Cordless Child-Safe Roller Retrofit on 12 School Reveals to Meet BS EN 13120

BS EN 13120 caps the accessible length of any operating cord or chain at 220 mm above floor level when a hazard cannot be otherwise removed, and requires a breakaway connector or a floor-anchored tension device on every retained loop. On a retrofit of 12 classroom reveals, the specification skipped the cord question entirely. Every unit went in as a spring-tensioned cordless roller, operated by a bottom-bar pull. That single decision removed the tension-device drilling from the scope and shifted the labour onto bracket alignment and spring calibration.

The reveals measured between 1180 mm and 1640 mm wide. Fabric was a 1 percent openness screen weave in white-backed grey, chosen so daylight control did not black out the room during projector use. Each blind was cut to a 4 mm deduction per side inside the reveal, leaving a 3 mm light gap that the facilities team accepted for a face-fixed alternative rejected on aesthetic grounds.

Why cordless changed the fitting order

A corded roller is hung, then the chain side is tensioned to a wall or sill anchor. A cordless spring roller reverses that. The spring is pre-charged inside the tube before the blind leaves the workshop, and the installer sets the final tension by rolling the fabric down and back up two or three times after the brackets are fixed. Get the bracket height wrong and the spring either stalls halfway or snaps the bar into the head with enough force to mark the fabric.

On the 12 reveals, brackets were set with a laser line struck across the full block so every head rail sat at one datum. That mattered because the classrooms shared a continuous run of glazing and any step between blinds would read immediately from the playground. The datum also let two fitters work the run in parallel, one measuring and marking, one driving fixings into the timber sub-frame behind the plaster reveal.

Spring calibration ate the time the tension anchors would have taken. Each cordless tube needed between two and five cycles to settle, and three of the wider units at 1640 mm were returned to the bench for an extra half-turn of pre-load because the bottom bar crept downward under its own weight after an hour. That creep is the known trade-off on wide cordless rollers, and it is why some specifiers cap cordless width at 1500 mm and move wider openings to a motorised tube.

The width limit nobody wants to discuss

Cordless spring mechanisms lose reliability as fabric weight climbs. Above roughly 1600 mm on a standard 38 mm tube, the spring that lifts the blind also has to hold it at any stop point, and a heavier drop overpowers the hold. Three of the 12 units sat right on that boundary and needed the extra pre-load noted above.

Motorised was quoted and declined

The original tender included a motorised curtain track fitting option for the hall adjoining the classrooms, using a Silent Gliss panel glide system on the wider expanse of glazing. The school declined it on cost and on the maintenance question of who recharges or rewires forty motors across a building. For the classroom reveals themselves, motorisation was never priced, because a 1 percent screen roller under 1640 mm carries no load that justifies a motor.

Heat loss and the case for a different fabric

A 1 percent screen weave does almost nothing for heat retention. It scatters glare and cuts solar gain in summer, but its open structure lets convection currents run straight through against the glass in winter. Where a room’s heating bill is the driver, a Duette cellular shade changes the physics. The trapped air in the honeycomb cell sits between the room and the cold glass surface, and independent glazing tests have put the added resistance of a well-fitted cellular shade in a broad range that meaningfully lifts the effective performance of single or older double glazing.

The school’s classrooms were not specified for cellular shades because the brief was glare and child safety, not thermal upgrade. That was a defensible call for south-facing rooms with projectors running most of the teaching day. It would have been the wrong call for the north-facing staff offices on the same block, where the complaint on file was cold radiant discomfort near the glass, not glare. Those offices still carry the original vertical louvres and remain outside the retrofit scope.

Cellular shades also demand a tighter reveal fit to work. A cellular blind with a 10 mm gap down each side leaks its trapped air and loses most of the benefit, which pushes the fitter toward a perfect fit frame installation that clips into the glazing bead and seals the perimeter. That frame system is what a cellular retrofit on those offices would need, and it is a different fixing method from the face brackets used on the classroom rollers.

The measurement tolerance tells the story. A screen roller forgives a 4 mm deduction because the light gap is cosmetic. A cellular shade fitted for heat loss cannot forgive it, because the gap is the failure. That difference in tolerance, not the fabric price, is why the two jobs cannot share a survey sheet.

Perfect fit frames and where they stop working

A perfect fit frame clips a slim aluminium carrier into the rubber glazing gasket of a uPVC or aluminium window, holding the blind flush to the glass with no drilling. On sealed casement units it is fast and clean, and it suits both cellular and pleated fabrics. The classroom reveals ruled it out for one reason: the windows were timber sash and box units with no glazing bead to clip into.

That same timber construction raised a separate question the survey flagged. Several of the sash windows showed draught paths around the meeting rail and along the staff-bead. Sash window draught proofing with a brush-pile carrier set into a routed groove would cut that infiltration, and it is a joinery task that sits alongside a blind fit but is not part of it. The facilities log recorded it as a separate line for a later visit, because routing a sash groove and hanging a cordless roller are different trades with different sign-off.

What the sign-off actually checked

Compliance with BS EN 13120 on a cordless installation is quick to verify because most of the standard’s test cases concern cords that are not present. The inspection confirmed no accessible cord or chain existed on any of the 12 units, that each bottom bar returned cleanly to the head without a stop cord, and that fixing pull-out resistance met the bracket manufacturer’s stated figure into the timber sub-frame. The screen fabric’s openness factor was recorded against the projector-use requirement, and the light gap was logged at 3 mm per side.

What the sign-off could not close was the thermal question on the north offices, still running louvres over cold glass. The retrofit answered the safety and glare brief in full and left the heat-loss brief open on a different set of windows, with a different fabric and a different fixing method waiting behind it. Whether those offices get cellular shades or sash draught-proofing first is a sequencing call the joinery survey has not yet resolved.