Transforming a Historic University Library with Bespoke Slimline Double Glazing

At CN Glass, we were proud to work with Lady Margaret Hall, part of the University of Oxford, on a complex heritage window replacement project for their historic library building. This project required careful balancing between preserving the building’s historic character and improving thermal performance to create a more energy-efficient and comfortable learning environment for students.

The Challenge: Deteriorating Single Glazed Windows

The existing timber-framed windows had significantly deteriorated over time – with rotting wood, warped frames, and outdated single glazing offering very little thermal insulation or soundproofing.

This is a common issue faced by schools, colleges, and universities housed in listed or heritage buildings, where original windows no longer meet modern energy efficiency standards.

In total, 105 casement windows across three floors needed attention, including 16 large arched windows at the top of the building, all requiring specialist templating and on-site routing to ensure a perfect fit.

Our Heritage Window Solution


Following an extensive site survey and consultation with the university’s facilities team, we proposed a tailored solution designed to upgrade the thermal performance of the windows while preserving the building’s heritage character.

The project involved the installation of new bespoke hardwood timber casements, manufactured at our Oxfordshire based factory and fitted with eco-slim heritage double glazing units filled with Krypton gas.

These specialist heritage double glazed units provided the essential thermal efficiency needed for a more comfortable learning and study environment, while being sympathetic to the building’s architectural heritage.

Wherever possible, our team retained the original window hardware, replacing only where necessary with matching brass fixtures and fittings to ensure continuity with the original design.

All glazing installation was carried out using traditional heritage putty, in line with heritage building conservation guidelines – a key requirement for window replacement projects in historic schools, colleges, and university buildings.

Working Safely in a Live University Environment


As with any window replacement project in a working school or university, we needed to minimise disruption. Our team worked carefully around students using the library for study, ensuring noise reduction, scheduling work flexibly, and fully protecting all furniture, books, and floors to avoid dust or accidental damage.

In addition, we:

  • Used a cherry picker and scissor lifts to access upper floor windows safely.
  • Carefully templated all arched windows to ensure millimetre-perfect replacements.
  • Routed out frames on-site to accommodate the slimline double glazing units.
  • Sourced and installed heritage-style brass fittings to replace original hardware that was no longer fit for use.

The Results


The completed project delivered a dramatic improvement in thermal performance, reducing heat loss and improving energy efficiency within this historic university building.

The upgraded heritage windows also enhanced acoustic performance, contributing to a quieter and more comfortable study environment.

By combining sensitive heritage restoration with modern double glazing technology, we preserved the character and charm of the Grade II listed library, ensuring the new windows looked entirely in keeping with the building’s historic façade.

The project was completed on time, with minimal disruption to students and staff, demonstrating our expertise in working in live school and university environments – a vital consideration for educational window replacement projects.

Why Choose CN Glass for Heritage Window Replacement in Schools, Colleges & Universities?

Whether your project involves a Victorian school building, a listed university library, or a historic college campus, CN Glass offers specialist heritage window solutions tailored to the education sector.

Our team has the experience and craftsmanship to:

  • Improve thermal efficiency while respecting conservation requirements
  • Manufacture and install bespoke timber windows and slimline heritage glazing
  • Work flexibly in live educational environments
  • Handle the challenges of listed buildings and planning approvals

If your school, college, or university is considering a heritage window replacement project, contact us today to discuss your requirements and arrange a free site survey.

Explore Our Work

See more of our school and university window replacement projects here.

Find out more about our bespoke heritage windows and glazing solutions here.

Ready to discuss your project? Contact us today.