External works and ancillary buildings (such as garages) are surely the most overlooked of all the costs on a home building project. These elements are frequently under-budgeted in the first place, plus people’s cash streams are often depleted by the time it comes to getting the landscaping done.
In fairness, if you’re taking a long-term approach then it’s often the right choice to allocate the vast majority of your funds to the principal house. But if you want to finish, move in and immediately enjoy your new home’s facilities to the fullest, then you should make a concerted effort to preserve your external works budget. And bear in mind, this stage of your project is likely to cost more than you think.
Building a typical garage
A detached double garage, built in matching bricks and tiles to the main house, may well cost you upwards of £18,000, as per the 'cost guide' table below.
Typical 36m2 Double Garage
|Trench fill foundations||£2,520|
|Lightly reinforced ground-bearing slab and backfill||£2,700|
|External walls, piers, steelwork and lintels||£3,900|
|Roof covering (felt, battens and tiles)||£1,260|
|Carpentry (soffits, fascia, barge board and gable claddings)||£1,350|
|Garage doors, access door and window||£3,000|
|Extras (decoration, security etc)||£500|
|Total cost for double garage||£18,620|
These costs are based on a specification that includes basic dimensions of 6m (wide) x 6m (deep) x 2.5m (high), a shallow pitched (25°) concrete tiled roof, half brick-thick external walls with brick piers, a simple ground floor slab and trench fill foundations (to a standard 1m depth). The breakdown also assumes two single garage doors, a personal door and window, simple electrical supply and some rainwater drainage.
It’s easy to see how this specification could be increased by changing the external walls to cavity construction, adding some insulation, sealing the floor, raising the roof pitch, including a smarter roof covering, adding some cold water plumbing etc. Many people would consider these quite normal requirements for a modern garage – and they could easily see the price escalate to £25,000 plus.
What’s more, the costs above are given on the basis of you project managing the build (pulling all of the trades together yourselves). If you leave it to a main contractor, you’ll need to add a management fee on top. In addition, don’t forget to add VAT if your project doesn’t qualify for a zero rated status (for example if you’re adding an outbuilding to an existing property, rather than creating a new home from scratch).
With a new build or major refurbishment project, some folks sensibly get their garages built first on site. This not only helps you to erect the structure to the original budget, but the building will also make fabulous dry storage facilities for many of your other materials throughout the project. It could also serve as an area for temporary site office functions. It all really depends on the project’s logistics and how much access space there will still be once the garage has been built.
Depending on the prevailing soil conditions on site, your driveway will need a proper specification in order to take all reasonable vehicle loads, effectively shed surface water and prevent local settlement and surface erosion.
Unless you’re building on exposed bedrock, some excavation for reduced levels (digging down around 250-300mm), geotextile membranes and filling with compacted hard-core will be necessary. This ground work will come in at about £18-£20 per m2. Thereafter, the choice of topping and finishes is up to you.
Concrete edgings set in lean-mix concrete can look neat and, in some cases, will be essential to stop the spread of your finishing material. Budget around £10-£12 per linear metre for this. Pea shingle (gravel) will be the cheapest surface option. It can easily be spread yourself and could cost as little at £4 per m2 depending on the thickness you choose.
Moving up the scale, tarmac is best built up in layers of circa 40mm thicknesses, with larger aggregate being used for the base course. Each layer will be circa £15 per m2 upwards and two well-compacted coats will always deliver a better result than one.
Concrete block paving is a popular choice. Prices start from about £28 per m2 for a typical installation loose-laid on a 50mm sharp sand blinding layer with fine sand brushed between the joints. This can rise to circa £35-£40 per m2 for coloured varieties laid in a herringbone (or similarly decorative) pattern.
Whatever covering you choose, it’s important to be clear about how your surface water will be managed either through a porous paved option, traditional gullies or some of the more sophisticated attenuation systems, all of which can only be priced once you’ve decided your final details.
Premiums will, of course, apply to small or complex areas. If you are going to need a builder to coordinate all of the above for you then you must allow for their management, overheads and profit on top.
First published: February 2014 Author: Tim Doherty