Written evidence submitted by the
Environmental Building Group, University of Plymouth

Call for Evidence: Protecting built heritage Inquiry

Examine the importance of built heritage in the UK and the barriers to its preservation.

This submission focuses on question 3 within the Culture, Media and Sport Committee’s Terms of Reference. What role does built heritage play in the regeneration of local areas and in contributing to economic growth and community identity?

How can heritage buildings be supported to increase energy efficiency and contribute to the Government’s net zero targets?

Use of novel breathable insulants for heritage buildings

The Environmental Building Group (EBG).

The EBG at the University of Plymouth have been researching the linkages between heritage buildings and the use of new/modified/adapted natural building materials to improve energy efficiency, whilst maintaining the long-term durability of the building fabric. 

Currently The EBG is monitoring an upgraded thermally efficient CobBauge building on the University campus using a mixture of sub soil and hemp shiv. The building is used as a timetabled part of the university’s estate and acts as a living lab gaining valuable insights into the moisture, heatflux, internal air quality performance of the treated walls.

The EBG is also working for Historic England assessing the current state of the art research linked to the performance of insulating lime renders for heritage buildings.

Requirement

Historic buildings need to be altered to effectively allow them to be more energy efficient whilst still maintaining their conservation status and the durability of their fabric.

Background

Most historic buildings (except for a number of post 1946 buildings) are built from materials that require the movement of moisture through their facades/roofs/glazing/floors.

To gain the advantages of reduced energy usage whilst still maintaining a durable historic building stock, one needs to balance efficiency gains and long-term durability. Any interventions such as added insulation to the building’s fabric, need to conform with any Statements of Heritage Significance (overall significance of the building, conservation area, neighbouring heritage assets and its setting).

The Problem

Much of the retrofits that apply to the majority of UK domestic scale buildings involve high performance products (in terms of excellent thermal insulation) made from materials that are suited to upgrading buildings constructed after 1946. These materials are also used in tandem with details that reduce air movement to achieve the limiting of air permeability for new buildings (8 m3/hr.m2, Part L). This aspect is very relevant to new building but severely restricts the migration of moisture in a historic building.

Moisture management is a key performance requirement of any energy efficient upgrade of a historic/heritage building as the prevention of the build up of moisture is key to ensuring the longevity of historic materials. Damp materials also have a higher thermal conductivities and much reduced insulation values, thus reducing the effectiveness of any added insulation.

The Solution

The above problem is taken into account in the current scope of the Building Regulations (Part L) Approved Documents as the following exception is stated, ‘The energy efficiency of historic and traditional dwellings should be improved only if doing so will not cause long-term deterioration of the building's fabric or fittings.’ (Volume 1, page 3, paragraph 0.9). However, this can act as a disincentive to try to maximise the energy efficiency of historic and traditional dwellings. ‘Why bother if your building is included in the exemption?’ 

Through the work of the EBG in the previously mentioned background, it is clear that where there is enough space within the detailed thickness of candidate walls for a layer of ‘light earth’ insulation, that heritage buildings can relatively simply achieve a U value of 0.3W/m2K (pre ’23 regulations) and with a high-performance insulating lime render achieve a U value of 0.26W/m2K (post ’23 regulations). The substantial monitoring undertaken on the aforementioned CobBauge building proves that there is sufficient permeability in this ‘light earth’ insulating layer to allow water vapour to pass through the wall and to behave in the same way as other historic building materials. Other natural insulants are likely to perform equally as well. 

It is therefore proposed that if a proven minimum permeability can be achieved for a whole insulation detail (including finishes and any layers of textile or building paper), higher insulation values (lower U values) can be expected. Work that Historic England and SPAB is/have undertaken can guide the committee as to more definite figures.  This would then substantially reduce the carbon emissions from retrofits of historic buildings and encourage a range of locally produced naturally based insulation materials. Appropriate reductions in carbon emissions will be achieved whilst ensuring that our heritage buildings are appropriately durable within the appropriate constraints of conservations statements.

Carrig (2019). 'Understanding carbon in the historic environment'.