Most of the price of a used building lies in its structure, yet the structure is the part least visible to the naked eye. Many buyers inspect the roof, electrical and plumbing systems in detail and then skip the foundations because they do not know how to check them — even though strengthening foundations afterwards usually costs many times more than a pre-purchase inspection, and in some cases makes the planned use impossible altogether.
Does a Used Building Need a Structural Inspection Before Purchase?
Yes, especially when the buyer's planned use differs from the current one. The highest-risk cases are buying a light-storage warehouse to turn into a factory with heavy machinery, buying a single-story building with plans to add a second story, or buying space where tall multi-level racking will be installed. All three put more load on the floor and foundations than they were originally designed for.
Even if the use stays exactly the same, a building that has been in service for 20–30 years has 3 issues to check: accumulated settlement that tilts the floor so machinery cannot be set level, carbonation deep enough to corrode the reinforcement and crack and spall the concrete cover, and foundations that were modified or extended without calculations. These issues do not make the building collapse immediately, but they are costs waiting to happen and should be factored into the purchase price.
If the goal is a change of use or an extension, the inspection goes a level deeper — read more in What to Check in an Old Building Before Extending It or Changing Its Use. For an overall checklist covering every aspect of a whole-building inspection before deciding to buy or lease, see Structural Inspection Before Buying or Leasing a Building or Warehouse: What to Check.
With No Original Drawings, How Can You Tell How Long the Piles Are?
With the Parallel Seismic Test following ASTM D8381, which finds the pile toe depth without excavating the full length of the pile. This is the most common problem when buying a used building, because many old buildings have no surviving as-built drawings. The previous owner can often only say "the piles are about 18 meters long" with no documents to back it up, which cannot be used in calculations for foundation strengthening.
The principle is to drill a small hole parallel to the pile or foundation being checked, install a casing pipe and fill it with water, then lower a receiver down to measure level by level while the pile head or the foundation above is struck with a hammer. Waves traveling down through the concrete reach the receiver sooner than waves traveling through soil alone. When arrival time is plotted against depth, the curve changes slope right at the pile toe.
Limitations to be aware of: the borehole must be reasonably close to the pile and drilled plumb — if the hole deviates too far, the results will be inaccurate. The method gives pile depth and continuity, but not load capacity directly. Read the test details in What Is the Parallel Seismic Test?
What Warning Signs Can You Spot by Eye Before Calling in an Inspection Team?
There are 6 signs a buyer can notice while walking through the building before hiring an engineering team. If several appear together, a detailed inspection should be done before deciding.
- Diagonal cracks at about 45 degrees in masonry walls, especially at door and window corners, wide at one end and tapering at the other — a pattern found where foundations have settled unevenly
- A tilted floor or a sagging dish — easy to check by placing a marble or using a water level. If a factory floor tilts visibly, machinery that needs to be level cannot be installed without re-leveling the floor
- Gaps between the floor and walls or columns — a classic sign of a slab on ground settling with the soil, while the columns, supported on piles, do not settle with it
- Spalled concrete exposing rusted reinforcement on columns, beams or slab soffits, especially in areas regularly exposed to moisture
- Signs of additions not tied into the original structure, such as columns that appear with no connecting beam, or slabs cast later with no visible pile lines
- Several doors and windows sticking abnormally in the same direction, which often goes with tilting of the structure
For details on telling different types of cracks apart, read 5 Warning Signs of House Foundation Problems, which applies the same principles as for industrial buildings.
What Should Be Checked Before Deciding to Buy?
You do not need to test everything. Start from what you want to know, then choose the method that answers that question directly. The table below matches 8 questions buyers commonly ask with the inspection methods actually used.
← Scroll to see the full table →
| What you want to know | Inspection method | Common reference standards |
|---|---|---|
| How long are the existing piles? | Parallel Seismic Test | ASTM D8381 |
| Do the existing piles have cracks or necking? | Seismic Integrity Test (Low-Strain) | DPT 1551-51, using the method of ASTM D5882-16 (ASTM withdrawn in 2025) |
| How deteriorated is the concrete? | Rebound Hammer + Ultrasonic Pulse Velocity + carbonation depth test | ASTM C805, ASTM C597 |
| Is the reinforcement corroding yet? | Half-Cell Potential | ASTM C876 |
| Where is the reinforcement and what size is it? | Rebar Scanner and Ground Penetrating Radar (GPR) | BS 1881-204 (cover meter), ASTM D6432 (GPR) · ACI 228.2R as overall guidance |
| What is the actual concrete compressive strength? | Concrete coring | ASTM C42 |
| How much load can the floor actually carry? | Floor Load Test with real weights | ACI 318-19 Chapter 27 |
| How much load can the soil beneath the building carry? | Soil boring and Plate Bearing Test | ASTM D1586, ASTM D1195 / D1196 |
For a medium-sized building with no data at all, the most cost-effective starter package usually has 3 parts: a condition walk-through by an engineer, Parallel Seismic to find pile depth at representative points, and non-destructive concrete testing where damage is visible — then decide whether the scope needs to extend to a load test.
For an overview of all non-destructive concrete testing methods, see the NDT Guide for Concrete Structure Inspection, and see the scope of work on the Non-Destructive Structural Testing Services page.
What Else Must Be Checked If You Plan to Increase the Load?
Two more things must be proven: that the floor can carry the new load, and that the soil under the floor can carry it. These are separate questions that use different test methods. A common case is converting a light-storage warehouse into an area for machinery or tall racking.
For a structural slab supported on beams and piles, the most direct answer comes from a Floor Load Test — placing real weights on the floor in a specified pattern and duration, then measuring deflection and recovery against acceptance criteria. This shows whether the floor can actually carry the required load, without relying on the original drawings. Read the details in What Is a Floor Load Test?
For a slab on ground, as in a typical warehouse, the key variable is the bearing capacity of the soil and sub-base, which can be assessed with a Plate Bearing Test together with soil profile data from soil boring. Long-term settlement needs particular attention in this case, because floors carrying high point loads from racking often show problems only after several months of use, not immediately when goods are placed.
The results of every method mentioned are input data for the responsible engineer to calculate and decide — not a ready-made conclusion on how much load the building can carry. Increasing the working load or extending the structure must be designed and certified by a licensed engineer as required by law.
How Do You Use Inspection Results to Negotiate the Purchase Price?
Use the results to turn vague risks into a clear list of repairs and costs, then take that to the seller. A buyer who tells the seller "the building is old, so please lower the price" usually gets nowhere, but a buyer who presents a report stating that the existing piles are shorter than claimed, that some floor zones carry less load than required, and how many square meters have corroded reinforcement has a much clearer basis for discussion.
A practical approach is to sort the findings into 3 groups
- Must fix before use — should become a price reduction, or a condition for the seller to fix before transfer
- Must fix within a few years — use to negotiate a partial discount
- Can be monitored — no need to bring into negotiation
Separating these three groups makes the offer look reasonable and closes the deal faster than submitting a long, unprioritized list of problems.
How Long Does the Full Inspection Take?
Fieldwork for a medium-sized building usually takes about 1–3 days, and the report takes about another 7–14 working days. The first step is to schedule an initial walk-through and define the scope with the engineer, which does not take long and helps cut out many unnecessary items. The most time-consuming fieldwork is opening inspection pits at the foundations and floor load testing, where the load must be held for the specified time.
Buyers who already have a fixed deposit or transfer date should allow time for the report in the sale and purchase agreement, or make the inspection results a condition precedent, so they do not have to decide before seeing the report.
This content explains pre-purchase building inspection for general understanding only. The choice of test methods, number of points and interpretation for each building must be determined by the engineer directly responsible for that work, and the terms of sale are a matter for the contracting parties to agree on.