What Is an Intrusive Structural Survey?

An intrusive structural survey physically exposes, opens, drills, samples or removes part of a building’s construction so that concealed structural information can be inspected and measured directly.

Unlike a visual inspection or non-destructive scan, intrusive work allows the investigation team to see the actual reinforcement, connection, material build-up, bearing detail or concealed condition at the selected location.

Intrusive structural surveys are commonly required where drawings are incomplete, where scanning cannot confirm a critical detail or where a structural engineer needs direct evidence before designing refurbishment, strengthening, demolition, temporary works or a new opening.

The key point is this: an intrusive structural survey should not begin with uncontrolled breaking-out. Each opening should answer a defined engineering question, be positioned using available drawings and non-destructive surveys, and include appropriate controls for structural stability, reinforcement, post-tensioning, services, hazardous materials and reinstatement.

What Does Intrusive Structural Survey Mean?

An intrusive structural survey involves physically disturbing part of the existing construction to expose or extract information that cannot be confirmed visually.

The intrusion may be small and localised, such as removing a patch of plaster to inspect a steel beam, or more substantial, such as forming a concrete breakout to expose several reinforcement layers.

Typical intrusive activities include:

Removing finishes, ceilings or encasements.
Forming inspection openings.
Breaking out concrete to expose reinforcement.
Extracting concrete cores.
Drilling borescope or endoscope holes.
Opening masonry walls or piers.
Exposing steel connections.
Removing local fire protection.
Lifting floorboards or roof finishes.
Opening timber floors, walls or roof zones.
Excavating trial pits beside foundations.
Taking mortar, steel, concrete or timber samples.

Intrusive surveying is therefore a broad category rather than one specific test. The method should be selected according to the concealed information required.

Intrusive Survey Versus Non-Destructive Survey

Area	Non-Destructive Survey	Intrusive Survey
Method	Uses scanning, measurement or testing without significant material removal.	Physically exposes, drills, cuts, samples or removes construction.
Evidence	Usually indirect or interpreted evidence.	Provides direct physical evidence at the opening location.
Disruption	Usually limited.	May create noise, dust, damage, access restrictions and repair requirements.
Typical information	Estimated reinforcement position, thickness, continuity or possible concealed features.	Actual dimensions, materials, connections, reinforcement and condition.
Main limitation	Some details remain uncertain or require interpretation.	Evidence is local and may not represent the whole structure.

The two approaches are often complementary. Non-destructive methods can map the wider area and help select intrusive locations, while opening-up confirms critical details physically.

Why Is an Intrusive Structural Survey Required?

An intrusive survey is normally required when an important structural detail cannot be established with sufficient confidence from drawings, visual inspection or non-destructive testing alone.

Common reasons include:

Confirming reinforcement bar diameter and arrangement.
Exposing a steel connection.
Determining whether a wall is solid, cavity or framed.
Confirming slab or wall construction.
Extracting concrete cores for strength testing.
Investigating corrosion, cracking or water damage.
Confirming a bearing or support detail.
Inspecting timber for decay or section loss.
Determining foundation dimensions.
Confirming how a façade or balcony is connected.
Identifying previous alterations or concealed repairs.
Supporting temporary works or demolition design.

The engineer should define why direct confirmation is necessary and what information each opening must provide.

When Drawings Are Missing or Unreliable

Existing buildings frequently have incomplete or inconsistent record information. Drawings may show the intended design rather than the final construction, and later alterations may not have been recorded.

Potential differences include:

Different reinforcement sizes or spacing.
Moved or additional structural members.
Altered connections.
Unexpected voids or infill.
Changed slab thickness.
Unrecorded openings.
Services occupying structural zones.
Previous repairs covering deterioration.
Different foundations from those shown.

Intrusive work allows selected critical assumptions to be checked against the actual structure.

Related STRUCTinspect Guidance

STRUCTinspect has discussed why refurbishment decisions should be based on verified site evidence in Structural Investigation for Office Retrofit: Beyond the Energy Model. Intrusive surveys are often necessary where the actual structure, service routes and concealed interfaces differ from available records.

What Questions Can Intrusive Surveys Answer?

Question	Possible Intrusive Method	Evidence Obtained
What reinforcement is present?	Controlled concrete breakout.	Bar diameter, direction, cover, layers and local condition.
How is a steel connection formed?	Remove ceiling, encasement or fire protection.	Plates, bolts, welds, bearings and member geometry.
What is the concrete strength?	Extract concrete cores.	Physical samples for laboratory compressive testing.
What is inside a wall?	Opening-up or borescope inspection.	Wall thickness, cavity, framing, ties and concealed services.
What foundation is present?	Trial pit or local excavation.	Foundation type, width, depth, material and bearing level.
Is timber decayed?	Lift finishes and expose joist ends or bearings.	Moisture, decay, insect damage and remaining section.

Types of Intrusive Structural Survey

The survey type should match the material and engineering question.

Concrete reinforcement breakouts.
Concrete core sampling.
Slab and wall opening-up.
Steel connection exposure.
Masonry construction opening-up.
Timber floor and roof exposure.
Façade support investigations.
Anchor and fixing exposure.
Foundation trial pits.
Borescope and endoscope surveys.
Local removal of fire protection.
Material sampling.

Opening-Up Works

Opening-up is a general term for removing finishes or structural material to inspect concealed construction.

An opening may pass through:

Plasterboard.
Suspended ceilings.
Floor finishes.
Screed.
Plaster or render.
Concrete cover.
Masonry.
Fire protection.
Roof or façade layers.

The scope should identify whether only the finish is to be removed or whether the structural material itself must be opened.

Borescope and Endoscope Openings

A small drilled access hole can allow a camera to inspect a concealed cavity with less disruption than a full opening.

Borescope inspection may help identify:

Cavity depth.
Wall or ceiling build-up.
Presence of insulation.
Timber or metal framing.
Moisture or visible deterioration.
Services.
Void formers.
Connection components.

The camera only shows what is visible from the access position. Limited lighting, obstructions and restricted viewing angles may prevent a complete assessment.

How Is an Intrusive Structural Survey Planned?

Planning should begin with the structural engineer’s information requirements rather than the tools available on site.

The brief should identify:

The engineering question.
The structure, level and element.
The exact investigation location.
The required opening dimensions.
The required exposure depth.
The feature to be confirmed.
The measurements or samples required.
Acceptable alternative positions.
The required photographs and drawings.
The repair or reinstatement requirement.

A vague request such as “open the slab and see what is there” provides insufficient control over the opening size, depth, purpose and stop conditions.

Why the Opening Size Must Be Defined

The opening should be large enough to answer the question but no larger than reasonably necessary.

A small opening may fail to expose:

The complete bar diameter.
Several reinforcement layers.
A lap or coupler.
The full connection plate.
The bearing detail.
The wall build-up.

An unnecessarily large opening can increase structural risk, noise, dust, repair costs and disruption.

The opening dimensions should therefore be agreed against the detail that must be verified.

Selecting Representative Locations

Intrusive locations should be selected because they are relevant, not only because they are easy to access.

The engineer may target:

A representative structural bay.
A support or connection zone.
An area of visible deterioration.
A proposed opening or fixing position.
A location where drawings are uncertain.
A change in construction phase.
An area of maximum anticipated loading.
A previous alteration or repair.

One convenient opening should not automatically be assumed to represent all similar-looking areas.

How Many Intrusive Locations Are Needed?

There is no universal number. The quantity depends on:

The size of the building or element.
Expected construction variability.
Reliability of record information.
Number of construction phases.
Importance of the proposed alteration.
Variation identified during initial investigations.
Access and disruption constraints.

A staged approach may begin with selected representative openings and expand the survey if unexpected differences are found.

Should Concrete Be Scanned Before Intrusive Work?

Concrete should normally be scanned before drilling, coring or breaking out where reinforcement, post-tensioning tendons or services may be present.

Scanning can help:

Target the reinforcement that needs to be exposed.
Avoid post-tensioning tendons.
Avoid embedded services.
Select core positions away from significant bars.
Estimate reinforcement depth.
Reduce unnecessary concrete removal.
Mark maximum safe breakout zones.

For wider context on detectable concealed features, read What Can a Concrete Scanner Detect?.

Scanning reduces uncertainty but does not guarantee detection of every small, deep or masked feature. The intrusive method should still include controlled depths and stop-work instructions.

Why Drawings and Scanning Should Be Used Together

Drawings provide the expected arrangement, while scanning provides evidence of the as-built concealed pattern.

Using both allows the team to identify:

Whether reinforcement appears broadly consistent with the design.
Whether unexpected bars or ducts are present.
Whether the intended opening location remains suitable.
Whether the survey area should be moved or enlarged.
Whether the structural engineer should review a discrepancy before work continues.

Neither drawings nor scanning should be used blindly where the consequence of damaging concealed construction is significant.

Concrete Reinforcement Breakouts

A concrete breakout removes the concrete cover around selected reinforcement so the steel can be inspected and measured directly.

A breakout may be used to confirm:

Bar diameter.
Bar spacing.
Bar direction.
Concrete cover.
Reinforcement layers.
Links or stirrups.
Laps or couplers.
Local anchorage details.
Corrosion or section loss.
Bond and surrounding concrete condition.

The operative should expose the reinforcement without cutting, heating or significantly damaging it unless specific approval has been provided.

How Is a Concrete Breakout Completed?

The precise method depends on the opening size, reinforcement depth, concrete strength, access and site restrictions.

A controlled sequence may include:

Review drawings and scan the area.
Mark reinforcement, services and breakout limits.
Confirm the maximum permitted depth.
Use suitable tools to remove the surface finish and concrete.
Reduce tool size and impact as reinforcement is approached.
Expose enough steel to take the required measurements.
Clean the opening without damaging the reinforcement.
Record dimensions, photographs and condition.
Protect exposed reinforcement.
Reinstate the opening using the agreed repair method.

The method should not rely solely on the operative stopping when metal is struck. Tendons and services may be damaged before their presence becomes obvious.

Can Reinforcement Be Cut During a Survey?

Reinforcement should not be cut merely to improve access or enlarge an investigation opening.

Cutting reinforcement can affect:

Structural capacity.
Crack control.
Local anchorage.
Load transfer.
Durability.
Fire performance.

Any proposal to cut steel should be specifically reviewed and authorised by the responsible structural engineer.

Concrete Core Sampling

Concrete cores are cylindrical samples drilled from an existing element. They may be used to investigate:

Compressive strength.
Slab or wall thickness.
Concrete density.
Layered construction.
Carbonation depth.
Chloride content.
Petrographic condition.
Cracking or material defects.

The core location should be selected to obtain representative material while avoiding significant reinforcement, tendons and services.

The engineer or materials specialist should specify the core diameter, orientation, depth, quantity and laboratory testing required.

What If a Core Intersects Reinforcement?

A core containing reinforcement may be unsuitable for some laboratory tests and can damage an important structural bar.

Where steel is encountered unexpectedly, the coring activity should stop and the location should be reviewed. The team should not automatically continue through the bar.

The event should be:

Photographed.
Recorded against the core reference.
Reported to the responsible engineer.
Assessed before the hole is enlarged or completed.

Intrusive Surveys of Existing Steelwork

Structural steelwork is often concealed behind ceilings, encasement, cladding, wall finishes or fire protection.

Opening-up may be required to confirm:

Steel section size and type.
Plate dimensions.
Bolt quantity, diameter and arrangement.
Weld type and extent.
Bearing length.
Connection geometry.
Corrosion or impact damage.
Fire-protection thickness and condition.
Relationship with adjacent masonry or concrete.

The opening should be large enough to inspect the connection detail required by the engineer. Exposing only the member flange may not reveal how the beam is supported.

Removal of Fire Protection

Removing spray-applied material, boarding or intumescent coating may affect fire protection and can introduce hazardous-material risks.

Before removal, the project should confirm:

The material type.
Hazardous-material survey information.
Required containment and PPE.
The permitted removal extent.
How the fire protection will be reinstated.
Who will inspect or certify the repair.

The structural survey should not leave a fire-protection defect without an agreed making-safe and reinstatement process.

Intrusive Masonry Surveys

Masonry opening-up may be required where wall construction, loadbearing status, support or condition cannot be determined visually.

The survey may seek to confirm:

Wall thickness.
Solid or cavity construction.
Brick, block or stone arrangement.
Bond pattern.
Wall ties.
Embedded columns or steelwork.
Lintel type and bearing.
Mortar condition.
Previous infill or alterations.
Connection to floors and roofs.

Care is required around arches, piers, bearings and slender wall sections because local material removal can affect stability.

Opening Masonry Near Bearings

Removing masonry close to a beam, lintel, arch or slab bearing can disturb a load-transfer zone.

The structural engineer should define:

The safe opening size.
The permitted location.
The sequence of removal.
Whether temporary support is required.
The stop conditions.
The required reinstatement.

Operatives should not enlarge openings around bearings without further approval.

Intrusive Timber Surveys

Timber members may be concealed by ceilings, floors, wall linings, roof finishes or insulation.

An intrusive timber survey may inspect:

Joist or rafter dimensions.
Spacing and direction.
Bearing details.
Moisture content.
Fungal decay.
Insect damage.
Splits and checks.
Connection details.
Remaining cross-section.
Previous repairs or strengthening.

Joist ends and wall bearings are often important because concealed moisture can cause local decay even where the visible central span appears sound.

Lifting Floorboards and Finishes

The scope should identify whether existing finishes are intended to be retained and whether boards can be lifted without damage.

Potential risks include:

Hidden electrical or plumbing services.
Asbestos-containing floor materials.
Fragile or historic finishes.
Loss of fire or acoustic separation.
Unprotected openings after inspection.

The work should include making-safe arrangements where immediate full reinstatement is not possible.

Foundation Trial Pits

A foundation trial pit exposes part of an existing foundation and surrounding ground.

The investigation may confirm:

Foundation type.
Width and plan dimensions.
Depth below ground level.
Founding level.
Concrete or masonry construction.
Relationship with the wall or column above.
Adjacent services.
Ground conditions at the exposed location.
Evidence of movement, deterioration or undermining.

Trial pits are local investigations. The foundation may change in size or type elsewhere.

Structural Risks During Foundation Exposure

Excavation beside a foundation can remove lateral support, disturb bearing material or affect nearby structures.

Controls may include:

Defined maximum pit dimensions.
Restricted excavation length.
Staged excavation.
Temporary support or shoring.
Service detection.
Groundwater control.
Engineer inspection before backfilling.
Specified reinstatement and compaction.

Trial-pit dimensions and sequence should be defined by the responsible engineer rather than decided during excavation.

Intrusive Façade Investigations

Façade investigations may expose brackets, anchors, rails, cavity barriers, insulation, membranes and interfaces with the primary structure.

The survey may seek to establish:

Bracket and anchor arrangement.
Connection to concrete, steel or masonry.
Anchor size and embedment.
Cavity depth.
Insulation and membrane build-up.
Cavity-barrier installation.
Corrosion or water ingress.
Fire-stopping condition.
Differences from façade drawings.

Removal of façade components can create falling-object, weatherproofing and fire-safety risks. The opening sequence and temporary protection should be planned in advance.

Anchor and Fixing Investigations

Existing anchors may be exposed where their type, embedment, substrate or condition is uncertain.

The investigation may confirm:

Anchor diameter.
Anchor type.
Embedment depth.
Edge distance and spacing.
Base material.
Installation quality.
Corrosion or damage.
Relationship with reinforcement.

Exposure does not by itself confirm anchor capacity. The responsible engineer may also require calculations, proof testing, material information or replacement.

Hazardous Materials Before Opening-Up

Intrusive work can disturb hidden hazardous materials. Relevant survey information should be reviewed before drilling, cutting or removing finishes.

Potential materials include:

Asbestos-containing boards, coatings or insulation.
Lead-based paint.
Silica-containing concrete and masonry dust.
Contaminated soil.
Biological contamination.
Historic fire-protection materials.

An existing management survey may not be sufficient where the planned work will disturb concealed materials. The project should confirm that appropriate intrusive hazardous-material information is available.

Site Controls for Intrusive Structural Surveys

Intrusive surveys can involve drilling, breaking, cutting, excavation and work at height. The RAMS should reflect the actual work rather than treating the survey as a simple inspection.

Typical controls include:

Permit-to-drill or permit-to-break-out procedures.
Service and post-tensioning checks.
Maximum drilling and opening depths.
Temporary works and stability controls.
Dust extraction and respiratory protection.
Noise and vibration management.
Water containment during coring.
Work-at-height arrangements.
Falling-object protection.
Exclusion zones.
Manual-handling controls.
Waste and sample management.
Emergency and stop-work procedures.

RAMS Must Match the Investigation Brief

The RAMS should identify the exact locations, opening sizes, tools and sequence rather than describing generic breaking-out work.

STRUCTinspect has discussed the importance of connecting technical methodology with real site controls in What a Structural Testing RAMS Must Contain Before Loading Starts.

Although an intrusive survey may not involve structural load testing, the same principles apply:

Responsibilities must be clear.
Equipment must match the method.
Stop conditions must be stated.
Unexpected findings must trigger review.
Exclusion and access controls must reflect the actual site.

Service Detection and Isolation

Drawings and scanning should be reviewed before intrusive work, but neither automatically confirms whether a service is live.

Where relevant, the project should provide:

Electrical service drawings.
Mechanical and public-health service drawings.
Isolation certificates.
Permit information.
Confirmation from the building operator.
Additional detection using an appropriate service locator.

Unidentified linear features should be treated conservatively until their nature and status are understood.

Post-Tensioning Risks

Drilling or breaking into post-tensioned concrete can damage stressed tendons and release stored energy.

Before intrusive work begins, the team should confirm:

Whether the element is post-tensioned.
Available tendon drawings.
The results of a suitable GPR survey.
The permitted opening location and depth.
Structural-engineer or post-tensioning-specialist approval.
The controlled drilling or breakout method.

A tendon-like response should normally be treated as a restricted zone rather than investigated by uncontrolled drilling.

Work at Height and Soffit Openings

Soffit and façade investigations may require scaffold, a MEWP or another working platform.

The method should consider:

Safe access and egress.
Tool restraint.
Falling debris.
Exclusion below.
Equipment weight and platform capacity.
Water and slurry containment.
Lighting.
Emergency recovery.

The access arrangement should allow the operative to control tools safely and take accurate measurements within the opening.

Dust, Noise and Water Control

Intrusive investigations can affect occupied areas and adjacent work zones.

Controls may include:

Local dust extraction.
Wet drilling where appropriate.
Sealed work enclosures.
Negative-pressure units.
Noise-restricted working hours.
Slurry collection.
Protection of finishes and equipment.
Fire-alarm isolation and reinstatement.

The survey scope should account for these controls because they affect programme, access and cost.

What Happens If Unexpected Construction Is Found?

Unexpected findings are common during intrusive surveys. The method should include a stop-and-review process.

Examples include:

Unexpected reinforcement or tendons.
A live or unidentified service.
Different slab or wall construction.
Corroded or damaged structural material.
Voids or loose construction.
Hazardous material.
Movement or instability.
A connection that differs from drawings.

The opening should not be enlarged automatically. The condition should be photographed, made safe and referred to the responsible engineer or project representative.

Samples and Chain of Custody

Samples must be linked reliably to their original location.

The sample record should include:

A unique reference.
The project and element.
The exact location.
Depth and orientation.
Date of extraction.
Photographs.
Sample dimensions and condition.
Requested tests.
Packaging and transport details.

A valid laboratory result may become unusable if the sample cannot be related confidently to the structure.

Reinstatement After an Intrusive Survey

Reinstatement should be planned before the opening is formed. The project should state whether the investigation contractor, principal contractor or another specialist is responsible.

The required repair may need to restore:

Structural integrity.
Concrete durability.
Reinforcement protection.
Fire resistance.
Acoustic performance.
Waterproofing.
Air tightness.
Thermal performance.
Surface appearance.
Security or compartmentation.

A cosmetic patch is not always sufficient, particularly where structural concrete, fire protection or façade weathering has been disturbed.

Concrete Breakout Repairs

A concrete repair may require:

Removal of loose or damaged concrete.
Cleaning of exposed reinforcement.
Corrosion treatment where specified.
Correct edge preparation.
Substrate cleaning and pre-wetting.
A suitable bonding system.
A compatible repair mortar.
Compaction and finishing.
Curing and protection.

The repair material and method should be specified for the element, exposure and opening geometry.

Temporary Making-Safe Versus Permanent Repair

Some openings need to remain available for engineer inspection before permanent repair. In that case, the project should define a temporary making-safe arrangement.

This may include:

Temporary covers.
Barriers or exclusion zones.
Edge protection.
Weatherproof sheeting.
Temporary fire stopping.
Labelling and inspection records.

The temporary arrangement should not be confused with final reinstatement.

What Should an Intrusive Structural Survey Report Include?

Project name, address and report reference.
Client and instructing party.
Purpose of the investigation.
Drawings and information reviewed.
Exact opening and sample locations.
Opening dimensions and depths.
Methods and equipment used.
Scanning or detection completed beforehand.
Observed construction and materials.
Measured dimensions.
Reinforcement, connection or support details.
Condition observations.
Sample references and laboratory requirements.
Photographs before, during and after opening-up.
Differences from drawings.
Unexpected findings.
Reinstatement completed or outstanding.
Limitations.
Recommendations for further investigation.

Each opening should have a unique reference that appears consistently on photographs, drawings, samples and written findings.

What Measurements Should Be Recorded?

Depending on the survey objective, measurements may include:

Overall element dimensions.
Layer thicknesses.
Concrete cover.
Reinforcement diameter and spacing.
Plate dimensions.
Bolt sizes and spacing.
Weld length.
Bearing length.
Wall or cavity thickness.
Foundation width and depth.
Timber section dimensions.
Crack width or section loss.

A scale, tape or calliper should be visible in detailed photographs where practical.

Photographic Records

Photographs should show both location context and technical detail.

A useful sequence includes:

The general area.
The marked investigation location.
The surface before opening.
Scanning or detection markings.
The opening during progression.
The fully exposed detail.
Measurements.
Samples.
Unexpected defects.
The repaired or made-safe opening.

A close photograph with no wider context may be difficult to relate to the correct structural location later.

Measured Evidence Versus Structural Interpretation

The investigation team should report what was exposed and measured. The structural engineer should determine what the findings mean for design, capacity or remedial work.

Type	Example
Observed	Two reinforcement layers were exposed within the breakout.
Measured	The nearest bar measured approximately 20 mm in diameter at 42 mm cover.
Interpreted	The exposed arrangement appears consistent with the top reinforcement shown on the drawing.
Assessed	The slab requires trimming reinforcement around the proposed opening.

The final assessment should be completed by the responsible structural engineer using the investigation evidence and project design requirements.

Limitations of Intrusive Structural Surveys

Intrusive work provides direct evidence, but only at the locations opened or sampled.

Important limitations include:

Construction may vary elsewhere.
Openings may be too small to expose the complete detail.
Access may prevent investigation of critical zones.
Finishes or hazardous materials may restrict work.
Structural stability may limit opening size.
Samples may not represent every concrete pour or material phase.
Immediate repair may conceal the detail after inspection.
Some deeper components may remain hidden.

The report should identify where findings can reasonably be applied and where further investigation may be required.

Can One Opening Represent the Whole Structure?

Not automatically. One opening confirms the construction at that local position.

Whether it is representative depends on:

Consistency of drawings.
Repeated scanning patterns.
Construction history.
Different building phases.
Variation between structural bays.
Previous alterations.
Differences in visible condition.

The structural engineer should decide whether additional locations are necessary.

Common Intrusive Survey Mistakes

Mistake	Why It Is a Problem	Better Approach
No defined engineering question.	The opening may not expose the information required.	State what must be confirmed before opening-up begins.
No scanning before concrete breakout.	Reinforcement, tendons or services may be damaged.	Use drawings, scanning and permit controls first.
Opening selected only for convenience.	The location may not represent the critical structure.	Select positions based on structural relevance.
Opening dimensions not specified.	Too little or too much material may be removed.	Define size, depth and stop conditions in the brief.
Unexpected findings ignored.	Continuing may cause damage or invalidate the method.	Stop, record and refer the condition for review.
No reinstatement plan.	Openings may remain unsafe or compromise performance.	Agree making-safe and permanent repair responsibilities in advance.
Poor location records.	Measurements and samples may not be traceable.	Use unique references, plans and contextual photographs.
Local findings applied everywhere.	Construction may vary between locations.	Assess representativeness and state limitations.

Intrusive Structural Survey Checklist

Engineering question: state exactly what each opening must confirm.
Location: identify level, grid, room and structural element.
Existing information: provide drawings, reports and alteration records.
Opening size: define width, height, diameter and depth.
Alternative positions: confirm permitted relocation where required.
Scanning: locate reinforcement, tendons and possible services before intrusive work.
Services: provide drawings, detection and isolation information.
Post-tensioning: confirm whether tendons are present or suspected.
Hazardous materials: review appropriate intrusive survey information.
Structural stability: confirm whether temporary works or propping are required.
Access: define scaffold, MEWP, ceiling removal or excavation arrangements.
Site controls: plan dust, noise, water, falling-object and exclusion controls.
Stop conditions: state what happens if unexpected construction is found.
Measurements: list the dimensions and details to be recorded.
Samples: define quantity, size, reference and laboratory testing.
Photographs: require context, progress, measurements and final condition.
Inspection: confirm whether the engineer must inspect before closure.
Reinstatement: define temporary making-safe and permanent repair responsibilities.
Reporting: agree drawings, tables, photographs and report format.
Interpretation: identify the engineer responsible for assessing the findings.

Evidence-Based Summary

An intrusive structural survey physically exposes or samples concealed construction to obtain direct evidence about an existing structure.

Typical methods include concrete breakouts, cores, connection opening-up, masonry inspection holes, timber exposure and foundation trial pits.

Each opening should be designed around a defined engineering question and positioned using drawings, visual evidence and non-destructive surveys.

Intrusive work can affect reinforcement, tendons, services, structural stability, fire protection and waterproofing, so the method must include project-specific controls.

Unexpected construction should trigger a stop-and-review process rather than uncontrolled enlargement of the opening.

Results provide direct evidence at the selected locations but should not automatically be assumed to represent the whole building.

The strongest intrusive survey combines a precise brief, controlled site methodology, traceable measurements, clear photographs, responsible engineering review and an agreed reinstatement plan.

FAQ: Intrusive Structural Surveys

What is an intrusive structural survey?

It is an investigation that physically opens, drills, breaks out, samples or excavates part of a structure to inspect concealed construction directly.

Why is an intrusive survey required?

It is required where drawings, visual inspection or non-destructive testing cannot confirm an important structural detail with sufficient confidence.

What is the difference between intrusive and non-destructive surveys?

Non-destructive methods investigate without significant material removal, while intrusive surveys physically expose or sample the structure to obtain direct evidence.

What does opening-up work involve?

It may involve removing finishes, concrete, masonry, fire protection, floorboards or other materials to reveal concealed structural construction.

Should concrete be scanned before breaking out?

Normally, yes. Scanning helps locate reinforcement, tendons and services and allows the breakout to target the required feature more safely.

Can reinforcement be cut during an intrusive survey?

Reinforcement should not be cut without specific approval from the responsible structural engineer or designer.

Can a survey expose post-tensioning tendons?

Intrusive work near tendons requires specialist planning. Tendon-like responses should not be exposed by uncontrolled drilling or breaking because the tendons contain stored force.

What is a concrete reinforcement breakout?

It is a controlled removal of concrete cover to expose reinforcement for measurement and inspection.

What information can a concrete core provide?

A core may provide information about concrete strength, element thickness, material layers, carbonation, chlorides and internal condition.

Do intrusive openings need to be repaired?

Yes, unless the project specifically requires them to remain open temporarily. The repair may need to restore structural, fire, acoustic, waterproofing or durability performance.

Who chooses the investigation locations?

The responsible structural engineer or designer should normally specify or approve the locations based on the information required.

How many openings are required?

The number depends on structural variability, available records, the proposed decision and the findings from the initial openings.

Can one opening represent an entire building?

Not automatically. The opening confirms the construction at its location. The engineer must assess whether it is representative of other areas.

What happens if an unexpected service is found?

Work should stop, the opening should be made safe and the feature should be identified and reviewed before the investigation continues.

What should an intrusive structural survey report include?

It should include the objective, locations, opening dimensions, methods, measurements, samples, photographs, unexpected findings, limitations and reinstatement status.

Does an intrusive survey confirm structural capacity?

The survey provides physical evidence. Structural capacity must be assessed by the responsible engineer using the findings, loading information and calculations.

Source Context and Editorial Note

This article is a STRUCTinspect technical explainer covering intrusive structural surveys, opening-up works, concrete breakouts, sampling, access, reporting and reinstatement.

It provides general construction information rather than a project-specific intrusive investigation specification. Opening locations, dimensions, methods, temporary works, service controls, sampling and repairs should be selected for the particular structure and engineering objective.

This article does not provide structural engineering, temporary works, hazardous-material, post-tensioning, health and safety, contractual or construction advice. Intrusive work should be designed, reviewed and controlled by the appropriate structural engineer, designer, contractor, specialist surveyor or competent professional responsible for the works.

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