Roof Lantern Installation
Flat-roof glazing sized to the room and detailed into the kerb below it.
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West Essex
Rooflight installation in Harlow
New town, flat roofs and uniform estates. What that means for getting glass into a roof here is the whole of this page.
We travel to Harlow
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HarlowTown covered
West EssexWithin
30Mile radius by road
10Year workmanship guarantee
In Harlow
What we install on Harlow roofs
Flat Roof Rooflight Installation
Flush and kerb-mounted units into single-ply, felt and GRP flat roofs.
View this service →Roof Window Installation
Roof windows trimmed into slate, clay and concrete tile without proud flashing.
View this service →VELUX Window Installation
We install VELUX alongside Fakro, Keylite and Roto roof windows.
View this service →Electric and Opening Rooflights
Actuated opening units, rain sensors and controls, wired and commissioned.
View this service →Energy Efficient Rooflights
Specified on U-value and g-value, not on the brochure photograph.
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The local detail
16 things worth knowing about Harlow roofs
Harlow is the one town in this part of Essex where the roof is usually flat, and that single fact reorganises everything else. A designated new town, master planned from 1947, built at speed with a consistent set of construction details across whole neighbourhoods. The result is a housing stock where the same handful of roof build-ups repeat street after street, and where the questions that decide a rooflight installation are about decks, falls and vapour rather than tiles and flashing kits.
That consistency is useful. Once the build-up on one house in a run is understood, the next twelve are broadly known. Sunspire works across Harlow from Chelmsford as part of its normal travelling radius.
- 01 The Gibberd plan, and what it left on the roofs
- 02 Cold decks, and the void above a Harlow ceiling
- 03 Built-up felt, and the layers laid over it since
- 04 Falls that have gone flat, and standing water round a kerb
- 05 Upstand measured from the deck upwards
- 06 Vapour control, and where the barrier has to sit
- 07 Mono-pitch roofs and shallow tiled slopes
- 08 Listed twentieth century housing in Harlow
- 09 Old Harlow, Churchgate Street and the older fabric
- 10 Church Langley and the trussed roof estates
- 11 Newhall, and roofs governed by a design code
- 12 Long terrace runs and shared roof structures
- 13 Garage courts, stores and outbuilding flat roofs
- 14 Overheating in a Harlow room under glass
- 15 Notification on a Harlow replacement
- 16 Where a Harlow enquiry starts
The Gibberd plan, and what it left on the roofs
Frederick Gibberd’s plan grouped the town into neighbourhoods separated by green wedges, each with its own centre: Mark Hall, The Stow, Bush Fair, Staple Tye, Potter Street, Katherines, Sumners. Each was built out in a defined period with a defined palette.
For anyone working on the roofs, the practical consequence is that the era of the neighbourhood predicts the construction. The earliest phases carry timber joisted flat decks with built-up felt and shallow mono-pitches in concrete tile. The 1960s and 1970s phases bring larger flat areas, more system building and some crosswall construction. The 1990s onwards, at Church Langley and later Newhall, return to trussed pitched roofs. Establishing which phase a house belongs to narrows the survey before anyone climbs a ladder.
Cold decks, and the void above a Harlow ceiling
A great many original Harlow flat roofs are cold decks. The insulation sits between the ceiling joists, the deck sits above on the same joists, and there is a ventilated air gap in between that is supposed to carry moisture away at the eaves.
Cutting a rooflight into a cold deck interrupts that ventilation path, and it does so at the exact point where warm moist air from the room below now has a route upwards. If the kerb is built without thinking about it, the void either side of the opening becomes a dead end where air stops moving. The detail that works keeps a continuous cross-ventilation route around the new kerb, or converts the local build-up to a warm deck with the insulation above the structure and the vapour control layer below it. Which of the two applies is decided at survey by opening up and looking, not by assumption.
On a cold deck the rooflight is the easy part and the air path around it is the whole job.
Built-up felt, and the layers laid over it since
The original covering on most Harlow flat roofs was three layer built-up bituminous felt on a chipboard or timber deck. Very little of that original felt is still the top surface.
What is usually found instead is an accumulation: felt, then a later felt overlay, then perhaps a liquid applied coating, then in the last twenty years a single ply membrane or a GRP laminate. Each layer added height without adding fall. That history matters for two reasons. It changes the finished level the kerb has to clear, and it changes how the new covering is terminated, because dressing single ply up a kerb and dressing felt up a kerb are different operations with different laps and different failure points.
Falls that have gone flat, and standing water round a kerb
A flat roof is never actually flat. It is laid to a fall, conventionally a designed minimum of 1:80 so that construction tolerance and deflection still leave something draining. On a Harlow deck sixty or seventy years old, deflection has usually eaten a good part of that.
Water standing more than forty eight hours after rain is ponding, and ponding against a rooflight kerb is the condition that finds any weakness in a perimeter detail. Where a survey finds a pond sitting where the glass is meant to go, the sensible order of work is to sort the fall first and set the unit into a deck that drains. Firring pieces or a tapered insulation scheme achieve that, and either is far cheaper than dealing with the consequence of not doing it.
Upstand measured from the deck upwards
The 150mm upstand figure that gets quoted across the trade is measured from the finished roof surface to the top of the kerb. On a Harlow roof with four coverings on it, the finished surface is not where the drawing says it is.
So the kerb has to be built taller than the nominal figure to end up at the right height once the make-up, the insulation and the new membrane are all on. Getting that wrong in the other direction is the common outcome: a kerb set out from the deck, four layers of build-up added on top, and a finished upstand of 90mm on a roof that ponds. The measurement that counts is taken after the build-up is decided, and it is worth 150mm as a floor rather than a target on any deck with a history of standing water.
Vapour control, and where the barrier has to sit
Warm moist air moving upwards through a roof build-up condenses when it reaches a surface below the dew point. In a warm deck that is prevented by a vapour control layer immediately below the insulation, sealed and continuous.
Around a new opening, continuity is the difficult bit. The vapour control layer has to be turned up the kerb and bonded to it, so there is no route for room air to get past the insulation line and into the cold zone. A layer that stops short at the kerb face leaves a gap a few millimetres wide running the full perimeter of the unit, and interstitial condensation collecting in a deck is slow, invisible and expensive. The flat roof rooflight page sets out how those layers stack up.
Mono-pitch roofs and shallow tiled slopes
Not everything in Harlow is flat. A signature of the early neighbourhoods is the mono-pitch: a single plane falling one way, often at 10 to 17 degrees, in concrete interlocking tile.
That pitch band is exactly where roof window ratings start and stop. Most units want 15 degrees as a minimum. A handful are rated from 10 with a manufacturer specified underlay detail carried down beneath the opening. Below 10, the honest answer is that the covering will not weather a trimmed opening reliably and the daylight has to come from something designed for a low slope instead. Taking the pitch with a level at three points along the plane, rather than reading it off a plan, is what separates those cases.
Listed twentieth century housing in Harlow
Harlow carries something unusual for a new town: nationally listed post-war housing. The Lawn at Mark Hall, the first residential point block in the country, is listed, and there are further listed and locally designated groups of Gibberd era housing and public art across the town.
Where a house sits in one of those groups, or inside one of the new town conservation areas, the roof is part of a designed composition and the rules tighten sharply. A flush unit that sits within the plane of the covering, in a dark frame, on a slope not visible from the principal public view, is the design that gets consent. A proud dome on a front elevation is not. Establishing designation status takes a minute on the council’s map and is done before a product is chosen.
Old Harlow, Churchgate Street and the older fabric
The new town was built around an existing village, and Old Harlow, Mulberry Green and Churchgate Street predate it by several centuries. Timber framing, plastered elevations, hand-made clay peg tile and steep pitches, inside conservation areas with the usual withdrawal of permitted development rights.
Work on that fabric follows different rules from the rest of the town. Openings placed between existing common rafters so no historic timber is cut, soaker based lead detailing rather than a proprietary kit, and a conservation rooflight with a slim cast frame sitting no more than about 20mm above the tile surface. It is the same county-wide picture set out on the pages for Epping and the older market towns.
Church Langley and the trussed roof estates
Church Langley, built through the 1990s, brought conventional trussed rafter roofs back to Harlow at scale: concrete interlocking tile, pitches around 35 degrees, trusses at 600 centres.
A truss is an engineered component and its webs cannot simply be cut. A roof window on this stock is sized to fit between trusses, which usually caps the width near 550mm unless a structural engineer designs a trimming solution. Two narrow units spaced across the slope give better light distribution than one wide one anyway, and they avoid the calculation entirely. The tile is deep profiled, so the flashing kit has to be the one made for that depth or the apron bridges the troughs and water tracks under it.
Newhall, and roofs governed by a design code
Newhall is the most architecturally deliberate housing in the town: contemporary house types built to a site wide design code, with roof forms that are part of the architecture rather than a default.
Two consequences follow. First, permitted development rights on newer estates are frequently restricted by planning condition, so the assumption that a rooflight needs no application does not hold and wants checking against the original permission. Second, the roof geometry is often asymmetric or monopitched with parapets, which means the position of an opening is constrained by where the covering can be terminated cleanly rather than by where the room below would like it. Both are answerable, and both are cheaper to answer before ordering.
Garage courts, stores and outbuilding flat roofs
The plan put parking in garage courts and gave most homes a small store or outbuilding, nearly all of them with a small flat roof. These are the easiest daylight wins in the town.
A modest flush unit into a garage or a store deck needs no structural conversation, sits on a kerb built off the existing joists, and turns a space people currently use a torch in into a workshop. Where the deck is genuinely small, spreading two small units rather than one large one keeps the joist spans untouched and gives more even light. It is also a good low-risk place to see how a build-up behaves before committing to the same detail over a living room.
Overheating in a Harlow room under glass
A flat rooflight faces the entire dome of the sky, which is why it delivers so much more light than a vertical window of the same area. It is also why it collects the July sun at a very high angle, straight down.
Two numbers describe the glass and they pull against each other. The U-value measures heat loss and lower is better. The g-value measures how much solar energy passes through, and lower means less gain and slightly less light. Optimising the first and ignoring the second produces a room that is cheap to heat in February and unusable by three in the afternoon in August. On a flat deck, solar control glass is close to a default, and an opening unit at the highest point lets the accumulated warm air leave without a fan.
| Harlow roof type | Usual unit | The detail that decides it |
|---|---|---|
| Original felt cold deck | Flush flat rooflight on a built kerb | Continuous ventilation path round the kerb |
| Overlaid warm deck | Flush unit or lantern where span allows | Vapour layer turned up and bonded to the kerb |
| Mono-pitch concrete tile | Roof window if pitch permits | Measured pitch against the unit’s minimum |
| Church Langley trussed roof | Roof window between trusses | Deep profile flashing kit for the tile |
| Store or garage deck | Small flush unit, or a pair | Existing joist span left undisturbed |
Notification on a Harlow replacement
Fitting a new rooflight, and replacing one that has reached the end of its working life, are both notifiable under Building Regulations in England. Part L is engaged for thermal performance, Part K where there is a risk of falling, and Part B where the opening serves as a means of escape.
Sunspire notifies as part of the job. That matters more than it sounds on a town of this age, because a great many Harlow roofs already carry units fitted at some point in the last few decades with no record at all, and the absence surfaces years later when a buyer’s solicitor asks for a completion certificate. A like for like replacement into a sound existing kerb is often a single day’s work and a good moment to correct that.
Where a Harlow enquiry starts
Useful first information is a photograph of the roof from above or from an upstairs window, a photograph of the ceiling from inside, the rough size of the room, and the neighbourhood, because the neighbourhood implies the build-up. If the property is a flat or maisonette, say so at the outset, since the freeholder conversation runs in parallel with everything else.
A range comes back by email from that, and a fixed written figure after the survey. The costs page covers what moves the number between the two. Harlow sits with the rest of West Essex on the areas we cover page, and the guides section goes further into cold and warm deck build-ups.
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We start with the building, the covering and the slope. Then we tell you what will suit it, and what it will cost, as a fixed written number.
- Surveyed before it is priced
- 10-year workmanship guarantee
- Building Control notification handled
- New installations and replacements