Adding a bathroom from scratch?

July 6, 2009 2:49 PM

Adding a bathroom to an old house from scratch?

My fiancee and I recently bought a 1925 Craftsman bungalow that had been completely renovated. New plumbing, electrical, roof, etc. We love it, but it only has one bathroom. We originally thought this would be OK, and it is in general, but we're starting to think about adding an additional one.

Reading online, I've only seen people mention converting existing rooms and spaces to new bathrooms. We don't really have any space we can afford to convert at the moment, but there is gap formed by the exterior walls of the master bedroom, existing bathroom, and second bedroom, and we were thinking of using that to create a new bathroom. Would this be feasible at all? The foundation is pier and beam. Both the foundation and roof would have to be extended, plus all the other work generally associated with adding a bathroom.

I'm sure we'd also need to get special permits since we're in a historical overlay, but I'm not as worried about that right now. It's going to be a future term project anyway but I wanted to get an idea of how manageable it would be.

posted by kmz to home & garden (6 comments total)

It's always feasible. It's often expensive.

There's nothing magical about a bathroom other than the pipes. You need to find a clear (or sneakily hidden) way to reach the water supply lines (usually easy to break off a small copper or PVC line from any other existing one) and the drain (harder, since it has to decline to destination), which has to meet up with your overall drain.

The usual place to "hide" these is up high in the ceilings for supply, and down low in the floor (or against the walls) for the drain. If you can logic out where to get water, and where to drain, the rest is pretty straightforward construction.

You may also need an air vent, but that's not difficult. Straight up, generally.

I've been thinking about adding a teeny tiny, Japanese-hotel-size mini-bathroom to my bedroom. You might be able to squeeze something into a closet-size space (do you really need a shower?) and thereby save a fortune on expanding your entire house.
posted by rokusan at 2:56 PM on July 6 [1 favorite]

If the new bathroom ajoins the existing one, as you describe, that's a plus because it should minimize plumbing costs. I'm picturing this "gap" you describe as being in the back of the house. If so, that should help alleviate the concerns of the historical zone board or whatever. For permits you will need detailed schematic plans, proessionally drawn, and be sure you're seated when the plumber hands you the estimate.
posted by longsleeves at 3:00 PM on July 6

I have been thinking about doing the same thing to my 1924 workman's tudor.

You have a few good things going for you..#1 Your house is pier and beam. That makes for an amazingly uncomplicated plumbing layout. You can pretty much place the supply and sewer lines anywhere you want without rerouting any existing plumbing. Adding a new floor structure to the existing is fairly straightforward since you will only be extending the grade beams or piers (whichever you have...my house has both).

The bigger issue is what exterior material you will use to enclose the new space. Trying to match existing brick / mortar color is next to impossible, so going with an exterior material that matches the character of your home is important (My house is brick so I am planning on using exterior lap siding...the real stuff, not that cheap vinyl business).

And there is always an issue with water-tightness when adding on to an existing structure. When adding new foundations next to an 84 year old existing foundation, settling and thermal expansion/contraction occurs which will most likely necessitate some sort of expansion joint. They come in all flavors, but if the expansion is less than a few 100 square feet, the movement will be minimal.

If you are serious about starting the project, be sure to add at least an additional 15-20 percent to your total budget. You never know what you are going to find.
posted by Benway at 3:18 PM on July 6 [1 favorite]

There are minimum dimensions to a bathroom, like clearances in front of the toilet, and
minimum sizes for a shower. Make sure you have enough room to lay out a legal bathroom.

To service the toilet, there are minimum slopes that must be provided for the outflow of
the toilet. Make certain that you have enough vertical clearance so that you can provide the
minimum slope for the toilet outflow to your city sewer line (or septic tank, whichever you
have). Otherwise, you'll need a sewage ejector to lift the black water to your sewer.

All drains require venting, which is a roof penetration, and the venting pipe diameter must
be of a certain minimum size, based on the number and size of the drains that are served.
These roof penetrations have clearances that must be maintained from openable skylights.

The drain lines for the shower, tub or sink must be (are you familiar with this phrase
yet?) a certain minimum size, and plumbing code prohibits you connecting a large
pipe to a narrower pipe.

The outlets in a bathroom must be GFCI protected, and lights
and fans must be no closer to showers than some minimum distance.

Adding a new roof structure outside can be problematic. The minimum roof slope permitted
is 3 in 12, and if you are adding a room that is bounded by 3 exterior walls, the water must
be designed to flow off easily. This might mean that your headspace in the new bathroom
will be cramped. There is a legal minimum for the height of a ceiling for a legal bathroom.

It'll be kind of expensive, no cheaper than about $15,000.

One more thing: exterior bathroom walls require extra attention for their insulation. It's
important to do a really good job. The slightly lower temperature provided by an
underinsulating exterior wall produces a disproportionally large amount of condensation,
and makes the bathroom much more uncomfortable.
posted by the Real Dan at 5:45 PM on July 6 [2 favorites]

Fine Homebuilding seems to have had a lot of articles about "bump out" type construction, here's one related to bathrooms, but not a entire new one.

Are you talking about an entire bathroom or a halfbath/powder room?
posted by electroboy at 7:50 PM on July 6

(Tiny footnote: depending on the building codes in your region, you may be able to skip the vent-to-roof by using a Studor vent, which can be a clever little problem solver in tight spaces sometimes.)
posted by rokusan at 2:35 PM on July 20