Basement construction in clay soil poses several problems. Expanded soil can bring about cracking in the basement walls, floor and foundation if proper precautions are not taken. Common movement caused by expansive clay soils also call for special precautions to be taken when installing basement plumbing. Its important to remember that pipes can burst if plumbing is too rigid.
Floating walls help keep the walls and floors from being damaged as the home moves with the expansion of clay soil. This allows the walls to shift independently from the floor of the basement. The pipes need to be able to move upward with the floor but not push against the first floor of your home. The drainage pipes under the basement floor need to be able to breathe as well.
When you install bathrooms, laundry room, or a mudroom in the basement you need to allow for natural movement of clay soil. Installing flexible expansion couplings and expansion joints on basement plumbing will allow for this movement and keep the pipes from leaking at the joints or cracking.
Your pipes should ideally be new during installation. If you are working with pre-existing pipes make sure not to go from one type of metal to another. If you are using copper stay with copper pipes and the same goes for other metals. Take care to not to change the size of pipes accidentally. It is possible to go from one size to another but it is not always usually wise idea. You should also start with new pipes whenever possible. Older pipes can have lead solder break up while you are working with them and you do not want this to get into your water supply, even if it is for a shower and not drinking water.
Anywhere that you are attaching one length of pipe to another you need to add an expansion coupling. Expansion couplings are made of a synthetic polymer sleeve that slips over the ends of both pipes. Steel clamps are used to hold the coupling and pipes together. Once applied, the coupling will allow for a small amount of movement in the pipes. It is important to make sure you have the expansion couplings and not regular couplings as the expansion couplings are made to breathe with the home and the regular couplings aren’t made to move.
When installing a shower you can use reverse floating walls to stabilize pipes in the basement and allow movement in the top of the pipes. You should put as much of the plumbing in the same area as possible and use the same wet wall. A chase should be included and access can be either along a wall or in the ceiling.
Flex lines are needed for water supply lines. The main water supply line should go into the chase and have flex lines attached in that area to the pipes used in the basement. The most logical place for the chase access panel is in the utility room along with the hot water heater.
As well as having expansion joints and flexible couplings installed the pipes there should be enough space between the pipes and the ceiling/floor to keep from having the pipes push into the ceiling as the ground expands with the changes in the moisture in clay soil.
Expansion joints will be needed for installation of ground water drainage pipes also. This can be done below the basement floor, above the foundation. Drains can be placed in the basement floor allowing moisture that does enter the basement to run into the drainage system and away from the home.