Translucent Wall in Polycarbonate and Channel Glass
A translucent wall is not designed to see out of: it is designed to bring light in without glare and without showing anything. It has two precise enemies — thermal movement, which here is enormous, and condensation, which forms inside the panes and does not leave on its own.
Overview
TAV. 00Multiwall polycarbonate and channel glass solve the same problem with opposite materials. Both give a continuous, diffuse light without the violent contrast of windows; both are dry-glazed into a perimeter frame and need no intermediate mullions, because the sheet carries itself. The differences matter: polycarbonate is light, resilient and expands more than three times as much as aluminium, so it lives or dies on installation clearances and on UV protection, which sits on one face only; channel glass is stiffer, more stable and heavier, but it is glass, so it forgives neither impact nor unplanned movement. In both cases the game is played on three points: frame tolerance, cavity ventilation and condensation drainage — which here is not a defect but a fact to be managed.
The site score
TAV. HThe detail of the craftthe gap that looks like a mistake
The perimeter frame and its tolerances
Fixing the aluminium or galvanised steel frame to the structure, checking flatness and providing the movement clearances.
Here the clearance isn't sloppiness: it's the most important part you're fitting. Take it away and in July the wall bulges.site notebook — editorial synthesis
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
Two materials, the same light
Polycarbonate or channel glass: what really differs
From a distance they look the same: a continuous surface diffusing light. Close up they are two materials with opposite temperaments, and the choice comes down to three questions — how much it moves, how much it weighs, and what happens if someone walks into it. Polycarbonate is light and resilient but lives in motion; channel glass is stable and durable but it is glass, and must be treated as such.
In publicly accessible areas the choice is not only aesthetic: both solutions require an impact safety check, resolved in channel glass with wired or laminated units and in polycarbonate with sheet thickness and support spacing.
The number that decides everything
How much a polycarbonate sheet moves
This is the figure that explains almost every defect in these walls. Polycarbonate expands about 0.065 millimetres per metre per degree: three times aluminium, five times steel, ten times glass. A dark sheet in the sun can reach seventy degrees while at night it drops below zero: over five metres that is nearly two centimetres of travel, every day, for thirty years. Any fixing that does not allow it becomes a permanent buckle.
Order-of-magnitude values, useful to grasp the proportions. The clearances to be used on site are those given by the system manufacturer, calculated on the actual temperature range of the site and on the colour of the sheet.
How it ages (and what betrays it)
TAV. PQuestions from the site
TAV. QHow well does a translucent wall really insulate?
Less than an insulated opaque wall and more than single glazing: we are in the order of a good double-glazed unit, and with many-wall sheets you approach triple glazing. But the point is not only the U-value: it is the overall balance. A translucent wall switches off the artificial lighting for most of the day and pushes daylight deep into the space, which a window of the same area does not do. In a warehouse or a sports hall that saving often outweighs the difference in insulation.
Can it be cleaned with a pressure washer?
No, and this is one of the commonest causes of damage after handover. A high-pressure jet drives water into the flutes through the tapes, scratches the protective layer and can open the joints. Correct cleaning is trivial: lukewarm water, neutral detergent, soft cloth and a rinse. Solvents, alcohol and alkaline cleaners are also to be avoided, since they cause stress cracking in polycarbonate. It is worth writing into the maintenance manual, because nobody expects it.
Why are there droplets inside the sheets in winter?
Because the air inside the flutes is room air, with its humidity, and the outer face is cold. It is the same phenomenon as a misted window, just inside a closed cavity. With the right tapes — solid at the top, microperforated at the bottom — and clear drains, the water runs down and out, and droplets appear only on the coldest days. If instead they persist and the lower part goes cloudy, the moisture has no way out: you open the drains, you do not seal further.
How long does a wall like this last?
Channel glass effectively has no expiry date: it is glass, and systems from the nineteen-sixties are still in service. UV-protected polycarbonate typically carries around a ten-year warranty on light transmission, but in practice lasts well beyond that if it is neither scratched nor chemically attacked. The practical difference is not made by the material but by maintenance: it is wrong cleaning methods and incompatible sealants that end the story early, long before sunlight does.