The document every heritage planning argument circles back to
Historic England's Good Practice Advice Note 2, Managing Significance in Decision-Taking in the Historic Environment, has underpinned heritage decision-taking since 2015. Its central mechanism, often shorthanded as the ‘harm test’, requires decision-makers to identify whether a proposal causes substantial harm, less than substantial harm, or no harm to a heritage asset's significance, and weigh that against the public benefits the proposal delivers. Almost everything in a heritage planning strategy exists to influence which side of that line a proposal lands on.
Why this is a structural engineering problem, not just a heritage one
The proposals that generate the most significant harm-and-benefit debates are frequently the ones with the biggest structural implications: new basements beneath listed buildings, openings through historic party walls, or the removal of internal partitions that turn out to be load-bearing. A structural strategy that respects historic fabric, backed by evidence rather than assertion, is very often what turns a proposal from ‘substantial harm, difficult to justify’ into ‘less than substantial harm, clearly outweighed by public benefit’.
A new basement beneath a listed townhouse is, almost by definition, an intervention with real potential for harm — excavation close to historic foundations, movement risk to neighbouring listed properties. A well-evidenced geotechnical investigation and considered construction methodology can turn that same proposal into one a conservation officer can genuinely support.
Understanding significance before designing the intervention
GPA2's most important practical instruction, and the one most often skipped under time pressure, is that assessing significance should happen before a scheme is designed, not afterwards as a justification exercise. A heritage assessment carried out early — examining what genuinely survives from a building's original construction, as opposed to what has been replaced over decades of subsequent alteration — fundamentally changes which walls a design team treats as sacrosanct and which can be more freely altered.
“Assessing significance after a scheme is already designed means reacting to a design rather than informing it — a much weaker position from which to build the evidenced case a conservation officer needs to see.”
Proportionality: the guidance's other central idea
GPA2 is equally insistent that the information required to support an application should be proportionate to the asset's significance and the scale of impact — no more and no less. Demanding exhaustive investigation for a minor alteration to a building of modest significance is as unhelpful as submitting a light-touch method statement for a major intervention into a Grade I building. Calibrating that level of evidence correctly, early, is one of the more valuable things a structural engineer experienced in heritage work can bring to a project team.
The public benefit side of the equation
GPA2's harm test is explicitly a balancing exercise, not a one-sided hurdle. Structural and condition evidence often does double duty here: a survey identifying genuine, worsening structural risk in an underused historic building doesn't just inform the repair strategy, it also strengthens the public benefit case for bringing that building back into active, maintained use — because continued vacancy and deterioration is rarely a neutral ‘do nothing’ option from a heritage perspective.
What this means in practice
For architects, developers and heritage clients we work alongside, the practical lesson from GPA2 is consistent: bring structural and technical evidence into the conversation early, calibrate its depth to the genuine significance and impact involved, and build a clear, honest narrative of what harm a proposal causes and what benefit it delivers in return. Done properly, that is also simply better engineering — understanding a historic building thoroughly before intervening in it produces better, safer, more durable outcomes regardless of what any planning policy requires.