Historic building considerations
Doing work in a historic building comes with its own special considerations and potential pitfalls, as you will already be aware from your project planning.
Building Conservation: 10 ways to ruin a historic building
Tread carefully. Where possible, always repair instead of replace and always practice good maintenance. This is summed up by William Morris (founder member of the Society for the Protection of Ancient Buildings):“It is for all these buildings, therefore, of all times and styles, that we plead, and call upon those who have to deal with them, to put Protection in the place of Restoration, to stave off decay by daily care, to prop a perilous wall or mend a leaky roof by such means as are obviously meant for support or covering, and show no pretence of other art, and otherwise to resist all tampering with either the fabric or ornament of the building as it stands; if it has become inconvenient for its present use, to raise another building rather than alter or enlarge the old one; in fine to treat our ancient buildings as monuments of a bygone art, created by bygone manners, that modern art cannot meddle with without destroying.”
SPAB: sense and sustainability
Use the right materials and methods
You should ensure that all plans and estimates allow for using materials and methods appropriate to your building, and that these are adhered to by contractors.
Buildings of traditional construction (generally those built before 1914) used soft weak permeable (or 'breathable') materials such as lime mortars. Using modern hard materials can cause long term damage by trapping moisture and reducing permeability. Even a small area of cement based mortar in an ancient stone wall (perhaps done by a well meaning local volunteer) can cause lasting damage to much larger areas of the structure.
Historic England: using the right materials
Historic England: all advice for Places of Worship
Stay within your permissions
Be careful to ensure that all the work carried out is included in your permissions. Where works have taken place that needed consent but no consent was obtained the authorities can rule that work is reversed, at full cost to you. In some cases unauthorised works may also be a criminal offence.
Historic England: unauthorised work and heritage crime