Granite window frame design: fix the width, the projection and the edge first
Granite window frame design comes down to three numbers: face width, projection off the wall, and edge treatment. With 30mm stock slabs the projection is the slab thickness itself, and a 100mm strip yields 10 linear meters per square meter — about 204 windows out of the 100 m² minimum order.
How do you design a granite window frame section?
A granite window frame design is fixed by three numbers and nothing else: face width, projection off the wall, and edge treatment. Once those are fixed the section is fixed, and everything else is a consequence. Width sets how many linear meters come out of one square meter of slab; thickness sets how far the frame can stand off the wall; the edge decides whether the piece goes on the polishing line at all. Edges come in three forms: square, with no work; chamfered, with a cut bevel; and stepped, where part of the thickness is ground back to leave a reveal line. The stepped edge takes an extra grinding pass, so it runs longer than the other two and uses up more slab thickness. Fix width first, then thickness, then edge. Do it the other way round and the drawing tends to show a profile the factory cannot cut.
How far can the frame project from the wall?
One layer projects exactly one slab thickness, plus the adhesive bed. Our stock is a 30mm polished slab, so a single-layer frame stands about 30mm off the wall before the bed; how thick that bed ends up depends on how true the wall is and on the fixing method, and we do not pin a number for it on the drawing. The projection follows slab thickness alone; a wider or taller opening does not change it. If you need more projection there are only two routes. Laminate two layers and you get 60mm, but the joint between them has to be dealt with, and a bad joint becomes a line that holds dust and water. Or order a thicker slab: that is not a stock item, so batch size and lead time are quoted separately rather than carried by the five-day stock schedule.
How wide should the face be, and how does width drive the material bill?
The face width is simply the strip width you cut. Adding width only adds material; it does not change the projection, so a wider band does not stand further off the wall. The conversion is direct: the strip width decides how many linear meters come out of a square meter. At 100mm you get 10 linear meters per square meter, at 150mm you get 6.67, at 80mm you get 12.5. Across the same 100 square meters an 80mm strip yields 1,250 linear meters and a 150mm strip 667, so the narrow strip gives 1.87 times the length. Settle the width on the cutting list first and judge it on the elevation second: a narrow band keeps the elevation light, a wide one holds a large opening, and that is a visual call made after the material is counted.
| Face width | Linear meters per m² | Linear meters per 100 m² | Effect on material |
|---|---|---|---|
| 80mm | 12.5 m | 1,250 m | more meters per m² |
| 100mm | 10 m | 1,000 m | stock cutting width |
| 150mm | 6.67 m | 667 m | fewer meters per m² |
Why does a window surround come in three strips instead of four?
Because the surround body is three strips: one head across the top and one vertical leg on each side. The fourth side is the sill, which has its own section and slope and is costed as a sill, not as surround. All four sides need an edge, but only these three come out of the same strip, so they can be cut in one pass. Whether the top of each leg needs one extra width depends on the joint: a mitre, or legs running up past the head to cover its ends, needs it because that length meets the head at the corner; where the head caps the legs it does not, since the head covers the leg end. The bottom never needs an allowance because it sits on the sill face. Mitre or butt at that corner gets one line here: it changes how the strip is cut, and the door frame corner article covers the rest. One more rule is geometry rather than a clause: the front edge of the sill must not sit further back than the outer face of the surround. Water leaves the sill edge, falls, and if it lands on the surround face it runs down that face onto the wall.
How much material does one window take?
Four formulas, written for a mitre or for legs running up past the head: head = clear opening width + 2 × strip width; each leg = clear opening height + 1 × strip width; total linear meters = head + 2 × legs; area = linear meters × strip width ÷ 1000. Switch to the head capping the legs and the legs give that allowance up: the head keeps its two ends, the legs drop back to the clear height, total 4700mm, which is 0.47 m² and 0.2 linear meters less per window. Run it on a 1500 × 1500 opening with a 100mm strip: head 1700, legs 1600 each, total 4900mm, which is 4.9 linear meters and 0.49 m²; the 100 m² minimum order ÷ 0.49 works out at about 204 windows. Then the same opening on a 150mm strip: head 1800mm, legs 1650mm each, 5100mm in total and 0.765 m² per window, so the same 100 m² covers about 130 windows. For loading: one 20ft container takes 346 m², roughly 28 tonnes at 2.7 t/m³.
| Corner layout | Head | Each leg | Total | Area per window |
|---|---|---|---|---|
| Mitre joint (base case) | 1700mm | 1600mm | 4.9 m | 0.49 m² |
| Butt joint, head caps the leg ends | 1700mm | 1500mm | 4.7 m | 0.47 m² |
| Butt joint, legs cap the head ends | 1500mm | 1600mm | 4.7 m | 0.47 m² |
What has to be on the drawing before you place the order?
Four groups, six figures: clear opening width and height, strip width, slab thickness (which is the projection), and the corner joint plus edge treatment. The opening is measured on site, so write the measured figure on the drawing, not the word "approx". Strip width is the designer's call, and it fixes the material bill the moment it is set. Thickness follows from the projection you want; 30mm is stock, anything thicker means asking about lead time first. Joint and edge are settled between you and the processor, because how much a stepped edge can grind back is limited by slab thickness. Ask the processor for the minimum thickness they can hold without chipping, and do not copy a number from another project. Write all four groups and the factory can quote material and hours in one pass; leave one out and the answer comes back as it depends.