European Tilt and Turn Window with Dual-Matrix Sealing: Eight Layers, Three Lines, and One State Nobody Declares a Class For

Ask ten people what the sealing system on a European tilt and turn window is for, and you will get the same answer three ways: it keeps out water, it keeps out air, and it keeps out noise. All three are true. Not one of them tells you what to write into a specification, and not one of them tells you what to ask for when a quotation arrives with the words “multi-layer sealing” printed on it.

Here is the sentence this article is built on. A tilt-and-turn window is bought for the position it is never tested in. The handle has several positions. Water, air and wind resistance are declared for exactly one of them — the closed one. The ventilation position that made you want the window in the first place has no declared class anywhere in the European system, and no manufacturer anywhere can quote you one.

That is not a criticism of anybody. It is what the standards measure. But it does mean that when someone sells you a sealing system by counting its layers, the count and the performance are two different conversations. This piece is about closing the gap between them. We have written elsewhere on this site about what a passive rating asks of a window, about what the hardware carries, and about how to read the numbers on a casement spec sheet. This one starts where those ended and stays on the seal line itself.

Three circuits, only two of which belong to the window

Before counting anything, it helps to know what is being counted. A window assembly has three places where things meet and have to be sealed, and they are bought, drawn and warranted by three different parties on three different drawings.

Circuit	What it separates	Who owns it	What happens when it fails
Sash to frame	The moving ventilator against the fixed outer frame. This is the circuit everybody means when they say “the seal”.	The window manufacturer	Draughts, whistling, water tracking around the sash, noise returning
Glass to sash	The double-glazed unit sitting in its rebate and held by the pressline (glazing bead)	The window manufacturer and the IGU supplier together	Water inside the rebate, a unit that rattles, eventually a failed unit edge
Frame to wall	The window against the building: air barrier, water barrier, insulation line	The builder, the installer, and whoever signed the wall detail	Everything the owner will describe as “the windows leak”

Most complaints that arrive at our inbox belong to the third row. Almost every marketing claim belongs to the first. Keep that asymmetry in mind for the rest of this article, because a lot of disappointment in this industry is not a product failure — it is a row-three failure billed to a row-one product.

What “eight layers” can and cannot mean

The AW90 inward-opening series we build publishes a sealing system described as a dual-matrix eight-layer construction, naming five families of strip inside it: extended, composite, welded, threaded and dense. We publish those names. We do not publish, in a table you can read on a product page, exactly which line of the section each one sits on, and neither does almost anyone else in this industry. That is the single most useful thing to know about the phrase.

A count of layers answers none of the questions that matter. The questions that matter are: how many continuous circuits are there, how many chambers do those circuits create between them, what are the corners made of, and what is the compression each one is held at by the hardware. Two strips on the same line are one line of defence that somebody counted twice. Three strips on three lines create two chambers, and the chambers are doing more of the work than the strips are.

Two gaskets or three: the AD and MD question nobody explains

European fabricators use two short German abbreviations that almost never appear in English-language marketing, and they explain more about a window than any layer count. AD stands for Anschlagdichtung, the two-gasket arrangement: one rebate seal on the sash, one on the frame. MD stands for Mitteldichtung, where a third gasket is added in the free space between sash and frame.

What does the third one actually do? The answer most people guess — “more airtight” — is the least interesting part of it. Fabricators who publish on this topic describe four consequences, and the second one is the one worth knowing:

• It creates a still-air chamber in the middle of the joint, which helps the thermal performance of the sash-and-frame assembly.
• It separates the hardware from the wet zone. In an AD window, the drainage hardware and the locking hardware share the rebate space. In an MD window, the centre seal keeps water, dirt and the drainage channel on one side, and the espagnolette, keeps and cams on the other. Published European descriptions are explicit about this: the hardware works in dry conditions, and so is not exposed to rust and dirt.
• It keeps dust and insects from travelling inward through the weep and drainage holes — which must be open, and therefore are always also open to something.
• It improves acoustic performance, for the same reason it improves everything else: another discontinuity between inside and outside.

A German window glossary describes the centre seal as having its own water-collection chamber that gathers penetrating or condensing water and channels it back outside. Read that twice. The middle gasket is not primarily a barrier. It is a partition that lets two incompatible things coexist in the same joint — a drainage path that has to be wet, and a mechanism that has to stay dry. Every claim about eight layers, six layers or twelve layers is worth exactly as much as the answer to “and where does the water go?”

The outer / middle / inner model

One European systems page lays out the three-level model in plain language, and it is worth repeating because it explains why a three-line window behaves differently from a one-line window even when the gasket material is identical:

Position	Its job	What it is paired with	It is not responsible for
Outer	First line against driven rain and wind pressure before they enter the profile cavity	Drainage slots and weep channels that take what gets past it back to the outside	Being the last line. It is designed to let some water in, then deal with it
Middle	Traps air in a dead zone; divides wet drainage space from dry hardware space	The drainage path on one side, the locking gear on the other	Carrying load. It is a divider, not a structural member
Inner	Final air seal on the warm side; supports acoustic performance	The interior finish line and the reveals	Stopping bulk water. If water reaches it, the outer two have already failed

The corollary: a window that has been built with only outside seals and no managed drainage will look fine on day one. The failure mode is corrosion of hardware you cannot see, which shows up years later as a sash that will not close properly, and gets diagnosed — wrongly — as “bad gaskets”.

The position nobody declares a class for

European windows regulated under EN 14351-1 ｄｅｃｌａｒｅ three familiar scales, and all three are measured on a closed, locked specimen:

Property and standard	Scale	Top of scale	Measured with the sash:
Air permeability, EN 12207	Class 1 to 4	Class 4, tested to 600 Pa	Closed and locked
Watertightness, EN 12208	1A to 9A, plus E above 600 Pa; A means unshielded, B means shielded	9A at 600 Pa of combined spray and air pressure	Closed and locked
Wind resistance, EN 12210	Class 1 to 5 for pressure (400 to 2000 Pa), plus deflection suffix A, B or C	Class 5 with the stiffest deflection limit	Closed and locked

Now put that next to how the window is actually used. In the tilt position the top of the sash leans inward. Air enters along the sides and warm air leaves at the top — that is the entire purpose of the position, and it means the sealing circuit is deliberately interrupted at one edge. Several manufacturers publish a maximum tilt opening; one North American fabricator of European-profile windows limits it to about 130 millimetres, small enough that it is described as secure ventilation and too narrow for entry. That is a real and useful feature. It is also, by definition, not a sealed state, and it is the state the window sits in for most of the night.

There is a fourth position that deserves its own paragraph, because it is the most misunderstood feature on this whole window. Many European systems offer a micro-ventilation or night-vent catch at an intermediate handle angle. One technical description of the hardware puts it at roughly the 45-degree position, engaging a catch on the top stay that holds the sash open a gap of about two to three millimetres while every locking pin stays engaged inside its keeper. Other hardware makers place their night-vent position differently — Roto, for example, describes a staged night-ventilation function at the 135-degree handle position on several of its hinge sides. The number is not universal. The principle is: a controlled leak, held by locks that are still doing their job, designed to be open for hours.

To be fair, this is also why the European lineage of this window matters. The reason it survives rain in the tilt position reasonably well is not the gasket; it is geometry plus drainage. The inner heart of the design is a pressure-equalised drainage path: water that gets past the outer line lands in a chamber, is directed to slots, and leaves. Descriptions published by European fabricators point at exactly this — pressure-balance drainage chambers, multilevel gasket systems, and full-perimeter compression as the seal of record. Which brings us to the sentence worth writing into a specification: do not specify “watertight in the tilt position”. Specify “measured and drained in the tilt position”, and ask for the drawing that shows where.

The corner is where the seal lives or dies

A rectangular window has four corners. Every continuous circuit has to negotiate all four, and in almost every real complaint that is where it went wrong. The sealing industry has essentially three answers to the corner problem, and the differences between them are more consequential than the difference between six, eight or ten layers.

Corner method	How it is made	Strength	Limitation
Vulcanised / welded	Heat and pressure cross-link the polymer chains across a cut, so the joint becomes one continuous piece of rubber	Works at any angle and therefore works on arched, angled and mullioned units, where other methods cannot go. Fabricators writing publicly on the subject put the welded joint at roughly 80 percent of the parent strip’s tensile strength	Quality depends entirely on mould, temperature and clamping discipline. A badly made weld is worse than a good mitre
One-piece bending	A continuous length is bent around the corner without cutting	No joint at all on simple rectangles; visually uniform	Published European commentary notes that the bend distorts the section on the inside of the curve, reducing contact area, and that complex shapes are not possible
Cut and mitred on site	Two lengths meeting at 45 degrees, sometimes bonded	Cheap, field-serviceable, no tooling	A butt joint rather than a mitre leaves a triangular void that water will find. Use 45-degree mitres, never square butt joints

Read the AW90 published feature list again with this table open and the word welded stops being decoration. A named strip family called “welded” inside a multi-layer system is claiming something specific about how those circuits turn their four corners. It is also the kind of claim a purchaser can actually verify with a sample, which puts it in a different category from adjectives.

Three field practices that quietly undo a good gasket

Because gaskets are the serviceable part of the system, they are also the part most often damaged by service. An Australian aluminium specialist publishing on glazing gaskets names the mistakes plainly, and all three are worth carrying into a toolbox talk:

• Never install under tension. Rubber is elastic and it is tempting to pull it taut around the perimeter. Stretched gasket slowly recovers toward its original length over weeks, then opens gaps at the corners. Lay it in with zero tension — a strip that is a millimetre too long is far better than one a millimetre too short.
• Mitre your corners, do not butt them. Cut both ends at 45 degrees so the joint closes as the section compresses. Use a sharp blade; a dull cut crushes the rubber and gives an uneven mating face.
• Never use a petroleum lubricant to get it into the channel. Petroleum products make EPDM swell and soften. Silicone spray or lightly soapy water does the same job without the chemistry.

Sealing is a state, maintained by hardware, not a material property

Here is the second sentence this article is built on, and it is the one that saves the most money: a compression gasket is not doing anything until something presses it, and the thing that presses it is a mechanism.

The mechanism on a European tilt-and-turn window is an espagnolette: a drive gear behind the handle moving a rod or set of rods in the sash groove, through corner drives that turn the motion 90 degrees at each corner, driving mushroom-headed cams into keeps fixed in the outer frame. Published descriptions of this family of hardware use the same word for what those cams do, and it is the right word: they clamp. A UK hardware maker describes its multipoint espagnolette as a bidirectional clamping system with adjustable compression, available in two cam heights, on standard handle centres with a standard spindle — which also tells you something useful: the compression is adjustable, which means it is also mal-adjustable.

This produces three practical consequences that rarely get said together:

1. Eight layers with half its lock points out of adjustment is a worse window than two layers with all of them right. The layer count and the commissioning are not the same subject.
2. Every modern European hinge group offers multi-axis adjustment — laterally, vertically, and in how hard the sash bears onto the gasket — precisely because buildings move and season after handover. Adjustment is expected maintenance, not evidence of a defect.
3. The whole thing is rated for a sash weight, and the sash weight is mostly glass. Roto’s published figures put its aluminium hinge side at 130 kg in the standard version with the option of raising it, and sash rebate heights up to 2800 mm; the heavy Power Hinge variant reaches 200 kg for tilt-and-turn and 300 kg for turn-only. Those numbers are not bragging. A sash too heavy for its hardware drops, and a dropped sash stops compressing its gasket evenly.

The AW90 addresses exactly this problem from the other end: it publishes 360-degree distribution of locking points and works with Winkhaus hardware, with C-slot ROTO hardware as an option. Full-perimeter lock distribution is often read as a security feature. On a tilt-and-turn window its first job is something duller and more valuable: making the compression uniform all the way round, so that there is no corner where the gasket is politely touching its opposite number instead of being squeezed into it.

C-slot, U-slot, and why “European groove” is not one groove

This is the most under-discussed line on any aluminium specification. “Euro groove” usually means a standardised channel machined into the sash to accept hardware from many suppliers, commonly around 16 mm wide. But there are two families, and confusing them costs money at replacement time. A Chinese industry article describing the difference puts it clearly: the aluminium version comes in 15 mm and 20 mm widths and is known as the C slot, fixed by clipping and embedding into the metal; the 16 mm version associated with plastic windows is known as the U slot, fixed by screwing through to reinforcement. Aluminium is formable enough to take either.

Why does any of this belong in an article about sealing? Because a standardised groove is what lets you ｒｅｐｌａｃｅ a worn cam, a stiff corner drive or a tired tilt stay in a decade without replacing the window. European and Australian commentators both make the point: the groove is geometry, not a guarantee — the hardware also has to match the axis dimension, the sash overlap, the allowable sash weight, the cam spacing and the routing depth. But without the groove you have no spare parts market at all. A sealing system you cannot keep adjusted is a sealing system with an expiry date.

The servicing advantage nobody puts in a brochure

An outward-opening casement on the fourth floor needs scaffolding, a cradle or a rope technician to touch anything on its outside face. An inward-opening tilt-and-turn window can be adjusted, re-gasketed and re-glazed from inside the room, on a Tuesday, by one person. European fabricators describe the install sequence in the same spirit: the sash can be removed so the frame goes in first, is levelled and sealed, and the sash is hung and adjusted afterwards — staged installation that protects the very geometry the seal depends on.

Owners rarely buy a window for this reason. Tenants, facility managers and hotel operators absolutely should. If your project has forty windows above the second floor, ask the question “what does it cost to re-gasket this” before you ask what the U-value is.

Sound finds the gap that heat and water walk past

Air, water and noise travel through the same discontinuities, but they are not equally sensitive to them. A joint that passes a water test comfortably can still be a wide-open door to sound, because air-borne noise exploits remarkably small apertures. In practical terms this means acoustics is the most sensitive diagnostic tool you own: if a room is noticeably noisier than the spec suggested, the cause is almost always a circuit that is not continuous or not compressed, long before it is a glass specification problem.

The European framework treats this honestly. Acoustic performance is declared as a single figure — the weighted sound reduction index Rw in decibels — not as a class. Published ranges for windows put common values roughly in the thirties to high forties depending heavily on the glazing build-up rather than the frame. Note also that the acoustic number is dominated by the glass and its build-up; the window’s job is to let that glass perform by not leaking around its edge. If your brief is acoustic rather than thermal, say so at enquiry stage, because the lever is usually asymmetric pane thickness and laminated interlayers, and the same reasoning applies whether the opening is a tilt-and-turn window or an acoustic swing door.

Where you own the risk: the third circuit and its junctions

Everything above describes the window. Most field failures happen in the wall. European fabricators selling into North America make this point directly: best practice treats the window as part of the continuous air and water control layers, rather than relying on a nail-fin and a bead of sealant. That framing is the correct one everywhere, not just in timber-framed construction.

Two corollaries follow, and they both scale with the amount of opening you are buying:

• Every additional infill adds corners, and every corner is a place a continuous line has to turn. A single-opening window has four. Add a mullion or a second leaf and you add junction after junction. This is exactly why the entry door with sidelight configuration deserves an extra hour of detailing compared with the same design without one: you have doubled the number of places where two different seal geometries meet in one opening.
• Seal perimeter scales faster than floor area. The most demanding case is all glass. When the majority of the enclosure is fenestration, the total length of joint you own becomes the dominant variable, and the difference between a continuously-welded circuit and a field-mitred one stops being academic. The same arithmetic governs a pop up sun room or any other fully glazed room: count metres of joint, not square metres of glass.

Reading the symptoms: which circuit is complaining

Once you accept that there are three circuits and one of them belongs to somebody else, diagnosis becomes much faster. This table is written for the person standing in the room holding the complaint, not the person holding the brochure.

Symptom	Which circuit	Most likely cause	First action
Draught felt at the handle side only	Sash to frame	Lock point nearest the handle not clamping, or the keep is misaligned	Adjust that cam, then the neighbouring one. Not a gasket replacement
Draught along the bottom rail in winter, none in summer	Sash to frame	Seasonal movement plus a hinge that has lost a little height	Vertical adjustment on the hinge. Re-check in the opposite season
Water on the internal sill after wind-driven rain	Sash to frame, plus drainage	Weep slots blocked, or the drainage path sealed by another trade	Clear the drainage path first. Escalate to the frame before blaming the gasket
Handle has become stiff; sash needs a shove	Hardware	Compression set too high at one or more cams, or sash has dropped onto a stay	Reduce compression at that point. Forcing the handle damages the drive gear
Fine in the morning, stiff in the afternoon	None — this is physics	Thermal expansion of the frame and sash	Leave a little more clearance. Replacing hardware to cure thermal movement is the most expensive mistake in this trade
Whistling at a specific wind direction	Usually frame to wall, not the sash	Air path around the outside of the frame, not through it	Test with the sash taped. If it persists, it is the wall, not the window
Noise noticeably louder than the schedule suggested	Any of them, plus glazing	A small discontinuity somewhere around the perimeter, or a glazing build-up that was never specified	Paper test around the whole perimeter. Sound is the detector; the fix is elsewhere
Fogging between the panes	Insulated glass unit	Failed unit edge seal — not the window’s gasket system at all	Unit replacement. This is one of the few complaints that is genuinely almost always a defect
Condensation on the indoor frame face	None	Warm moist air meeting a cold surface — a ventilation and temperature question	Improve ventilation and air movement. Note this is the opposite claim to the row above
Insects or grit inside the frame cavity	Missing middle line	Drainage zone not separated from the hardware zone	Check whether the specified build has the centre line at all. Then clear the drainage

What we publish, and what you still have to ask for

Every ALPES series sheet has gaps on it, and we would rather name them than have you discover them on site. The right-hand column below is the part worth reading.

What is published	What it does and does not mean	Why there might be a gap next to it
Dual-matrix eight-layer sealing, naming extended, composite, welded, threaded and dense strip families	Names the components. Does not publish which line of the section each one occupies	Component names fit on a page; a cross-section does not. Ask for the section
Full injection adhesive process across frame, mullion, glass sash and screen	Addresses the joints. Note it is a different mechanism from a gasket and does the same job at the corner	Two different things both called sealing. Nobody’s fault, but a common source of confusion
Opening and fixed both use a full closed-chamber pressline structure	This is the glass-to-sash circuit, and it is specified for both ventilating and fixed elements	The rebate depth, which is what actually limits glass thickness, still has to come off the drawing
360-degree locking point distribution	Gives uniform compression, which is the precondition for any gasket doing anything. Often misread purely as a security claim	We do not publish the number of points. Ask for count, position and adjustment range per point
Winkhaus hardware, with C-slot ROTO as an option	Names the mechanism family and therefore the spare-parts ecosystem	Model numbers, sash weight rating and cycle class belong to the hardware maker. Ask for them by name
240-hour salt spray and 5,000 N shear resistance	Coating-and-substrate durability, and the strength of the thermal break composite bond. Neither is a water, air or wind rating, and neither transfers to another series. Notably, 240 hours also appears as a corrosion grade in the hardware sector’s own scale	These answer different questions entirely. They are the ones most often misquoted as performance ratings
Thermal value K = 1.3 for the AW90	A system value, not a whole-window value for your opening and not a certification	A thermal number belongs to a size, a glazing build-up and a standard. Change any and you have a new number
Frame wall width 90 mm; glass sash thickness 90 mm; mullion published as 72/4 mm	Three different measurements that happen to share digits. The first is depth into the wall, the second is the sash build-up, neither is a glass dimension	On the mullion pair we read the first number as depth and the second as visible face, following the convention used elsewhere on this site — but confirm both against the section rather than taking our word for it
Air permeability, watertightness and wind resistance classes	Not published for any series in our current line	Absence of a published class is not evidence that the window is worse. It means there is nothing to compare. Ask for a calculated or tested value for your own opening size and configuration, under a named standard
Cycle-test figures such as 30,000 operations quoted on some hardware	A bench result on a mechanism, not a service life for a window. In Europe this family of tests is classed under EN 13126-8, where the published classes step at 10,000 and 20,000 cycles	A cycle on a hardware rig and a year of operation on a building are not the same measurement. Ask what was cycled, at what sash weight, in what configuration

Ten lines to put in your enquiry

Most enquiries that arrive at a factory contain the opening size, a drawing reference and a request for a price. What comes back is therefore a price, and the comparison afterwards is between prices rather than between windows. The last column is the reason this table exists.

Ask	What a good answer contains	Sounds reasonable, carries no information
Which classes, and on which specimen	Standard name, class, test report number, laboratory, date, and the specimen drawing with your sizes on it	“Meets European standards”
How many continuous circuits between sash and frame	A number, plus which one is outer, middle and inner, plus a section drawing	“Multi-layer sealing system”
How each circuit turns its corners	Vulcanised, one-piece bent, or field-mitred — stated per circuit, with the arched units addressed explicitly	“Seamless corners”
Gasket material and hardness	Compound family, hardness figure, and the recovery value the supplier quotes after compression	“High quality EPDM”
Glazing rebate depth in millimetres	A dimension on a drawing. This is what limits your IGU build-up	“Standard double glazing”
Hardware brand, model, sash weight rating and cycle class	Four concrete answers, cross-checked against your heaviest sash including its glass	“German hardware”
Groove type and axis dimension	C-slot or U-slot, stated width, axis dimension, and confirmation the hardware actually fits that combination	“European standard groove”
Locking point count, positions, and adjustment range each	A layout drawing plus the range of movement at each point	“Fully adjustable”
Behaviour and policy in the tilt and night-vent positions	An honest statement that those positions carry no declared class, plus what the fabricator recommends and what the drainage does	“Watertight in all positions”
Replacement gasket part number and who stocks it	A part number, a local stockist, a unit price basis, and a lead time	“Spare parts are always available”

When the sealing system is the wrong thing to optimise

It is worth saying out loud that spending more on an eight-layer system can be entirely wasted money in some projects. If the wall opening does not have a defined air barrier, or if nobody has drawn where the window sits in relation to it, the best sealing system available will be asked to cover for a detail nobody drew. Six situations in particular:

• The opening detail has no air barrier continuity drawn, and the installer is expected to work it out
• Nobody has decided whether the junction is barrier-sealed or drained-and-vented, so both happen by accident
• The schedule will never be commissioned — no one will walk the building adjusting every cam before handover
• The budget cannot also cover the reveal detail: sub-sill flashing, external slope, and a drainage discharge that someone actually has to connect
• Local spares do not exist and nobody will import them — in which case a simpler, more replaceable gasket geometry may serve the building better
• The windows see very little weather and no acoustic load, where the money is better spent on glass

Frequently asked questions

Does a higher layer count mean a better window?

Not by itself. Two strips on the same line are one line counted twice; three strips on three lines create two chambers and behave completely differently. What you want is the number of continuous circuits, what their corners are made of, and what keeps them compressed. Then ask for the section.

Is the tilt position watertight?

It is a ventilating position with an opening along the top edge, so no. Good tilt-and-turn windows manage rain in tilt by geometry and drainage rather than by sealing. No classification exists for that position, and any supplier who quotes you a class for it has misunderstood the question.

Can you supply EN 12207, EN 12208 and EN 12210 classes?

We do not publish them for any series in the current line. That is a gap on our sheet, not a statement about how any particular window performs. Ask for a value calculated or tested for your own opening size, glass build-up and hardware configuration, named against a standard, and read it together with the specimen drawing, because a class without a specimen is only half an answer.

Can the gasket be replaced later?

On an inward-opening tilt-and-turn window, yes, and that is part of the reason to choose the type: everything is reachable from inside the room. Order spare length with the original shipment, install it slack rather than stretched, mitre the corners, and keep petroleum products away from it.

Do I need the middle gasket?

It earns its place for a reason most people do not expect: it keeps the drainage zone and the hardware zone apart, so your locking gear lives somewhere dry. If you are buying for a long service life, a coastal exposure, or fine dust, that matters more than the modest thermal gain.

What actually causes most complaints?

In our experience the order of frequency runs: the joint with the building, then commissioning, then drainage that somebody sealed up, and only then the gasket itself. The fastest diagnostic is still the paper test — trap a strip in the closed sash and pull it at each lock point. Where it slides out freely, that point is not clamping.

The short version

• There are three circuits — sash to frame, glass to sash, frame to wall — and only the first two are the manufacturer’s. Most complaints live in the third.
• Counting layers tells you nothing that a cross-section would not tell you in ten seconds. Ask for the drawing.
• The middle line is not an extra air seal. It is the partition that lets a wet drainage zone and a dry mechanism coexist in one joint.
• Every European class you have been quoted was measured closed and locked. Nothing is declared for tilt or for micro-ventilation.
• Four corners decide more than eight strips. Welded, one-piece or field-mitred — get it in writing, per circuit.
• A gasket is a compression state maintained by hardware. Budget for commissioning, and for re-commissioning after the first full year of seasons.
• Never seal the outside continuously and never block drainage. Water is supposed to get in there and leave by another route.

If you want the drawings, the section with every seal named, or the honest list of what we can and cannot ｄｅｃｌａｒｅ for your opening, write to us with your sizes, your city and the exposure your building actually sees. That last one changes more answers than people expect.