7 factors that can influence costs
Consider the intended use of the additional loft space prior to making any application for planning permission so that you understand exactly what your budget can achieve. Once permission has been granted, if the design is changed significantly, you may need to go through the whole process again at increased cost and time delays.
Rooflight loft conversions are generally the cheapest option. A dormer conversion would be the mid-range option, with a full ‘roof-off’ (single or double hip-togable or mansard loft conversion) coming in at the most expensive.
Prior to 1965, roofs were traditionally cut, which left ample space for converting the loft. Since then, though, prefabricated ‘fink’ (W-shaped) trusses have been the preferred option, for faster roof construction, but these also reduce the space available for potential conversion.
Trusses can cause a problem when converting a loft, as structural support needs to be introduced to compensate for the removal of the truss and floor supports, adding cost and time to the conversion. Houses constructed prior to 1930 may pose similar issues, such as insufficient head height.
Bungalows are generally the cheapest properties to convert because most (but not all) have spacious lofts. The taller the building the greater the cost due to all the extra fire safety work and additional lifts of scaffolding.
A structural engineer should always be engaged to design a solution where these problems arise. There are solutions for loft conversions with difficult roof constructions.
Most houses will have long since converted to combiboilers and other more efficient heating solutions, but water tanks may still exist in the loft. Plumbers tended to leave existing water tanks in place, as they were often too cumbersome to remove, especially through a loft hatch. It would be an ideal opportunity to remove the tanks at a small cost during a major loft conversion.
There may also be a redundant chimney stack which could be very costly to remove in terms of both time and money, to gain a small amount of additional space. The benefits of removing it need to be carefully weighed up in terms of the potential additional space against the time and cost elements.
Adding just bedrooms alone will not be as costly as installing a new bathroom or bedrooms with en suites. Such facilities will obviously add to the cost and timescale of the loft conversion. An en suite will require the extension of services such as drainage. Designing these in such a tight space will require careful planning and budgeting.
You may need to budget for a survey, at a cost of around £250, to identify asbestos or other harmful products, which could have been used during the original construction.
If you find bats in your loft, a bat survey costing around £350 will be needed. If migration measures are required, certain parts of the survey can only be carried out from May to September inclusive, which could add time and money to your budget.