What is a drainage diagram? It’s a certified document that’s filed with your particular state’s water board that illustrates your property’s layout and where the pipes are located, including where they connect to the primary wastewater system.

Although there are various kinds of drainage diagrams, there’s one in particular that can offer you the best view of the water pipes and drains on a property and it’s known as a sewerage service diagram.

This main diagram will enable you to clearly see where the original plumbing was installed and if it’s ever been moved. If any pipes were moved around, this information is critical to know since it may be a clue to a subpar renovation. On the other hand, an expert contractor could have moved them, which means the potential buyer is in good hands.

Why You Need to Check the Drainage Diagram

If you’re considering buying a home that was previously renovated, it would be quite unfortunate if you bought the property and had to immediately start ripping up the brand new floors in the extension or take down the new deck in order to repair the plumbing and rebuild it from scratch. Buyers should always beware.

While the most obvious kinds of renovations impacting a property’s drainage system are kitchens, bathrooms, and laundry rooms, there are a few other add-ons you should check out, which include:

  • New deck
  • New extension

If a new deck or extension was installed directly over the home’s old sewer pipes, there’s going to be a problem if the drain pipes start leaking. With regards to older clay piping, it’s not a matter of if they’ll leak, but rather when they’ll leak. However, with today’s new and improved plumbing methods that utilize modern valves allowing for better and more efficient water flow, the chance of serious plumbing issues and bursting disasters is greatly decreased. You can check the different types of valves and terminology here.

A drainage diagram shows if the sewer was indeed upgraded when the property was renovated. If it was, then you’ll know that extensive and attentive work was performed on the property, which is a very good sign. If it wasn’t, that doesn’t necessarily indicate the work was poorly performed, but it does mean there’s a certain associated risk with older sewer pipes and new construction.

When and Where to Get an Official Drainage Diagram

Ideally, you should obtain a copy of your property’s drainage diagram prior to your next home inspection regarding the selling contract. Also, you can ask your contractor to provide you with a copy. Alternatively, you can likely get a copy from any major plumbing supplier.

Red Flags to Look Out For

Usually, the drainage diagram of a property will contain some important clues on it, such as one of the following stamp labels:

  • Final inspection required
  • Work not finalized

Before you panic, realize that these two labels are just parts of the process or administrative issues. But, you should bring it to the attention of the vendor so it can be resolved. On the other hand, if the drainage diagram is stamped “Work does not comply”, this is a red flag that needs to be addressed.

Check the Drainage Diagram’s Date

If the property is renovated, sometimes you can find a handwritten date on the stamped area of the diagram. If you can’t find a date, get in touch with your Office of Fair Trading or water provider and ask them for the most pertinent date. If the dates are approximately the same timeframe as the renovation period, it’s a positive sign since it means the renovations were updated. But, if the diagram is dated prior to when the renovation took place, there might be a problem.

Overall, it pays off to check the drainage diagram of a property whether it’s one you’re considering buying or preparing to renovate since it could save you a great deal of time, money, and effort in the end.


Author bio: Matt is a blogger who likes to write about home remodeling and renovation and share his tips based on personal experience in home improvement.