How much will my building project cost?

 

Why your architect can't give you a simple answer

"How much will it cost?" It's literally the million dollar question - though my clients are usually hoping for an answer that doesn't run to seven figures in sterling or dollars.

Architects are not costing professionals, though they'll have an idea of typical costs in your area, based on experience. They'll have asked broad questions about your budget before getting to work on designs. But it's difficult to establish costs accurately at the outset of a project, in a variable market with many factors that can affect cost considerations.

If you want to get an accurate costing for a project, you could employ a quantity surveyor - a building cost specialist. Some quantity surveyors will give you a broad-brush estimate for the build cost that you can use as a benchmark for comparison with tenders. If you want very accurate prices, they can also do a more detailed assessment, but this can cost a lot.

Your architect may be able to recommend a quantity surveyor if you want or need this level of detail. Generally, they're used for commercial projects or developments - or for particularly complex and expensive individual builds.

Estimating for different project elements

So, how else can you get an idea of costs? One way is to look at the different aspects of your project.  Every project, location and existing building has different details, so it's impossible to give hard and fast rules. But as an example, here's some guidance I recently gave a client for their major extension and renovation, using rules of thumb to break down the main elements of their build. These kinds of principles help clients to get a better sense of the main elements and variables in a building project.

Your side extension kitchen is quite straightforward. For this, I would allow a sum of £2,000 per square metre of floor area. This allows for a finished building of average standard, including electrics and standard heating solutions, but without kitchen or utility fittings. You'd need to budget for VAT at 20% on top.

For this particular project, the next part is less easy, as there are structural elements to the two-storey design that will likely push the cost above the standard amount. So, I advised:

For the front extension, I would use the footprint of the first floor x 2 rather than the reduced area of the ground floor, as the reduction of floor space and materials is probably outweighed by the complexity of the steelwork needed for your bay window, overhang and post arrangement.

Kitchen and bathroom costs - from basic to luxury finishes

As in many projects that aren't new builds, this project has a renovation element, changing the internal layout and features of the existing house.  I said:

It's harder to assess the renovation element on a square metre rate. I would allow an average of £5k for each steel beam, to include supply and fitting. I would allow £10-15k for a good quality bathroom or shower room, including supply and fitting of sanitary ware and tiling. (Your builder may be able to supply standard finishes and sanitary ware for less, if budget is tight.) I would allow a minimum budget of £30k for supply and fit of an average sized kitchen to a standard spec, including appliances. (The kitchen cost can be a lot more than that depending on your choice of units, specification of fittings and types of work surface.) To renovate and fit out the laundry and boot room might be roughly £5k each. Again, plus 20% VAT.

Windows, doors and walls

Window provision and replacement is another big cost in a renovation. It may be included in the per square metre build cost of new build elements of the project, but not in refurbishment. I explained to my client:

There will be some builders' work in relation to the replacement of existing windows - such as replastering the window reveals. I would allow a 10% builders' cost on top of any supply and fit quote from window suppliers. You might reasonably deduct the cost of new windows from the new build elements.

There are extra elements of renovation to be factored into this particular client's project. So:

We need to think about allowing labour costs for wall repositioning. For new internal doors, count the doors and allow £150 per door, unless you have any specific details for these. I would suggest approximately £5k for the new staircase.

I recently put a designer staircase into a house that cost £33,000. If this client wants to make a grand feature of theirs, the cost could spiral (along with the staircase!) And again, don't forget the VAT on these additions.

Popular contemporary choices

Sliding folding doors and underfloor heating are popular features in current home design. They add to the wow factor and comfort of your renovation, but they come at a price, of course. I said:

Sliding folding doors would be extra on top of any standard square metre build cost. Underfloor heating would be above a standard radiator cost that might be included in the square metre costings. I would allow an extra £5k for that.

The cost of special technologies, like air or ground source heat pumps or solar panels, also need to be added on. These won't be included in a standard per metre build cost.

Floor and tiles

Another important budget item is floor finishes - these are seldom included in builders' costs and can vary wildly. If you know the floor area for the property, you can work out an approximate budget for what you want by looking online at an average square metre cost for carpet or vinyl, including underlay and fitting. This can add up fast, especially for floor tiling.

Builders give costings to compare when they tender

Asking some builders to tender for your job is a good way to get a true sense of the costs. Once you've had some prices back, you or your architect can make comparisons and even negotiate with the preferred builders to work out a way to reduce or change elements of the planned renovation, if the costs are too much.

Contingency is crucial

I recommend allowing 5-10% contingency for unforeseen issues that sometimes crop up once the builder digs into the ground or begins to deconstruct the existing building. This could be unmarked drains, poor foundations, unconventional building materials or structural defects that were undetectable before work started.

At the moment, I'm also advising clients to set aside a minimum 10% further contingency to cover all the current, widely reported issues with price fluctuations in material costs and as a result of Brexit tariffs.

For many projects, there can be one, two or more years between my first meeting with the client and estimating build costs through a tender. Lengthy decision-making, delays to planning consents, seasonal ecological surveys, saving up or changes in clients' priorities can prolong the process. A lot has changed in the last two years - designs drawn up with a ballpark £100k budget in mind in 2020 will cost significantly more to build in 2022.

Professional fees are separate from build costs

Separate from the build costs, don't forget your budget for professional fees. Most of these will be incurred before you go out to tender or appoint a builder, but bear them in mind if you're only at the thinking stage right now.

Depending on how large and complicated your project is, you might need to use the services of a structural engineer, planning consultant, conservationist, ecologist, bat surveyor or landscaper as well as your architect. There may also be local authority costs in applying for planning consent, building regulations and other necessary certificates and compliance.