On a house, a solar shading overhang is a horizontal canopy above an opening, and the French 3CL-DPE 2021 method models it as the near-shading class « baie sous un balcon ou auvent ». The factor there depends on projection alone: 0.8 below 1 m, 0.6 between 1 and 2 m, 0.5 between 2 and 3 m, 0.4 from 3 m up, with no orientation split. The geometry, on the other hand, is in no table: the projection that fully shades a 2.15 m opening at solar noon on the summer solstice runs from 1.09 m in Plymouth to 1.37 m in Edinburgh, and that same projection leaves only 0.26 to 0.32 m of shadow on the head of the opening at the winter solstice, 12 to 15% of its height. That ratio, and not a promise of comfort, is what stands up in front of a client and in front of a cheaper quote.
What a solar shading overhang is worth in the assessment, and under what name
The near-shading class and its factor table
The 3CL method has no word for overhang. It has four families of near-shading obstruction, and a horizontal projection above an opening falls under « baie sous un balcon ou auvent ». The table is short and not open to interpretation.
| Near-shading recorded | Projection | Orientation | Factor |
|---|---|---|---|
| Opening under a balcony or canopy | under 1 m | all | 0.80 |
| Opening under a balcony or canopy | 1 to 2 m | all | 0.60 |
| Opening under a balcony or canopy | 2 to 3 m | all | 0.50 |
| Opening under a balcony or canopy | 3 m and over | all | 0.40 |
| Opening at the back of a balcony or loggia | under 1 m | South | 0.50 |
| Opening at the back of a balcony or loggia | 3 m and over | South | 0.20 |
| No near shading | not applicable | all | 1.00 |
Two lessons for pricing. The first step is the profitable one: going from nothing to 1 m of projection takes the factor from 1.00 to 0.60, that is 40% less solar gain, while going from 2 to 3 m only removes another ten points. And the table gives no credit for orientation on a canopy, unlike a recessed balcony: a north-facing overhang scores like a south-facing one, which is a limit of the method and not a selling point.
Near times distant, or why an overhang never works alone
The sunlight factor of an opening is the product of the near obstruction and the distant one. A 1.20 m overhang in front of an opening already blocked by a neighbouring wall stacks both coefficients, and the calculation turns pessimistic on winter gains fast. On a fully open façade, by contrast, the overhang carries the whole effect on its own. The distant obstruction is surveyed separately, and how shading enters the assessment calculation is worth checking before you conclude anything about the gain.
What you record on the survey to hold the entry under audit
Three dimensions are enough, and all three are needed. The projection in horizontal terms, measured from the outer face of the glazing to the nose of the overhang. The height from the nose of the overhang to the head of the glazing, which pushes the shadow line down and which the table ignores but the building does not. The orientation of the opening on a compass, for the rest of the calculation. A photo from outside with a tape open in shot beats a round number typed from memory.
Sizing the projection: solar geometry, not the supplier's catalogue
The projection that shades the opening at the solstice, latitude by latitude
At solar noon, the sun's altitude is 90° minus the latitude, plus or minus a declination of 23.44°. The projection that puts the whole glazed height in shade is then the height of the opening divided by the tangent of that angle. For a common 2.15 m opening with the nose of the overhang level with the head, that gives figures that vary by a quarter across the country.
| City | Latitude | Sun altitude on 21 June | Projection to shade 2.15 m | Sun altitude on 21 December | Shadow left on the opening on 21 December |
|---|---|---|---|---|---|
| Edinburgh | 55.9° N | 57.5° | 1.37 m | 10.6° | 0.26 m |
| Manchester | 53.5° N | 60.0° | 1.24 m | 13.1° | 0.29 m |
| Birmingham | 52.5° N | 61.0° | 1.19 m | 14.1° | 0.30 m |
| London | 51.5° N | 61.9° | 1.15 m | 15.1° | 0.31 m |
| Plymouth | 50.4° N | 63.1° | 1.09 m | 16.2° | 0.32 m |
Cross that with the factor table and the reading is clear. Everywhere in the UK the geometrically correct projection sits between 1.09 and 1.37 m, that is above the first threshold, so a correctly sized overhang lands in the 0.60 band rather than the 0.80 one. Northern latitudes pay for that in depth: Edinburgh needs a quarter more projection than Plymouth for the same shadow, which is a structural cost, not a detail of the finish.
What that same projection costs in winter gains
The standard client objection is that you are taking January sun away. The arithmetic answers it. At the projection above, the shadow on the opening at noon on 21 December stays within 0.26 to 0.32 m whatever the city, 12 to 15% of the height of a 2.15 m opening, and it falls on the head of the glazing, the part that lights the back of the room but does not warm the storage surfaces. So the ratio is roughly one to seven between what you cut in June and what you lose in December. That is the one sentence in this article that argues itself in a meeting.
East and west: where a horizontal projection stops working
Facing south, the sun's altitude differs by more than 46° between the two solstices, and that difference is what the overhang exploits. East and west, the sun that causes the problem is low on the horizon early and late in the day, whatever the month: a 1 m horizontal projection cuts almost nothing there, and the factor table still awards it the same 0.60. The answer is vertical, side fins or adjustable brise-soleil, and the client should hear it rather than buy an overhang that will never work.
Where the overhang belongs in the works programme
Its rank against insulation and ventilation
An overhang acts on solar gains, not on fabric heat loss: it does not move the EPC band and it opens no grant. So it is proposed after the fabric and the ventilation, and justified opening by opening rather than dwelling by dwelling. On a well-insulated post-1975 house, large south-facing openings are often the first overheating source, ahead of the roof, and the measure moves up the list. The full list of passive measures to work through before any cooling is there to place the overhang in that order, not to force it in.
House, block, commercial: what changes on the quote
On a house, an overhang is a façade element: structural fixing, weathering, finish, and a line for scaffold or a platform that often costs as much as the profiles. In a block, the façade is common structure and the works go through the freeholder, which moves the signature by a year or two. In commercial work, the glazed area changes the scale: wind loads become the governing case, a structural calculation is expected, and maintenance goes into a contract. Those three cases do not price at the same rate per linear metre.
The protections to pair it with, by exposure
An overhang on its own answers one orientation and one time of day. The rest is made up elsewhere.
- Adjustable brise-soleil on east and west façades, where the sun is low.
- External blinds and shutters, which work in front of the glazing rather than above it.
- Roof overhangs and pergolas where the existing geometry allows an extension.
- Deciduous planting, which shades in August and lets light through in January.
Installation: what your liability cover answers for
Materials and metal compatibility
Powder-coated aluminium remains the standard for its weight and stability, provided galvanic couples with steel, copper or stainless are separated, particularly in a marine atmosphere. Steel needs hot-dip galvanising and systematic touch-up on cut edges, or corrosion starts at the cut. Timber calls for a use class that matches the exposure and a design that does not hold water. Concrete is robust but heavy: loads, cracking and the drip edge all need checking before you propose it in a retrofit.
Fixings and getting through external wall insulation
The fixing goes into the structural substrate, never into the insulation. On solid masonry, an anchor or a resin fixing depending on the embedment available. Through external wall insulation, set-out brackets or thermally broken plates sized for the site's wind and snow loads, with weathering returned to the breather membrane: this is where thermal bridges at junctions and water paths are manufactured. The constraints specific to an insulated substrate are set out in our article on external wall insulation.
- Pre-drilling and packing, so the insulation is not crushed under the plate.
- Insulating washers between dissimilar metals, standard on the coast.
- Seals compatible with UV and differential movement, replaced under the maintenance contract.
Water, corrosion and the sheets that belong in the O&M manual
A fall to the outside, a drip that throws the water clear of the façade, no standing point anywhere: that is the trio that decides how long the element lasts. Stainless fixings are chosen compatible with the profile, not to the shortest lead time. On the paperwork side, the O&M manual takes the load calculation, the fixing detail signed off by the supplier, the third-party approval where one exists and the exact references of the profiles installed. When a claim lands, that bundle answers instead of the contractor.
Holding your price against a cheaper quote
What you can demonstrate, and what you must not promise
What you can demonstrate: the projection chosen, the sun's altitude at the latitude of the site, the shading factor that follows, the exact period during which the opening is shaded. What you must not promise: an internal temperature, a number of degrees gained, a substitute for cooling. An overhang treats neither internal gains, nor thermal mass, nor night ventilation, and a dwelling with no scope for night purge ventilation will stay hot in spite of it. Saying so up front is what separates a technical offer from a sales one.
What goes on the quote
The line gets itemised: projection in horizontal terms, girth and material of the profile, fixing method and number of brackets, weathering, soffit finish. The soffit deserves its own mention, because a light colour bounces light into the room and produces glare late in the day, which turns into a dispute if nobody wrote it down. Access equipment goes on a separate line. A quote carrying those five lines no longer compares to the competitor's lump sum.
Which opening to start with
Start with one to three openings, the ones that combine a large glazed area, a south or south-west orientation and a living space used in the afternoon. That assumes you have the inventory: Argile's AI picks out the openings on each façade and works out their areas, which gives you the list to sort by orientation before the survey even happens. The remaining openings go in as a priced option, which leaves the client a decision to make rather than a price to accept.
