After hundreds of commercial building surveys, our lead surveyor James Whitfield has seen it all — from catastrophic roof collapses to insidious rising damp that hid behind a fresh coat of paint. Here are the 10 defects he encounters most often, what causes them, and what they'll cost to fix.
Why Understanding Common Defects Matters
A commercial building survey exists to uncover defects before they become your problem. But knowing what to expect — what the most common issues are, how serious they tend to be, and what they'll cost to fix — helps you interpret survey findings intelligently and negotiate effectively.
The 10 defects below appear, in some combination, in the majority of commercial buildings I survey. Some are minor nuisances. Others are deal-breakers. All of them are better discovered in a survey than after you've signed.
1. Flat Roof Failures
Flat roofs are the most common source of water ingress in commercial buildings — and the most frequently deferred maintenance item. Built-up felt, asphalt and single-ply membrane roofs all have a finite life-expectancy, typically 15–25 years depending on material and maintenance.
When a flat roof fails, it rarely does so dramatically and obviously. More commonly, water finds its way through laps in the felt, around upstands and parapets, or at seams in single-ply membranes — and may track horizontally before appearing internally as a stain on the ceiling. By the time you see the stain, the damage to the roof deck, insulation and internal finishes may be extensive.
What to watch for: Ponding water, blistering, splitting or cracking to the surface, vegetation growth, and any visible daylight or gaps at upstands and parapets. Internal water staining and mould growth.
Typical remediation: Strip and renew flat roof covering, including repairs to deck where damaged. Allowance for new insulation to meet current Building Regulations standards where practicable.
2. Damp Penetration and Rising Damp
Damp is one of the most common and most damaging defects in commercial buildings. There are several distinct types — rising damp, penetrating damp, and condensation — and they require different treatments. Misdiagnosis is common and can lead to expensive, ineffective remediation works.
Rising damp occurs where ground moisture wicks up through porous masonry due to a failed or absent damp-proof course (DPC). It typically affects the lower metre of internal walls, causing salt staining, plaster damage and mould growth. In older commercial buildings, rising damp is extremely common.
Penetrating damp enters through defects in the external envelope — failed pointing, cracked render, defective flashings, or failed sealant around windows. It can occur at any height on the building and is often confused with rising damp.
What to watch for: Tidemark staining, salt efflorescence, peeling paint or plaster, mould growth, and musty smell. Use of a moisture meter by the surveyor is essential.
3. Structural Cracking and Movement
Structural cracking is one of the most alarming findings in a commercial building survey — though not all cracking is serious. The key is distinguishing between cosmetic cracking (hairline cracks in plaster or render due to thermal movement or shrinkage) and structural cracking (wider cracks indicating movement in the building's structure or foundations).
Structural movement can result from foundation settlement, subsidence (often tree-related), differential thermal expansion in long buildings, and overloading of structural elements. Diagonal cracking at window and door openings, stepped cracking through brickwork and cracking that continues to grow over time are all red flags.
What to watch for: Cracks wider than 5mm, diagonal cracking from openings, stepped cracking through brick joints, doors and windows that stick or fail to close properly.
Typical remediation: Dependent on cause and severity. May range from crack stitching and repointing (£8,000–£20,000) to underpinning of foundations (£50,000–£150,000+).
4. Asbestos-Containing Materials
Asbestos was widely used in commercial building construction until the late 1990s, when all forms were banned in the UK. It appears in many forms — asbestos cement roof sheets and cladding panels, textured coatings (Artex), pipe lagging, ceiling tiles, floor tiles and adhesives, and insulation board around structural steelwork.
In good condition, asbestos-containing materials don't need to be removed — they need to be managed in place. But ACMs that are deteriorating, friable, or at risk of disturbance during refurbishment works require careful management or removal.
The duty to manage asbestos under the Control of Asbestos Regulations 2012 falls on the building owner or occupier. An asbestos register and management plan is legally required for all non-domestic buildings. Many commercial properties we survey don't have one.
5. Failed Window and Door Seals
Failed window and door seals — both the double-glazing unit seals and the external sealant joints between frame and wall — are among the most ubiquitous defects in commercial buildings. Double-glazed units lose their seal over time, resulting in misting between the panes, condensation and reduced thermal performance. External sealant joints crack, shrink or delaminate, allowing water ingress.
In modern commercial buildings with significant glazed areas, failed window seals can be a substantial cost — replacing all double-glazed units in a multi-storey office building can run to tens of thousands of pounds. Our surveys always check window and door performance carefully.
6. Defective Drainage and Rainwater Goods
Gutters, downpipes and underground drainage are regularly neglected in commercial buildings — partly because they're out of sight and partly because their failure doesn't cause immediately obvious problems. But defective drainage allows water to concentrate against the building structure, causing damp penetration, erosion of pointing, staining and — over time — structural damage.
We assess all visible rainwater goods during our surveys and, for higher-value properties, recommend a CCTV drain survey of underground drainage to check for root intrusion, collapsed sections and offset joints.
7. Roof Structure Deterioration
Beneath the roof covering, the structural elements — timber rafters, purlins, trusses, or steel frames — can deteriorate over time. Timber is particularly vulnerable to rot (wet rot and dry rot) and insect attack, both of which can dramatically reduce structural capacity without being visible from below.
I once surveyed a retail warehouse where the roof appeared perfectly sound from inside the building. When I accessed the roof void, I found that approximately 30% of the softwood timber rafters were affected by wet rot — some had lost 80% of their section. The covering had been holding the structure up as much as the other way around. Immediate works required: £85,000.
What to watch for: Roof deflection or sagging, water staining at the ceiling/roof junction, any visible evidence of past leaks above the ceiling level.
8. Non-Compliant Electrical Installations
Electrical installations in commercial buildings have a recommended service life of 25–30 years before full inspection and test is needed. Many commercial buildings we survey have electrical installations well past this age, with wiring and distribution equipment that no longer meets current standards.
Outdated electrical installations pose fire risk and may not be able to support modern IT and power demands. A full electrical inspection and test (EICR) is strongly recommended for any commercial building acquisition — and any commercial building where no inspection record is available.
9. Inadequate Fire Compartmentation
Fire compartmentation — the division of a building into fire-resistant compartments using fire-rated walls, floors and doors — is a critical life-safety requirement. Deficiencies in fire compartmentation are common in older commercial buildings and in properties where significant fit-out or service installations have been carried out without proper fire stopping.
The most common failures we find are: holes in fire compartment walls or floors where services have been installed without fire stopping; fire doors that have been propped open or modified; and fire barriers that have been removed during fit-out works and not replaced. Any of these could have serious consequences in the event of a fire — and could expose a building owner to significant legal liability.
10. Unauthorised Alterations Without Building Regulations Consent
Structural alterations, extensions, changes of use and significant service installations in commercial buildings require Building Regulations approval. In our experience, a significant proportion of commercial buildings have had alterations carried out without the required consents — either through ignorance, oversight or deliberate avoidance.
Purchasing a property with unauthorised alterations can expose a buyer to enforcement action by the local authority, costs of regularisation (bringing the works up to standard retrospectively), or — in some cases — requirements to demolish or reverse the works.
Your solicitor should check for Building Regulations completion certificates as part of conveyancing searches. Your surveyor should flag any alterations that appear to have been carried out without consent and recommend appropriate investigations.
Conclusion: Always Survey Before You Buy
These 10 defects represent a significant proportion of what our team finds in commercial building surveys every week. The good news is that all of them are identifiable by a qualified, experienced surveyor — and all of them can be factored into your acquisition strategy, whether that means negotiating a price reduction, requiring remediation before completion, or walking away entirely.
The cost of discovering these issues after you've signed is almost always far greater than the cost of the survey that would have found them beforehand. Get in touch to discuss your commercial property survey requirements — we respond within 2 working hours.