The sum insured under a buildings policy must be the full rebuilding cost of the home. You should make sure it is kept up to date to allow for the escalation of building costs. Some insurers will index link your policy. Your sum assured needs to be correct at the beginning to correctly increase over time.

You must inform your insurer of any increases in home improvements such as loft conversions or extensions. You should review your cover every few years at least. The market value of your home or the Council Tax band valuation will not help you to calculate the rebuild costs.

You could obtain a copy of 'Guide to House Rebuilding Costs' published by the Building Cost Information Service of the Royal Institution of Chartered Surveyors. The cost of outbuildings or garages should also be taken into consideration as should swimming pools, fencing, patios, drives, gates and walls.

To calculate the rebuild cost you should find out the external floor area of your home – measure the length and width of your home and multiply those figures together.

If you can't do this by going outside, measure the inside both up and downstairs and then add the thickness of the walls. If your house has three storey's then add a further 70% of the floor area.

If you live in a flat or maisonette, you should have shared insurance with the other residents – this will often be included in any annual maintenance/service charge.

  Where it is necessary for your home to be rebuilt exactly in its original style to comply with local authority requirements, you must allow for the additional costs and a professional Rebuilding Cost Assessment is essential.