s a rare close-up inspection. With people and water already up on the roof, you can trace the whole surface for signs of leaks — at covering seams, glazing bars and gutter laps. Any water stain, rust streak or drip can be marked on the spot and fixed early. Finding it only when the crop below is soaked usually costs several times more.
- Seams and glazing bars: is the film loose or punctured; have the twin-wall PC-sheet or glass fixings shifted.
- Gutter laps and outlets: has the joint silicone aged and cracked; is an outlet half-blocked by debris.
- Steel and bolts: rust streaks below the gutter or along the covering edge are usually a clue to a leak or ponding.
How Often?
There’s no single right frequency — it depends on the environment and the crop — but here is a minimum cadence Hwa-Nan suggests:
| Minimum frequency | Best timing | |
|---|---|---|
| Wash the covering | At least 1–2× a year | Before the seasons that need the most light |
| Desilt the gutters | At least 2× a year (non-negotiable) | Before both the plum-rain and typhoon seasons |
| Leafy or dusty sites | Add rounds on top of the above | Don’t wait until it’s visibly filthy |
A greenhouse’s lifespan isn’t decided only by how good the steel and aluminium were at the start — it’s decided by whether it’s well maintained afterwards. Washing and desilting are the most basic, and the most cost-effective, step of all.