An aluminium roof lantern installation gets you the slimmest sightlines available in a self-supporting lantern frame, a powder coated finish in any RAL colour you specify, and, within reach of the Suffolk coast, a fixings and coating specification that resists salt attack for decades rather than a handful of winters. It is the default frame material for modern kitchen and dining extensions across Ipswich, Suffolk and north Essex, and it is what we fit on the large majority of the lanterns that go out from a survey.
This page covers the material in depth: the thermal break that makes aluminium viable at all, the finish options, standard span capability, and the coastal specification that separates a lantern that lasts twenty years at Felixstowe from one streaking with rust by its third winter. For the structural and conservation side, our roof lantern installation hub sets out the wider picture, including when a timber frame is the better call.
Why aluminium is the default system
Aluminium alloy has a strength-to-weight ratio that timber and uPVC cannot match. A stronger material allows a narrower glazing bar, and a narrower bar means more glass and less frame in view. On a well-made system, the visible sightline at a corner post is commonly 60 to 90mm, against 100mm or more on a comparable timber section. Multiply that saving around a five or six bar lantern and the difference in daylight is real, not marketing.
The trade-off is thermal. Aluminium conducts heat roughly a thousand times faster than timber, so a lantern frame with no thermal interruption becomes a cold bridge running the full perimeter of the glazing, and condensation forms on the inside face in winter almost as a matter of course.
The polyamide thermal break
Every aluminium lantern we specify has a polyamide thermal break: an insulating strip of glass-reinforced nylon running the length of each profile, physically separating the cold outer aluminium extrusion from the warm inner one. Heat has to cross that strip to get from inside to outside, and it does so far more slowly than through solid metal. This is what allows an aluminium lantern to reach whole-unit U-values around 1.2 to 1.4 W/m²K when it is paired with argon-filled double glazing and a warm-edge spacer bar, comfortably clear of the Part L replacement floor of 2.2 W/m²K.
Cheaper systems sometimes skip the thermal break, or use a thinner strip than the profile was designed for, to save cost on the extrusion. You cannot see the difference in a photograph, only on the plasterboard reveal in January, as a line of condensation tracking down from a cold frame that a proper thermal break would have stopped. If a quote does not confirm a polyamide thermal break, ask.
Finish: powder coating and RAL colours
Aluminium lantern frames are finished by powder coating, an electrostatically applied dry powder baked onto the profile in an oven, which gives a harder and more consistent finish than a sprayed wet paint. The colour is specified to a RAL number, which is a standardised European colour reference, so what you agree at survey is exactly what arrives on site.
| RAL colour | Common name | Typical use |
|---|---|---|
| RAL 7016 | Anthracite grey | The default. Suits the large majority of modern extensions and most render or brick. |
| RAL 9005 | Jet black | Increasingly requested on contemporary schemes and dark window and door suites. |
| RAL 9010 | Pure white | Suits period properties, painted timber joinery, and lighter render. |
| Dual colour | Two RAL colours, one per face | Grey or black outside, white inside is common. Adds £250 to £500. |
Dual colour solves a genuine tension. An anthracite frame reads well from the garden against modern render, but a white or off-white frame usually sits better against a plastered ceiling and painted joinery indoors. Specifying two colours on the same section, one external and one internal, is a standard option on most premium systems, not a special order. It adds a modest amount to the unit cost and a little to lead time, so it is worth deciding early rather than after the frame has been ordered.
Span capability and typical extension sizes
A standard aluminium lantern bar, on a good modern system, will span comfortably up to around 2.5 to 3.0m without needing anything beyond the manufacturer’s own structural spine detail. That covers the great majority of domestic extension work we see: 1.0 x 1.0m over a small snug or utility roof, 2.0 x 1.0m over a modest kitchen extension, and 2.5 x 1.5m to 3.0 x 2.0m over the larger open-plan kitchen diners that make up most of the enquiries we take.
| Kerb size | Typical application | Bars per side |
|---|---|---|
| 1.0 x 1.0m | Utility, boot room, small kitchen extension | Hipped corners, no intermediate bar |
| 1.5 x 1.0m to 2.0 x 1.0m | Standard kitchen extension | 1 to 2 |
| 2.5 x 1.5m | Larger kitchen diner | 2 to 3 |
| 3.0 x 2.0m | Open-plan kitchen diner, the practical ceiling for a standard bar | 4 to 5 |
Beyond roughly 3.0m in either direction, a standard bar starts to need help. That is not a failure of aluminium as a material, it is simply the point where deflection under glass weight and wind load needs a structural spine or a multi-section frame rather than a single unbroken bar. If your room is heading toward that territory, our page on large-span and multi-section roof lanterns covers ridge beam sizing, when an engineer needs to be involved, and how bigger units are delivered and set in sections.
Coastal specification: what actually changes at the coast
This is where the material choice and the location interact, and it is worth being specific rather than general about it, because the difference between the right specification and the standard one is the difference between a lantern that looks the same in year one and year fifteen, and one that is showing rust streaks by its third winter.
Within roughly a mile of open sea at Felixstowe, Harwich, Frinton, Clacton, Aldeburgh or Southwold, salt-laden air deposits chloride continuously on every exposed surface, and wind-driven rain arrives close to horizontal rather than falling vertically, which drives moisture into laps and fixing points that an inland specification never has to resist. The wetting and drying cycle concentrates that chloride at fixing heads rather than washing it away, which is exactly where standard fittings fail first.
316L stainless fixings, not A2
Most manufacturers supply their systems as standard with A2 grade (304) stainless steel fixings, which performs well inland but is not sufficient at the coast. A2 stainless has no molybdenum content, and chloride ions find the weak points in its passive oxide layer and cause pitting corrosion, showing up first as rust-coloured spots at the screw head and then as staining down the frame. We saw it on a 304 screw at Felixstowe inside two winters.
316L stainless, sometimes called marine grade, contains around 2 to 3 per cent molybdenum. That addition is specifically what resists chloride pitting, and it is why every fixing on a coastal lantern, from the eaves beam bolts through to the glazing capping screws, goes in as 316L rather than 304. It costs more per fixing. On a lantern that might be forty or fifty fixings, the difference to the total job cost is small; the difference to how the frame looks in ten years is not.
Marine-specification powder coating
The powder coat itself also changes. A standard system is tested and warranted to an inland exposure category. Marine-specification coating uses a different pre-treatment, usually a chrome-free conversion coating designed for salt exposure, and a coating system tested and rated to a coastal category under the relevant standard for architectural aluminium finishes. Most manufacturers offer it as a named upgrade rather than a bespoke request. It typically adds a modest amount to the unit cost and extends the finish guarantee considerably. On any lantern going in within a mile of open sea, we specify it as standard, not as an option you have to ask for.
Galvanic isolation
Aluminium in direct contact with a different metal, in the presence of moisture and salt, sets up a galvanic cell: one metal corrodes preferentially to protect the other, and near the coast that reaction runs faster. Where a lantern’s eaves beam meets a steel ring beam, or dissimilar fixings are unavoidable, we isolate the two metals with proprietary washers and tape rather than letting them touch directly. It is a small detail, easy to skip and expensive to fix once corrosion has taken hold behind a capping strip.
| Detail | Standard inland spec | Coastal spec, within roughly a mile of open sea |
|---|---|---|
| Fixings | A2 (304) stainless | 316L stainless throughout |
| Powder coating | Standard architectural grade | Marine-specification pre-treatment and coating |
| Kerb height | 150mm minimum above finished roof at the lowest point | 200mm, because driven rain climbs the vertical face |
| Flashing laps | Standard lap length | Longer laps, mechanically fixed terminations |
| Dissimilar metals | Direct contact generally acceptable | Isolated with washers and tape against galvanic corrosion |
Estuarine locations sit between the two. Woodbridge, Wivenhoe, Manningtree, Shotley and Pin Mill face tidal saline water and real wind exposure across open water, producing moderate salt loading that makes upgraded fixings sensible. That is not open-sea exposure, and we do not specify full marine treatment on an estuarine job as though it were Southwold. Further inland, at Stowmarket, Bury St Edmunds, Lavenham, Colchester and Hadleigh, none of this applies; the specification decision there is about structure and conservation, not corrosion. Our roof lantern coastal corrosion page explains the mechanism in more detail.
When timber, not aluminium, is the right call
Aluminium is not always the right answer, and we say so at survey rather than after you have ordered. On a listed building, in a conservation area with a visible principal elevation, or on a period property where a slim modern profile would look wrong next to sash windows and painted joinery, a timber frame usually satisfies both the aesthetic and the conservation officer. Timber costs more, typically 40 to 70 per cent above an equivalent aluminium unit, and carries a maintenance cycle aluminium does not. Our page on timber roof lanterns for period and listed properties covers sightlines, consent and the redecoration cycle in full, and our aluminium versus timber cost comparison sets purchase price against lifetime maintenance.
The specification is decided at survey, not guessed at over the phone. We measure the site, check exposure against the actual distance to open water, and confirm the glazing and fixing specification in writing before you commit to anything. If your property sits on the coast, marine specification is included as standard, not offered as an upsell once the order is placed.
Glazing and the rest of the specification
The frame is one half of an aluminium lantern’s performance. Glazing choice, particularly the g-value for south and west facing rooms, matters just as much to how the finished room feels. Our roof lantern installation page carries the full glazing specification table, and our guide to roof lantern installation costs in Suffolk breaks out what a coastal or dual-colour upgrade adds to a quote. Our answer page on how big a roof lantern should be for the room gives the working proportion ratio we use at survey.
Frequently asked questions
What is the difference between A2 and 316L stainless fixings?
A2, also called 304, is standard stainless steel and performs well inland. 316L contains molybdenum, which specifically resists chloride pitting, the corrosion mechanism driven by salt-laden air. Within roughly a mile of open sea, A2 fixings can show rust staining within two or three winters. 316L is the specification for coastal work and it is what we use on any lantern within reach of the Suffolk or north Essex coast.
Does marine-specification powder coating cost much more?
It adds a modest amount to the unit cost, typically a small percentage of the lantern price, and it extends the finish guarantee considerably. On coastal jobs we include it as standard rather than an upgrade you have to request, because a standard coating is simply the wrong specification for that exposure.
Can an aluminium lantern span 3.0 x 2.0m without extra structure?
Yes, on a good modern system a standard bar comfortably spans up to around 3.0m, which covers the majority of domestic kitchen extension lanterns. Beyond that, deflection under glass weight and wind load means a structural spine or a multi-section frame is needed. Our large-span page covers what changes above that point.
Do I need a thermal break on every aluminium lantern?
Yes. Without a polyamide thermal break, the aluminium frame conducts heat straight through from inside to outside, and condensation on the inner face in winter is close to guaranteed. Every lantern we specify has one, and it is worth confirming on any quote you are comparing.
Get a fixed quote
Tell us the room, the approximate size, and where the property sits, and we will survey it, confirm whether coastal specification applies, and give you one written price with the frame, finish and fixing specification stated on it. Every installation carries a 10-year workmanship guarantee. Request a fixed quote for an aluminium roof lantern in Ipswich, Suffolk or north Essex.
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.