The first time that many people hear about radon is if they are planning to buy or sell a home and it is located in a designated radon ‘affected area’.

When buying a property, your solicitor will carry out various checks (called Searches), including whether the property is in a flood risk area, a former mining area and an area affected by radon gas. If the Search shows that the property you are interested in is in a radon ‘affected area’, don’t panic!

The house is in a radon ‘affected area’ – what does this mean?

The likelihood of a property being affected by high levels of radon is partially determined by the underlying geology in the region, as well as other contributing factors such as the way in which the property is designed and built and occupancy habits, including heating and ventilation. The Health Protection Agency (now part of Public Health England) has used available data to produce a set of maps indicating the areas of the country where it is estimated that the greatest number of properties will be affected by radon. These maps can be found here.

Areas of the country where it is estimated that less than 1% of properties will contain high levels of radon are termed ‘Lower Risk’ areas, and are shown in white on the maps.

Areas of the country where it is estimated that between 1 – 10% of properties will be affected are termed ‘Intermediate Risk’ areas, and areas where over 30% of properties are estimated to be affected are termed ‘Higher Risk’ areas.

Properties with basements or cellars, or those built into a hillside are automatically at higher risk of radon as there are extra surfaces in contact with the ground through which the gas can permeate into the building. The maps are therefore not relevant to such properties, and the property should be considered to be in a ‘higher risk’ area.

It is important to recognise that these maps are simply a guide and that high levels of radon can be found in properties anywhere in the country, even in Lower Risk areas. Equally, not all properties in Higher Risk areas will be affected.

It is also important to understand that these maps are showing the estimated likelihood that a property will contain radon levels in excess of the ‘action level’ of 200 Bq/m3 – they do not show how high the radon levels may be.

For example, the report that you receive from your solicitor might state that the property you are looking to buy is located in an area where 1-3% of properties are estimated to be affected by radon. This tells you that if there are 100 houses in that area, between 1 and 3 of them are expected to have radon levels over 200 Bq/m3 where it is advisable to carry out remedial works.

What next?

You should ask the vendor whether any radon testing has been carried out within the property and if so, request to see a copy of the results report.

If testing has not been carried out, it would be a sensible precaution to arrange for the property to be tested. The UK Radon Association advises that all properties are tested for radon, regardless of whether they are located in a lower, intermediate or higher risk area, however it is especially important to test if the property is in the upper two bands or if the property has a basement/cellar or is built into a hillside.

Testing for radon is simple and inexpensive and involves small plastic detectors being placed in the property for a period of time.

As radon levels fluctuate constantly, the longer the test period the more accurate the result, so it is usually advised that detectors are left in place for three months. Short-term screening tests where the detectors are left in place for 10 days are available and give a good indication as to the likely long-term radon concentrations.

These 10-day radon detectors are commonly used during property transactions, and if the vendor is serious about selling the property they should not object to them being used.

In a standard-sized domestic property, a set of two detectors is usually advisable. One detector will be placed in a ground floor living room and one in a first floor bedroom so that the areas that are most occupied are tested.

The detectors can be sent and returned by post and will come with full instructions for use. On completion of the test, the detectors are analysed in a laboratory and you will be sent a report detailing the radon levels that were detected.

If the results of the short-term test were only marginally above or below the “action level”, you may wish to carry out a longer term test to confirm whether action is required. This is often carried out after the property transaction has been completed. See below for information on the Radon Bond scheme that might be applicable in this instance.

What happens if I get high results?

Firstly, don’t panic! This doesn’t mean that you shouldn’t buy the property or that you’ll never be able to sell it in the future. Just as a structural survey might reveal that the property has rising damp or woodworm, a high radon test result simply means that you have been alerted to a potential issue that you probably want to resolve before continuing with the purchase.

High levels of radon can be reduced through carrying out remedial works to the property. The two most common methods are either the installation of a positive pressure fan inside the property or the excavation of a small hole beneath the property (called a radon sump) that is connected to an exhaust pipe and fan on the outside of the building.

Just as you might wish to negotiate a discount on the property price if you discover it needs a new damp course, you should speak to your vendor about the results and the fact that remedial works are required.

How much will radon remediation works cost?

The cost of radon remediation works will vary according to the size and layout of the property, the radon concentrations that have been found and other factors such as location of electrical circuits and what type of ground the property is built upon.

Costs are likely to run from around £800 for a simple measure and a single retrofit sump system may cost between £1000.00 and £2000.00.

Remember that more than one system may be required.

Every property is individual and so the remediation system needs to be designed for that particular property and then costed by a specialist.

The Radon Bond

If short-term radon screening tests were unconclusive, or the purchaser would prefer to carry out a full three-month test, it may be possible to arrange a ‘radon bond’.

Under this system, the buyer and seller agree on a sum of money that is likely to be enough to cover the cost of a typical radon remediation system. The money is taken out of the buyer’s purchase price and held by a third party (for example, a solicitor) until the test result is known and any reduction measures have been done. Both parties sign a contract that stipulates how the bond will work.

If the test shows low radon levels and that no further action is necessary, the bond money is released to the seller. If the test shows that high radon levels are present and that remediation is necessary, the work work is paid for from the bond money; any excess is released to the seller.

For the bond system to work, it must be fair to both parties. It must reflect reasonable but adequate costs. The UK Radon Association suggests that £2500 is usually a realistic sum to cover most scenarios, but advice should be taken on a suitable value for individual properties to ensure adequate provision. The bond’s life must also be realistic, allowing – for example – four months from completion of house sale to obtain a radon test result. If this result is at or above the Action Level another three months should be allowed for the completion of remediation work.