Guide · Skylight & Rooflight Installation & Replacement Chelmsford
Cleaning and maintaining a rooflight
A rooflight asks for very little once it is in. Twice a year with warm water and a soft cloth covers the glass, and ten minutes clearing debris from around the kerb each autumn covers almost everything else. That is the honest answer, and it is shorter than most people expect.
The useful detail is in the exceptions. Glass in a flat roof soils differently from glass in a slope. A north facing plane grows things a south facing one does not. Coatings behave badly with the wrong cleaner, opening gear wants a different kind of attention from fixed glazing, and the parts that matter most are the ones you cannot see from the sofa. This page works through the whole cycle for Chelmsford and the roofs around it.
Why roof glass soils faster than a wall window
Gravity. A vertical pane sheds rain down its face and takes a good deal of its own dirt with it. A rooflight in a flat roof holds a shallow film of water after every shower, and when that film evaporates, everything carried in it stays behind as a ring.
The result is that a flat unit shows its dirt as tide marks and a hazy bloom rather than as streaks. A pitched roof window sits somewhere between the two. At thirty degrees the rain still runs, so the glass mostly keeps itself presentable and the soiling collects at the bottom edge where the water slows against the flashing.
What actually lands on Essex roof glass
Four things, and the mix depends on where the house sits. In the Chelmsford terraces and along the arterial routes towards the London fringe it is traffic film: a fine oily grey deposit that water alone will not shift. Out in the arable country between Dunmow, Braintree and Witham it is harvest dust, worst in a dry August when the combines are running and the wind is easterly.
Near the estuary, at Maldon, Burnham and out onto Canvey, there is salt in the air, and salt is the one deposit that matters beyond appearance because it holds moisture against the frame. And everywhere with mature trees there is organic fall: lime honeydew that goes sticky then black, plane seed, and in the older suburbs the fine sooty deposit that sits under a stand of conifers.
Rain does not clean roof glass, it redistributes the dirt and then leaves it where the water dried.
How often is genuinely enough
Twice a year suits a pitched roof window on a suburban plot. Once in spring after the winter grime, once in autumn after the seed and pollen have finished falling.
A flat rooflight over a kitchen or a garden room usually wants three or four passes, because it holds water and because you are looking straight up through it from a metre and a half away, which is an unforgiving viewing angle. A unit under trees can want more. A unit on an exposed plot with nothing overhanging it can go a full year and still look reasonable.
Cleaning from the inside on a pivoting unit
Most roof windows are designed so the sash rotates in the frame and locks in a reversed position, which brings the outer face of the glass indoors at a comfortable working height. There is usually a barrel bolt or a catch on the top of the sash that holds it there.
Two habits are worth forming. Engage the catch before letting go of the sash, every time, because a half rotated window on a windy day is heavy and unpredictable. And put a towel on the floor below, because the water that runs off the bottom edge lands on your ceiling line and not in a bucket.
Reaching the outer face of a fixed unit
Fixed glazing has no trick to it. It is cleaned from outside, and the question becomes how you get there safely.
On a single storey rear extension the glass is often reachable from a stepladder set on firm ground with a water fed pole, which is the sensible tool: soft bristle head, filtered water, no ladder leaning against anything. On a two storey slope or a third floor unit over a narrow side return, it is a job for someone with the correct access equipment. Standing on a flat roof to reach a lantern is a common and bad idea, because a warm single ply membrane is slippery and the fall is off the edge you cannot see behind you.
What to wash with, and what to keep away from the glass
Warm water with a drop of washing up liquid, a soft cloth or a microfibre head, and a rinse with clean water. That is the whole specification for ninety per cent of jobs.
Things that cause trouble: abrasive cream cleaners, which micro scratch the outer surface and make future soiling stick harder. Solvent based glass cleaners on a coated pane. Anything containing bleach near an aluminium or a coated timber frame. Scrapers and blades, which will take the coating off in one pass. And a pressure washer, which can drive water past a gasket that was perfectly sound at atmospheric pressure.
Self cleaning coatings, and what they actually do
Many modern units come with a factory applied coating on the outer pane. It works in two stages. A photocatalytic layer uses ultraviolet light to break down organic deposits, then the surface sheds water as a sheet rather than as beads, so the loosened material washes off in the next decent rain.
It reduces the frequency of cleaning rather than removing it. The coating needs daylight to activate, so a pane in permanent shade under an overhang does less well, and it does very little against inorganic dirt like traffic film or estuary salt. Treat it as a coating that buys you a couple of months, not as a reason to never look at the glass again.
Cleaning a coated pane without ruining it
The coating is a few nanometres thick and it is bonded into the glass surface rather than sitting on it as a film, so it is more robust than people fear. What kills it is mechanical abrasion and strong solvents.
Use water and a soft cloth, work in cool conditions or on a dull day so the pane is not drying as you go, and rinse thoroughly. Skip anything marketed as a rain repellent additive, because those products deposit a hydrophobic layer that fights the sheeting behaviour the coating relies on. If a coated pane has been washed with something aggressive it will not look damaged. It simply stops behaving differently from ordinary glass.
Moss, lichen and the north facing slope
Moss does not grow on glass. It grows in the tile courses around the unit, on the flashing upstand, and in the shaded corner where the apron meets the covering. A north facing slope on a Victorian terrace, shaded by the ridge for most of the day, will carry a green fur that the south slope of the same roof never gets.
Moss around a rooflight is a drainage problem before it is a cosmetic one, because it dams the channel the flashing was designed to drain. Take it off mechanically with a stiff brush, working down the slope so you are not lifting the courses. Leave the chemical treatments alone unless a roofer has specified one, because the run off from most of them lands on the glass and on any planting below.
The autumn clear round the kerb
On a flat roof this is the single most valuable ten minutes of the year. Leaves, seed, moss fragments and grit collect on the upstream side of any raised object, and a rooflight kerb is the largest raised object on most flat roofs.
What accumulates there does two things. It holds water against the base of the kerb, which is exactly the condition the hundred and fifty millimetre upstand exists to survive rather than to invite. And it drifts towards the outlet and closes the drainage path. Clear it by hand with a glove, check the outlet is running, and do it once the last of the leaves are down rather than in the middle of the fall.
Outlets, gutters and where the water goes next
A rooflight is only ever as dry as the roof it sits in, and the roof is only as dry as its drainage. On the Harlow and Basildon flat roofs a single outlet often serves the whole area, and when that outlet blocks the water level rises across the entire roof until it is standing against the kerb.
Two checks a year cover it. Look at the outlet grating and lift anything sitting on it. Then, during or just after heavy rain, look at where the downpipe discharges and confirm water is actually arriving. A dry downpipe in a downpour means the water is sitting somewhere it should not be.
Inspecting the perimeter without getting on the roof
Most of what you need to know is visible from a ladder at the eaves or from an upstairs window with a decent pair of binoculars.
- The flashing apron should sit tight to the covering with no lifted edge and no daylight under it.
- The side soakers on a pitched unit should be dressed into the courses, not sitting proud of them.
- The covering at the kerb on a flat roof should be dressed up the full height and terminated under the unit, with no shrinkage pulling it away at the corners.
- The glass edge seal, the black band around the perimeter of the pane, should be even and unbroken, with no milky bloom creeping in from a corner.
Anything on that list that has moved is worth a look by somebody with a ladder before the winter rather than after it.
Hinges, gaskets and the moving parts
An opening unit has mechanical parts and they last longer with a little attention. The friction hinges on a centre pivot window carry the whole weight of the sash and they want the pivot points wiped clean and given a drop of light machine oil once a year, then worked open and shut a few times to distribute it.
The compression gasket around the sash is the part that decides whether the unit shuts weathertight. It wants wiping with a damp cloth so grit does not sit in it, and it wants keeping away from oils and silicone sprays, which make the rubber swell and go soft. A gasket that has flattened permanently and no longer springs back is a replaceable part, and swapping it is a great deal simpler than most people assume.
Ventilation flaps, filters and trickle vents
Many roof windows have a ventilation flap in the top of the frame with a small filter behind it, and it is almost universally forgotten. The filter collects dust and insects and eventually stops passing air, at which point the room loses a ventilation path it was designed around and the glass starts misting on cold mornings for no obvious reason.
The flap usually opens without tools. The filter lifts out, gets rinsed under a tap, dries, and goes back. Once a year is plenty, and in a kitchen or a bathroom it makes an immediate difference to how the glass behaves in January.
Blinds, side channels and the bit that jams
Rooflight blinds run in side channels within the frame, because a blind on a sloped or horizontal surface has gravity working against it. Those channels collect dust, and a blind that has become stiff or that sits crooked is usually telling you the channel needs a wipe rather than that the mechanism has failed.
Run a dry cloth or a vacuum crevice tool down each channel, then work the blind fully up and down. Blackout fabrics attract dust and are best brushed rather than washed, since wetting the coated side can mark it permanently. Electric blinds share the same channels and the same habits.
Electric units, sensors and the battery question
An electric rooflight adds three things worth a yearly look. The rain sensor, which is a small pad on the outer frame that closes the unit when it gets wet, and which stops working reliably when it is covered in the same film that is on the glass. Wipe it with plain water and nothing else.
The remote handset takes a battery, and a unit that has become intermittent is usually flat cells rather than a fault. A solar powered opener has its own panel and internal battery: keep the panel clear of leaves, and expect the internal cell to have a working life of several years rather than forever. None of this needs a visit. It needs a cloth and a note in the calendar.
The signs a unit is near the end of its working life
Cleaning solves a lot and it does not solve everything. Misting between the two panes means the sealed unit has lost its edge seal and the desiccant is saturated, and nothing applied to either surface will clear it. A frame that has gone chalky and powdery to the touch has lost its surface finish. A sash that no longer pulls up tight against the gasket, after the hinges have been cleaned and adjusted, has usually distorted.
Twenty to twenty five years is a normal working life for a sealed unit, and the domed acrylic and polycarbonate lights fitted across Essex in the seventies are well past it. At that point a replacement unit into the existing kerb is often a single day, and it is the sensible moment to move up to a better glass specification.
A year round rhythm that actually gets done
Schedules only work if they are short. This one has four entries and it fits on a kitchen calendar.
| When | Job | Why then |
|---|---|---|
| March | Wash the glass, wipe the gasket, oil the hinges | Winter grime is at its worst and the sash gear has been shut for months |
| June | Rinse the ventilation filter, wipe the rain sensor | Pollen and seed have finished, before the summer heat |
| September | Second glass wash, check the flashing edges | Anything loose is found before the autumn gales |
| November | Clear the kerb and the outlet, brush moss from the courses | The leaves are down and the wet season is starting |
Keeping to that is the difference between a rooflight that is invisible for twenty years and one that becomes a running conversation. The background to all of it, including how the perimeter detail is built in the first place, sits on our main page about rooflight and skylight installation in Chelmsford. If you are weighing up a unit that has reached the end of its life against keeping it going, the costs page sets out how a range becomes a fixed figure, and the workmanship on anything Sunspire installs carries a ten year guarantee.
Keep reading
More on skylight & rooflight installation & replacement chelmsford
Sizing a rooflight for the room
Read the guide →Roof window or rooflight, and the difference
Read the guide →Flat roof against pitched roof rooflights
Read the guide →What happens on installation day
Read the guide →Rooflight planning permission and building regulations
Read the guide →All about skylight & rooflight installation & replacement chelmsford →
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