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What is a Build Over Sewer Agreement (“BOSA”)

Build over sewer agreement

Is there a sewer running through your property boundaries? If you have a manhole cover in your garden then yes there is. Lifting your manhole cover should give you a rough idea of the sewer route. If you can see your manhole cover your property (and any extension) are not likely to be built over the sewer.

However, if you can see the sewer line passing under your house, lean-to, extension or conservatory then you will need a Build Over Sewer Agreement from your Water Authority. Obtaining a Build Over Sewer Agreement can cause serious delays when selling your property. They are not instant. Not having one will be problematic on sale and remortgage as mortgage lenders will not be happy.

Why Is It Needed?

It is recommended that you do not build over the route of your sewer line as your Water Company will need to come onto your property to access the sewers if they need to carry out maintenance and repairs. As you can imagine this is in everyone’s best interests. The Water Company are also required to make good any damage caused whilst carrying out maintenance and repairs. They may need to knock down part of your extension during the process so they can gain access and work on the sewer.

If you think your sewer has been built over, but you do not have a Build Over Sewer Agreement, then this is an issue when you sell. It is advisable to contact your Water Company about this before sale. A Build Over Sewer Agreement is a fairly straight forward document however the Water Company will instruct their own solicitors and there is a fee for drafting the BOSA. You are required to cover the costs. A site visit may also be required.

Bear in mind that if you are selling or remortgaging, the mortgage lender is going to insist on either a Build Over Sewer Agreement or indemnity Insurance for lack of Build Over Sewer Agreement. You will not need both. In some instances Indemnity Insurance will suffice. But Indemnity Insurance does not solve the problem. It offers a payment if a claim is successful. To be successful you must not have breached the policy terms and conditions. Indemnity insurance usually covers loss of property value and/or enforcement action being taken against you. It can be relied upon on future resale and passes to the next owner. Indemnity insurance requires a one-off premium payment.

The Build Over Sewer Agreement should have been obtained at the time your Extension or Conservatory was built. But can be obtained later. Unfortunately most builders do not seem to take this into consideration. Luckily, they can be retrospectively obtained. They are not free and you will need to pay for it. They take time and the Water Company may need to attend at your property at least once. Not obtaining or not having a Build Over Sewer Agreement WILL delay your sale as it will result in enquiries being raised.

Contact Dwr Cymru for Welsh properties. There are various water companies in England.

Your Conveyancer will be familiar with the above and able to assist you.

Read more about Build Over Sewer Agreements here…

(Your boundaries will be edged red on Land Registry plans and hopefully your fence line and physical boundaries match. You can obtain copies online from Land Registry for £3. See my other blog articles on this process)


I act for people Buying, Selling or Remortgaging In England & Wales

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