Sunday, August 7, 2011

Wet Basements

While nothing is quite as frustrating as dealing with a wet basement. Water can damage walls and flooring and ruin irreplaceable things like photo albums and family heirlooms. If left uncontrolled foundation damage can occur. Knowing the causes of wet basements and how to prevent water damage can help prevent this frustration.

Where Wet Basements Come From
In order to prevent a wet basement, it is important to understand where the source of the water. There are four common sources of water that seeps into your basement:

Surface water running down foundation walls

Groundwater in water-saturated soils being pushed into the basement by hydrostatic pressure

Storm sewer water from the municipal storm sewer system backing up into the home's existing perimeter foundation drain and leaking into the basement (this can only occur if the perimeter foundation drain system is connected to the municipal sewer system)

Sanitary sewer water from a combined municipal storm/sanitary sewer system backing up into the home's drain system, causing sewer water to come up through sink drains and floor drains on lower levels.
When you experience a wet basement for the first time, it is imperative to determine if the water problems are going to reoccur or if it was a one-time event. Essential to solving this question is determining the source.

Controlling Surface Water
If this is your first time for basement water problems, the first thing to check for is surface water draining down next to the foundations. Water coming in at one location and only at the exterior foundation wall are typical indications of surface water problems. Here are some things to look for:

1.Are the gutters overflowing because they are blocked? Keeping gutters clean of debris should be a part of every homeowner's routine maintenance program.

2.  Are gutters overflowing because there are not enough downspouts on the house?

3.  Do the downspout outlets extend at least 10 feet from the home?

4.  Do the downspouts drain into the footing tile system? 

5.  Are there any paved areas next to the house that slope toward the house? 

6.  At paved areas that abut the house, is there sealant in the joint at the pavement and  house wall intersection, and if so, is it cracked?

7.  Is the ground around the home sloping away from the home at least 10 feet? 

8.  Are there any hills sloping down toward the house that may be the source of the water? 

9.  Is there a lawn/shrub irrigation system discharging too much water next to the house?
Controlling subsurface groundwater
If no surface water sources are found, then the source of the water is likely subsurface groundwater under hydrostatic pressure. Unfortunately, subsurface groundwater problems are more difficult and more expensive to fix than surface groundwater problems. When the groundwater levels outside the basement rises above the level of the floor, the basement acts like a boat in a pond. If a boat is sitting in water, water will leak in through any open cracks or holes. It works the same way with a basement. Hydrostatic pressure can push water through hairline cracks. Symptoms of this are water coming up through cracks in the basement concrete floor or water coming in at multiple locations.

If you have an older house within town and the house has a basement with no sump pump, it is likely the perimeter foundation drain system connects directly into the city storm sewer system. If the level of the basement is below the street level, there is the potential of storm water backing up in the city storm sewer system and being pushed into the perimeter foundation drain system. This can saturate the soils around the house at the basement level with storm water under hydrostatic pressure, causing water to leak in.

No matter where it is coming from, the best way to control subsurface groundwater is to install some type of perimeter drain and waterproofing system to relieve hydrostatic pressure. The groundwater is pushed into the drain system and not into areas where it can damage carpets, walls or belongings. The water drains by gravity into a sump pit where a sump pump discharges it out of the house.

There are two basic types of drain systems for wet basements. One is a perimeter above-slab gutter system installed at the base of the exterior foundation walls on top of the floor slab. It doubles as a base material for the wall. The other type of drainage system is a below slab interior drainage system. The below slab system requires the partial removal of the concrete floor slab and installation of drainage pipe making it more expensive than the base gutter system.

It is commonly known that an under-floor drainage system is better because the under-floor drains are believed to relieve the hydrostatic pressure before the water reaches the bottom of the floor slab.

Storm water backing up into your home
In many older houses with basements (mostly pre-1980), there is a perimeter foundation drain outside the exterior wall, at the level of the basement floor, next to the footings at the time the house was built. A pipe was usually installed from the perimeter foundation drain to the street where it was connected to the city storm sewer system or to a sump pump system.

If it is connected to the city storm sewer it can become a problem as the city storm sewer system becomes too small when more development causes more rain runoff. When this happens, the rainwater in the sewer system can get so high that water flows backwards toward the house. The perimeter foundation drain fills with water and releases large quantities into the soil next to the footing and basement floor. The soil becomes water-logged and the water which is under hydrostatic pressure leaks into the basement.

Usually the installation of an interior perimeter basement drain system connected to a sump pump will take care of the problem. The interior perimeter basement drain system can usually pump the water out and onto the ground as fast as the water is backing up from the city storm sewer system.

If that doesn't take care of it, the other, more expensive alternative would be to dig up and cap the pipe that is running from the house to the street from the perimeter foundation drain. However, this is not always possible because many times, this pipe is also draining sanitary waste from toilets and sinks in the house. If you believe you have this problem, contact an experienced contractor for advice.

Sanitary sewer water backing up into your home
If the water is coming up through floor drains or sink drains in the basement, then the problem is likely water backing up from the municipal sanitary sewer system. This usually occurs in older sections of some cities that have combined sanitary and storm sewer systems. During heavy rains, combined sewer systems can become overwhelmed with water. This can cause sewer water to back up in the system and sometimes into homes.

You can imagine the mess this creates for homeowners because it usually means they are getting other people's fecal waste backing up into their basement. To correct this, cities should update their sewer systems so the sanitary sewer and storm sewer are running in separate pipes. Until this work is complete, the homeowner can install backflow preventers that help stop sewer water from flowing backward into the house.

Unfortunately, because the city sanitary system works in conjunction with every house sanitary piping, the backflow preventer usually cannot be located on the house's main sewer line. It usually requires several backflow preventers at all basement drain locations, such at every floor drain, sink and toilet. These backflow preventers require routine maintenance to make sure they are kept free of debris