Skylight Installation in Kesgrave
- Fixed quote before we start
- Roof never left open overnight
- 10-year workmanship guarantee
- Fixed quote before we start
- 10 years workmanship guarantee
- 25 years fitting rooflights
- Skylights only, not a general roofer
Kesgrave builds big rear extensions. That has been the pattern here for years. The housing is largely 1970s to early 2000s detached, generous plots, and a steady appetite for opening the back of the house into one wide kitchen-diner. Extend across the full width of a detached house and you get a large expanse of felt or single-ply over a room the original windows barely reach. That is the job a roof lantern exists for.
It is roughly 3.6 miles east of Ipswich as the crow flies. Allow about a quarter of an hour on the road, a little more if you hit the school run.
A lantern is a heavy thing to stand on a flat roof
People choose a lantern for how it looks, then assume fitting it is the same as dropping in a flat unit. It is not. A four-metre lantern in glass and aluminium is a serious load, applied at the edges of an opening you have just cut in a roof deck.
The kerb, the timber upstand the lantern bolts to, must be built off something that carries load. A ring beam around the opening, or joists trimmed and doubled with the trimmers sized for the span. Not the deck. A kerb fixed into decking board is holding a lantern up on sheathing, and within a few years you get deflection at the corners, the frame goes out of square, and the seals start working. If the trimming is inadequate we price the correction into the quote.
Kerb height, and why 150mm is not an arbitrary number
The glazing has to sit clear of the roof surface. We build to a minimum of 150mm above finished roof level, measured to the finished surface rather than the deck, so insulation and covering are already accounted for.
Water does not sit still on a flat roof. It pools slightly, carries grit and leaf litter, and in heavy rain moves across the surface in a shallow sheet. Anything reaching the base of the glazing sits against the seal and works its way in. Lift the glass 150mm and that sheet never gets near it. Drop the kerb to 75mm for a lower profile from the garden and you have built in a problem that shows on the ceiling in about five years.
Fall on the surrounding roof
Flat roofs are not flat. We work to a nominal design fall of 1:80, and the reason it is not shallower is deflection. Timber deflects under load, coverings settle, and a roof laid dead level holds standing water within a year. Build in 1:80 and after everything has moved you still have gradient enough for water to leave.
Around a lantern it matters twice over, because the kerb obstructs the middle of the roof. Water arriving on the upslope side has to shed around it, not into a dead corner. Where the roof is already built and already ponding, we say so at survey. A good lantern does not fix a bad roof.
What we check before pricing a lantern: what the opening is trimmed with, whether there is a ring beam, the existing fall and where water currently goes, and whether the ceiling below is being kept or lost.
Why a lantern beats a flat unit on a dull Suffolk afternoon
On a bright day everything works. The difference shows on an overcast January afternoon, which is most of the winter here. A flat rooflight looks at one patch of sky, straight up. A lantern presents pitched glazing on four sides, so it collects from a far wider slice of the sky dome and keeps collecting when the brightest part of the sky is low and off to one side. It also throws light sideways instead of dropping it in a column under the opening. On a kitchen-diner where the far corners are eight or nine metres from a window, that is the whole point.
Hot air sits at the ridge, so give it somewhere to go
The other side of a big lantern is summer. Warm air rises and collects at the highest point in the room, which is now the lantern ridge. You get a layer of hot air two metres up that nothing disturbs, and opening the back doors barely touches it because the hot air sits above the door head.
A high-level opening vent fixes it. Hot air leaves at the top, cooler air comes in at low level, and the room turns over. On a lantern this size the vent is out of reach, so it wants to be motorised, which is why we specify electric skylight installation on most Kesgrave lanterns. A rain sensor closes it when the weather turns. Pair that with solar control glazing and the summer performance changes completely.
Upstairs is a different roof entirely
Worth knowing if you are doing the extension and a loft room in the same year. The houses here span roughly thirty years of construction, and later phases increasingly went up with prefabricated trussed rafters rather than cut timber. A truss web cannot be cut to suit a window opening without an engineer redesigning that truss, so a first-floor roof window is constrained to what fits between adjacent trusses. You can end up with a lantern of almost any size over the extension and a modest roof window in the bedroom above. Two different roofs on one house.
The steel under the room decides the lantern above it
A wide Kesgrave extension almost always means the back wall of the original house comes out, and that opening is carried on a steel, often a goalpost of two beams and posts where the span is large. That steel is not just a downstairs problem. It sets the ceiling line, it sets where the flat roof can be trimmed for the lantern opening, and on a full-width knock-through it can dictate whether the lantern sits centred over the room or offset towards the garden. We would always rather see the structural drawing before pricing the lantern, because the beam layout and the lantern opening have to be designed together. Trim the roof for a lantern in the wrong place relative to the steel and you either lose the position you wanted or you add trimming that should have been designed in from the start.
The glass on a big lantern is where the money and the comfort sit
On a lantern this size the glazing specification does more than the frame ever will. Three things are worth getting right:
- Solar control. A large area of upward glass over a kitchen gains a lot of heat on a bright day. A solar-control coating cuts that gain at the glass before it becomes a problem, which on a south or west-facing extension is the difference between a comfortable room and a conservatory.
- A genuine thermal break in the frame. Aluminium conducts heat and cold readily, so a lantern frame without a proper thermal break runs cold on the inside and streams with condensation on a frosty morning. A thermally broken frame keeps the internal surface warm enough to stay dry.
- The U-value of the unit as a whole. A big lantern is a big hole in an insulated roof, so the glass has to pull its weight against Part L. The numbers are on energy efficient skylight installation.
Self-cleaning glass is worth a mention too, because a lantern is not a unit anyone wants to be up a ladder cleaning. On pitched lantern glazing the rain does most of the work, and a self-cleaning coating helps it along, which on a four-sided lantern well above head height is a practical rather than a luxury choice.
The four jobs we are called out for on this side of Ipswich
- Roof lantern installation, the main job here, driven by the width of the rear extensions these plots allow.
- Flat roof skylight installation for narrower side returns, or a second unit over a utility or hallway.
- Electric skylight installation for the high-level vent, because a manual pole is not a realistic answer at this scale.
- Custom skylight design service when the opening does not match a catalogue size, or a steel beam dictates the layout.
We also cover Rushmere St Andrew, Martlesham and Purdis Farm close by, with the rest on areas we cover.
One quote, and it does not move
Tell us the extension width, the roof covering and whether the ceiling is coming down. We survey the structure, quote once, and the price holds unless the specification changes. Every installation carries a 10-year workmanship guarantee. Request a fixed quote.
Lantern or flat rooflight on a wide rear extension in Kesgrave?
Once the room is wider than about four metres, a lantern earns the extra cost. The pitched glazing collects daylight from more of the sky and pushes it sideways, which is what a wide kitchen-diner needs at the far corners. Under four metres, or on a narrow side return, a flat unit gives a better result per pound. We give a straight recommendation at survey rather than defaulting to the lantern.
Do I need planning permission for a lantern on my rear extension?
Generally not, if the extension itself is permitted development. A rooflight on a rear extension normally falls within permitted development provided it projects no more than 150mm above the roof plane and sits below the ridge of the original house. An Article 4 direction changes that. Building Regulations always apply regardless, and on a lantern that means the structure carrying the kerb as well as the glazing.
Will a lantern make the kitchen too hot in summer?
It can, with clear glass and no vent. Hot air stratifies at the ridge and stays there. Solar control glazing cuts the gain coming in, and a motorised vent at high level lets the hot layer escape so the room turns over. With both, a large lantern is comfortable through a Suffolk summer. With neither, it is a greenhouse by two in the afternoon.
We are knocking the back of the house through. Does the steel affect the lantern?
It affects it directly. The beam or goalpost carrying the opened-up wall sets the ceiling line and constrains where the flat roof can be trimmed for the lantern, so on a full-width extension it can decide whether the lantern sits central or offset towards the garden. We ask to see the structural drawing before pricing, so the beam layout and the lantern opening are designed together rather than one being worked around the other on site.
My old lantern runs with condensation in winter. Why?
Usually the frame rather than the glass. Aluminium conducts heat and cold well, and a lantern frame without a proper thermal break runs cold on the inside face, so warm moist kitchen air condenses on it every frosty morning. A modern thermally broken frame keeps that internal surface warm enough to stay dry, and pairing it with a warm-edge glazing unit deals with the pane as well. We do not reseal or repair old lanterns, but a replacement specified properly removes the cause rather than wiping the symptom.
How do you keep water off a flat roof around a lantern?
By building the surrounding roof to a designed fall, usually a nominal 1:80, so water is led to a defined outlet rather than sitting still, and by lifting the lantern on a kerb at least 150mm above the finished surface so the glazing seal is never in standing water. The kerb obstructs the middle of the roof, so we make sure water arriving on the upslope side sheds around it rather than into a dead corner behind it. On a roof that already ponds before we start, we say so, because a good lantern will not rescue a roof that was laid dead level.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.