Plumbing a Bathroom Into an Upstairs Extension


Modern trends in interior design seem to be driving us towards more bathrooms, in some cases one for each bedroom. Most of us can’t afford such opulence but if you are putting in a two-storey extension as part of a home renovation, then it makes sense to add a bathroom at the same time.

Bathroom or Bedroom in a Two-Storey Extension?

If you are looking at the project in pure financial terms than two bedrooms might deliver the best return. This is because we in the UK are fixated on bedrooms as a way of setting house price brackets, and of course you’ll save the extra cost of fitting out the bathroom. Even if you aren’t selling the house for the foreseeable future, if you are investing in a renovation project you want to get the best reward for that investment in the end.

Buyers aren’t stupid though. If, for example, you turn a three-bed home into a five bed but there’s still only one bathroom for all those people, you will be putting off a large number of buyers. And that’s particularly the case if the two bedrooms are poky and there are very few five-bed houses in the street. A four bed home with a good sized master bedroom with en suite and one family bathroom would appeal to far more families.

Installing the New Bathroom

But what are the practicalities of plumbing in a bathroom in a two-storey extension? It’s not as difficult as it sounds, although there are some areas where you will need expert help, so consider getting a plumber in rather than doing it all yourself if you are unsure.

The closer you can get to the existing water and waste pipes the easier and cheaper it will be to connect up a second bathroom. From the outside of most houses you can follow the pipes to see where the supplies are, and very often you will find that the bathroom is above the kitchen. This is for the same reason, it makes the house cheaper to build in the first place.

The bit where you are going to need the expert help is probably with the hot water supply and the waste pipes. If there are tanks in the roof you will need to make sure they have enough capacity to supply the two bathrooms. If you have a combi boiler it may need uprating to cope with the extra demand. If these issues aren’t addressed you are likely to have cold baths or showers that go hot and cold when other people use water elsewhere in the house

Dealing With Waste

Getting the waste out of a second bathroom shouldn’t be too difficult although the outlet pipes are four inches in diameter so large holes are in order. The waste pipe simply has to join the existing pipe on the wall outside by the original bathroom. There is a huge variety of junctions available and the only thing you really need to do is try and site the new bathroom, in the extension, as close as possible to the original one.

The ‘fall’, the incline from the toilet to the junction with the waste pipe is critical though. If the fall isn’t right the waste will not move swiftly enough through the pipe and you could get blockages, particularly at the junction. This is also the case with the waste outlets from the bath and basin but as the pipe is a smaller bore there’s more room for manoeuvre.

If you find that joining up to the existing waste pipes is just not viable you can use small-bore piping and a macerator. You’ll find more information about these in our article about putting a bathroom in a loft conversion.

Now Finish off the Bathroom

Apart from the issues we’ve discussed here the fitting of a bathroom in a two-storey extension is no different to putting a bathroom in anywhere else in the house. You can find more about working with bathrooms as part of a home renovation in the plumbing and electrics section of our site.

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