1. Why standard conditions are not enough
Standard conditions of contract are designed for new build, where the client knows the brief, the contractor knows the substrate, and the hazards are limited. In refurbishment, three contractual realities change the balance fundamentally.
The substrate is only partly known: a contractor cannot price properly what it does not know. Conditions with no unforeseen works clause force the contractor to cover its risk in the tender price, which pushes tenders up and creates gaps that are hard to compare.
Varied work is predictable: it is not an exceptional event but a normal feature of a refurbishment project. It deserves a procedure as well rehearsed as the procedure for paying valuations.
The building is often occupied: the constraints on access, noise and protection of the occupants have to be contractual, or they become a source of delay attributable to the client and of claims for compensation.
2. The eight adaptations
| Clause | Standard new build | Refurbishment adaptation | Risk if not adapted |
|---|---|---|---|
| Unforeseen conditions | A general 5–8 % contingency, no dedicated clause | An explicit clause with a procedure: instruction, time to price, basis of valuation | Variations with no procedure lead to disputes at final account and two to three times the cost |
| Hidden work | Not mentioned; new build has none | A clause on work to existing fabric: work made necessary by latent defects, valued on net cost | The contractor claims with no contractual basis and negotiation becomes difficult |
| Phasing in occupation | Free access to the site assumed | Define the working zones, days and hours, tenant interfaces, reinforced safety planning | Delays attributed to the client, and compensation claimed |
| Continuity of services | Interruptions free within the programme | A maximum interruption per service, notice to the occupants, a temporary alternative | The contractor is blocked by constraints that were never contractual |
| Price adjustment | A standard parametric formula | A formula with the published indices plus an interim adjustment where the works exceed 12 months | The final account is contested on the adjustment |
| Retention | 5 % as standard | 5 % with the option of substituting a bank bond, released a year after completion | Retention held too long strains the contractor's cash position |
| Liquidated damages | Standard, on the overall contract period | Periods stated by phase where the works are phased, with damages on each identifiable phase | Damages are unenforceable if the overall period was never broken down |
| Liability for retained work | Not applicable | A clause defining liability for the existing fabric retained and for the interfaces with the new work | Disputes at completion over existing fabric damaged during the works |
The most critical is the first. With no contractual procedure, every discovery generates an ad hoc negotiation whose outcome is uncertain. With a well-drafted clause, both parties know the procedure from signature: a recorded instruction, a time to price, a basis of valuation, and a variation before execution.
3. A model unforeseen conditions clause
The unforeseen conditions clause is the heart of a refurbishment contract. It has to cover six elements to be workable and enforceable.
| Part | Recommended content | Why it matters |
|---|---|---|
| Definition | Unforeseen conditions are the works made necessary by discoveries in the existing fabric that were not foreseeable when the contract was made, recorded jointly by the parties. | Defines precisely what qualifies, forestalling both abusive claims and unjustified refusals |
| Trigger | Any unforeseen condition must be the subject of an immediate joint record by written instruction, before any varied work is carried out. | The recorded instruction is the cornerstone; without it the condition is not enforceable |
| Time to price | The contractor has eight working days from the instruction to submit a price for the varied works. | Frames the period, and stops the negotiation dragging while the site stands still |
| Basis of valuation | Valuation is made first on the pricing schedule rates for identical or similar items, failing which on the schedule of rates, failing which on net cost plus the stated percentage for overheads and profit. | A clear hierarchy, which forestalls invented prices and disputes at final account |
| Dedicated provision | A stated sum is reserved in the client's budget for unforeseen conditions, released against a signed variation for each condition above a stated threshold. | Makes the provision visible and contractual, and releases it progressively |
| Cap | The total of the unforeseen conditions is capped at a stated percentage of the original contract sum; beyond that, a global variation is drawn up with the client's express agreement. | Limits the overall drift and triggers a control procedure above the threshold |
ℹ Sizing the dedicated provision The provision for unforeseen conditions has to be calibrated on the uncertainty of the building. On a 1920s block with few surveys: 15 % of the structural package and 10 % of the others. On a well-surveyed 1970s building: 8 to 10 % of the total. The provision is not an automatic variation; it is released progressively as conditions are recorded and valued under the contract procedure. Any unused balance stays with the client and reduces the final account.
4. The occupied-building clauses
Where the works are carried out in an occupied building, a block with tenants in place, a public building partly in use, workplaces, the conditions of contract have to make the constraints binding on the contractor, failing which every disturbance becomes a dispute about who caused the delay.
Working hours: the days and hours permitted for each type of work, noisy work, dusty work, services work. State the prohibited periods and the procedure for exceptional dispensation.
Working zones and access: a phasing plan annexed to the contract, showing the accessible zones, the prohibited zones and the routes for removing waste.
Protection of retained fabric: the contractor is responsible for damage to existing retained work within its zone, which should be made contractual with a joint condition record before commencement.
Communication with the occupants: define who informs the residents, client, architect or contractor, with what notice, 48 hours as a minimum for disruptive work, and under what procedure.
Continuity of communal services: the maximum interruption for each service, four hours for water, according to season for heating, two hours for power to the common parts, and the notice due to the occupants.
5. The five commonest surprises
| Surprise | Frequency | Typical cost | Contractual prevention | Treatment if discovered on site |
|---|---|---|---|---|
| Residual asbestos missed by the survey | ★★★★ | + 50–150 €/m² over the zone affected | A clause suspending the works if asbestos is detected, plus a supplementary survey procedure | Instruction to suspend, supplementary survey, instruction to vary with removal valued |
| Floors or structure decayed beyond the survey | ★★★★★ | 10 000 – 80 000 € by extent | An unforeseen conditions clause, a dedicated provision, and an engineer's report on the risk zones before tender | Instruction recording the fact, engineer's design, instruction to vary and a variation |
| Non-compliant or blocked services | ★★★★ | 2 000 – 15 000 € by package | A compulsory prior survey of the drainage, water and gas services, with the findings issued before tender | Instruction recording the fact, a priced proposal, a variation signed before resuming |
| Masonry decayed behind the render | ★★★ | 5 000 – 30 000 € by area | A specification stating that the condition behind the render is unknown, with a lump sum for making good | A joint record with photographs, valued per m² on the schedule of rates |
| Lead on elements never tested | ★★★ | 3 000 – 20 000 € by area | A complete lead survey before tender, and a clause suspending the works if lead is found outside the surveyed area | Instruction to suspend, supplementary survey, instruction to vary with removal valued |
The table illustrates a general rule: contractual prevention through well-drafted conditions and specification is always cheaper than curing an unanticipated surprise. Decayed structure and residual asbestos alone account for 60 to 70 % of budget overruns in refurbishment. Preventing them, through a survey before tender and a dedicated clause, costs between 1 000 and 5 000 € of preparation. Curing them on site costs 10 000 to 80 000 €.
6. What the specification must state
A refurbishment specification has to state explicitly what the architect and the economist know about the existing building, and what uncertainty remains. That is not a disclaimer: it is contractual information that lets the contractors price properly and that founds any later claim for unforeseen conditions.
The known condition of the substrate: the findings of the surveys available, with the reports annexed to the tender package.
The risk zones identified: areas where defects have been detected without being fully resolved, so the contractor can either carry a provision in its price or flag it in its technical submission.
The phasing and access constraints: the conditions of occupation in detail, the periods when work is permitted, and the access available.
The existing fabric to be retained: an explicit list of what has to be preserved, for which the contractor becomes responsible from the instruction to commence in its zone.
The procedure for recording and valuing the unforeseen: repeat in the specification the references to the corresponding contract conditions, so that the site managers have the information to hand.
In summary
Standard new build conditions are not enough for refurbishment, and eight clauses have to be adapted. The unforeseen conditions clause is the most critical: a precise definition, a trigger by written instruction, a time to price, a hierarchy of valuation from schedule rates to schedule of rates to net cost, a dedicated provision, and a cap. The occupied-building clauses make the constraints on access, hours, protection of retained work and continuity of services binding. The five commonest surprises are decayed structure, residual asbestos, non-compliant services, masonry behind render and residual lead. Contractual prevention costs 1 000 to 5 000 € of preparation against 10 000 to 80 000 € to cure on site.
The nature of the figures quoted
The percentages and amounts quoted on this page are orders of magnitude for framing, not measurements. They illustrate mechanisms and proportions, and they substitute neither for a tender exercise nor for an estimate prepared on drawings.
Articles liés
Sources: the BT construction cost indices published monthly by INSEE on its 2010 base, used to update the figures · construction cost statistics from SDES, the statistical service of the ministry responsible for construction · regulatory texts published in the Journal officiel and consolidated on Légifrance for the requirements cited.