We have already written about sun room glass and ultraviolet light, about shading systems, about ventilation, and about the hardware on a sun room door. Every one of those pieces had to assume a location. This is the piece about the location itself. It turns out to be the hardest one to write, because the location is described by a word that no two documents define the same way.
If you read only one section, read the second one. It is a table of five distances from the water and how many of the published definitions call each one coastal. The answer is not a number you can look up. It is a number that somebody else has already picked for you.
Ask six published documents where the coast ends and you get six answers. Four of them are in miles, one is in yards, one is in metres, and one is given as a range in kilometres. Converted to the same unit, the smallest is a little over four hundred and fifty metres and the largest is ten thousand metres. That is the spread you are specifying inside.
| Document type | Distance as printed | Unit it was printed in | Same distance in metres | What it is used to decide |
|---|---|---|---|---|
| UK fabricator guarantee, paint exclusion clause | 500 | yards | about 457 | Whether the paint warranty is valid at all |
| Same UK guarantee, corrosion exclusion clause | 500 | metres | 500 | Whether aggressive-environment corrosion is excluded |
| Two US window manufacturers, finish and hardware warranty | 1 | mile | about 1,609 | Whether exterior hardware is warranted, and the cleaning obligation |
| US window and door manufacturer, finish warranty | 3 | miles | about 4,828 | Whether the finish term is the long one or the short one |
| US aluminium window and door manufacturer, full warranty | 4 | miles | about 6,437 | Whether coastal hardware is mandatory and the finish term collapses |
| European coating quality label, seaside class | 5 to 10 | kilometres | 5,000 to 10,000 | Which coating class applies to the specification |
Ten thousand divided by four hundred and fifty-seven is about twenty-two. Four miles divided by one mile is exactly four. Both of those gaps sit inside one product category, on the same coastline, for goods that are sold as the same thing.
Take six houses at different distances from the water and run all six definitions against each one. The result is not a boundary. It is a gradient, and the middle of the gradient is where almost every coastal sun room is actually built.
| Distance from the water | How many of the six definitions call it coastal | Which ones say no | What this means in practice |
|---|---|---|---|
| 300 metres | six of six | none | Every clause in every document applies. There is nothing to argue about and nothing to save. |
| 800 metres | four of six | the two UK figures | Coastal to every US and European document, inland to the shortest UK clause. |
| 2,000 metres | three of six | the two UK figures and the one-mile figure | Exactly half. This is the most common distance for a coastal villa, and it is the least certain. |
| 6,000 metres | one of six | all except the four-mile figure | Inland to most documents. Still inside the widest seaside coating band. |
| 15,000 metres | none of six | all six | Inland everywhere. Sand, wind and salt can still reach you, but no document says so. |
A house two kilometres from the water is coastal under exactly half of the published definitions. That is not a tie that gets broken in your favour. It gets broken by whichever document the person assessing your claim happens to be holding.
The distance is not an academic question, because crossing it does five concrete things at once. None of them are improvements.
| What changes | Inland position | Coastal position | Who decides |
|---|---|---|---|
| Finish warranty term | The long term printed on the sheet | The short term printed underneath it | The warranty document, not you |
| Hardware specification | Standard hardware is covered | Coastal hardware becomes a condition of cover | The warranty, again |
| Your maintenance obligation | Clean when it looks dirty | Clean on a stated interval or the warranty is void | You, and you must be able to prove it |
| Corrosion as a claim | Sometimes covered as a defect | Explicitly listed as an environmental exclusion | The exclusion clause |
| Which coating class is specified | General architectural class | Seaside class with its own pretreatment | The specifier, before anyone quotes |
The last row is the one worth acting on, because it is the only row where you still have the pen. Everything above it is decided after the goods are made.
The cleanest illustration of how loose this word is does not come from comparing two companies. It comes from reading one guarantee document all the way to the end.
A UK fabricator publishes a paint guarantee. One clause invalidates the paint warranty where the location is within five hundred yards of the coast. Twelve clauses later, the exclusions section removes cover where the material is within five hundred metres of the high tide line. Five hundred yards is about four hundred and fifty-seven metres. The two clauses in the same contract draw the line about forty-three metres apart, in two different units, and neither one acknowledges the other.
| Where the two lines sit | Clause one | Clause two | What the gap contains |
|---|---|---|---|
| Same guarantee document | 500 yards, about 457 metres | 500 metres | About 43 metres of ground where the paint is excluded but corrosion is not, or the reverse depending on which clause is read |
| Two US manufacturers | 1 mile, about 1,609 metres | 4 miles, about 6,437 metres | About 4,828 metres, inside which one company owes coastal hardware and the other owes nothing extra |
| One manufacturer, finish term | Long term outside 3 miles | Half that term inside 3 miles | The same coating on the same profile, with two different expiry dates set by geography |
| One manufacturer, finish term | Long term inland | One year within 4 miles | The same product with a term that falls by a factor of ten when the address changes |
There is no scandal here. Each company drew the line where its own claims experience told it to. The problem is that they drew different lines and used the same word for all of them, so the word arrives at your project carrying six numbers and no instruction about which one applies.
There is one classification system that does measure coastal exposure properly, and it does not contain a single distance. ISO 9223 classifies atmospheres by what actually lands on the metal, measured with a wet candle over a defined exposure period, in milligrams of chloride per square metre per day.
| Chloride class | Deposition rate in milligrams per square metre per day | What it is usually taken to mean | What the standard itself warns |
|---|---|---|---|
| S0 | up to 3 | Minimal, typical of inland sites | Published tables differ on whether the second band starts at 60 or 61 |
| S1 | 3 to 60 | Low deposition, basic protection | The bands are descriptive, not site-specific |
| S2 | 60 to 300 | Moderate risk near coastlines | One published table caps the top band at 1,500; another leaves it open |
| S3 | above 300 | Highly corrosive, marine or industrial marine | The classification is described as useful for sites closer than one kilometre to a source of sea water |
Read that last cell again, because it quietly disqualifies the system everybody quotes. The chloride classification is described as useful for evaluating sites closer than one kilometre to a source of sea water. Most coastal houses are further away than that. The one measurement that genuinely describes your site is the one measurement the standard says has a working range of one kilometre.
The same standard does supply a dose-response function for aluminium in which the chloride term is deposition in milligrams per square metre per day, alongside a sulfate term, relative humidity and temperature. It uses deposition. It never asks how far you are from the beach.
ISO 9223 also gives corrosivity categories for aluminium, expressed as first-year corrosion rate in micrometres per year. These are the numbers that get quoted in coastal specifications.
| Category | Aluminium rate, micrometres per year | Roughly what that is on a 2.0 millimetre wall over twenty years | Why the arithmetic does not work |
|---|---|---|---|
| C1 very low | up to 0.1 | under 2 micrometres | Rounded figures, and the rate changes after the first year |
| C2 low | above 0.1 to 0.6 | 2 to 12 micrometres | Same |
| C3 medium | above 0.6 to 2.0 | 12 to 40 micrometres | Same |
| C4 high | above 2.0 to 5.0 | 40 to 100 micrometres | Same |
| C5 very high | above 5.0 to 10.0 | 100 to 200 micrometres | Same, and this is the band people divide by |
| CX extreme | above 10.0 | more than 200 micrometres | The standard says this category refers to specific marine and marine industrial environments |
The practical use of this table is not to predict a service life. It is to force a comparison. If two suppliers both claim suitability for a coastal site, ask both which category they designed to and what deposition figure they assumed. A supplier who cannot name a category has not thought about it, and a supplier who names one without naming the deposition figure has read the table but not the caveats.
Distance is the weakest of the variables. Published corrosion guidance repeatedly identifies other factors that move a site by a whole class without the address changing.
| Variable | Direction of effect | What it means for a sun room specifically |
|---|---|---|
| Prevailing onshore wind direction | Salt aerosol is carried inland on the wind; exposure falls with each kilometre of travel | The sea-facing elevation and the land-facing elevation of the same room are not in the same environment |
| Whether the elevation is sheltered | The sheltered side of a building can sit a full class below the exposed side at the same address | A sun room tucked into a courtyard may need none of this; the one on the corner does |
| Height above ground | Wind-driven spray concentrates near the ground; exposure drops noticeably by about six storeys up | A sun room is a ground-level structure. It sits at the bottom of the salt gradient. |
| Orientation of the surface | Horizontal samples corrode fastest, then surfaces at 45 degrees, then vertical | A sun room is the only glazed product with a horizontal face, and that face is the roof |
| Whether rain reaches the surface | Sheltered areas collect more salt but do not necessarily corrode more, because wetness time drops | The underside of a roof overhang, and the top of a glazing bar, behave differently from the wall below them |
| Airborne sand | Grit abrades glass and coatings, and the damage often happens during cleaning | Wiping a dry salt-and-sand film is the abrasion event, not the salt itself |
| Local geography | Prevailing winds and currents make some stretches of the same coast markedly worse than others | Your neighbour's experience two streets away may not transfer |
None of these variables appear on an order form. All of them appear in the failure. That is the gap this article is about.
Three independent facts meet on the roof of a coastal sun room, and nowhere else in a fenestration order.
| Fact | Where it comes from | Consequence on a sun room |
|---|---|---|
| Horizontal surfaces corrode faster than inclined ones, and inclined ones faster than vertical ones | Published corrosion research on building metals | The roof is the worst-oriented aluminium on the building |
| Published coastal glass cleaning schedules describe vertical glass at reachable height | Window cleaning companies in several countries | No published interval describes overhead glazing, because nobody can reach it routinely |
| Nobody looks at the outside of a roof from inside the room | Simple geometry | The first sign is usually a stain on the inside of the glass, by which time the salt has been there for years |
Every coastal maintenance article gives a cleaning frequency. Almost none of them agree, and the spread between the most relaxed and the most demanding is roughly six to one.
| Exposure described in the source | Published interval | Washes per year | Note |
|---|---|---|---|
| Near the beach, within one kilometre | No more than six months between cleans | two | The most relaxed figure we found |
| Within one mile of the coast | Every three to four months | three or four | Given in both UK and US sources |
| Absolute beachfront | Quarterly, at minimum | four | Stated as a floor, not a target |
| Oceanfront, direct exposure | Every two to three months | four to six | Heavy salt spray and sand |
| Ocean-facing glass in summer | Monthly | twelve | Six times the most relaxed figure, on the same coast |
Two useful things hide in these sources. The first is that salt contaminates the cleaning water itself, so a single bucket used around the whole building spreads salt back onto clean glass; the method matters as much as the interval. The second is that sand on glass acts as an abrasive, so wiping a dry, gritty surface is what scratches it. A coastal maintenance schedule that only says clean more often has told you the easy half.
This is the part that surprises people who have been choosing between frame depths and glass build-ups. In the model residential codes, a sun room is not classified by what it is made of. It is classified by what the space is used for.
Sunrooms are required to comply with a dedicated voluntary specification developed jointly by the American Architectural Manufacturers Association, the National Patio Enclosure Association and the National Sunroom Association. For the purpose of applying that specification, the sun room is identified as one of five categories. The identification is made by the permit applicant, the design professional, or the property owner or the owner's agent, and it is recorded in the construction documents.
| Category | How it is enclosed | Extra requirements the fenestration must meet | Habitable | Conditioned |
|---|---|---|---|---|
| I | Open, or insect screening, or plastic film no thicker than 0.5 millimetres | None listed | No | No |
| II | Enclosed walls, openings glazed or plastic | None listed | No | No |
| III | Enclosed walls, openings glazed or plastic | Air infiltration resistance and water penetration resistance | No | No |
| IV | Enclosed walls, thermally isolated, heated or cooled by a separate control or system | Water penetration, air infiltration and thermal performance | No | Yes |
| V | Enclosed walls, heated or cooled, open to the main structure | Water penetration, air infiltration and thermal performance | Yes | Yes |
Now read the third column from the top down and stop at row three. Two of the five categories carry no listed requirement for water penetration resistance at all. In a coastal location, wind-driven rain is the dominant water load and it arrives horizontally. A sun room legitimately declared as Category I or Category II under this structure is a sun room with no listed obligation to keep driven rain out.
This is where many enquiries for a 4 season sun room quietly go wrong. Buyers assume that a room described as usable all year is automatically in a category with thermal and water requirements. It is not. The category is a declaration someone makes on a form, and the cheapest declaration is the one that removes the requirements.
The Florida Building Code contains a dedicated section for sunrooms inside its high velocity hurricane zone provisions. It uses the same Roman numerals and the same idea. It is not the same list.
| Number | In the Florida high velocity hurricane zone section | In the model residential code | Do they mean the same thing |
|---|---|---|---|
| I | Roof over an outdoor space, screening or thin film. Non-habitable, unconditioned. | Thermally isolated, screening or thin film. Non-habitable, unconditioned. | Close enough |
| II | Roof and enclosed walls, glazed or plastic. Non-habitable, unconditioned. | Same description, with thermal isolation stated | Close enough |
| III | Adds forced-entry resistance, air leakage resistance and water penetration resistance | Adds air infiltration and water penetration only | No. Florida adds a security requirement the national text does not list. |
| IV | Heated or cooled by a separate control, thermally isolated, with forced-entry, water, air and thermal requirements. Habitable and conditioned. | Same build but Non-habitable and conditioned | No. The same numeral is habitable in one document and not habitable in the other. |
| V | No fifth category in this section | Open to the main structure. Habitable and conditioned. | Not comparable |
A Category IV sun room is habitable in Florida and not habitable under the model code. If you write Category IV in an enquiry without saying which document you mean, you have written a word that means two things.
Florida is also the clearest illustration of how a single jurisdiction can define coastal twice, for two different purposes, using two incompatible methods.
| Designation | How the line is drawn | What it triggers | Type of line |
|---|---|---|---|
| Wind-borne debris region | Within one mile, stated as 1.61 kilometres, of the coastal mean high water line where the ultimate design wind speed is at or above 130 miles per hour; or anywhere the ultimate design wind speed is at or above 140 miles per hour | Glazed openings must be impact resistant or protected | A distance from a tidal datum |
| High velocity hurricane zone | Miami-Dade County and Broward County | A dedicated sunroom section, higher design wind speeds, and exposure category rules | A county boundary on a map |
Inside the high velocity hurricane zone, the code section on wind loads states a design wind speed of three-second gust of 170 miles per hour, given as 76 metres per second, in Broward County, and 175 miles per hour, given as 79 metres per second, in Miami-Dade County. The sunroom subsection then requires that sunrooms, including exposed structures, components, cladding and roof covering, resist the wind loads established by that section.
So one clause measures from a tide line and the other is drawn on a county map. A house thirty kilometres inland inside one of those counties carries the coastal requirement. A house three hundred metres from the water in a neighbouring county does not. The coastal rule is not measuring the coast in either case.
Australia takes the third approach: it defines wind regions by distance from a coastline, but not the coastline you can see. The published design guidance uses distance from a smoothed coastline.
| Region | How the published guidance describes the band | Examples given | What the smoothing erases |
|---|---|---|---|
| D | Within 50 kilometres of a smoothed coastline in Western Australia between 20 degrees south and 25 degrees south | Onslow, Port Hedland | Every gulf, inlet and harbour on that coast |
| C | Within 50 kilometres of a smoothed coastline between 20 degrees south in Western Australia and 25 degrees south in Queensland, and other stated bands | Darwin, Townsville, Broome | Same |
| B | Between 50 and 100 kilometres in some bands, within 100 kilometres in others, and between 100 and 150 kilometres in one band | Brisbane, Geraldton, Collinsville | Same |
| A | Everywhere else, explicitly including all of Australia south of 30 degrees south | Melbourne, Sydney, Launceston | The fact that those cities are on the ocean |
The national construction code tables add a further wrinkle: for the two cyclonic regions, only the maximum values are tabulated, and lower values may apply depending on the distance of the site from the smooth coastline. So even where distance is the rule, the table gives you the worst case in the band and leaves the actual value to be determined.
Almost every coastal enquiry eventually cites a coating standard. It is worth knowing precisely what those standards measure, because the best-known one is a weathering test that happens to be performed in a coastal place.
| Specification | Real-world exposure required | Key pass criteria that get quoted | Film thickness |
|---|---|---|---|
| AAMA 2603 | One year of Florida exposure | Minimal colour and gloss retention requirements | Not the figure people quote |
| AAMA 2604 | Five years of Florida exposure | Defined chalking, colour change and gloss retention thresholds | Not the figure people quote |
| AAMA 2605 | Ten years of South Florida exposure, plus 4,000 hours of accelerated laboratory correlation | Colour change no more than five Delta E units, chalk rating no less than eight, at least half of the original gloss retained, film erosion under one tenth | Eight readings in ten at 30 micrometres or more, no single reading below 25 micrometres |
AAMA 2605 also carries laboratory corrosion requirements, including salt spray exposure and humidity resistance measured in thousands of hours, and cyclic corrosion testing. That is a genuine coastal-relevant test regime. But published commentary on these ratings makes the point directly: they test resistance to ultraviolet light and weathering, and they are not a salt-belt service-life figure. The exposure site is coastal because coastal Florida is a severe ultraviolet environment. That is not the same as testing your house.
The European counterpart works differently, and the difference matters more than the numbers.
| Class | Accelerated weathering | Extra requirements | When it is called for |
|---|---|---|---|
| Class 1 | 1,000 hours | Standard adhesion and impact tests | General architectural work, inland |
| Class 2 | 3,000 hours | Higher durability | Commercial architectural work in many European markets |
| Class 3, Seaside | 4,000 hours or more, plus a real-world Florida correlation | Additional sulfur dioxide and salt spray testing, and a specified pretreatment | Published comparison describes it as required for any coastal architectural application within 5 to 10 kilometres of salt water |
Note the structural difference. The North American specification is a product performance specification: it does not dictate the pretreatment chemistry, it tests the finished part. The European label is a process specification with certified facilities and annual third-party audits: it dictates chemistry and process control. Asking a factory are you coastal certified is therefore two different questions depending on which label you meant, and a yes to one does not answer the other.
When a coastal sun room fails, the frame is rarely the first thing. Published guidance on stainless steel and on building metal corrosion converges on the same small parts.
| Part | Why it goes first | What to write in the enquiry |
|---|---|---|
| Fixing screws and bolts | They are the smallest section, they are often a different metal from the part they hold, and they are hidden until they have already failed | List fastener material as its own line item, not as part of the hardware set |
| Dissimilar metal contacts | A stainless component against an aluminium profile in a wet, salty film forms a couple, and the less noble side pays | Ask what isolation is used at every stainless-to-aluminium contact, and ask for it on the drawing |
| Insect screen mesh | It is a permanently exposed woven metal with a very high surface area, and it is usually the cheapest line on the order | Ask for the alloy grade by number. A catalogue that says stainless mesh has not answered. |
| Rollers and tracks in sliding elements | They sit in the drainage path, and a coastal site adds salt to water that is already there by design | Ask what the wheel, the axle, the bearing and the housing are each made of, separately |
| Cut ends, drilled holes and site-modified sections | The coating is a barrier, and every hole made after coating is a place the barrier stops | Ask what touch-up system is supplied and who applies it |
Published stainless steel guidance also gives cleaning intervals by environment and grade, and two of the cells in that table read not suitable rather than a number of months. That is the most useful thing in it. When a published table says a grade is not suitable for a coastal location, no maintenance schedule rescues it.
We sell aluminium windows and doors, and this is the part where we say what our catalogue does and does not support. Nothing below is a claim of suitability for a coastal site.
| What we publish | What it actually is | What it is not |
|---|---|---|
| 240 hours salt spray resistance | A published test result on one series, on a coated substrate and a composite bond | Not a coastal qualification, not a service life, and not transferable to any other series in the catalogue |
| 5,000 newtons shear resistance | A strength figure on the same single series | Not a wind rating and not a water penetration rating |
| Thermal values of 1.3, 1.6 and 1.7 | System values, each attached to a named series | Not whole-window values, not values for the sliding series, and not values produced under the rating system used in North America |
| Load figures of 200, 220 and 400 kilograms | Three separate measurements taken on three separate products | Not one ranking. Printing them in descending order in one column is the single most common way our catalogue is misread. |
| 304 stainless steel high load hinges | The only stainless component we publish with a grade number, on one casement series | Not a coastal specification. Published stainless guidance lists this grade as not suitable in coastal locations. |
| Stainless steel mesh, 40 and 80 mesh counts | A mesh aperture, which is a count of openings per inch | Not an alloy grade. Our catalogue does not publish the mesh alloy. |
| 6060-T66 profile across the range | A true statement about every series we list | A differentiator. If it is on every line, it cannot help you choose between them. |
| Sun room category | A category page exists on this site | A product. The page currently lists none. If you need a purpose-made sun room system, we will say so rather than offer you a door. |
| Two production centres | Foshan and Zhaoqing, both in Guangdong | A single answer to where will my goods be made. Ask, and get it in writing. |
We do not publish air infiltration, water penetration or structural test ratings, maximum sash sizes or sash weights by series, glass rebate dimensions, or a coating specification by a named performance class. Those are not omissions we can fill in an email from memory. They are things you should ask us for, in writing, against your own opening sizes and glass build-up. You can see the kind of work we have done at different scales on our project pages, and reach us directly through the contact page.
Everything above reduces to a block you can send. Fill in the blanks. The point of each line is not the answer, it is that the question is documented before anyone quotes.
| Line | What to write | A useless answer looks like |
|---|---|---|
| 1 | Distance from the site to the water, in metres, and whether that is to the mean high water line or to the nearest visible shore | Coastal area |
| 2 | Prevailing wind direction relative to each elevation, and which elevation the sun room faces | A drawing with north on it and nothing else |
| 3 | Which corrosivity category the design assumes, and what chloride deposition figure it was based on | Marine grade |
| 4 | Sun room category, and which document it is being declared under | Category IV, with no document named |
| 5 | Which coating specification is specified, by number, and whether the seaside class or the highest performance class is required | High quality powder coating |
| 6 | Alloy grade of every stainless component, listed separately for fasteners, hinges, locks, mesh and rollers | Stainless steel throughout |
| 7 | Isolation method at every contact between stainless and aluminium | No answer, because nobody thought of it |
| 8 | Design wind pressure for the site, and who calculated it | A value copied from another project |
| 9 | Water penetration test pressure required, and the standard it is tested to | Watertight |
| 10 | How the outside of the roof will be reached, by whom, and how often | A maintenance schedule that only lists windows |
| 11 | Touch-up system supplied for cut ends and site-drilled holes, and who applies it | Standard touch-up paint |
| 12 | Which production centre the order will be made in, and confirmation that the coating batch is from one batch | Our factory |
| We can give you | You must ask for it from us or from your designer | Neither of us can supply |
|---|---|---|
| Series drawings with frame depth, sash thickness, mullion dimensions and track heights | Water penetration, air infiltration and structural ratings for your opening sizes | A corrosivity classification for your site, which has to be measured or declared by your designer |
| Profile alloy and temper, and wall thickness by series | Maximum sash size and sash weight for the glass build-up you intend | A local approval, which is issued by your authority to a tested configuration and an applicant |
| The published test results we hold, with the series they belong to | Coating specification by a named performance class, with the applicator's certificate | A maintenance schedule that covers roof glazing, which no published schedule does |
| Hardware platform by series, and the configuration options available | Alloy grades for fasteners and mesh, as separate line items | A guarantee that a coastal exclusion clause elsewhere will not apply to you |
| A straight answer that our sun room category is currently empty | The production centre for your order, in writing, before production | A distance threshold that every document will accept |
| Situation | Why this piece does not help | What to do instead |
|---|---|---|
| Your site is inside a named high velocity hurricane zone | The applicable requirements are set by that jurisdiction and attach to a tested configuration, not to a series name | Work from the local product approval and the tested configuration, then ask what can be built to match it |
| You are replacing glass in an existing coastal sun room | The frame's coating and its remaining life are already fixed, and the new glass will outlast them | Assess the frame and fasteners first. Re-glazing a corroded frame buys glass, not time. |
| You want a retractable or removable enclosure | A sun room kit that opens is a different structural problem, and usually a much lower wind category | ｄｅｃｌａｒｅ the lowest category honestly and price the whole replacement cycle, not the first installation |
| Your openings are small and individually framed | Corrosion and wind behave differently on a small opening than across a glazed structure | Treat each opening on its own. A small 36 x 36 casement window in a coastal wall is a window specification, not a sun room specification. |
| Your main concern is overheating | That is a solar control and ventilation question, and we have separate pieces on both | Read the shading and ventilation articles, then come back to this one for the parts that survive the salt |
| Your project is more than a few kilometres from the water and sheltered from onshore wind | Most of the clauses above will not be triggered, and over-specifying costs real money | Write the distance and the wind direction down, then let the clauses that do apply be the ones you pay for |
There is no distance at which you need to worry and none at which you can stop. Published thresholds run from about four hundred and fifty-seven metres to ten thousand metres, and the same house can be coastal to one document and inland to another. What actually determines the dose is wind direction, shelter, height above ground and whether rain reaches the surface, and none of those are distances. Write your distance in metres so nobody has to guess the unit, then specify by measured exposure rather than by how far you are.
As a marketing phrase, it is not attached to any test we can find. As an engineering question, it resolves into three specific things: the alloy and temper, the coating system and the pretreatment, and the material of every fastener and contact. Ask for those three separately. If a supplier answers with the phrase marine grade, none of the three has been answered.
Not in the way the question assumes. The coating specification sets a minimum film thickness for a reason, and the highest performance class asks for eight readings in ten at thirty micrometres or more with no single reading below twenty-five. But the coating is a barrier, not an allowance, and the failures we see at the coast start at cut ends, drilled holes and fastener heads, where thickness is irrelevant. Ask for the specification number and the pretreatment, and ask what happens at a hole.
No, and this is the most expensive assumption in the category. Stainless steel is a family, not a grade, and published guidance lists some of that family as not suitable for coastal locations. Our own catalogue prints one stainless component with a grade number, and it is one of the grades that guidance says not to use there. Separately, stainless against aluminium is a dissimilar metal couple, so a stainless upgrade can move the corrosion onto the profile. Name the grade for each component and ask for isolation at every contact.
Everything, and it is the step people skip. Two of the five categories in the model code carry no listed requirement for water penetration resistance at all, and wind-driven rain is the dominant water load at the coast. The category is declared on a form by the applicant, the designer or the owner, so the classification that decides whether your sun room has to keep driven rain out is a decision made before anybody chooses a profile.
Stop using the word. Write the distance in metres, name the datum you measured it to, state the prevailing wind direction for each elevation, name the corrosivity category or the chloride deposition figure the design assumes, name the coating specification by number and class, and list the alloy grade of every stainless component as its own line. None of those depend on anyone's definition of coastal, and every one of them is checkable after delivery.
