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Construction Estimating for Historic Building Restorations

Saving historic buildings is not something that can be done alone. It’s important to find a non-profit organization that is passionate about historic preservation and can give you the backing and reach to save your building.

Archival research may be able to identify missing elements or show how other features might best be incorporated into the project. A detailed site visit is necessary and a contingency allowance should be built into the estimate.

Preparatory Work

A successful rehabilitation project requires more than just the use of skilled workers. Preparatory work must be completed to establish the scope of a project and determine what can be done and what cannot be done. In historic restorations the building may have been altered over time and the alterations may have left evidence behind that must be considered during a rehabilitation project. This work involves determining the condition of the building and its components and making decisions about whether or not to repair, replace or remove elements of the structure.

The evaluation of a building can be performed by facility staff personnel, an architect or a design professional with experience working on historic buildings. For larger projects the evaluation is often undertaken by a team of design professionals that may include structural, civil, mechanical, electrical, plumbing and fire protection engineers, architects, landscape architects, acoustics, cost estimating and historic preservation specialists.

It is important that the evaluation process includes a detailed survey of the existing conditions of the building. This will provide the information needed to prepare an engineer’s estimate. The evaluation should also consider the site, accessibility and environmental issues that could impact the costs of a renovation.

When preparing an estimate, the designer should consider all the alternatives to ensure that the project can be built within budget. This will usually require the use of a spreadsheet or computer program that allows for a flexible design. This approach can be used to compare the cost of options to a budgetary figure and can help to avoid costly mistakes early in the construction process.

Historical cost data is very useful in preparing estimates and should be kept on file. However, it is difficult to produce a satisfactory estimate using unit rates alone (for example costs per square foot) without the support of measured quantities. Developing a set of base drawings is a worthwhile early investment. Basic wall, floor and roof area quantities are helpful but a more comprehensive survey is usually necessary.

When the engineering estimate has been prepared, it can be used by the owner to solicit construction contractor bids. The bid estimate will include the direct construction costs plus expected amounts for contractor overhead and profit. The bid estimate is revised during the construction period to reflect actual costs and any change orders initiated by the owner or due to unexpected construction delays. The revisions can be beneficial to both the contractor and the owner as they provide a baseline against which actual costs are compared and negotiated. The revisions can also help the contractor develop more accurate schedules and reduce the risk of cost overruns.


The quantity surveying or cost estimating phase of the project focuses on the detailed work of preparing an accurate estimate of the cost of the building restoration, based upon the design drawings and specifications. The estimate is prepared for the contractor to bid on the construction and for the owner to use as a basis for budget control.

A QS prepares the preliminary estimate in two primary ways, using measured quantities or a quantity takeoff method. Quantity takeoff is more time consuming than measuring and can be less reliable than the unit rate method, but it does allow a level of detail that a QS can use to develop an order of magnitude estimate.

During the initial evaluation stage of the renovation project, a QS will work with an architect or other design professionals to establish what is required for the rehabilitation of the historic structure. This work will include a review of the existing conditions, including a careful analysis of the historic features and characteristics that make the building significant. Recommendations will be made as to how these features can be rehabilitated to meet current occupancy requirements without damaging the historical significance of the structure.

Preparation of a detailed estimate requires research of alternative design solutions and the collection of unit costs of the major elements in the scope of works. If the building is listed, it may also require consultations with a variety of organisations, and the cost data collected must be carefully compiled in order to take account of the varying levels of pricing information for such elements as repairs to early concrete framed structures, 18th century wallpaper or 19th century laminated beams.

The final estimate that a QS prepares will often be based on the detailed design work and on an assessment of the risks associated with particular elements of the work such as the need to open up the structure or the potential requirement for listed building consent. The result is a comprehensive and detailed document with a defined scope of work, a clear brief, the quantity of work to be done and an outline schedule of unit costs.

A definitive estimate is often used to spot check a contractor’s bid or to investigate disputes. According to the AACE, it takes 5 to 100 times as much effort to produce as a Level 1 estimate. It is often called a full-detailed, tender, final, control, trial, firm price or as-built estimate. The preparation of this estimate will usually rely heavily on a site visit, which should be conducted in the presence of the architect. This will ensure that the QS can understand and record all the information that will be needed for the estimate preparation.