Lucy Mawer, Head of Plumbing at University of Lincoln, examines some of the most common oversights when it comes to Building Regulations.

Building Regulations are intended to protect people's safety, health, and welfare in and around buildings. The regulations are also designed to improve conservation of fuel and power, protect and enhance the environment, and promote sustainable development, but just how much do we actually know and remember from our training days?

Regulations are updated frequently and, unless they’re in your bedtime reading routine, the myriad updates may just slip by without you noticing. Here, I have highlighted just a few of the common oversights of the regulations that I often come across.

Approved Document Part A: Structure, which covers the notching and drilling of joists is a good example. All too often, I see incorrect holes and notching in building joists. The safest place to penetrate a joist is right through the centre which, being halfway between the compressed top and the stretched bottom, is what is called the neutral axis.

Even so, drilling should not be done at the mid-span of the joist, nor too close to the supporting ends, but in a zone between 0.25 and 0.4 times the span from the end.

Where more rigid copper pipes must run perpendicular to joists, however, they have to be laid in notches. These should be cut only in a zone between 0.07 and 0.25 times the span from the end. For a typical floor joist spanning 3m, this means the notches should be cut only between 210mm and 750mm from the wall.

More importantly, the maximum safe depth for a notch is one-eighth the depth of the joist. For 150mm joists – often found in older properties – notches should be no deeper than 18.75mm, which presents a bit of a problem for plumbers trying to install central heating using standard 22mm copper pipes.

This guidance is given to avoid affecting the structure of the building, as well as the all-too-common complain of creaking pipes. Pipes too close to the wood will expand and contract with the building fabric, rubbing against the wood and leading to the annoying creaking noise that wakes you up in the night. This is also a ruptured pipe waiting to happen.

Approved Document Part H of the Building Regulations covers drainage and waste disposal, including the pipework to the sewers from inside the building, as well as rainwater systems.

One common oversight is incorrect waste pipe falls. Regulations provide good guidance on appliance waste falls to ensure a good self-cleansing velocity is able to take place. WCs are required to have at least an 18mm fall for every 1m of pipe. If this is not adhered to, then blockages can occur.

Another common issue is the incorrect termination of the ventilation stack on a building. Part H1 1.31 states that any ventilation pipes in the outside air should finish at least 900mm above any opening into a building if the termination is within 3m from that opening. Not ensuring this leads to foul smells from the drains entering back into the building.

This can be overcome by installing an air admittance valve (AAV) as long as it is the correct type for installation outside in order to withstand freezing weather conditions.

Approved Document Part G covers sanitation, hot water safety, and water efficiency. A common oversight featured here is the termination of the temperature and pressure relief discharge pipe. Part G3 3.62 states that the D2 discharge pipe should terminate using one of the following arrangements:

  • To a trapped gully with the end of the pipe below a fixed grating and above the water seal
  • At low level, an external surface should be covered by a wire cage or similar guard, to prevent contact but still be visible
  • High level discharge into a metal hopper and metal downpipe, with the end of the discharge pipe clearly visible

Water exiting the pipe could potentially be 100c, certainly not safe to discharge into a public area. Although, after travelling from the unvented cylinder in the pipework, assuming that the length of the pipework has been calculated and installed correctly, the water could be 80c, this is still not safe.

The diagram above left is from Part G3 of the Building Regulations, showing how the discharge pipework arrangement should be fitted. The image to the right of the diagram shows an incorrect installation of the discharge pipe. This pipe discharges onto a school playground, is not below the grating, and is also installed with push-fit waste plastic pipework.

Building Regulations are all easy to access and freely downloadable in PDF format, easy to store on a smartphone or tablet for quick reference. Make sure you’re up to date.