Kieran McCarthy: Where to locate the downstairs loo

The so-called ‘smallest room’ can do a lot if it is well-configured. Picture: iStock

Dear Kieran,

I live in a three-bed semi-d in the suburbs. The house doesn't have a downstairs toilet. Where is the best place to locate it?

I have a cupboard under the stairs (no real height in it) and backing on to it, from the dining area of the kitchen (the kitchen back wall), is a full-height storage closet. I also have a garage, which adjoins the house and is on the same side as the stairs, also partially behind the back kitchen wall.

Would it be possible to install a WC by converting the under-the-stairs and kitchen closet combination, or are their requirements regarding a foyer? Or should I break through from the back wall of the kitchen and incorporate part of the garage to create a new WC and foyer?

Also, I know it's hard to gauge without seeing the house, but could you give me a ballpark cost?

Many thanks, Terry Mullins

Hello Terry, A new WC seems like a small addition to your house, but it is the highest-cost-per-square-foot room because of the need for a sewer and the level of fit-out required, and, in your case, you have to build the room.

I have not seen your house, so I assume that you have adequate free space in your garage to accommodate this new room (after all, no one keeps their car in the garage anymore). Make the entrance to the WC from the kitchen.

This will allow for more space in the lobby to access your WC and help create space aligned to wheelchair accessibility. This would be best practice in a WC downstairs and add value to your home.

You will need to break out from the kitchen back wall to the garage and insert a concrete lintel. It may also be that your garage floor is lower than your house, so you will need to create a new floor slab to make up these levels as you build the new structure. You will also need to form a small lobby and then the WC enclosure room.

The first thing we need to install is the new sewer. This will be the messiest and most disruptive part of the project and an experienced tradesperson should carry out these works.

Ideally, you would map out your sewer in the front or rear garden. If you have a suspended floor in your hallway, you could intercept the sewer here and this would save a considerable amount of work and disruption.

If not, take a sewer through your garage by cutting out a slot in the concrete floor slab and digging under to get an adequate fall in the new sewer. Connect outside while capping off the sewer end internally to guard against smells until the new toilet is connected. At this point, ask a plumber to bring a water source and sink drain (connected to your new sewer) to the area.

The next step is to pour a new concrete slab to even up the floor heights and include for insulation and a damp-proof membrane. This slab should be at least as wide as the outside of your new walls. The new timber stud walls can now be built to form the walls of the WC and lobby, allowing two new doors: through the end kitchen wall and at the entrance to the new WC. Next, it's time for an electrician to bring wiring for a light and an extractor fan (vented to outside) and then you can start installing the soundproof insulation into the walls.

Now you are ready to begin the plastering. This involves installing plasterboard fixed on both sides to your timber stud walls. Once this plasterboard is plastered (along with any repairs to the new openings through the wall) you can tile the new floor and bring the plumber and electrician back.

The plumber will make all the final connections and fit the bathroom ware (sink and toilet bowl) and the electrician will fit the extractor fan unit and install the light fitting and switches. Assuming the walls have fully dried out, you can fit the skirting board, architrave and the new doors. Now your new WC is complete and ready to be painted.

Cost depends. If you hire a small builder I would expect a price of about €18,000-€20,000 plus Vat, excluding tiles and bathroom ware.

There are no economies of scale and it's all down to labour and no great amount of materials will be required.

The most costly elements will be the new sewer and the demolition. It is a big investment in your home and it wouldn't be a huge cost to add a laundry room to the garage to increase the practical space of your home.

It would mean reorganising the space a little so that your new laundry becomes the lobby for the WC, but it would certainly be worth it.

Practical spaces like these really allow you to enjoy the more high-profile spaces in your home more, now that the clothes-horses are no longer obstructing the views of your garden!