China Sliding Window Fabrication Drawing: Seven Sheets, One Number That Is Really a Band, and the Signature That Turns a Sentence Into a Cut Length

We have argued elsewhere that a specification clause is a sentence that must later be proved or disproved, and that four operations in a sliding window leave nothing visible in the finished product. This article starts where those two ended. A clause becomes enforceable only when somebody turns it into a number, and that conversion happens on exactly one document: the fabrication drawing.

There Is No Such Thing as the Drawing

Ask a supplier for a sliding window fabrication drawing and, nine times out of ten, you will be sent an elevation. It is the wrong sheet. An elevation tells you what the window will look like from one side. It cannot be cut from, it cannot be glazed from, and it cannot be ordered from. It is the cover page of a package, and the package has seven sheets.

Here is the definition we will use for the rest of this article, because almost every dispute about drawings comes from two people using different ones. A fabrication drawing is not a description of a window. It is a set of instructions that three departments read independently of each other: the saw, the glass supplier, and the hardware buyer. Anything that one of those three cannot read off the package was never specified. It was merely described, and a description cannot be failed.

A published Chinese fabrication-office standard for door and window packages lists the sheets and, usefully, the order in which they are bound. That order is itself a statement of priority.

The published binding order runs cover, index, profile order list, accessories schedule, glass schedule, glass fit table, optimisation list, split elevation, sections, itemised list, fabrication and assembly drawings. Note what that order says. The two documents everyone asks for first, the elevation and the render, are the ninth and the absent. The three documents that actually determine what arrives are the first three.

Three Numbers, One Name, and None of Them on the Same Sheet

The reason a fabrication drawing cannot be replaced by an email is that the word size does not mean one thing. GB/T 5824-2021, the Chinese standard for opening size systems for doors and windows, sets up a three-level dimension system that is worth learning even if you never build in China, because every window industry on earth has the same three levels and most of them have never written them down.

• Marking dimension. The coordination dimension. The 2021 edition added a definition note saying explicitly that the marking dimension is the nominal dimension. It is a name, not a measurement. The standard even encodes it: a window opening nominally 1200 wide and 1500 high is written as the six-digit code 120150.
• Construction dimension. The actual design dimension, of the opening and of the window, taken from the locating line.
• Installation gap. Given the symbol J, with sub-gaps J1 through J8 depending on which side of the locating line you are standing on.

Now the sentence that should be printed at the top of every approval sheet. Clause 5.2 of that standard says the construction dimension may be greater than, equal to, or less than the marking dimension, depending on where the locating line sits. Three legal answers to the same question. A frame that is larger than its own name is not an error; a frame that is smaller than its own name is not an error either. Which one you get is decided by a clause most buyers have never read.

Clause 5.3 then lists what you need to get from the marking dimension to the construction dimension: the installation form, the installation method, the thickness of the wall finish, and the structural gap. Published readings of that clause give the two installation methods their own gap figures. Dry installation, where a metal subframe is set into the opening first and the window is fixed to it after the wet trades finish, is given as J not less than 15 mm. Wet installation, where the window goes straight into an unfinished opening and the gap is filled during finishing, is given as 10 to 20 mm. And the finish thickness is counted inside the total, so that J equals J1 plus J2.

Read that list again and notice who owns each item. The installation form belongs to the detailer. The installation method belongs to the builder. The finish thickness belongs to the tiler or the renderer. The gap is the arithmetic result of the three. The factory owns none of them, and the factory is the one that has to print a number.

So this is what actually happens. An enquiry arrives saying 1200 by 1500. No installation method, no finish thickness, no locating line. Somebody in a drawing office makes three assumptions, writes the resulting frame size on a sheet, and sends it for approval. From that moment the assumption looks like a fact, because it has a dimension on it and a border around it. A callout such as 36x80 entry door is a marking dimension in its own system, in exactly the same way: it is the one number that will never appear on a cutting list.

A published shop-drawing guide for aluminium windows puts the practical rule plainly. There is no single installation gap suitable for every aluminium window; the allowance must suit the selected system, the wall construction, the installation method and the expected movement. It also says to record who supplied the dimensions and whether they were field verified or taken off design drawings, and not to calculate manufacturing dimensions by scaling a drawing or by applying an unconfirmed deduction to every opening.

The Number on the Drawing Is a Band, Not a Number

Suppose the marking and construction questions are settled, and the drawing says 1200. What does it mean? Not 1200. GB/T 8478-2020, the aluminium door and window product standard, gives the manufacturing tolerances in its Table 6, and they are not rounding errors.

A drawing that says 1200 is therefore not a contract about a window. It is a contract about a band roughly three millimetres wide, plus a separate promise about squareness and a separate promise about the step at every joint. Two windows can both be compliant and differ from each other by more than the gap a fitter tries to shim.

Now look at the row nobody dimensions. The frame to sash lap width is the tightest tolerance in the whole table for windows, plus or minus 1.0 mm, and on a sliding window the lap is where the interlock, the seal line and the anti-derailment geometry all live. It is the dimension that decides whether a panel sits quietly in its track or chatters in a wind. It is almost never dimensioned on an approval drawing, because it is not a visible dimension, and because nobody asks.

Notice also the asymmetry with doors, at plus or minus 2.0. If the product you are approving is a sliding door rather than a sliding window, the applicable column changes, and a drawing that quotes the window figure has quietly claimed a tighter promise than the standard requires.

The Groove Is a Sum, Not a Dimension

Here is the most expensive omission in a window drawing package, and it is almost universal. The drawing specifies the glass. The drawing does not specify the groove the glass sits in.

JGJ 113-2015 does not give a groove size. It gives two formulas, in clauses 12.1.2 and 12.1.3, and a table of minimum values to feed them.

For insulating glass, the published table gives two rows. For 4 plus A plus 4 and 5 plus A plus 5 builds, the front and back clearance is 5.0 mm with sealant glazing and 3.5 mm with gasket glazing, the engagement depth is 15.0 mm, and the edge clearance is 5.0 mm. For 6 plus A plus 6 and thicker, up to 12 plus A plus 12, the clearance is 7.0 mm with sealant and 5.0 mm with gasket, the engagement depth is 17.0 mm, and the edge clearance is 7.0 mm.

Do the arithmetic for one of the most common insulating builds in the world, 6 plus 12A plus 6. Its nominal thickness is 6 plus 12 plus 6, which is 24 mm.

• Gasket glazed: 5 plus 24 plus 5 gives a groove width of 34 mm.
• Sealant glazed: 7 plus 24 plus 7 gives a groove width of 38 mm.
• Either way, the groove depth is 17 plus 7, which is 24 mm minimum.

The same standard sizes the blocks that hold the glass off the metal. A setting block must be at least 50 mm long, as wide as the glass plus both clearances, and as thick as the edge clearance. A location block must be at least 25 mm long. Published glazing practice adds that setting blocks are placed at the quarter points of the bottom rebate.

There is a published design review note from a Chinese curtain wall engineer that is worth repeating here, because it is the cleanest illustration of what goes wrong. A detail showed a laminated insulating unit around 60 mm thick with an engagement depth of 18 mm. The author's point: 18 mm is barely above the 17 mm floor that applies to a build a fraction of that thickness, the published table does not even contain a row for that glass, and beyond the table the engagement depth is a calculation against wind uplift and self weight, not a lookup. The detail had been built on many projects and had never visibly failed. That is exactly the problem. The groove is the one part of the window that fails late, fails suddenly, and fails in a way that nobody connects back to a number on a sheet.

Why the Catalogue Is an Index, Not the Drawing

This is the part where we talk about our own numbers, and the honest version is slightly uncomfortable. A catalogue is a collection of system properties and visible properties. A fabrication drawing is a collection of the things in between, and the things in between are almost all of them specific to your opening.

Read down the middle column. Every single published number is either a property of the system or a property of what you can see. Not one of them is a property of the joint, the groove, the cut, or the route the water takes. Those are the four things that fail.

This is also why a drawing package has to be written per product family and cannot be templated. A sliding window set and a custom bi fold doors set share a cover sheet and almost nothing after it: different load paths, different panel parking, different hardware schedules, different assembly sequences. In the same way, a vertical bi-folding doors manufacture package and a horizontal slider package do not use the same sheet list at all.

The Two Drawings Are Mirror Images

A published Taiwanese site engineering checklist for reviewing aluminium window fabrication drawings contains one line that deserves to be on every approval email ever sent, and to our knowledge it has never been written in English for an export audience.

The architect's door and window elevation is drawn as an exterior view. The aluminium fabricator's elevation is drawn as an interior view. The two documents that must agree with each other are mirror images.

The same checklist gives the method for catching the error, and it is not "look more carefully". It is to walk the floor plan clockwise or counter clockwise and check the left and right edges and the opening direction against it, rather than trying to compare two pictures that were drawn from opposite sides of the wall. Every handing error ever made was made by someone comparing two drawings that were both correct.

It also gives the rule for sliders, and it is the kind of rule that sounds like taste until you work out the consequence. The panel that is used most often should sit on the inner, interior side track. Which sounds ergonomic. Then remember that on a horizontal slider the insect screen is mounted on the outside of the operating panel. So the panel you touch every day is the one nearest to you, the screen is outboard of it on the outer track, and the fixed panel, which is the one most likely to take a knock from a ladder or a ball, is on the far side of both.

And the checklist says the quiet part out loud, in as many words: the dimension on the door and window drawing is not the dimension on the aluminium fabrication drawing. Everything in the previous section is the long form of that sentence.

The published section drawing convention from a Chinese fabrication office is in the same spirit, and equally easy to get wrong when the package crosses a language. Section details must show both a horizontal and a vertical cut; on the horizontal section, the bottom of the sheet is the exterior; on the vertical section, the left of the sheet is the exterior. A reviewer who assumes the opposite will read every drainage slope backwards and every thermal break upside down, while agreeing with every number.

What a Slider Adds to the Package

Take a competent casement drawing set and ask what a sliding window adds to it. The answer is not fewer sheets. It is nine items, and six of them are invisible in the finished window.

The Drawing Decides Whether the Glass Can Ever Be Replaced

Nothing about a slider's finished appearance tells you this, and it is the single most consequential thing on the sheet.

Published service instructions for horizontal sliding windows give a fixed order of work. To remove the fixed panel you must first remove the operating panel: unlock it, slide it to the middle or beyond, lift it up and over the bottom track, and bring it into the room. Only then can you reach the fixings of the fixed panel, which on many products are accessed from the exterior. And some fixed panels cannot be removed at all, because the glass is set directly into the frame and the replacement path is a call to the manufacturer.

Published glazing guidance adds the two numbers that make any of this possible. The head channel usually has somewhere around 10 to 15 mm of clearance above the panel, and that clearance is the entire reason a panel can be lifted out at all. And on some systems the panel has to be slid to one specific position where a removal notch lines up before it will come out. If that notch is not on the drawing, it is discovered on a ladder, with a panel in two hands.

The same guidance covers the glazing beads, and the advice is a sequence rather than a rule. Start with the shortest bead, usually one of the verticals, because beads overlap at the corners and taking them out in the wrong order cracks the neighbouring piece. Pry at the middle first and work toward the ends, never at the corners. Set the blocks at the quarter points. Every one of those is a statement about order, and order is the one thing a photograph of a sample can never show.

Three Lines That Separate a Drawing Set From a Picture

A published Chinese fabrication office specification contains three lines that very few buyers ever see, that almost no supplier volunteers, and that are the clearest available test of whether you are looking at a real package.

• Profile cut lengths are given to one decimal place.
• The water blocking edge on an openable sash is the calculated theoretical dimension minus 2 mm. The threshold is minus 1 mm.
• The 0.2 mm gap between an adapter frame and the main frame is not included when calculating cut lengths.

The same source gives the kerf allowance: 25 mm for a 45 degree cut, and 15 or 10 mm for a square cut. This is the line that explains why a cutting list can never be read off an elevation. Every mitred corner on a sash consumes 25 mm of bar. Four corners is 100 mm of profile per sash that never appears in the window, never appears in the elevation, and is paid for.

None of these three lines is visible in a finished window. All three determine whether the window works. That is the practical answer to the question "can't I just approve from the sample I was sent?" No. The sample is evidence that a sample exists. The three lines above are evidence that somebody has done this before.

The Signature Is a Trigger, Not a Courtesy

The most quoted sentence in a published aluminium window shop drawing guide is also the least followed. The release record should make it possible to answer one question: exactly which windows may be made, to which revision?

Everything else in that guide is a mechanism for answering it.

• Issue a complete package: drawing numbers, revisions, dates, schedules and the specifications they reference.
• Revise affected documents together. A change to an elevation also changes the schedule, the glass specification and the installation detail. Changing one is not a revision; it is a contradiction.
• Issue a specific release naming the revisions, the window marks and the quantities.
• Have the manufacturer acknowledge the release and mark superseded documents in its production records.
• Avoid an isolated approved message that does not name the drawings it covers. If a status such as approved as noted is used, agree in writing whether it permits production and how the notes are incorporated.
• For a partial release, list the approved items and keep everything else explicitly on hold, including any separate authorisation for early material buying.
• An unresolved item should have a named reviewer and a stated resolution before the affected units are released.

A published Chinese fabrication process note puts the same idea more bluntly, and it is worth quoting because it changes the tone of the whole exercise. All dimensions and technical parameters must be confirmed in writing by all parties, signed and sealed, before they become the sole basis for production, and that written confirmation is an important legal document. Not a step in the schedule. A legal document.

One more item belongs in that written confirmation, and it is the one most often left out: who performs the first adjustment on site. On a sliding window with rollers, keeps and an interlock, the difference between a window that seals and a window that nearly seals is a hex key and a quarter turn. If that is not assigned to a named party, it will be assigned by default to whoever is holding the tool, and it will not be recorded.

Six Things That Look Like a Fabrication Drawing and Are Not

What the Drawing Cannot Do

• It is not evidence. A performance value written on a drawing is not by itself proof that the proposed window achieves it. A whole window thermal value and a centre of glass value are different measurements, and only one of them is what a project requirement usually asks for.
• It does not carry an approval. Approvals are issued by the authority having jurisdiction to an applicant, for a tested configuration. A drawing can support one. It cannot be one.
• It cannot fix an opening that does not exist. If the openings are not built yet, the drawing records an assumption. Say so on the sheet, and say who owns the assumption.
• It does not install itself. It tells you where the anchors are. It does not tell you who sets the frame level, who seals the perimeter, or who signs the interface with the wall.

Where that leaves us is a short and honest list. We can issue a revision controlled package with drawing numbers, marks and quantities, in metric, with cut lengths to one decimal place. We can put your opening dimensions on the elevation rather than only ours. We can print the glass build next to the roller rating on the same sheet. We can draw the drainage as a route with outlet positions, and the thermal break section with the anchor positions on it. And we will say in writing which published figures are system values and which are not published at all. What we cannot do is sign for your opening, your wall, or your local code.

What We Publish and What You Still Have to Ask For

The Drawing Review Card

This is the part to copy into an email. Twenty lines. If a supplier can fill fewer than fifteen of them from the package they intend to build from, you do not have a fabrication drawing; you have a quotation with pictures attached.

Ten Questions, and the Answers That Sound Like Answers

Six Questions People Actually Ask

Do I need a fabrication drawing if I am ordering standard sizes?

Yes, and the reason is not the size. It is the mark. The moment more than one opening is involved, the drawing is the only document that connects a window to a location, a handing and a screen. A schedule of standard sizes without drawings produces a container full of correct windows in the wrong rooms.

Can I approve it by email?

Yes, and it is probably the best way, because email leaves a record. But the email has to name the drawing number, the revision, the marks and the quantity. A reply saying approved, with a drawing attached, has recorded that a conversation happened.

Why is the frame smaller than my opening?

Because a gap is required, and its size depends on the installation method and the finish thickness, neither of which is the factory's to choose. If the drawing does not say which method and which finish thickness it assumed, the gap is a guess with a dimension on it.

The drawing says 1200. Is that the frame?

Ask. It may be the marking dimension of the opening, in which case the frame is smaller and the number still has to be resolved through the installation method. It may be the unit construction dimension, in which case it is subject to the tolerance band. It may be the visible glass width, which is a third thing again. A drawing that uses one number without saying which of the three it is has not finished being drawn.

Can I change the glass after approval?

Before the saw, yes, and it costs nothing but a re issue. After it, the change runs through four documents at once: the groove width and depth, the roller rating and maximum panel size, the sash weight the hardware was chosen for, and the glass schedule. That is why a published guide treats a glass substitution as a coordinated drawing revision, not a note.

When do I get the drawing?

Put it in the order. Name the drawing package as a deliverable, with a revision number, and require a written production release naming revisions and quantities before anything is cut. The sequence you want is drawing, revision, release, production. The sequence that causes trouble is deposit, production, drawing.

The Short Version

1. There is no such thing as the drawing. There is a seven sheet package, and the elevation is the sheet that cannot be built from.
2. A fabrication drawing is a set of instructions read by three departments that never speak to each other: the saw, the glass supplier and the hardware buyer.
3. A marking dimension is a name. A construction dimension is a measurement. The gap between them is decided by the installation method and the finish thickness, which belong to the builder.
4. Every dimension on a drawing is a band. Ask for the tolerance table, and for the frame to sash lap width.
5. The groove is a sum, not a dimension. The same glass needs a 34 mm or a 38 mm groove depending on how it is glazed.
6. The catalogue is an index. Every number in it is either a system property or a visible property, and the four things that fail are neither.
7. The architect's elevation is drawn from outside. The fabricator's is drawn from inside. They are mirror images, and both are correct.
8. On a slider, the panel most likely to be broken is often the one that cannot be lifted out. Ask whether the fixed panel is removable or direct set.
9. Cut lengths to one decimal place, kerf allowance stated, and the water blocking edge minus 2 mm. These three lines are invisible in the finished window.
10. An approval that does not name a revision number has approved a conversation.
11. A performance value on a drawing is not evidence, and a drawing is not a local approval.
12. Ask for the drawing as a named deliverable in the order, with a revision number, before any production release. It is the last document on which a change is free.