Glazed partitions: how to read and write the specification

What a glazed partitions specification has to pin down

A specification for glazed partitions exists to make two quotations comparable and to make a dispute resolvable. If a clause does not do one of those jobs, it is decoration. The clauses that matter fall into six groups: the glass make-up, the framing and finish, the perimeter and junction detailing, the acoustic requirement, the doors and ironmongery schedule, and the setting-out and tolerances. Miss any one of them and the gap between two prices will be bigger than the gap between two specifications.

We read a lot of these documents. The common failure is not that they are too loose, it is that they are tight in the wrong places. A spec will run to four paragraphs on powder coat pretreatment and then describe the glass as “toughened safety glass to suit”. The contractor is then free to choose, and will choose the cheapest compliant option, which is exactly what the document invited.

• Glass: nominal thickness, toughened or laminated, interlayer type where laminated, standard referenced, edgework, and any applied coating or film
• Framing: system depth, face width, material, finish standard and colour reference, and whether frames are visible on one or both faces
• Perimeter: head detail including deflection allowance, floor track and fixing substrate, abutment profiles at walls, columns and mullions
• Acoustics: target expressed as a laboratory or field value, the element it applies to, and whether the figure covers the door and the plenum
• Doors: leaf size and make-up, hardware schedule by item, closing device, seals, and whether the opening is on patch fittings or a frame
• Setting out: datum, who takes site dimensions, permitted deviation, and what happens when the building is out of tolerance

Writing the glass line so it can only mean one thing

Start with thickness and process. For single glazed partitions, “10mm clear float glass, thermally toughened to BS EN 12150” is unambiguous. If you want laminated, say so and say what the interlayer is: a standard clear PVB laminate behaves quite differently from an acoustic PVB, and a stiff ionoplast interlayer different again. Writing “laminated glass to BS EN 14449” without naming the interlayer leaves the acoustic and structural behaviour open.

Then safety. Glass in the critical locations described in Approved Document K has to be safety glass, and in practice that means toughened or laminated glass meeting the impact classification in BS 6206, Class A at the top of the range. Internal partitions and glazed doors generally sit in those critical locations, so the clause is not optional, but writing it does not make the partition better than another one that also complies. Treat it as a floor, not a feature.

Edgework is the clause everyone forgets and everyone notices. An arrissed edge is a hand-dressed edge for glass that will be hidden in a frame. A flat ground edge is matt and even and fine where it is semi-visible. A flat polished edge is clear and used on exposed edges, which includes every vertical butt joint in a frameless run and every exposed edge of a door leaf. If the spec does not say “flat polished edges to all exposed edges”, a frameless job can arrive with ground edges and a visibly frosted line at every joint. That is not a defect, because nobody asked.

If a surface treatment is involved, keep the glass clause and the film clause separate. Acid-etched or sandblasted glass is a change to the glass and has to be processed before toughening. Applied frosted vinyl is a film on finished glass and can be changed later. They look similar at a glance and they are not the same purchase, and the one you want depends on whether the pattern is permanent.

Describing the framing, the finish and the junctions

Name the system depth and face width, even if only as a maximum: “slim aluminium framing, face width not exceeding 50mm” tells every tenderer the same thing. For finish, reference a real coating standard and a real colour. Architectural powder coating to BS EN 12206 with a RAL or BS 4800 reference, stated as matt, satin or gloss, is enough. Anodised is a different process with a different tolerance on colour matching, so do not write the two as alternatives unless you genuinely do not mind which arrives.

Junctions are where a specification earns its fee. Say that the head detail must accommodate structural deflection and state the allowance if the structural engineer has given you one. Say what the floor substrate is and whether there is a raised access floor, because fixing a track into a floor panel rather than through to the structural slab is the difference between a stable wall and a wobbly one. Say what happens where glazed partitions abut plasterboard, columns, perimeter trunking and window mullions, and make it the contractor’s duty to land the partition on a mullion centre line where the geometry allows.

One line worth including: require the contractor to state, in the tender, what they have allowed for making good the ceiling and floor finishes at the junction. It is a small amount of money that otherwise lands on the client at the end of the job, and asking the question in advance tells you which tenderers have thought about the installation and which have priced a product.

Specifying the acoustic requirement without writing nonsense

The commonest bad clause in glazed partitions specifications is “acoustic partition, minimum 45dB” with nothing else. Forty-five decibels of what, measured how, applying to which part of the construction? Laboratory sound reduction for a glazed element is given as a weighted index, Rw, derived from measurements made to BS EN ISO 10140 and rated to BS EN ISO 717-1. A figure measured on a finished room on site is a different quantity, usually reported as a standardised level difference, and it will always be lower than the laboratory number for the glass alone.

So write it properly. State the laboratory Rw you require for the glazed element, state separately what you require of the door, and state whether the partition is required to extend to the structural soffit or be accompanied by a plenum barrier. If a tested room performance is genuinely required, say that it will be tested, say by what method, and expect the price to reflect the risk somebody has taken on. The detail behind these numbers, and why the door usually decides the outcome, is covered on our acoustic glass partitions page.

Doors and ironmongery: schedule them by item

Never let the door hardware disappear into “ironmongery to suit”. List the items: hinges or patch fittings, pivot or floor spring with its closing force, handles with their finish and fixing centres, lock case and cylinder, intumescent and acoustic seals if they apply, and a door stop. State the leaf: thickness, toughened or laminated, edgework, and the size of any cut-outs, because cut-outs and holes must be made before toughening and cannot be added afterwards. A toughened pane cannot be drilled, notched or trimmed once it has been through the furnace. Every change to a hole is a new pane.

On closing devices, resist the instinct to specify the most robust option everywhere. A concealed transom closer or a floor spring belongs on a main meeting room door, a reception entrance or anything on a busy route. On a quiet internal office door it is money spent on a specification line. By the same token, do not accept a surface-mounted overhead closer on a frameless glass door in a reception, where it will be the only thing anyone looks at.

Setting out, tolerances and who owns the dimensions

Glazed partitions are made to measure from site dimensions, and the specification should say plainly that the contractor takes and owns those dimensions after the structure, floor and ceiling in that zone are complete. That single sentence prevents the most expensive argument available on a fit-out: panels manufactured from drawing dimensions, delivered to a floor that is 18mm out, and nobody willing to pay for the remake.

State what deviation the finished work must be within, and state what the contractor must report rather than absorb. If the floor falls 15mm across a run, the installer can take it up in the track, scribe it, or set the glass level and leave a tapering shadow gap. All three are legitimate and they look different. Requiring the contractor to propose the approach in writing before manufacture puts the decision where it belongs.

The clauses to delete, and the quote lines to challenge

Delete “or similar approved” wherever it appears next to something you care about. Either you have a performance requirement, in which case write the performance, or you have a named product, in which case name it and let tenderers propose alternatives against the performance. “Similar approved” means the decision gets made later, by whoever is under most pressure.

Delete blanket laminated glass. Specifying laminated throughout an internal office partition is a habit carried over from overhead and barrier glazing. Toughened glass to BS EN 12150 satisfies the safety requirement for the critical locations in an ordinary internal screen. Laminated earns its place where the glass forms a barrier and has to hold a load to BS 6180, where the glass must stay in the opening after breakage, where acoustic performance is the point, or where security or a specific risk justifies it. Otherwise it adds cost and weight for nothing.

And challenge any quotation that offers a lower price against your specification without listing the departures. A tender that is ten per cent cheaper has usually changed something: a shallower head channel, ground edges instead of polished, a surface closer instead of a floor spring, or a thinner frame with a different finish standard. Ask for the departures in writing. If you want someone to read your specification back to you, point by point, with the departures named, that is what we do at survey. The glass itself is cut, edged, polished and toughened in our own Wembley workshop, which is also why we can tell you what a clause will cost before you commit to it.