when costing a project it is important to understand the following; if the data entered is incomplete or inaccurate, the results will be too.
Architectural drawings are no more than a model. pricing early sketch designs and even planning drawings will invariably prove inaccurate. The more detailed and accurate the plans (with dimensions, steel sizes, materials, insulation and specifications) the more accurate the cost estimate, or quote will be. Estimating accurate costings at the very outset of a project is difficult as we do not have all the information to hand. Builders are often reluctant to provide a quotation on anything other than detailed Building Regulations drawings.
Estimates are based on assumptions, not fact. Design is an evolving process.....Pricing up preliminary sketches that will change is the estimating equivalent of nailing jelly to a wall. Project costs are only likely to increase if quotations are given on incomplete information and for this reason is is easy to understand why builders are reluctant to quote on incomplete information.
Site conditions can also add to the the costs; sloping sites, the proximity of trees and hedges (regardless of size) will all add to the cost. Legal requirements with neighbours such as party wall issues will all add to the cost (Even neighbours can all add to the cost of a project if they choose not to cooperative). Information not available at the outset, such as undiscovered drains, culverts, poor ground conditions and the discovery of asbestos on site will all serve to put the price up. With this in mind it is easy to understand why a building contractor will only price detailed drawing packages and specifications.
Fortunately, there are some basic rules of thumb that allow project costs to be estimated with some degree of accuracy at the outset, without having to run to additional design fees at the outset.
for a straightforward new build houses on a flat site, the general rule is to estimate the value of a project on a cost per square metre basis. of between £1000-£1200/sqm/ If the design is more innovative this figure will increase.
Extensions and renovation projects are more difficult to cost as there are generally more unknowns, given the uncertain nature of existing buildings. For all projects a good measured survey at the outset is essential, as correct and accurate information will inform you and the architect when making design decisions. Base your initial build cost on a figure between £1200 and £1600/square meter to provide a rough idea of costs. Remember this is a rough estimate. The more complex the design the more expensive it will be. 2 storey extensions will be slightly cheaper as there will be fewer junctions and there are economies of scale (only one roof and the same foundations as a single storey extension, for example).
Choice of fittings will also push up the price of any project. You only need to look at the huge variation in cost of kitchens to demonstrate this.
Don't forget professional fees and fees payable to the Local Authority for planning and Building Regulations, which can be overlooked. Of course you can do much of the work yourself to reduce the costs; self-builders sometimes look to project manage the project to reduce costs. It all depends in the level of risk you want to take on board.
It is always a good idea to get a quantity surveyor to provide a build cost, based on a priced bill of quantities. This is an inexpensive way to establish a benchmark to test your builder's quotations against.
Homebuilding and renovation magazine provide useful on-line articles on project costs. Their website also provide a project cost calculator that will help inform the costs (please note....they do stress the cost calculator is no substitute for professional advice).