Converting your garage : Drainage

Drainage is a very important aspect of any garage conversion - it is generally one of the first tasks to be completed during a conversion project. It is vital to ensure that any drainage systems are in good condition and are working optimally, both externally and internally, to avoid potential problems in the future. Please find below general advice on drainage building regulations and a few tips on internal drainage requirements for your conversion.

Please note: this guide is not exhaustive, if you have any questions about drainage relating to your specific project you should seek professional advice before commencing with any work.

Building regulations for Drainage

Drainage applies to your garage structure as a whole as well as any internal drainage requirements. If your garage conversion is likely to place additional pressure on existing drainage, you may need to take additional steps to avoid potential flooding or blocked drains. As weight from the foundation of a garage is transferred onto the soil/ground below, it will spread downwards outside of the footprint of the foundation at an average angle of 45 degrees.

Generally speaking, if a sewer or drain is located within this 45 degrees area - there is a chance that it could be adversely affected by the weight of the foundation and may crack. To avoid this occurrence, the foundation excavation should usually be at least to the same depth as the invert (bottom) of the deepest part of the sewer, drain or trench. Always speak to your local authority or building officer for more advice on exact drainage requirements.

Drainage requirements

The internal drainage methods required will depend on the kind of room that you are creating i.e. bathrooms, kitchen areas and utility rooms will require specific drainage systems for any water-based installations. New pipe work will be required to allow for water flow and drainage on the following appliances;

  • Kitchen/bathroom sinks
  • Showers
  • Baths
  • Washing machines
  • Dishwashers
  • Hot tubs

If you are not a qualified plumber, it may be a good idea to enlist the help of an expert when you are dealing with any plumbing work, including drainage to and from the building. Incorrectly-fitted pipe work and drains can result in a number of unwanted scenarios, including leaks, flooding (internal and external) and the back-up of waste water. As well as proving to be very costly, any such occurrences can also be a serious health hazard – especially if you are dealing with toilet facilities.

Always check that drainage and sewer components are in good condition – if you notice any cracks or obvious damage, get them seen to straight away. Also remember to keep clear access to any drains or sewer outlets. Many people make the mistake of concreting over drain covers when they are extending their garages – this can be a very costly mistake. Should problems occur with your drainage system, full access will be required to the system. In an extreme scenario, you may have to dig up the floor to gain access to the drain.

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