Existing fabric of the listed building

It is vital that the unique characters of historic homes are not put at risk by unsympathetic alterations, unnecessary intervention, or changing environmental conditions: each owner is, after all, only a temporary guardian of this heritage. When considering refurbishment, it is the owner’s responsibility to ensure that any work does not cause unlawful or unnecessary damage to the building (fabric and indoor building environment).

Older properties, and especially historic buildings, need to ‘breathe’ through the entire envelope (i.e. the external walls, floor and roof), allowing moisture to escape and so preventing damp. A thorough understanding of each building’s unique environmental characteristics will avoid detrimental effects to the building’s breathability caused by misguided material changes.

As a first step, specialist guidance should be sought from the local building conservation officer and, ideally, at least one of the organisations listed on page 2 of this guide. While detailed general rules are not appropriate for individual historic properties, preparation work should include the following:

1 A good understanding of the building’s historic significance (refer to the Listed Building Description or Conservation Area Designation if applicable): this will help to create a sympathetic approach to the existing building materials and structure.

2 An assessment of the building’s heating and ventilation needs.

3 A presumption of minimal intervention.

4 If possible, any new work should be designed to be reversible by future generations.

Modern homes use physical barriers to stop moisture from penetrating the building envelope, whereas older homes tend to be made of porous materials and are permeable. Be aware that there is an important difference between porosity and permeability:

Porosity is the ratio of the volume of pore space to the total volume of a solid material. Pores may or may not be interlinked.

Permeability is the rate at which a liquid or vapour passes through a solid material. Pores must be interlinked.

Modern materials such as concrete or plastic are often inappropriate for use in older homes, harming aesthetics and durability.