How to Calculate House Rebuilding Costs

Item: Ellis David
Rating: 4.7
Author: Ellis David

When you arrange home insurance you will be asked for your home's rebuild cost — what it would cost to rebuild the property from scratch, not what it would sell for. The two figures are rarely the same, and getting the first one wrong is expensive in a way that only becomes apparent at claim.

Insure for too little and most policies allow the insurer to cut the claim in proportion. Insure for too much and you pay for cover that will never pay out, because settlement is based on what rebuilding actually costs.

This guide explains what goes into a rebuild cost, how to arrive at a figure, and when a calculator is enough and when it is not.

What Is a Rebuild Cost?

A rebuild cost is what it would cost to reconstruct your home if it were destroyed by an insured event such as fire, flood or explosion.

It includes far more than bricks and mortar. A rebuild cost estimate typically covers:

Demolition of what remains, and site clearance
Labour and building materials
Professional fees (architects, surveyors, structural engineers)
Planning and building-control costs
Permanent fixtures and fittings
VAT, where it applies
The cost of meeting current building regulations, which may be stricter than those the house was built to

For insurance purposes, the rebuild cost is the basis on which your sum insured should be set.

Rebuild Cost vs Market Value

Confusing market value with rebuild cost is the most common mistake homeowners make.

Market Value

Market value is what a buyer would pay. It reflects:

Location and local demand
School catchment areas and transport links
The value of the land
Market conditions

Rebuild Value

The rebuild value covers reconstruction only. It excludes the land, local demand and market movements entirely.

A house with a market value of £1,600,000 might cost £1,200,000 to rebuild. Equally, a listed cottage worth £600,000 could cost more than that to rebuild in matching materials, because heritage work is expensive and the land under it is not.

For insurance, it is the rebuild cost that matters. Land is not destroyed by fire.

How to Calculate Your Rebuild Cost

Use the BCIS Rebuild Cost Calculator

Most homeowners start with a calculator. The free residential rebuilding cost calculator at abi.bcis.co.uk is operated by BCIS — the Building Cost Information Service, part of RICS — and is commissioned by the Association of British Insurers. Registration is required, and use is capped at a few estimates a year.

It asks for property type, number of storeys, postcode, age, external floor area, number of bedrooms and bathrooms, wall type and roof type, and returns an estimated rebuild cost with a range.

Its scope is the important part. The calculator is built for standard, brick-built houses. If your home is built of non-standard materials, has special architectural features, or is listed, BCIS and the ABI both direct you to a chartered surveyor instead. For those properties the calculator output is not a figure you should put on a proposal form.

Commission a Professional Assessment

For anything outside standard construction, a chartered surveyor carrying out a reinstatement cost assessment is the right route. It is particularly worth it where:

The property is listed or in a conservation area
Non-standard materials have been used
Significant extensions or conversions have been added
The house has unusual architectural features
The property is high-value, where the sums at stake justify the fee

Review Your Existing Documents

Your current buildings policy will already show a sum insured. Treat it as a starting point rather than an answer.

Building costs move, and many policies index-link the sum insured to the BCIS House Rebuilding Cost Index between renewals. Indexation keeps a correct figure roughly current; it does not correct a figure that was wrong to begin with, and it does not know about your extension.

Why an Accurate Sum Insured Matters

Most home insurance policies rely on the sum insured you provide, and most contain a condition of average.

If the sum insured is lower than the correct rebuild cost, the insurer may pay only the proportion of the claim that your sum insured bears to the true figure. In other words the payment is reduced to that proportion, not reduced by it:

claim × (sum insured ÷ correct rebuild cost)

For example:

Actual rebuild cost: £1,500,000
Sum insured: £1,200,000
The property is insured for 80% of its rebuild cost

On a £100,000 claim, the insurer may pay £80,000. You would fund the remaining £20,000 yourself. The same proportion applies to every claim, not only to a total loss.

Underinsurance is a subject in its own right, particularly on high-value homes — we cover it in more detail in how underinsurance could cost luxury homeowners.

What Goes Into the Calculation

Building Materials

Construction type drives cost. Brick, stone, timber frame and non-standard materials sit at very different price points, and some are considerably more expensive to source and install than they were when the house was built.

Labour

Labour costs vary with the complexity and size of the property, the workmanship required, and the region. Specialist trades — thatchers, stonemasons, heritage joiners — are both scarcer and dearer.

Demolition and Site Clearance

Before rebuilding starts, what is left has to come down and be taken away. Access matters here: a terraced house on a narrow London street costs more to clear than a detached house with a drive.

Professional Fees

Architects, structural engineers, surveyors and planning consultants all have to be paid before and during a rebuild. These are commonly allowed for as a percentage of the rebuild cost — check that your sum insured includes them rather than assuming it does.

Permanent Fixtures

Kitchens, bathrooms, built-in wardrobes and fitted units form part of the building, not the contents. They belong in the rebuild figure.

Factors That Affect Rebuild Costs

Property type. Detached, semi-detached, terraced, flats, period and listed properties each rebuild differently.

Floor area. The larger the footprint, the higher the cost. Measure carefully, and be clear whether you are giving external or gross internal area — calculators differ, and garages, outbuildings, conservatories and basements are often counted separately.

Location. Labour and materials vary by region, and access affects both.

Special features. Bespoke joinery, decorative stonework, period features and heritage materials all add cost.

Extensions and loft conversions. These increase the floor area to be rebuilt, and therefore the rebuild cost. Many homeowners forget to update the sum insured after building work — this is the single most common cause of accidental underinsurance.

Listed status. Listed buildings may require specialist materials and craftsmanship, and consent for the works. Rebuild figures are frequently far higher than owners expect.

Rebuild Costs for High-Value Homes

Owners of high-value properties face a harder version of the same problem. Bespoke interiors, high-end finishes, specialist construction and unique architectural features all raise the cost of reinstatement, and none of them are captured by a general calculator.

For these properties a professional reinstatement assessment, reviewed periodically, is the sensible baseline. See our high-net-worth home insurance and high-net-worth insurance pages.

Rebuild Costs for Non-Standard Homes

Non-standard construction — anything other than brick or stone walls under a tile or slate roof — needs specialist techniques, bespoke materials and skilled trades, all of which push the cost up.

Examples include:

Thatched properties
Timber-framed homes
Listed buildings
Barn conversions
Steel or concrete-frame construction
Homes with unique architectural features
Eco and self-build properties

Standard calculators do not model these properly. A chartered surveyor or a specialist broker is the right starting point.

Rebuild Costs for Flats

If you live in a flat, responsibility for buildings insurance depends on how the building is held.

Leasehold Flats

In most leasehold blocks the freeholder or management company insures the whole building and recovers the cost through the service charge. That policy normally covers the structure, communal areas and permanent fixtures.

Two things are worth checking rather than assuming. First, whether improvements you have made inside the flat are covered by the block policy — often they are not, and they may need to be insured under your own contents policy or declared to the freeholder's insurer. Second, whether you need liability cover in your own name as occupier.

Freehold and Share-of-Freehold Flats

Genuine freehold flats are rare, and most people who believe they own one actually hold a share of freehold or a long lease. Where flats are held freehold, who must insure the structure depends on the covenants in the deeds. There is no automatic shared duty, so check the deeds rather than assuming the building is insured.

Where a joint or block arrangement is in place, the sum insured must reflect the rebuild cost of the whole building, not one flat's share of it.

Purpose-Built and Converted Flats

Whether the block is purpose-built or a converted house, establish who arranges the buildings insurance and how the rebuild figure was reached. Your managing agent, freeholder or broker should be able to tell you.

Why Listed Properties Need Extra Attention

Rebuilding a listed building may involve specialist craftsmen, heritage-approved materials, additional planning and listed building consent, and conservation restrictions on how the work is done.

The labour content is often far greater than for a standard house, and the programme longer. Listed properties routinely carry rebuild values well above what their owners expect — and above what a general calculator will produce.

What Happens If You Get It Wrong

Underinsurance

Underinsurance means the sum insured is lower than the cost of rebuilding. Where a policy contains a condition of average, the insurer may reduce the claim in the same proportion — insured for 80% of the rebuild cost, and 80% of the claim may be paid.

It can lead to reduced settlements, larger personal contributions, compromises on materials and specification, delays while funding is found, and — after a total loss — not enough money to rebuild what was there.

Whether average applies, and on what basis, depends on the policy wording. It is one of the things worth checking before you need it rather than after.

Overinsurance

Overinsuring is less damaging but still wasteful. Insurers settle on the cost of rebuilding the property, up to the sum insured. Insuring for more than the rebuild cost does not increase what an insurer will pay — the sum insured is a ceiling, not a target.

A property with a rebuild cost of £400,000 might have a market value of £650,000 because of its location and land value. Insuring it for £650,000 buys nothing extra; it simply raises the premium every year.

The aim is an accurate figure: enough to rebuild, and no more.

How Often Should You Review?

Review the rebuild cost:

At each renewal
After extensions, loft or garage conversions and structural alterations
After significant refurbishment
Every few years in any case, and more often for listed and non-standard homes

Common Mistakes

Using market value. The most frequent error, and the one that produces the largest shortfalls.

Forgetting building work. Extensions and conversions increase the rebuild cost. Tell your insurer.

Ignoring building inflation. Labour rates, material prices and supply chains all move. A figure set several years ago is unlikely to be right today.

Relying on old paperwork. Renewing on last year's figure year after year compounds any error in it.

Assuming the insurer works it out. Some insurers offer guidance or a calculator, but the sum insured is normally the homeowner's responsibility.

Choosing the Right Buildings Insurance

An accurate rebuild cost is the foundation, but it is not the whole job. Buildings cover should also reflect:

The rebuild cost, correctly assessed
The construction type and age of the property
Listed status, where it applies
Your claims history and risk profile
The policy wording — particularly whether average applies, and the excesses that attach to subsidence and escape of water

Speak to Ellis David About Your Home

Ellis David has been arranging home insurance from Essex Road in Islington for around 50 years, and holds agencies with more than 100 UK insurers and MGAs. For listed, non-standard and high-value homes we can arrange a professional reinstatement cost assessment rather than relying on a calculator, and we will tell you plainly whether your current sum insured looks right.

Speak to us for impartial advice and a no-obligation quotation.

This article is general information, not a personal recommendation. All cover is subject to the terms, conditions, limits and exclusions of the policy. Ellis David Ltd is authorised and regulated by the Financial Conduct Authority, register number 442066.

Have you ever been convicted of any offences involving fraud, theft, false accounting or other dishonesty or an offence (whether or not in the United Kingdom) relating to companies, building societies industrial and provident societies, credit unions, friendly societies, insurance banking or other financial services, insolvency consumer credit or consumer protections, money laundering, market manipulations or insider dealing? (required)	YesNo
Are you the subject of any current criminal proceedings? (required)	YesNo
Have you any convictions for any offences other than those listed in question 1 a) above which are not spent, whether or not in the United Kingdom (excluding traffic offences unless these resulted in a ban from driving or involved driving without insurance)? (required)	YesNo
Are you or have you ever been the subject of any civil proceedings, arbitration or litigation, including proceedings that resulted in a County Court Judgment (CCJ) or other judgement debts, in the United Kingdom or elsewhere? (required)	YesNo
Are you aware of any intention to begin such proceedings against you in the future? (required)	YesNo
Do you have any judgement debts (including CCJs) made under a court order still outstanding, whether in full or in part? (required)	YesNo
Have you ever failed to satisfy any such judgement debts within one year of making of the order (required)	YesNo
Are you or have you ever been, the subject of any bankruptcy proceedings, or proceedings for the sequestration of your estate? (required)	YesNo
Have you ever entered into a deed of arrangement or an individual voluntary arrangement (or in Scotland a trust deed) or other agreement in favour of your creditors, or are you doing so? (required)	YesNo
Have you ever been found guilty of conducting any unauthorised regulated activities or been investigated for possible conduct of unauthorised regulated activities? (required)	YesNo
Are you, or have you ever been, the subject of an investigation into allegations of misconduct or malpractice in connection with any business activity? (required)	YesNo
Have you ever, either in the United Kingdom, or elsewhere been - (required)
- refused entry to, or been dismissed or requested to resign from, any profession, vocation, office or employment, or from any fiduciary office or position of trust, whether or not remunerated? (required)	YesNo
- refused, restricted in, or had suspended, the right to carry on any trade, business or profession for which specific licence, authorisation, registration, membership or other permission is required? (required)	YesNo
- disqualified by a court from acting as a director of a company or from acting in a management capacity of conducting the affairs of any company, partnership or unincorporated association? (required)	YesNo
- the subject of a disqualification direction under section 59 of the Financial Services Act 1986 of a prohibition order, under section 56 of the Financial Services and Markets Act 2000, or received a warning notice to make such a direction or order? (required)	YesNo
Have you ever been a controller, director, senior manager, partner or company secretary of a company, partnership, or unincorporated association? If you answered "no" to question 8 you may proceed to section 12. Please tick (required)	YesNo

In respect of activities regulated by the FCA have you, or any company, partnership or unincorporated association of which you are or have been a controller, director, senior manager, partner or company secretary, during your association with that entity and for a period of three years after you ceased to be associated with it, ever - (required)
- been refused, had revoked, restricted or terminated any licence, authorisation, registration, notification, membership or other permission granted by any such body? (required)	YesNo
- been criticised, censured, disciplined, suspended, expelled, fined, or been the subject of any other disciplinary or intervention action by any such body? (required)	YesNo
- resigned whilst under investigation by, or been required to resign from, any such body? (required)	YesNo
- been the subject of any civil action which has resulted in a finding against you or it by a court? (required)	YesNo
Has any company, partnership or unincorporated association for which you have been a controller, director, senior manager, partner or company secretary, in the United Kingdom or elsewhere, at any time during your involvement or within one year of such an involvement – (required)
- been put into liquidation, wound up, ceased trading, had a receiver or administrator appointed or entered into any voluntary arrangement with its creditors? (required)	YesNo
- been declared by a court liable for any fraud, misfeasance, wrongful trading or other misconduct? (required)	YesNo
- been investigated or been involved in an investigation by an inspector appointed under companies or any other legislation, or required to produce documents to the Secretary of State, or any other authority, under any such legislation? (required)	YesNo
- been convicted of any criminal offence, censured, disciplined or publicly criticised, by any inquiry, by the Takeover Panel of any other governmental or statutory authority or any other regulatory body (other than as already indicated under 10 b))? (required)	YesNo
Are you currently a director of any company other than one which is a part of this company? (If “yes” please give details on the supplementary sheet). (required)	YesNo