How to produce a reliable refurbishment budget with no drawings

Producing a refurbishment budget without complete drawings is legitimate; it is indispensable to any feasibility decision. But any budget produced in those conditions has to state explicitly how reliable it is and what contingency it carries. An estimate presented without that information creates a false precision that turns against both the client and the architect.

The rule is simple: the more incomplete the documentation, the wider the range and the higher the contingency. That is not a sign of poor work by the economist, it is an honest quantification of the uncertainty remaining in a building whose secrets are not all known.

ℹ The sentence to include in any refurbishment budget without complete drawings "This estimate is prepared on the basis of the drawings available, a partial measured survey, or a visit without drawings, at the date stated. In the absence of complete drawings, an asbestos survey or a structural survey, a contingency of the stated percentage has been applied. The estimate will be revised once the measured survey, the survey findings or the developed design drawings are available. Current accuracy: the stated range."

The overall rates method is the only one possible without complete drawings. It works from the building's approximate areas, measured by eye or taken from the land registry, and from cost rates by type of work. The result is a range, not a line-by-line estimate. Presenting a line-by-line estimate with no drawings amounts to inventing precision, and it is the commonest and most dangerous error of all.

Even with no drawings, approximate areas are obtainable. The land registry record gives the footprint and the number of storeys. The energy performance certificate, where one exists, states the habitable area. A quick visit with a laser measure gives floor areas to within 10 %. Those imprecise areas are enough for an estimate from rates: their precision matches the precision of the method.

The scope has to be defined package by package: which trades are involved, at what level of specification, light, intermediate or heavy, and which parts of the building are included. A vague scope produces a vague estimate, and it is for the economist to force that clarification with the client before producing any figure at all.

Rates are applied package by package on the reference area appropriate to each trade. The reference area is not the same for every package: habitable area for the internal trades, partitions, floors, paint, electrical, plumbing, façade area for external insulation, roof area on the slope for the covering, and numbers for the windows.

Three items specific to refurbishment always sit on top of the ordinary trades: strip-out and selective demolition, at 5 to 12 % of the budget before surveys; the compulsory surveys for asbestos and lead and the advisable ones for structure and energy; and waste disposal, calculated in tonnes by waste stream. These items are systematically missing from do-it-yourself estimates, and their omission is the leading cause of divergence between the initial budget and the final cost.

The contingency is calculated as a percentage of the works total and shown as an explicit line in the estimate, never as a hidden uplift. Its rate depends on the precision of the documentation: 10 % as a minimum, 15 to 20 % on an old or poorly documented building. That line should carry a note stating the conditions under which it can be reduced, after the survey, after the survey findings, after the developed design drawings.

The example below is an estimate from rates on a 320 m² town house built in 1935. No drawings exist. A visit allowed the approximate areas to be measured. The asbestos survey has been commissioned but not received, so a provision is carried. The scope is a complete refurbishment including insulated façades, the roof, all the finishing trades and the services.

The table makes two points. The structure is not priced at all: the visit revealed cracking in the façade and old floors of doubtful condition, and pricing that package without a structural survey would be manufacturing false precision. The final figure of 891 €/m² is consistent with the heavy refurbishment range of 700 to 1 200 €/m², which validates the overall order of magnitude even with one package missing.

• 1. The compulsory surveys: the asbestos survey before works is compulsory on any building predating July 1997, and the lead survey on any dwelling predating 1949. Their cost is modest, 800 to 4 000 € together, but their findings can move the estimate by tens of thousands.

• 2. Strip-out and disposal: removing the existing fabric costs money, and so does taking it away. Asbestos waste is charged at five to ten times the rate for inert waste. This item is 3 to 8 % of the budget depending on the extent of the strip-out.

• 3. The measured survey: with no drawings, a survey is indispensable before the tender. Its cost, 1 000 to 5 000 € depending on the size of the building, is negligible against the measurement errors it prevents, and it is systematically missing from feasibility budgets.

• 4. Compulsory compliance works: accessibility, bringing the electrical installation up to standard, gas compliance. These can represent 5 to 12 % of the budget depending on the starting condition, and they are often discovered at tender stage when no regulatory review was done beforehand.

• 5. Design and consultancy fees: architect at 8 to 12 % of the works, economist at 1 to 3 %, services and structural engineers at 2 to 4 %, approved inspector at 0,5 to 1,5 %, structural damage insurance at 2 to 4 %. Together these can be 15 to 20 % of the works cost, and they are systematically absent from feasibility budgets.

A refurbishment budget with no drawings is legitimate provided it states its reliability and its contingency explicitly. The method depends on the documentation available, from semi-detailed quantities on existing drawings at ± 15 % with a 10 % contingency, to an order of magnitude on an inaccessible building at ± 50 % with 20 %. The rates method runs in five steps: areas, scope, rates by package, refurbishment-specific items, explicit contingency. The five items most often forgotten are the compulsory surveys, strip-out and disposal, the measured survey, compliance works, and the design fees. The eight-point checklist confirms the prerequisites before any calculation.

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.

• Refurbishment economics in France: the economist's tools and methods
• Asbestos, lead and the works budget: reflecting the surveys in the estimate
• Structural risks in refurbishment: assessing the unforeseen before you start