I have obtained a figure from the calculator but it is very different to the market value of my home - why is there such a difference?

The rebuilding cost is not the same as the market value and it is the rebuilding cost that the property must be insured for. The rebuilding cost is frequently less than market value, but it can be higher. If you insure for the market value and the rebuilding cost is less than the market value then you will be paying additional premiums for no benefit. If you insure for the market value and the rebuilding cost is more than the market value then you will be under insured.

My house has a loft conversion – how should I allow for the loft conversion?

If you have a two storey house where the roof was converted into additional living space then you should describe your house as three storey. Make sure that you add the floor area of the loft conversion to the areas from the ground and first floor. It will normally be difficult to measure the external dimensions of the loft conversion so measure the internal dimensions and add an adjustment for each wall thickness (30cm or 1ft for each wall should be close enough).

My house has a cellar – should I include the cellar when I calculate the floor area?

If you indicate that your house has a cellar then you should not include the area of the cellar when calculating the floor area.

My home is in a conservation area – can I use the calculator?

Possibly. Just because your house or flat is in a conservation area it does not necessarily mean that it will be more expensive to rebuild. The rebuilt property will have to match what was destroyed, but unless it is ornate or uses construction techniques that are difficult to reproduce using modern technology then the rebuilding cost guidance figures will be appropriate. If you are in doubt then seek professional advice.

My home is a listed building – can I use the calculator?

No. There will be requirements to recreate the building which will vary depending on the circumstances and terms of the listing. It occasionally costs a similar amount to rebuild a listed building, but more likely there will be additional costs which may be very substantial. Professional advice must be sought.

My house was built before 1720 – can I use the calculator?

No. Houses built before 1720 will almost certainly be listed with all that implies. In addition, there was no common style for housing built before that date so we cannot provide general advice. Professional advice must be sought.

My house is timber framed – can I use the calculator?

Timber construction, such as log cabins or timber framed and clad houses, are not covered by the calculator, but if your house is timber framed and clad in brick then it would be reasonable to use the calculator based on a brick house.

Does the calculator cover prefabricated houses or system builds?

Where a house has been constructed using a system, such as pre-cast concrete panels, it is most likely that it would be rebuilt using brick or rendered blockwork construction. Provided that it would be possible to rebuild the house in brick and that the layout is not unusual for an equivalent house in standard construction then the rebuilding cost for brick walls can be taken.

My home was designed by a famous architect and won a design award – can I use the calculator?

No. The rebuilding cost calculator gives guidance for general houses and flats and does not cover unusual designs. Your property may or may not cost more than the norm to rebuild, but you will need to seek professional advice.

The report shows a range of rebuilding costs – how can I decide where in the range my home will come?

There are many things that will affect the rebuilding cost, such as number and quality of kitchen and bathroom fittings; quality of construction; ornamentation; wall to floor ratio; type of heating; external works (sheds, garages, walls, paved surfaces, etc) and much more. The expected rebuilding cost represents a typical property of the type described with good quality, but not expensive, fittings. The bottom of the range represents a home with minimal fittings from 'contract' ranges while the top of the range includes for more fittings of above average quality. The range is intended to encompass 90% of properties of the type described, so if your home is especially simple and sparse with minimal services, it may cost less to rebuild than the range indicated. Likewise, a home with a high level of quality fittings and extensive services can easily cost more to rebuild than the top of the range shown.

My home is in poor condition – will it cost less to rebuild?

Just because a property is not in good repair does not necessarily mean it will cost less to rebuild. It will have to be rebuilt to modern building regulations and materials. However, an older property that has not been updated is likely to have less fittings and services than one that has been kept up to date and that will have an effect on the rebuilding cost. On the other hand, if an older property retains many of its original features it may cost more to rebuild.

I live in a terraced house - how can I measure the gross external floor area?

The gross external floor area for a terraced house should be measured to the middle of the party wall. It may not be as easy to measure the house from the front to the back, but you can measure the depth of the house from the inside and add an allowance for the external walls (30cm or 1ft for each wall should be close enough).

Can I use the gross internal floor area from my EPC rather than the gross external floor area?

If you have the gross internal floor area, perhaps from an EPC, it will be less than the gross external area so you need to make an allowance which could be in the region of 10%-20%. The smaller the house the larger the percentage and the taller the house the larger the percentage so add most for a tall narrow house and least for a large bungalow. For a bungalow of 120m2 you might add 11%; a semi-detached house of 120m2 15%; a three-storey house of 160m2 16% and a four-storey house of 200m2 17%.

For a more accurate figure you can assume the walls are roughly 0.3m (1ft) thick so for a detached dwelling take the width and add the depth and multiply by two (to allow for four walls). For a semi-detached dwelling take twice the width and one and a half times the depth (because you only have to cover half of the party wall). For a terraced dwelling take twice the width and once the depth (because you only have to cover half of each party walls). Multiply by the number of storeys. Multiply by the thickness of the wall (0.3m or 1ft depending on whether you are working in imperial or metric). Add the result to the gross internal area.

Why is it not advisable to insure a single flat?

If at all possible, you should insure an entire block of flats (or converted house) rather than individual flats. If you insure your own flat and the property were to be destroyed then you would only be able to afford to rebuild the whole building if every other flat owner had adequate insurance. Since the cost of rebuilding is not the same as the value of your flat, you may not be able to afford to repay your mortgage or purchase a replacement. Even if the claim is for partial damage rather than a complete loss, it is more complicated if individual flats are insured separately: resolving the question as to which policy covers damage to the roof, foundations or drains may cause delay and frustration.

Why does the calculator not work for a whole block of flats?

BCIS offers services to support rebuilding cost assessments on blocks of flats which are designed for use by surveyors or other suitably qualified people. A block of flats will be a significant asset that needs professional advice. It will also, normally, be a commercial undertaking, which is not covered by the free calculator.

Can the calculator be used for a maisonette?

There are two different types of flat that may be described as a maisonette. Firstly there is a two storey building which typically contains four flats – two on the ground floor and two on the first floor with those on the first floor having their own front door and staircase. The rebuilding cost of this sort of maisonette can be calculated using the purpose built flat property type. Secondly there are flats which are in a taller block where the accommodation is split across two floors with an internal staircase not shared by other flats. The calculator does not cover this second type of maisonette.

My flat is in a block that was built before 1946 – can I use the calculator?

The rebuilding cost models used by the BCIS calculator are based on the style of flats built since 1946. If your block was built before 1946 but the style is similar to a more modern block then it would be reasonable to use a rebuilding cost based on a more modern block. However, older blocks of flats are frequently more ornate, or have distinctive features (such as curved facades) that can significantly add to the rebuilding cost. BCIS may offer guidance for older blocks of flats in future but we cannot help you at the moment and you should seek professional advice.

Does the rebuilding cost given by the calculator include VAT?

If your home needs to be completely rebuilt then it would be treated as a new dwelling for VAT purposes. In this case the building work itself will be zero rated, although professional fees (architect, engineer and surveyor) would be subject to VAT at the standard rate. For this reason the rebuilding cost shown by the calculator includes VAT payable on fees but not on the building.

I obtained a rebuilding cost figure from an insurance web site that was supposed to be based on BCIS figures - why is it different from the figure I get from this site?

Several of the insurance aggregators use a service provided by BCIS which offers a check on the rebuilding cost using minimal information about the property. Typically, the calculation is based on a style of property and a number of bedrooms or rooms, which means that an estimate of the floor area must be used in the calculation. Since the most important factor in calculating the rebuilding cost is the floor area, any calculation using this calculator, based on the actual floor area of the property, will be more accurate than a figure based on the number of rooms or bedrooms.

I used this calculator before June 2011 and the answer I get now is different, even allowing for inflation. Why is this?

The free rebuilding cost calculator was updated in June 2011 and now includes some allowances for fences, walls, paths and other parts of your property outside the building. It also uses a more detailed adjustment for location which will mean calculations for some areas will go up while others go down. At about the same time, all the BCIS residential rebuilding cost models were updated to allow for stricter building regulations aimed at reducing energy consumption.

I have a rebuilding cost from a professional survey - why is it different from the figure I get from this site?

A surveyor who has visited your home will be able to take into account many factors that will affect the rebuilding cost and their assessment will always be more reliable than the general guidance available from this site. The date on which the assessment or calculation was made will need to be taken into account when you compare different rebuilding costs and an indication of the annual increase in rebuilding costs can be found at https://bcis.co.uk/insight/index-bcis-house-rebuilding-cost-index/. If you are concerned about the difference between the rebuilding cost provided by your surveyor and the guidance on this site then your surveyor should be able to explain.

Why am I limited to four calculations per year?

The free rebuilding cost calculator is provided to help individuals check the rebuilding cost of their home. Use for commercial purposes is expressly excluded by the terms and conditions, as BCIS offers a range of products aimed at surveyors, loss adjusters and the insurance industry that are designed to meet the needs of those users. If you own a portfolio of properties then this is considered to be commercial use and you should either subscribe to a service such as BCIS Rebuild Online (if you have the appropriate expertise) or seek professional advice.

I am a surveyor who only occasionally needs to do a rebuilding cost assessment – why can't I use the free calculator.

Use for commercial purposes is expressly excluded by the terms and conditions. BCIS takes the view that the level of detail provided by the free calculator is only adequate for checking a rebuilding cost and is not appropriate for a rebuilding cost assessment. We believe that a surveyor using this calculator to provide advice would have difficulty defending a claim for negligence if the sum insured proved to be incorrect.

I have typed in the correct postcode but the calculator comes back with a message saying 'Invalid Postcode' - what should I do?

Once you have checked that you have typed in the postcode correctly and typed the number zero or letter O where appropriate, there may be rare occasions where your postcode will not be found. The calculator uses a list of postcodes provided by the Royal Mail to work out where your home is situated. This list is updated regularly, but there may be some delay. If your postcode has recently changed then try entering your old postcode. You may still be using your old postcode after the Royal Mail have changed it, so check on the Royal Mail's postcode finder at https://www.royalmail.com/find-a-postcode. Rebuilding costs are available for the United Kingdom, Channel Islands and Isle of Man.

I am trying to use the calculator but get a message 'Area out of range' – what should I do?

The BCIS rebuilding cost models cover common properties and larger houses or unusually small homes are not covered. You will need to obtain professional advice for properties that are not covered.

I am trying to use the calculator but get a message 'No Models available for this combination of property type and year built' – what should I do?

The BCIS rebuilding cost models do not cover every combination of age and style of home. If you see this message, you should first check that you have entered the details correctly. If the details were correct then it means that we cannot provide any guidance on your property. All the most common combinations of age and type are covered by the existing guidance. While it is likely that the range of properties covered will be increased in future, in the short term you will need to obtain professional advice.

How long will my account stay on the system?

If you do not use the calculator (that is attempt a calculation – not just login) for 62 months your account will be automatically deleted. If you wish to use the calculator again you will need to register again. 62 months is just over 5 years: BCIS recommends that you review your rebuilding cost every few years. The period chosen for retaining your account is selected to allow you to easily check your rebuilding cost after a few years.

If you ask us to delete your account this will normally be done within 24 hours of your request being processed unless you have used the calculator within the last year and in that case your account will be disabled and set to be automatically deleted 12 months after the last successful calculation.