The Abbey Estate

The challenges of assessing a historic building

Westminster Abbey is prioritising sustainability, with a clear goal to reduce its carbon impact, ideally by 2030. The Deanery was identified as one of the most energy-intensive residences on the estate, requiring thorough investigation. Thick masonry walls, timber panelling and original metal-framed windows made any traditional assumptions that might be made about thermal performance unreliable.

 

Keegans was brought in to conduct a detailed assessment, but standard evaluation methods proved insufficient for a structure with such a complex history.

 

our retrofit coordinator, Justyn Tiptaft, explained, “If you just do a visual survey, you miss half the picture. It’s easy to assume a building is losing heat through its walls from outdated or failing insulation, but without measuring, you don’t know the true extent. We needed real-world data to understand what would work and what wouldn’t.”

 

Bringing in cutting-edge measurement techniques

Keegans adopted technology developed by Build Test Solutions (BTS) to gather accurate measurements of the heritage property. Pulse air permeability testing was selected because it could assess airtightness without disrupting the building’s delicate structure. Heat3D was used to measure the U-value of the main solid brick walls of the building, as well as the 13th century stone-walled extension. Temperature and humidity monitoring was also carried out over several weeks to assess moisture risks and the impact this could have on the delicate materials, artwork, and furniture in the Deanery.

 

The results were surprising. The airtightness level was measured below 10m³/m²h@50Pa – far better than expected for a building of this age. The wall U-values were also much lower (better) than assumed, both for the solid brick walls of the main building and also the 13th-century stone walls that make up part of the Deanery.  This insight enabled Westminster Abbey to be confident that investing in secondary glazing and targeted draught-proofing was the better option over internal insulation options.

 

	Predicted	Measured	Difference
Main wall U-value, rendered solid brick (W/m2K)	1.7	0.8	-0.9 (-53%)
Wall-U-value, 13th Century fair-faced stone (W/m2K)	2.0	0.9	-1.1 (-55%)
Air Permeability (m3/h.m2 @ 50Pa)	15	10.46	-4.54 (-30%)

 

We used the measured U-values and air permeability to calibrate their SAP model of the Deanery to the actual building performance. This calibrated model gives more accurate estimates of energy demand and cost, and in turn more accurately predicts the effect of retrofit measures.

 

SAP Prediction	Original Model	With Measurements	Difference
HTC	2,671	2,141	-530 (-20%)
Space heating requirement (kWh)	118,155	97,757	-20398 (-17%)
Space heating per m2 (kWh/m2)	185	153	-32 (-17%)
Annual energy demand (kWh)	143,068	119,174	-23894 (-17%)
Annual energy cost	£6,390	£5,361	-£1,029 (-16%)
SAP Rating	45	54	9 (20%)

 

Anna noted: “We were expecting the walls to be a big problem, but they actually performed well. That allowed us to shift our focus to simpler, less intrusive fixes like improving heating controls and tackling draughts.”

 

For Keegans, the testing validated our approach of our heritage retrofit suggestions.

 

Justyn said: “This is exactly why accurate measurement matters. Without this data, we might have recommended changes that weren’t necessary, or worse, missed easy wins that will make a real difference.”

 

The next steps

 

This project highlights the importance of using real-world data instead of relying on theoretical models. Every historic building is different, and assumptions can often be misleading, leading to less effective retrofit investments. In-situ testing provides clarity and ensures that retrofit measures are both effective and appropriate.

 

Richard Jack, technical director at BTS, reflected on the project and said: “People often assume you can’t accurately measure the performance of a historic building, but that’s just not true. This project proves that if you use the right tools, you can get reliable data and make smarter decisions that make the building suitable for future generations, without compromising on the historic character.”

 

This project demonstrates Keegans' ability to deliver innovative, data-driven solutions tailored to the unique needs of heritage buildings.

 

Westminster Abbey now plans to apply similar testing across its estate. By prioritising measurement-led retrofit strategies, the project was a great example of how the heritage retrofit sector can use new technology to make properties more energy-efficient, without using any destructive methods.

 

Learn more about BTS’s product on the website https://www.buildtestsolutions.com/.