Cal­cu­lat­ing your Self-build Costs

A sim­ple cost es­ti­mat­ing guide for peo­ple build­ing their own home

Homebuilding & Renovating - - Contents -

Our handy guide to self-build costs around the UK

One of the most im­por­tant as­pects when plan­ning your self-build or home ren­o­va­tion/ex­ten­sion project is work­ing out how much it is go­ing to cost. This fig­ure will de­pend on the size and shape of the house, the level of your own in­volve­ment, where in the coun­try you in­tend to build, and the ma­te­ri­als you’re go­ing to use. If you can make even rough de­ci­sions about th­ese fac­tors, then you can be­gin to work out how much it is go­ing to cost.

As a very gen­eral rule of thumb, ex­pect a build­ing plot to cost be­tween a third and a half of the end value of the fin­ished house. The costs of build­ing a house will then de­pend on the vari­ables listed above. All build­ing work is usu­ally quoted on a cost/m2 ba­sis. For ex­am­ple, a typ­i­cal new four bed­room self-built home is around 200m2 (with 100m2 on two storeys) and usu­ally varies be­tween £900-£1,500/m2 (although self-builders can achieve costs of be­tween £300£3,000/m2).

Ren­o­va­tion costs are more dif­fi­cult to es­tab­lish as they in­volve many vari­ables, but al­low at the very least £1,000-£1,300/ m2 for work. This, added to the cost of the plot/house and with a 10-30% con­tin­gency, should re­sult in less than the fi­nal end value of the house.

The ta­ble be­low, based on in­for­ma­tion from the Build­ing Cost In­for­ma­tion Ser­vice (part of RICS, the Royal In­sti­tu­tion of Char­tered Sur­vey­ors), is up­dated monthly to help you work out a more ac­cu­rate es­ti­mate (note, how­ever, that th­ese fig­ures are for build costs only and do not ac­count for VAT, which is not charged for self-build projects). There is a free on­line ver­sion at home­build­ing.­cu­la­tor.


Iden­tify your build route from the four op­tions Your level of in­volve­ment in the project will in­flu­ence the build costs. For sim­plic­ity, the four most com­mon build routes have been iden­ti­fied be­low:

Build Route A: DIY + Sub­bies Build­ing on a largely DIY ba­sis, sub­sti­tut­ing around 30% of labour costs with DIY, and em­ploy­ing help with the rest of the build­ing work. Ma­te­ri­als pur­chased di­rectly.

Build Route B: Sub­bies Build­ing us­ing trades­peo­ple hired di­rectly — you will be project man­ag­ing, but there is min­i­mal DIY in­volve­ment. Most or all ma­te­ri­als pur­chased di­rectly. l Build Route C: Builders/sub­bies Build­ing us­ing a main con­trac­tor or pack­age sup­plier to com­plete the struc­ture to a weath­er­tight stage, with the re­main­ing work un­der­taken by sub­con­trac­tors and most ma­te­ri­als pur­chased by self-builder di­rect from sup­pli­ers. l Build Route D: Main con­trac­tor Build­ing us­ing a main con­trac­tor. Build­ing in this way re­quires the least in­volve­ment from the self-builder.


Iden­tify your ex­pected level of spec­i­fi­ca­tion The stan­dard of spec­i­fi­ca­tion that you choose will have an enor­mous in­flu­ence on your build cost. For es­ti­mat­ing pur­poses, three gen­eral cat­e­gories of qual­ity have been iden­ti­fied: l Stan­dard: This rep­re­sents a ba­sic build qual­ity equiv­a­lent to that of­fered by most spec­u­la­tive de­vel­op­ers. A house may in­clude stan­dard soft­wood join­ery, studwork par­ti­tions, a con­tract kitchen, ba­sic san­i­tary­ware and ra­di­a­tor cen­tral heat­ing. l Good: This is equiv­a­lent to that of­fered by qual­ity de­vel­op­ers. Fea­tures may in­clude high-end off-theshelf soft­wood join­ery, block­work par­ti­tion walls, con­tract qual­ity kitchen and san­i­tary­ware and un­der­floor heat­ing (UFH) down­stairs. l Ex­cel­lent: A very high stan­dard. This house may in­clude hard­wood join­ery, block­work par­ti­tion walls, a be­spoke kitchen and qual­ity san­i­tary­ware, and UFH, for in­stance.


Mul­ti­ply the fig­ure by your house size We have used gross in­ter­nal floor area as a mea­sure (it’s the most com­mon in the in­dus­try). It’s the area of a build­ing mea­sured to the in­ter­nal face of each perime­ter wall for each floor level. It in­cludes ar­eas oc­cu­pied by in­ter­nal walls and par­ti­tions.

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