Vitavia Greenhouse Glazing Compared with Palram Polycarbonate Panels

Impact decides many glazing arguments early

A falling branch or a fist-sized hailstone treats the two materials in completely different ways. A Vitavia toughened pane struck hard enough breaks into thousands of blunt cubes across the whole panel. A Palram 6mm twin-wall polycarbonate sheet usually shows a dent, a white stress mark or a crack following one flute, while the sheet remains in the frame.

That behaviour matters because many greenhouse glazing replacements follow one violent event before age becomes the issue. Toughened glass weighs roughly three times as much per square metre as twin-wall polycarbonate, so the damage, handling and refitting all feel different once a pane has gone.

Vitavia supplies horticultural glass and toughened glass. Palram builds most of its greenhouse glazing around 4mm, 6mm and 10mm polycarbonate. Clean glass transmits about 90 percent of light, while clear Palram polycarbonate sits a few points lower. Twin-wall and triple-wall construction reduce transmission further as extra layers are added for insulation.

Growers chasing the highest photosynthetically active light for early tomatoes have a real reason to favour Vitavia glass. The cost of that brightness is exposure to breakage on open, wind-raked ground. Over a decade, a glass house on such a site can collect damage that a polycarbonate house avoids, so the plot often has more influence than the brochure.

Heat loss, summer heat and ventilation

Single-skin horticultural glass has a U-value around 5.8 W/m2K, which means it offers little resistance to heat leaving the greenhouse. Vitavia toughened glass performs the same thermally; the toughening process changes the fracture pattern, not the insulation. On a frosty night, a single clear pane lets warmth radiate away quickly.

Palram 6mm twin-wall polycarbonate sits closer to 3.6 W/m2K, and 10mm triple-wall polycarbonate drops lower again. Anyone overwintering tender perennials, or running a paraffin heater or electric tube heater through to March, will see that difference in energy use. The trapped air between the polycarbonate walls carries much of the insulating effect.

The same trapped air changes summer behaviour. A sealed Palram house can overheat faster than a glass house with the same ventilation because heat escapes more slowly through the glazing. Roof vents and a Bayliss-style autovent become especially important on a polycarbonate structure. Glass can lose more daytime heat through the panes themselves, which can help during hot spells.

Fifteen years on a 6ft by 8ft footprint

For a standard 6ft by 8ft greenhouse, Vitavia glass glazing generally costs more at purchase than the equivalent Palram polycarbonate kit. The difference becomes larger when toughened upgrades are added for lower panes near foot traffic.

Over fifteen years, two broken glass panes from wind and impact would mean buying replacements and losing an afternoon to fitting them. In the same period, a polycarbonate house might show surface yellowing and one cracked flute panel, since ultraviolet degradation is the usual polycarbonate failure mode and it advances gradually.

The two repair patterns feel different in use. Glass damage arrives suddenly and takes out a whole pane. Polycarbonate usually gives warning through colour change, surface wear or a local crack before the panel becomes unusable. A sheltered urban garden may run glass for years without a single broken pane, while the owner notices the slight cloudiness of polycarbonate every day if they chose it. On an exposed allotment edge, repeated glass refits can make the Palram choice look sensible after the first few winters.

Wind exposure is where buyers often under-estimate their own site. Fences, hedges, nearby houses and the direction of the prevailing south-westerly all change the calculation. A price comparison made indoors misses the pressure that arrives across an open plot in winter.

Patio water, base height and glazing clips

Water collecting where the greenhouse base meets a paved patio will damage the installation regardless of glazing material. A fall of 1 in 80 away from the structure, draining into a channel along the lower edge, keeps the aluminium base dry and reduces capillary damp moving into the lowest glazing bars. Polycarbonate base panels tolerate standing water better than glass beading, though neither material benefits from sitting in a puddle through a freeze.

A common patio mistake is setting the greenhouse level while the paving drains toward the door. Each rainstorm then sends a thin film across the threshold and into the growing area. Raising the base onto a low brick plinth, two courses high, with a slot left for runoff, deals with the problem more reliably than sealant. Many owners only discover the issue after water reaches the staging.

Vitavia glass is usually retained with stainless steel W-clips and overlap clips. If too few clips are fitted, storms can pop them loose. Palram polycarbonate uses a profiled retaining system with rubber strips. Losing a glass clip or two in a gale is normal enough that a small box of spares belongs in the staging drawer.

Crops and seedlings respond to the glazing

Heritage seed library tomatoes, including indeterminate varieties such as Brandywine and Costoluto Fiorentino, need a long warm season to ripen well. In a cool-summer region, the extra light from Vitavia glass can matter. Those varieties stall in low light, and the few percentage points between clear glass and twin-wall polycarbonate can bring ripening a week or two earlier at the end of the season. That margin can decide whether ripe fruit is picked from the plant or green trusses finish indoors on a windowsill.

A cut flower border raised under either structure responds more to heat retention than maximum light. Sweet peas and early antirrhinums hardened off in a Palram house get a gentler transition because the insulated walls smooth the night-to-day temperature swing that can check young growth. Outside the greenhouse, low-maintenance planting based on hardy geraniums, alchemilla and ornamental grasses asks little of the glazing choice. Some garden decisions simply sit beyond the greenhouse frame.

Twin-wall polycarbonate also changes propagation. It diffuses light, scattering it across the benches so seedlings on the back staging receive more even illumination and lean less toward the brightest side. A glass house gives sharper light and harder shadows, so trays near the north wall often stretch toward the south-facing panes.

For large batches of plug plants, that diffusion can produce stockier and more uniform seedlings. The benefit is separate from insulation and breakage resistance, and it rarely gets as much attention as winter heat loss or storm damage.

Watering still needs its own system

Hozelock watering timers cover the task that glazing cannot: keeping plants watered when nobody is available at 7am and 6pm in July, as a greenhouse can reach 35 degrees by mid-morning. A Hozelock Sensor Controller or the simpler AC1 timer can feed a drip line or seep hose along the staging. Whether the roof is glass or twin-wall polycarbonate has no bearing on whether tomatoes wilt by Friday.

Pressure matters more than the timer model. A gravity feed from a water butt rarely drives a drip system reliably, so the setup that works through a heatwave is a mains-fed Hozelock timer with a pressure-reducing dripper line. The line is best installed before the staging is loaded, since threading dripper pipe behind a bench full of seed trays is a job easily abandoned halfway. Glazing affects how fast an unwatered house cooks, while the watering layout decides whether the plants keep up.

Where the comparison still refuses to settle

A sheltered town garden behind a fence and a hedge can keep Vitavia glass intact for twenty years and gain the brighter growing space throughout that period. An open allotment catching the prevailing south-westerly may break a pane most winters and make Palram polycarbonate look tougher with each storm.

The unresolved case is the bright, exposed plot where tomatoes would use every extra ray from glass while the weather keeps testing the panes.