Do I need a bigger septic tank if I have an extension?

property having a 2 storey extension

If you’re building (or considering building) an extension to your house, you may be wondering if you’ll need to increase the size of your septic tank accordingly.

The short answer is ‘maybe’ – but it’s likely to depend on variable factors such as the following.

Extra plumbing

If the extension being built is likely to result in a corresponding increase in discharge, then your septic tank may need an upgrade.

By creating rooms that are connected to your existing plumbing, you’ll see more output into your septic tank system.

Examples could include an additional bathroom, or maybe a utility room downstairs.

Extra people

Even without any extra plumbing, more people will still mean more waste. So, if you’re adding bedrooms for increased occupancy, be aware.

A small septic tank serving a property with two people living in it is unlikely to encounter any problems.

Once four or five people are in the same home , then the household waste may become too much over time.

What issues might there be?

If a septic tank has to deal with more waste than it was designed for, there are various problems you could encounter following an extension.

These could include blockages, backing up of wastewater into the house, or unpleasant odours.

If you experience any of these soon after completion of your building project, it may mean your extension is a contributing factor.

To avoid such issues, it may be worth working out beforehand whether you might need a different sized septic tank or even a small sewage treatment plant.

Variables to consider include:

  • Your property’s square footage after extension
  • Number of intended occupants
  • How many installed items like sinks, showers, baths and toilets there are
  • Number of connected appliances such as washing machines and dishwashers

By considering factors like these, it’s easier to get a clearer idea of what your maximum volume of discharge per day is likely to be.

Consulting the Government’s Approved Document H on drainage and waste disposal can help demystify some of the requirements.

However, talking to an experienced professional is the surest way to allay any concerns you may have before building work begins.

Still got questions about the size of your septic tank?

Although there’s plenty of guidance and best practice information about the capacity of the tank you need, there’s only one way to be certain whether you need a bigger septic tank.

A professional septic tank survey will confirm whether your incumbent system will cope with any increased volume, or if you need a replacement.

To speak to a member of our helpful team or arrange a visit, please get in touch today.

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