One of the most important aspects when planning your self build or renovation/extension project is working out how much it is going to cost.
There are, however, many variables that can significantly alter build costs beyond the average, which could prove potentially disastrous for someone working to a limited budget.
Therefore, it is extremely useful for anyone contemplating a self build to have an understanding of what changes to the design, build route or specification will alter costs from the average, and how to make savings off these figures. Unless otherwise stated, per square metre costs relate to the whole floor area, rather than facing areas.
How Much will it Cost to Build my Own Home?
If you are new to self build and want to get an idea of what you can afford to build, you first need to establish how much you have available to spend by combining your savings, equity from the sale of your current home, plus any funds available via a self build mortgage.
Unless you already own a building plot, the next step is to take a look at the price of land in your area and set aside a sum for the cost of buying a site plus legal fees and Stamp Duty (visit hmrc.gov.uk for the latest SDLT rates). You can get a good idea of plot prices by visiting plotfinder.net — the UK’s largest database of small development sites.
You also need to set aside around £7,500–10,000 to bring in water, drainage, electricity, gas and telephone. If the site is a replacement dwelling, you may save the cost of some or all service connections, but will need to set aside a similar sum for demolition and site clearance.
Set Aside a Contingency
The balance of funds is your build budget. It’s a good idea to set aside 10–15% of this as a contingency for unforeseen costs and to pay for architectural design fees (typically around 5–6% of the build cost).
How to Calculate Your Build Cost
Now refer to the Build Cost Table and establish the average build cost/m² that applies to your project, based on your chosen build route, location and quality of specification. Divide the balance of your available build budget by that figure (£/m²) and it will give you a good indication of the size of house you can afford to build.
If you already have a design and want an idea of how much it will cost to build, first calculate the internal floor area across all storeys and then multiply this by the cost/m² relevant to you. To get a more accurate idea of costs you need to make adjustments based on the information that follows…
What Factors Affect Build Cost?
The bigger the house, the more it will cost to build, but there can be some economies of scale achieved that reduce the average cost/m² for larger houses, making a carefully designed large house better value.
The savings are primarily in the cost of building the superstructure, especially the foundations, walls and roof. The cost/m² of gross floor area for external walling elements decreases as the wall/floor ratio decreases.
Other one-off unit costs for items such as service connections, staircase, kitchen and boiler are spread out further on a larger house. To maximise efficiency, the design needs to be kept simple and avoid unusually large spans for floor joists/beams, rafters etc.
Plan, Shape and Layout
Complexity of design is one of the biggest factors affecting build costs. The simplest and most cost-effective floorplan is square. Compared to a square plan, a rectangular plan requires more wall for the same floor area, thus increasing costs. The longer and narrower the floorplan, the less efficient it is to build.
Building straight walls is cheaper than building corners, which slows down the build process — adding to labour costs. Consequently, the more angles introduced into a floorplan, the greater the cost, so a simple design with few corners is cheaper to construct.
Angles other than 90° right angles are even more time consuming to set out and build and so will increase costs further. Curved walls are among the most expensive to build of all.
Number of Storeys
Two of the largest fixed costs in constructing a house are the groundworks/foundations/slab and the roof. The specification and cost for a set footprint and roof layout will not vary whether the design is single storey, two storey, or three storey, yet the overall area of the design will increase dramatically — spreading out the cost. Multiple storeys also make better use of land — the most expensive element of all.
The average cost/m² for a bungalow is therefore greater than for a two storey house with the same footprint (all other things being equal), whilst a three storey design, or a two-and-a-half storey design using the roof space, will be even better value for money in terms of lower average cost/m².
If you want to get the maximum development return on a site, it often pays to build as many storeys as possible.
The cost of constructing a basement largely depends upon the digging out and removing of spoil. This cost – and the cost of waterproofing the structure – is mitigated to some extent by the fact that fewer windows are usually used than for above-ground storeys, and there is no external wall cladding (e.g. brick or stone).
As ever, the quality of fixtures and fittings will be a major factor in the final cost. For the purposes of producing a budget figure for your basement, measure the gross internal floor area and use the same costs/m² as for above-ground space.
There are instances where a basement makes better sense — for instance where ground conditions require very deep foundations. The cost of going down just a little further and excavating between the footings may not be that much greater. On a sloping site where the basement will only be partly below ground, it can make better use of the site than cutting or filling the slope to create a level area to build on.
The water table and ground conditions are another factor that will affect costs. If the sides of the excavation are likely to collapse, for instance in sand, and this will affect neighbouring structures, it may be necessary to create a retaining structure around the basement using concrete piling, and this will add considerably to costs.
There is little variance in costs between basement wall and waterproofing types (e.g. textured membranes or waterproof renders).
How Your Own Involvement Affects Build Costs
The average build costs are based on the cost of using a main contractor to manage the whole build.
- co-ordinate the trades, materials, plant, tools and scaffold;
- liaise with the architectural designer;
- co-ordinate the statutory inspections for Building Regulations and warranty;
- and take legal responsibility for the site.
If you take on this role by hiring subcontract labour directly, providing materials and facilities as required, you can reduce the build cost by 10-15% depending on how efficiently you manage the project.
If you decide to substitute some or all of the labour costs with your own DIY labour, you can reduce the average build cost substantially. You can undertake almost every aspect of the building work for which you have the time and skill to complete competently, with the exception of connecting gas appliances.
Approximately 35% of the total cost of building a house is labour, so if you do all of the work yourself you could reduce the costs by a third, as in the process you would also be taking on the role of project manager, saving 10-15% on the remaining materials costs.
In practice, very few self builders do everything themselves, although there are a few exceptions, who often take several years in the process. Most DIY self builders leave the more skilled trades to the professionals, especially those that require a good finish such as brickwork, plastering, rendering and groundwork/excavation.
Trades more easily undertaken by the DIY self builder include:
- fitting insulation
- roof tiling
- general labouring
- assisting plumbers and electricians on second fix
- floor laying
Typical savings for a DIY self builder doing roughly 25-30% of all the work amount to 20-25% of the total cost compared to using a contractor.
On larger projects a professional such as an architect, surveyor or engineer is usually retained to put the project out to tender, appoint the contractor and administer the contract through to completion. The fee for this is typically 3-5% of the total contract value (construction cost). If you take on this role yourself you can save this fee (which isn’t included in our base figures).
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How Your Specification Affects Build Cost
The HB&R Build Cost Table shows three levels of quality: Standard, Good and Excellent. Although the cost of many of the construction elements such as the foundations do not vary based on quality, the cost of external facings, joinery, flooring, fittings – and renewables – can potentially double the cost of building the same house compared to a standard specification.
For purposes of illustration, we have provided ‘live’ costs for a 220m² house based on £1,000/m² build costs (figures shown in italics and include labour, ignoring VAT).
Claddings, Renders and Exterior Finishes
Brick typically represents around 5% (£11,000) of the cost of building a house based on stock bricks costing £350/1,000. Upgrading to character bricks at £850–950/1,000 can more than double the cost of this element (to £20,460) by the time additional labour is taken into account to lay the irregular-shaped bricks, especially if they are laid in a traditional bond such as Flemish. Additional costs can be incurred with detailing, such as brick arches.
Natural stone is a more expensive cladding choice than stock bricks. Using cropped coursed stone blocks to form an independent outer leaf of a cavity wall (with a blockwork or timber frame inner leaf) works out at a very similar cost to handmade brick. Using reconstituted stone costs much the same for labour but slightly reduces materials costs.
Building using traditional random stonework is slower and although the materials cost is similar, the labour cost is higher, making it more expensive — used at a depth of 250mm against full-fill cavity insulation and waterproofed blockwork (if acceptable to Building Control in your area) is the most cost-effective option. Building against a backing block to form a cavity, with an inner leaf of blockwork or timber frame, will add around £20/m².
Sand and cement render on blockwork is one of the cheapest options, especially if it is self-coloured using white cement and local sand, so it does not require painting (which typically costs around £10/m² or £2,200).
Adding lime will make the render more forgiving but will marginally increase costs. Modern polymer renders are more flexible but add more to materials costs
Painted softwood shiplap can prove a cost-effective choice, especially on a timber frame structure, where no backing block is required. Dense timbers such as oak, western redcedar and sweet chestnut, and also heat-treated softwood such as larch, are good choices and comparable in cost to using a good-quality brick. Find out more about timber cladding.
The load-bearing structural walls of a house typically represent around 13–15% of the total build cost (£30,000) based on using concrete blockwork for the external walls and ground floor partitions, with timber partitions on the first floor.
The cost of switching to a different construction system, such as an ecological timber frame with 140mm studs width, is surprisingly small across the whole house. Even if the frame costs 10% more than using blockwork, the overall impact on the cost of the house is only 10% of 15% — around 1.5% (£3,000).
The same applies to switching to structural insulated panels (SIPs) or insulated concrete formwork (ICF), which manufacturers claim to be between 5–20% more expensive than blockwork, adding 1–3% (£6,000) to overall construction costs, but bringing benefits in terms of faster build speed and superior levels of airtightness.
Building using oak frame construction is perhaps as much as 40–50% more expensive than using blockwork. Overall this is likely to add 6–7% (£15,000) to total construction costs.
Roof costs are made up of the structure, insulation, felt and battens, roof covering and flashings/detailing. The cheapest option is to build a simple rectangular-format low-pitched roof using manufactured trusses. The low pitch means the rafter lengths are shorter, using less timber, and the manufactured trusses use a web of thinner timbers, again reducing materials costs. This is what most speculative developers use.
The more complex the roof shape, the more likely it will have to be cut on site, using more labour and timber than factory-made trusses, thus adding to costs and taking longer to construct. It will also require an engineer to check the design and produce calculations for Building Regulations purposes, for which there will be a fee that would otherwise be covered by the truss manufacturer. More complex roof designs may require structural steelwork, too.
The steeper the roof gets, the more expensive the roof will be to construct. As a rule of thumb, increasing the roof pitch by 5% will double the cost of the roof, while increasing it by 10% will triple it.
The design of the roof structure will change if the roof space is to be used for accommodation, utilising either factory-made attic trusses, or a traditional cut roof built on site. Both options will increase the costs of the roof structure, but this will be mitigated by the additional space created. Accommodation in the roof space generally costs around 60–70% of the average cost/m² for the rest of the property.
Developers favour large-format concrete interlocking tiles with a coverage as low as 8–10 tiles/m², keeping labour and materials costs down. Most self builders choose to use more attractive, smaller-format tiles made from natural materials such as clay or slate. Unfortunately, however, smaller tile formats will increase labour and material costs.
If you plan to use a roofing material other than that allowed for in the average costs (£20/m² Standard, £40/m² Good, £80/m² Excellent) you need to add an allowance for the net difference in cost. If you decide to go for decorative details to the ridges or verges, or to use very irregular handmade tiles, this will add to the cost of labour and materials.
Service Connections Costs
If your plot is not connected to mains services, allow £10,000 for connection to water, sewers, electricity, telephone and gas. If the site does not have access to mains gas, you will need to budget an extra £2,000–2,500 — more for renewables.
If there is no mains sewer, you will need to budget for an off-mains alternative (in place of a mains drainage connection for which you can deduct £2,500). As a budget figure, allow £2,500–3,500 for a small family and £3,500-5,500 for a larger household.
Unlike most costs, which vary according to the quality and size of house you are building, foundation costs/m² are likely to be more or less the same whatever you build. However, it is one of the few aspects of housebuilding that you cannot accurately predict until you actually start digging.
Unlike almost every other aspect of your build, where you are in control of the specification, it is the local authority Building Control surveyor (or licenced inspector) who will ultimately decide the foundation solution that is acceptable for your site. If the ground conditions demand an engineered foundation solution, such as a raft, piles and reinforced ringbeam, or a reinforced slab, allow an additional £10,000 in your budget.
Variables that will influence your costs will be the proximity of your site to the nearest ready-mix concrete plant, and the nearest tip for removing spoil (known as muck away).
Building on a sloping site will also increase costs due to the work involved in cutting and filling the site to create level terraces, landscaping work to create retaining walls for drives and paths, and the additional cost of complicated designs. As a general rule, each 5° of slope from level on the site will increase your build costs by £5,000 (according to Brinkley’s Slope Law proposed by Mark Brinkley, author and HB&R Contributing Editor).
Floor Structure Costs
Concrete slab, suspended timber or beam and block? All are a viable choice for your ground floor structure. If you are not sure which to choose, read this article on ground floor structure costs by David Snell, or read on to find out what the options are for first floors and beyond.
The standard specification for first floors is to use softwood joists covered with flooring grade chipboard; the cost of which is £16–19/m² (approximately £3,200–3,800). If you opt to use engineered joists such as I-beams or beams with a steel web such as Posi-joist, this will add to your costs by £2–3/m² (£4–600) but the more regular dimensions and improved stability can help avoid squeaky floors.
If you are building a masonry or concrete (ICF) house, you could opt for a concrete first floor structure, using either pre-stressed concrete beams infilled with concrete blocks or large-format concrete floor panels. This offers superb strength and acoustic separation, and allows you to have masonry first floor walls throughout. This specification will add to your costs by £8–12/m² (£8-1,200).
Walls and Ceiling Costs
There is little cost difference between blockwork and timber frame internal partition walls.
Developers looking to keep down costs work with a standard ceiling height of 2.4m. Changing the ceiling height adjusts the average cost/m² for that storey by approximately 1.6% for each extra 100mm (meaning a 2.7m ceiling height on the ground floor adds £4,800 to the total costs). Following industry standards allows you to use industry standard sized materials such as plasterboard on your walls.
Wall and Ceiling Finishes
Costs are similar for both wall finish options (wet plaster or dry-lined). The standard specification assumes emulsion paint throughout, with minimal tiling to kitchen and bathrooms at £64/m² (£14,080). The good specification includes more tiling in the kitchen and bathrooms and wallpaper in the living room at £80/m² (£17,600). The excellent specification also includes wallpaper to the bedrooms at £96/m² (£21,200).
Ceilings are usually covered with plasterboard and finished with a two-coat skim of fine gypsum plaster and emulsion paint at £17–20/m² (£3,700). If you decide to add decorative coving, ceiling roses or other decorative plasterwork, you will need to allow for extra.
How Much Will My Staircase Cost?
The main staircase is an opportunity to add individuality to a property and to make an architectural statement, and if this is your plan then you need to make an additional allowance for this above the staircase allowance included in these build costs.
The standard specification solution is a softwood staircase consisting of two straight flights linked by a half-landing, with a softwood balustrade, painted or stained, at a cost of around £1,250.
The good specification includes a single straight flight in painted softwood at around £1,500, whilst the excellent specification allows for a straight flight in hardwood, with hardwood balustrade at around £2,150. Obviously this is removed from your total build cost if you’re building a bungalow.
Many modern houses do not include a chimney — especially those built by speculative developers, largely because of the cost, which starts at £6,100 for a standard specification. Many ecological houses also forgo a traditional open flue chimney in favour of a woodburning stove and stainless steel flue, at an installed cost of around £1,650–2,500.
The standard specification has an allowance of £6,600 for the fireplace and flue; the good specification has an allowance of £8,300, and the excellent £11,300.
Windows and Doors
External joinery is another feature that self builders place a great deal of value on, and consequently tend to invest in quite heavily.
- The standard specification house has off-the-shelf painted softwood casement windows and external doors, with double-glazed units and factory-fitted aluminium ironmongery at a cost of £60–86/m² (£13–19,000).
- The good specification includes high-performance, off-the-shelf painted softwood casement windows and external doors at £81–107/m² (£17–23,500).
- The excellent specification includes double-glazed aluminium frames in hardwood surrounds and a hardwood panelled front door and good-quality ironmongery at £121–146/m² (£26–32,000).
If you want to go for bespoke windows, then get a quote from a joinery supplier and substitute their price for the allowance/m² (joinery allowance for your chosen specification multiplied by your gross internal floor area).
This is another area where many self builders choose to make an upgrade from a standard specification.
- The standard specification includes hardboard-faced hollow-core flush doors in softwood frames, hung and decorated at around £250 per door (£4,000 based on 16 doors) including all ironmongery.
- The good specification includes slightly better hollow-core flush doors in softwood frames, hung and decorated at around £350 each (£5,600).
- The excellent specification includes hardwood veneered solid-core doors in softwood frames, hung and decorated with quality ironmongery at around £450 each (£7,200).
If you plan to put in more expensive doors, you will need to account for this in the total build cost.
Kitchen Build Cost
- The excellent quality specification price includes an allowance for a quality kitchen from a mid-market supplier with timber worktops.
- The good quality specification includes top-of-the-range units from a contract supplier such as Howdens or Magnet with timber worktops.
- The standard specification includes standard MFC units with a laminate worktop, contract quality from a merchant or DIY shed.
If you are going for a top-of-the-range designer kitchen then get a price from your supplier, including fitting, and substitute this for the kitchen allowance per square metre when calculating your build cost.
Kitchen Cost Allowance Guide
|Standard range contract fittings||£14–20/m²|
|Top of range contract fittings||£40–60/m²|
|Top of range bespoke fittings||£110–120/m²|
Bathroom Build Cost
Plumbing costs are much the same regardless of the specification you choose, but the cost of sanitaryware and brassware varies enormously. The quality and area of tiling on the floor and walls varies from £23/m² upwards, and then you can add showers and enclosures, heated towel rails, underfloor heating, luxury baths and more.
The costs in the tables allow for two bathrooms and one cloakroom at the relevant cost. If you plan to fit more bathroom facilities, or better quality facilities, then use the typical cost allowances below to allow for this in your overall build cost.
|Bathroom (WC, basin, bath and additional plumbing, doors, walls, windows and finishes)|
|Shower room (WC, basin, shower cubicle, doors, walls, windows and finishes)|
|Cloakroom (WC, basin and additional plumbing, doors, walls, windows and finishes)|
Working out the Cost of Fixtures, Finishes and Utilities
This section covers:
- Built-in cupboards
(laid prices including painted softwood skirting)
Alternative Floor Finishes
|100% wool carpet||£45–55/m²|
|Laminate (wood effect)||£20–25/m²|
|Engineered oak flooring||£60–65/m²|
|Reclaimed pine floorboards||£40–50/m²|
|Natural stone flags||£70–80/m²|
Built-in wardrobes and storage areas are already allowed for within the costs at roughly £20/m², £30/m² and £40/m² for standard, good and excellent specifications.
A standard heating solution is a radiator system with a gas boiler and basic controls. A standard central heating system will cost £18–23/m² (£4–5,000 for our house)?and this is the allowance in the average build costs.
Underfloor heating is typically more expensive, so allow £30–40/m² (£6,600–8,800). If you want renewables, add this in to your budget accordingly. The standard costs allow for the inclusion of a mechanical whole-house ventilation system with heat recovery, costing around £1,600 for houses under 150m² and £2,100 for larger houses.
Standard costs do not vary much from house to house other than by scale. If you decide to fit anything out of the ordinary (e.g. a whole-house structured cabling network), you will need to make an allowance for these upgrades.
|Standard||£37–45/m² (£9,900 for our house)|
Electrical additions (per room)
|Low voltage down lights (7)||£350–400/room|
|Structured cable network||£200–250/room|
|Separately switched 2a lamp circuits||£250–350/room|
|Security alarm system||£600–1,500+|
Every month in Homebuilding & Renovating magazine, we publish a Build Cost Table showing average construction costs for self builders across the UK. This makes it easy for anyone to get an idea of how much it is likely to cost to build their own home.
The table includes variables for build quality, discounts for DIY involvement as project manager or tradesperson, the economies of scale achieved with larger houses and the number of storeys, plus regional variations.
The result of using the table, even though based on averages, is remarkably accurate — making the figures extremely useful in working out what it is worth paying for a particular building plot, or how large a house you can afford to build.