Probably the greatest challenge in remodelling a bathroom is how to achieve the style and features you want within the limits of the smallest room in the house. The location of the plumbing affects everything, so this must be decided first. Retaining the location of existing plumbing and drainage pipes will save you money.
Remodelling a bathroom is relatively easy if you don't have to move them. If you make radical changes in the existing layout, you'll need to investigate whether or not you can build what you want without making structural changes.
As a rule of thumb, there are three key bathroom layouts that work for most houses.
Most bathrooms suffer from poor ventilation which leads to condensation forming and causing mould to grow. It is essential that the bathroom has good ventilation. Ideally this should be an electrically operated fan venting to the outside. These fans are usually connected to the light switch so that when the light is switched on the fan starts and runs on for about 15 minutes after the light is switched off. Plan and install this while the lighting is being renewed.
Don't neglect lighting when you redesign your bathroom. You'll need strong lighting over the mirror you may also want to consider pinpoint task lighting and soft ambient lights. If you plan to install a whirlpool built for two, indirect mood lighting may fit well.
Think about the maintenance problems you have in your existing bathroom–stained grout, mildew, soap build-up, etc. Some materials look great when they're brand new, but don't weather very well in a high-moisture location. As you choose materials, make sure they are waterproof and washable–resilient vinyl flooring, for example, a fibre glass tub surround and semi-gloss enamel paint will all wear well.
Are you going to fit a shower or not? If so take care to get the correct type of shower that fits your plumbing system. Most DIY stores will have a guide to help you choose the correct type. If you can only get cold water to the shower then it must be an electric one (check you can get an electricity supply to the shower). If you have hot and cold supplies to the shower then you can have a mixer shower. If there is plenty of pressure in both the hot and cold water an ordinary mixer is needed. However, if the pressure in either hot or cold or both is low then a pumped shower may be necessary
Is the shower going to be into the bath or a separate cubicle? If it is a separate cubicle, check that the waste pipes can be run to the outlet. Take care to waterproof the edges of the bath or shower tray properly. It is best to fit a waterproofing strip before the new tiles are fitted - this makes a more waterproof seal. Resin stone shower trays are more expensive but they do not twist under weight and so are easier to waterproof.
Building regulations insist that the waste trap for the shower tray can be accessed for cleaning. This will probably mean fitting a removable hatch to the front of the tray.
The waste system is the least flexible aspect of the bathroom the waste pipes must run downhill from the appliance to the soil pipe or outlet. Bear this in mind when planning the new location of the appliances. The waste system includes the soil pipe - the large (100 mm) diameter pipe that the WC flushes into. In newer houses this will be plastic. In houses built before the 1960's this may be cast iron. Some older houses (1930's) may have a system where the water from the sink and bath (this is called grey water) go into a hopper set on top of a down pipe on the outside wall.
If this is the case, run the new waste pipe to this hopper. Bath and shower wastes are very close to the floor - to get a good slope (fall) the entry into the soil-pipe must go quite low - in many cases this will be under the floor. Waste water does not run uphill so plan carefully. The only way to overcome this is to fit some form of sewage pump like a Saniflo. However, this may be an expensive way to do the job and a Saniflo does make a noise when pumping.
The waste pipe to the basin and shower tray will probably be 1.5" (32 mm) and that to the bath 1.5" (38 mm). Building regulations will specify the sizes and fall of the waste pipes so, if in doubt, contact your local building control office - in most cases this will not be necessary. Remember to clip these pipes once they have been run- any sagging will allow gunge to build up in them and its weight may pull the fittings apart or cause the pipe to sag even more.