Two buildings can be the same height, the same use, and both classed as Higher Risk Buildings under the Building Safety Act — and still need meaningfully different structural risk assessments, simply because of their age. A building's age doesn't just affect how old its structure looks; it determines what evidence is available, what can safely be assumed, and where the real risk is likely to be hiding.
This guide sets out how a structural risk assessment approach differs for historic buildings, modern buildings, and the hybrid case of a historic building with a later extension.
Why Age Changes the Assessment, Not Just the Building
A structural risk assessment is ultimately about evidence: what do we actually know about this structure's ability to perform safely, and where are the gaps in that knowledge? Age changes where those gaps sit. Older buildings tend to have a long service record but thin design documentation. Newer buildings tend to have the opposite — good design information, but no track record. Each gap needs to be closed in a different way.
Historic Buildings: Proven Service, But Not Proven Robustness
A building that has stood for decades, or longer, has clearly demonstrated it can carry normal, everyday loading. That's real evidence, and it shouldn't be dismissed. But it's evidence of one thing only — performance under the loading the building has actually experienced.
It says very little about how that structure would perform under an accidental design situation it has never been exposed to: an accidental explosion, a vehicle impact, or fire-induced structural damage. A building can have an impeccable service history and still lack the robustness — the ability to avoid disproportionate collapse — that would be expected of it under those scenarios. Long service history simply isn't evidence either way, because the event hasn't happened.
Historic buildings are also, on average, more susceptible to condition deterioration: masonry decay, timber decay, corrosion of embedded or historic steelwork, and cumulative movement or fatigue that has built up gradually over a much longer period than a modern structure has had time to experience.
Practical implication: for historic buildings, a structural risk assessment needs to put significant weight on the condition survey — to evidence, rather than assume, current structural quality — and on an ongoing planned preventative maintenance (PPM) programme covering both structure and fabric, so deterioration is tracked and managed continuously rather than caught only at the next periodic review.
Where a condition survey identifies areas of genuine uncertainty — active or unexplained cracking, suspected material degradation, or historic movement of unknown cause — a visual inspection alone often isn't enough to reach a defensible conclusion. Further investigation is sometimes needed: meter surveys to monitor movement over time and establish whether cracking is active or dormant, alongside other targeted structural investigations to confirm material condition and properly inform the risk assessment.
We Organise and Carry Out the Investigations For You
You don't need to find, brief, and manage separate specialist contractors for monitoring or testing. BSA Structural Compliance can organise and carry out any further investigation your building needs — meter surveys, material testing, and other targeted assessments — as one coordinated part of your structural risk assessment, with a single point of contact throughout.
New Builds: No Service History, So Design Information Is Everything
A new or relatively modern building has the opposite problem. It has no meaningful service history to draw on — there simply hasn't been time for one. That removes one source of evidence entirely, which means the structural risk assessment leans much more heavily on the existing design information: structural calculations, drawings, specifications, and as-built records from construction.
Modern buildings also tend to be structurally more complex than their older counterparts, and one of the most common sources of that added complexity is the transfer structure — most often a transfer slab, used where a different column or wall grid is needed at a lower level than above, typically to create open-plan retail, parking, or amenity space beneath residential floors.
A transfer structure concentrates load paths from many elements above onto a much smaller number of critical elements below. That's an efficient design solution, but it also means those elements carry a disproportionate share of the building's overall risk — the loss or degradation of a single transfer element has a much larger consequence than the loss of an equivalent element in a conventional, well-distributed structural grid. Transfer slabs and transfer structures therefore require further input and closer consideration within a structural risk assessment than the rest of the building typically does.
Design information isn't always available, even for a relatively modern building — records can be incomplete, held by a third party, or simply never passed on to the current Accountable Person. Without it, there's a real gap in the evidence a Building Assessment Certificate application needs, and it has to be closed one way or another before the risk assessment can reach a defensible conclusion.
We Help Close the Information Gap
Where original design information can't be located, we can liaise directly with the original structural engineer or design team on your behalf to recover it, or, where that isn't possible, arrange the further testing and investigation needed to establish the right level of information for a BAC application — all managed through a single point of contact.
Historic Buildings With a Modern Extension
Many buildings don't fall neatly into either category — a historic core with a later extension is common, particularly in refurbished or converted stock. These need a genuinely hybrid assessment: the original structure is assessed the way any historic structure would be, on condition, deterioration, and the same caveats around unproven accidental robustness, while the extension is assessed primarily against its available design information, in the same way a new build would be.
In practice, a lot of the assessment effort on the extension goes into establishing exactly what design and construction information is actually available from the more recent works — drawings, calculations, and building control records from the extension are usually far more complete than anything that exists for the historic core, and should be gathered and reviewed thoroughly before falling back on intrusive investigation.
The interface between old and new structure deserves specific attention in its own right: the connections between historic and modern elements, any differential movement between the two, and how load is actually transferred across that junction are common areas where risk is under-assessed if the building is treated as a single, uniform structure rather than two connected structural systems with different evidence bases.
At a Glance: Historic vs Modern Structural Risk Focus
| Historic Buildings | New / Modern Buildings | |
|---|---|---|
| Primary evidence base | Service history & condition survey | Existing design information |
| Main uncertainty | Accidental / abnormal load robustness | No proven in-service performance |
| Key deterioration risk | Material decay & long-term movement | Generally lower, but design-dependent |
| Structural complexity risk | Historic detailing, limited documentation | Transfer structures & transfer slabs |
| Ongoing management focus | PPM for structure & fabric | Verification against original design intent |
Not Sure Which Risk Profile Applies to Your Building?
We carry out structural risk assessments across the full range of building ages and forms — from historic stock to modern transfer-structure buildings — for Higher Risk Buildings across England and Wales.
Get In TouchFrequently Asked Questions
Does an older building need a different type of structural risk assessment?
The assessment framework is the same, but the emphasis shifts. For historic buildings, more weight is placed on condition survey findings and ongoing planned preventative maintenance, because a long service history does not, on its own, demonstrate the building's ability to withstand accidental events such as explosion, vehicle impact, or fire-induced structural damage.
What is a transfer slab and why does it need extra consideration?
A transfer slab or transfer structure redistributes loads from columns or walls above onto a different, often wider-spaced, arrangement of supports below. This concentrates load paths onto a small number of critical elements, so a structural risk assessment needs to give these elements closer scrutiny than a conventional, more redundant structural form.
Why can't a building's age alone prove it is structurally safe?
A building that has stood for decades has proven it can carry normal, everyday loading. It has not necessarily proven it can withstand abnormal or accidental actions such as explosion, vehicle impact, or fire damage, simply because it may never have experienced them. Age also increases the likelihood of material deterioration, which a structural risk assessment needs to evidence through inspection rather than assume from service history.
How do you assess a historic building with a modern extension?
A building combining a historic core with a modern extension needs a hybrid approach: the original structure is assessed on condition and deterioration in the same way as any historic building, while the extension is assessed against its available design information. Particular attention is also given to the interface between the two — the connections and load transfer between old and new structure.