How is glazing replaced in a building that stays in use?

Removing a window leaves a hole in the building. On an occupied site that hole is a security breach, a weather exposure and a fall risk at the same time.

So the unit that comes out is the unit that goes back in, that day.

One opening at a time

The sequence is deliberate: remove, prepare, install, seal, secure. Then the next one.

Opening up a whole elevation and working across it is faster and it leaves a building that cannot be closed at four o'clock. On a school or a public facility that is not an option.

Where a unit cannot be completed in a day, because a replacement is damaged or a frame needs remedial work, the opening is boarded and made secure and weathertight before the site is left. That is a planned contingency rather than an improvisation.

Glass is the hazard

Removing old glazing produces broken glass, and it produces it above people if the work is at height.

The area below and around is cleared and protected before the unit is touched. Old glass is removed into containment rather than dropped, and the area is swept and checked before it is reopened.

On a school this is the control that matters most, because small fragments in a play area are not acceptable at any concentration.

Where the existing glazing is not safety glass, which is common in older buildings, removal is more hazardous and is treated accordingly.

What is behind the frame

Glazing replacement frequently uncovers more than the scope allowed for.

**Rot or corrosion in the frame or the reveal,** particularly in older timber windows where water has been getting in for years.

**Failed flashing,** which is usually the reason the window was leaking in the first place. Replacing the unit without fixing the flashing puts a new window into the same problem.

**Lead paint** on older frames, which changes how they can be prepared and disposed of.

**Asbestos** in older putty, sealants and surrounding materials. Where it is suspected it is tested before disturbance, not after, under the same approach as [asbestos in school refurbishment](/answers/asbestos-in-school-refurbishment).

These are the latent conditions that produce variations, and identifying them at tender through investigation is considerably better than finding them in week two.

What the replacement has to achieve

**Safety glazing** where the location requires it, which includes doors, side panels and low-level glass. Many older installations do not comply and the replacement brings them up.

**Fall protection.** Openable windows above a certain height need restriction, and on a school that requirement is applied strictly.

**Thermal and acoustic performance** where the brief calls for it. The seal between the frame and the wall decides whether the specified performance is delivered, and it is the detail most often compromised.

**Operation and security.** Hardware that works, locks that engage, and restrictors that cannot be defeated.

Working at height

Anything above ground level is managed under the [work at height](/answers/working-at-height-on-occupied-buildings) controls: exclusion zones below, secured access equipment, tools tethered, and the zone held outside working hours.

Access equipment beside an occupied building is secured at the end of each day so it cannot be climbed.

Making good

A window replacement is not finished when the glass is in.

Internal reveals, sills and architraves are made good and painted. External sealing and flashing are completed and inspected. The area is cleaned to a standard that lets the room go back into use immediately.

On a classroom that turnaround matters, because the room is needed the next morning. Coordinating it with the [internal refurbishment](/answers/painting-and-refurbishment-in-occupied-buildings) rather than leaving it as a second visit is what takes the room out of use once instead of twice.

[Talk to Monument about a glazing project](/contact).