What is a typical road map to decarbonisation for a historic or listed property?
An Article By: Mesh
Sophie Williams, Building Performance Engineer, at energy consultants Mesh, looks at practical measures for owners of historic and listed homes and buildings to reduce energy consumption and accelerate decarbonisation.
- Discussions start with the architect and heritage consultants to ascertain the level and depth of upgrades – and any constraints – that we can work with without compromising the character of the building. This is particularly important for listed buildings.For example if we are unable to upgrade the single glazing on listed buildings, we would specify secondary glazing. On other projects the glazing could be upgraded but discussions are needed about maintaining the size of the openings and the aesthetic. Slim double glazing may be an option, although it can be a costly addition.
- We then need to look at options for upgrading the building fabric. A full strip-out is often not an option so extensive retrofits are not possible, ruling out new cavity insulation. Adding internal or external insulation poses a condensation risk meaning these options are also not typically available.
- Other upgrading options depend on the building – such as the installation of additional floor insulation if the flooring can be removed. Loft insulation is a good solution to improve thermal performance.
- We always recommend air tightness testing so we can understand how much heat loss there is from the baseline building before improvements are made. This then gives us an indication of the worst-case heat loss to allow plant to be correctly sized for the building.
Thermographic surveys allow us to understand the areas of the building where heat loss is highest and therefore the main target points to address. We would also advise commissioning a survey of the existing architecture ahead of any retrofit works so we know exactly what we are working with.
5. We need to understand if existing radiators can be removed or whether they are required to remain, and if flooring can be removed for the installation of underfloor heating. Can weather walls be removed to allow the relaying of pipework?
6. All of these factors will influence our recommendations for the energy strategy and source of heating. Heat pumps may not be suitable where upgrades have to be minimal and less invasive, as the building may simply not sufficiently air tight and that would result in a very large heat pump that is costly to run.
7. Where pipework cannot be re-layed, we are reliant on pipework that is sized for a boiler. Because of the lower flow rates of heat pumps, boiler pipework is typically not correctly sized for a heat pump, reducing its efficiency and negating its purpose.
8. If solar panels are permitted on the roof and in the grounds, we would typically recommend solar panels.
9. We would then undertake a building fabric optimisation study to model the benefit of different fabric options. This would give us the data needed to develop the energy strategy and assess the most suitable options for heating, cooling and hot water – and the optimum locations for the plant and equipment.
Have you successfully delivered projects on Grade I, Grade II*, or Grade II listed buildings?
Yes and we are working on a number of listed dwellings at the moment. We have delivered many more in the past, as well as Grade I* listed heritage buildings for commercial use.
How do you improve airtightness while maintaining breathability – or is air tightness not as vital as it once was?
Air tightness is important to minimise heat loss and is the result of good construction, or retrofit improvements – but without an extensive retrofit, achieving air tightness becomes very difficult.
High levels of air tightness are vital, not just for reducing unwanted heat loss but also for avoiding heat gain that leads to overheating – a significant issue with climate change.
Leaky buildings lose heat quickly in the winter and equally have the ability to gain heat rapidly in the summer. Mitigating the risk of overheating should be a key part of any energy strategy.
Making improvements with sealing as part of a refurbishment can improve the air tightness, but architects can be cautious in aiming for anywhere near the new build requirements – a minimum of 5 m3/hr/m2. If a building had air tightness of 10 m3/hr/m2, they may aim for 8 m3/hr/m2 if significant improvements were being proposed. To achieve closer to new build standards, an extensive retrofit will be required.
Why are Air Source Heat Pumps (ASHPs) now viable for old country houses when they weren’t a few years back – what’s changed?
Suitability completely depends on the house.
The benefit of an ASHP is that the system is powered by electricity rather than gas or oil. If the system uses renewable energy – such as solar, then there is a clear benefit making these systems a viable option.
Options for listed buildings – such as better quality slim-line double glazing will reduce heat loss and that strengthens the case for ASHPs which otherwise is a marginal gain.
However, public attitudes are changing and many of our clients are keen to remove the need for gas or oil regardless of the expense and complexity. In reality, ASHPs are no more viable than before but the demand for fully electric systems is growing as the perceived value of ASHPs has changed.
What internal temperatures can be achieved without extensive alterations?
Heating systems will achieve the set temperatures they are designed for. They just become more expensive to run without alterations to the building and its fabric.
In summer months older buildings have a higher risk of overheating if they have single glazed windows and a building fabric that is not airtight. However, there is no fixed temperature they will achieve – they are just generally colder in winter and warmer in summer.
What is the expected capital cost of different retrofit packages? and how long to see a return?
There is no set capital cost, it really is project-by-project. Some upgrades never even see a return on investment, the upgrading may be a preference, such as to reduce environmental impact, rather than being driven by cost.
Where do you see the biggest opportunities over the next 10–20 years?
There will be more options – new products, technology improvements and innovations – that are specifically designed for listed and heritage buildings.
We expect our work with heritage officers to increase and that will deliver more flexibility on the scope of upgrades if the aesthetic of the architecture will not be compromised.
As in the commercial sector, we expect the level of collaboration between design teams to increase – building engineers, surveyors, architects and designers. Working together always results in better solutions for the client.
About Mesh
Mesh offers a range of design and engineering services to help organisations in the public and private sectors to improve the energy efficiency of new and existing buildings, housing and estates. This includes support for architects; planning; thermal modelling and overheating analyses; carbon reduction strategies; feasibility studies for renewable technologies; MEP design, and regulatory compliance.
Image credit – Joseph Asghar
