From the HES website:
Advice on repairing traditional buildings, including finding the cause of an issue, using skilled tradespeople and using suitable materials.
Overview | Find the cause | Use skilled people | Source suitable materials | Keep a record of repairs
Overview
Repairs to resolve the cause of the problem should be made as soon as you find a defect in a traditional building. You’ll need to engage skilled tradespeople to do the work, and the materials for the repairs should match as closely as possible those used originally.
Neglecting the cause and simply doing a ‘quick fix’ to keep the symptoms at bay could make a straightforward problem much worse. Unsuitable or unsightly repairs may bring down the value of a property and damage its fabric over the longer term.
Always aim to repair rather than replace, as historic materials are generally much better quality than their modern equivalents.
Common repairs will often need to be organised in tenements and other buildings with multiple owners. This involves all owners in the building agreeing to the work and sharing its cost. Some buildings have a scheme or a factor to help with this.
Find out if you might need permission to make repairs.
Find out about Historic Environment Scotland grant schemes.