When you start building foundations over drains one of the most important things you need to keep in mind is what exactly is lying beneath your feet. Making miscalculations with where you start digging can create a huge problem for you and your team, especially if you hit a drain or sewer.
There are many rules and regulations that need to be followed when building foundations over drains, and failure to check on these is the number one problem small projects face when building foundations.
Accurate drain alignment
Water authority consent is required when construction begins within 3 metres of a public sewer or 1 metre of a public lateral drain, according to Building Regulation H4. Simply put, if there is a misalignment between the drain below and the structure above it then regardless of if it\’s a public or private drain, you will have problems.
The simplest solution to the various problems that drains cause is simply to keep it as a focus during the planning process. Before you have even acquired planning permission for the structure you should understand where the drains are, their depth and how you are going to adapt your build to the drain.
The type of soil you build over should also be considered when deciding how to deal with your drain. There are specific rules on certain types of soil such as sand or silt that can dramatically change how deep you should build unless you plan very carefully.
Public or private drain
When you are building foundations over drains, one of the first things you should find out is if you are constructing a public or private drain/sewer. Here are some key aspects of public and private drain construction to consider.
- A public drain is one that goes through your land but also serves another property.
- Any sewer that serves only your own property is considered private.
- A private drain can be built over. The piping will be inspected and approved as part of your extension by building control.
- A public drain, on the other hand, is managed by your local water authority. They are in charge of the drains, and they may require access in the future. Every public drain has an easement on both sides, which is a protected space.
- As a result, you must apply to the water authority for permission to develop within or over the easement.
- You will always need to take time to consider and examine the easement with your project manager and consult with the local authority about needing to make an application.
With public drains, one of your responsibilities is to apply for permission to build over the drain. In most circumstances, obtaining approval is straightforward and may be accomplished using an online self-certification questionnaire; nevertheless, some water authorities are far more helpful than others, and a simple national approach would help eliminate regional differences.
If you can\’t self-certify, you can apply for an approved build-over agreement. This must be submitted to the Building Control body before any work begins.
Manholes
Manholes and junctions are also important to consider when you are designing your structure. There are additional specifications you need to keep in mind with manholes and junctions that the local authorities will want you to stick to.
- All drains from the house or expansion must be routed to the outside, where they will be intercepted by a manhole.
- You\’ll need at least one manhole along the public sewer on your property.
- Buildings and additions should never be built over a sewer manhole or inspection point. As part of the construction, access points on a sewer may need to be relocated and included in the design.
The expansions must also include a 3m zone to allow for future sewer reconstruction if the water authority deems it required. That zone must be accessible to a mechanical excavator, depending on the depth of the drain.
How we can help
In practical terms, this can all be summed up as: when building foundations over drains, figure all of this out at the planning stage. You do now want to get yourself caught in a situation where you are going to need to spend far over your budget and give yourself a huge headache just because you failed to account for drains.
We at Dart and Co provide a wide range of different foundation services from pilling equipment, concrete foundation and underpinning to engineering design. Our piling contracting team specialises in comprehensive groundwork solutions including mini piling, CFA piling, foundation structures, underpinning and engineering design services. Contact us now to learn more about how we can help you with your foundation needs.