What is a Build Over Agreement?

A build over agreement (BOA) is needed if building work is to take place within 3 metres or over an existing drain or public sewer. Work involving underpinning, new foundations, piling or basements requires the prior approval of the water company in your area before any work can begin on site.

What is a build over agreement?

A build over agreement gives the water company peace of mind that any works to be undertaken will not negatively impact or affect the sewer beneath it, and it also makes sure that the water company has sufficient access to the sewer so it can be maintained and repaired. If you are planning on carrying out building work close to or over a public sewer, you should initially contact the water company to find out their requirements.

It is important to note that from October 2011, the vast majority of privately owned drains and sewers were transferred into public ownership to be maintained and repaired by the local water company.

Alternatives to a build over agreement

Before you apply for a build over agreement to your local water company, it is worth considering the following options:

• Avoiding the sewer by modifying the plans

This tends to be the cheapest and simplest option but is only really feasible on an extension where the original design does not reach too far into the 3-metre area, meaning a minor revision to the plan solves the problem. Any changes you make to your plans must be communicated to your local planning authority, which may delay the work.

• Diverting the sewer

This option requires professional design input and you would also need to obtain prior consent from the water company. It may also prove to be cost prohibitive and potentially disruptive.

If, after considering the alternatives above, the only option is to apply for a BOA, then you should make the application direct to your local water company. Unfortunately, there is no one set of rules and each water company follows a different process and sets different costs.

How to apply for a BOA

Together with the payment of the appropriate fee and completed application form, you will also need to send basic scale drawings of your property, proposed works and drainage system. Typical examples of what you will need to send are listed below:

• A plan showing the existing house and drainage layout

You must include the location of any inspection chambers and the sewer with the direction of flow clearly marked.

• A plan detailing your proposed works and drainage layout

You must note the position of the sewer and inspection chambers. If you intend to build over the sewer, you will need to show where any existing manhole is to be removed and replaced with a new chamber in the garden.

• A site location plan

This is an outline Ordnance Survey style of plan of the street showing the position of your property in relation to the neighbouring buildings and road.

• A cross-section drawing

This is only usually needed when you are building directly over the sewer or within 1.5 metres of it. The drawing must clearly illustrate the new foundations in relation to the sewer pipe and detail how you propose to bridge over the pipe, for example by using concrete lintels.

How long does a BOA take?

BOA applications tend to be processed by water companies within 3 weeks of receipt. As soon as the water company issues the agreement, you can being work straightaway. Delays are usually because of applications being submitted with missing information or drawings.

How much does a BOA cost?

As stated above, each water company charges their own fee, however it will typically set you back around £300 (on average). There may also be a small additional cost to produce suitable drawings for the application.

What to do after a BOA is put in place

Following receipt of the BOA from the water company, building control will make regular site inspections during construction and examine your drainage provision. In relation to building regulations, it is important to mention that when making your application to building control, you are not permitted to use the “Building Notice” shortcut method if you are proposing to build close to or over a public sewer.

Why you should have a build over agreement?

Sometimes issues can arise when homeowners decide to sell their property, which is either partly or wholly built over a public sewer. Extensions and conservatories are the usual culprits. If a BOA was not obtained when the work was originally carried out, then the water company has a right to enter the property to access the sewer, even if this means demolishing the structure you have built over it.

That said, a water company will always use their best endeavours to avoid causing any damage, where possible, and search for alternative ways to access the sewer. However, you should be prepared, a certain amount of damage may be unavoidable. If a BOA was entered into, then the water company does not have any right to demolish or remove the structure above the sewer.

Will the lack of a BOA affect any subsequent sale?

When your conveyancing solicitor checks the drainage report, they will look at the plans and location of the drains and sewers. If any part of the property appears to be within 3 metres of a drain or sewer, then the solicitor will need to investigate and ensure a BOA was provided by the water company. If a BOA is referred to in the drainage report, then your solicitors will be required to obtain a copy.

There are two options if a BOA was not entered into:

Indemnity insurance for Lack of Build Over Agreement –

Where a Build Over Agreement has not been sought prior to construction having taken place. Typically, you could expect the policy to cover the cost of reinstating the property where damage is caused to the property as a result of a utility provider requiring access to drains or sewers which have been built over. This option is usually the cheapest and quickest option and avoids notifying the water company about work they may not agree with. That said, there may be instances where such a policy alone would not be acceptable to a buyer’s mortgage lender or their conveyancer. Equally, it is difficult to speculate what the cost of such a policy will be without considering the exact circumstances surrounding a transaction. Your conveyancer will be able to advice you in detail as to whether Indemnity Insurance for a Build Over Agreement would be the most appropriate solution at the time.

You can read more details with regards to Indemnity Insurance here.

Retrospective consent from the water company

There is no guarantee you will be provided with consent when you apply for it. The seller should have a CCTV survey of the sewer carried out and then send the footage to the water company. If they are satisfied the sewer is in good condition, they will issue a “comfort letter” giving retrospective consent and confirming the sewer is in a satisfactory condition. The comfort letter is generally sufficient to satisfy the buyer and their mortgage provider that the water company will not take any steps to tear down the offending construction built over the public sewer.

If you do not receive retrospective consent, you may be requested to make changes to the property, which may result in significant expense on your part. It should be noted that you are unable to obtain indemnity insurance once the water company has been notified of the issues.

If you are considering selling your property and are aware that there may be an issue with part or all of it being built over a public sewer, it is always worth discussing your options with a professional property adviser before putting your property up for sale. 

If you are purchasing a property and you are concerned about a lack of build over agreement, discuss this with your conveyancing solicitor to see what your options are.