Lack of maintenance is a key reason why old buildings deteriorate. Maintenance essentially means preventing rainwater getting in where it can cause harm. Water is potentially most likely to enter through the roof, so putting right minor problems here before they worsen can avert the need for more extensive repair.
The unnecessary replacement of old timber windows is of continuing concern to the SPAB. Such work can diminish both the character and value of an older building. Neighbouring properties could well suffer too.