Assessing An Existing Building With No Drawings

Ask for the structural drawings of a building from the 1960s and the usual answer is that nobody has them.

That does not stop the project. It changes how it starts.

Why it matters before anything else

You cannot check whether a structure can take a new load without knowing what the structure is.

Every question a client actually wants answered, whether a wall can come out, whether another storey can go on, whether the roof will take plant, whether the floor will take a new use, depends on establishing the existing structure first.

Assuming it is the single most common cause of serious problems in refurbishment work.

Start with what does exist

Council records. Development applications, building approvals and occasionally archived drawings. Hit rate varies and it is always worth the search.

Dial before you dig for services, which is relevant the moment anything below ground is involved.

Previous reports. Building inspections, strata records, past engineering advice. Strata schemes frequently hold more than they realise.

The original builder or engineer, where the building is recent enough that the practice still exists.

Aerial and street imagery over time, which establishes when extensions were added. An extension is usually built differently to the original, and the junction between them is where problems concentrate.

Then survey what is there

Measured survey. Dimensions, levels, member sizes, spans and positions. This is the base drawing everything else hangs on and it has to be accurate, because [steel fabrication](/blog/steel-fabrication-tolerances-and-site-fit) and any new structure will be set out from it.

Visual inspection of exposed structure. Basements, roof spaces, service risers and car parks show structure that is hidden everywhere else. A roof space frequently reveals the entire framing system.

Opening up. Removing linings at selected points to see what is behind. Invasive, disruptive, and frequently the only way to be certain. It is planned at specific locations chosen to answer specific questions rather than done at random.

Non-destructive investigation

Cover meter and rebar scanning, which locates reinforcement, its spacing and the cover over it in concrete. This establishes how a concrete element was reinforced without breaking it open.

Concrete core sampling for compressive strength, and testing for carbonation and chloride content, which tells you the durability position as well as the strength. That connects directly to [crack width and durability](/blog/crack-width-in-concrete-and-when-it-matters).

Ferroscanning and, on significant elements, radiography where the reinforcement arrangement has to be known precisely, particularly before [core drilling](/blog/core-drilling-and-penetrations-in-existing-slabs).

Timber inspection for decay, insect attack and member sizes.

Masonry assessment, including whether a wall is solid or cavity, and whether it is loadbearing.

Hazardous materials survey. In anything pre 1990, asbestos is assumed present until tested, and it governs how any opening up is done.

Establishing material properties

Old material is not modern material.

Concrete strengths were lower and more variable. Reinforcement grades and bar types have changed. Steel sections that are no longer manufactured have different properties and dimensions to their nearest current equivalent.

Where the assessment is marginal, testing samples is worth far more than assuming a conservative value, because a conservative assumption frequently produces an unnecessary strengthening scheme.

Load testing

Occasionally the right answer, where calculation is inconclusive and the consequence of getting it wrong is high.

The structure is loaded under controlled conditions with deflection monitored. Expensive, disruptive, and definitive.

What the output should be

A set of drawings recording the structure as found, a statement of what was established and how, and an explicit list of what remains unverified and what assumption has been made in its place.

That last part matters most. Every existing building assessment contains assumptions. Writing them down, with the conservatism applied to each, is what lets a certifier, a client and the next engineer rely on the work.

It is also what allows a contingency to be set honestly, because on refurbishment the latent conditions are the budget risk.

Where it leads

Once the structure is established, the actual question becomes answerable: [removing a load bearing wall](/blog/removing-a-load-bearing-wall-what-it-takes), a [second storey addition](/blog/second-storey-addition-can-your-footings-take-it), a [change of use](/blog/change-of-use-structural-assessment), or [rooftop plant](/blog/rooftop-solar-and-plant-structural-adequacy).

None of those can be answered first.

ACSES provides structural engineering and existing building assessment across Sydney. Talk to us about a building.