When shopping for an existing home, homebuyers are limited to making the best choice among houses available in their chosen area while they are in the market. This is not necessarily a bad thing as choosing an existing home works out well for the vast majority of buyers.
For those who are very specific in their needs or who are participating in a real estate market that doesn’t offer many options, building a home to their specifications can be a great alternative. Buyers can choose their location, the size and style of their home and can add whatever options their imaginations (and bank
Initially, most buyers involved in the construction of a custom home will direct their attention and resources to size and design issues of the home:
Is the kitchen the right size and layout?
Do we have the right number of bedrooms?
Should we get the currently popular FROG (Finished Room Over Garage?)
Typically, their next area of focus will be facets of the home that are visible and contribute to creature comforts, like windows, flooring and wall finishes. Depending on the home and the buyers, their attention may be directed toward any number of details but, as is the case with most people building new homes, little thought may be given to such things as ensuring that the basement stays dry.
Many builders will take some limited steps to keep basements dry in their homes but a wise homebuyer will go beyond the minimum in protecting their investment.
Many contractors who build homes will apply “damp-proofing” to the foundation during construction and many homebuyers who have never had the difference explained to them confuse “damp proofing” with “waterproofing.” They are very different processes with very different results.
“Damp proofing” is accurately named because its purpose is to prevent dampness from seeping through foundation walls, whether they are built of poured concrete or masonry. It consists of a thin coating of bituminous mastic that is sprayed onto the wall in liquid form while the foundation is exposed. When the coating dries it will repel moisture from the soil and prevent the basement from feeling damp.
The difference between damp proofing and waterproofing is defined by the American Society for Testing and Materials (ASTM) this way, to paraphrase:
Damp proofing resists the passage of water in the absence of hydrostatic pressure; waterproofing stops the passage of water under pressure.
This means that if damp soil exists outside the foundation, a damp proofed wall should prevent the dampness from penetrating the basement. This may be sufficient only in areas where the soil is very well drained and the water table is low.
Waterproofing, by various means and methods, will prevent water under pressure, whether that comes from hydrostatic pressure below the foundation or lateral pressure caused by saturated soil outside the foundation walls, from entering the basement. The conditions that cause water to build pressure against the foundation are much more commonly found than not, meaning that mere damp proofing will not protect the majority of basements.
The great thing about waterproofing a home under construction is that cost and inconvenience are significantly reduced because work can be done before the foundation is backfilled or the basement floor has been poured. This eliminates labor costs for demolition and excavation and allows the new homeowner to move right into a home that is permanently protected against seepage.
There are three ways to waterproof a home under construction and, depending on circumstances, homebuyers may choose one or all three.
Exterior Waterproofing Membrane – An exterior waterproofing membrane is what damp proofing wants to be when it grows up.
As referenced in the explanation of the difference between damp proofing and waterproofing, water can exist in the soil either with or without building pressure. In soil that drains especially well, such as sand, water entering the ground from rain or snowmelt passes through the upper layers of soil quickly and doesn’t saturate the soil and build pressure. In more expansive soil, such as the clay that is common in the Chicago area, the soil is denser with less space between soil particles for water to flow through. The water accumulates in the soil, saturating it, and causes the soil to swell, creating pressure that is exerted against foundation walls.
This water under pressure will make its way through a damp-proofed wall (not to mention into cracks and openings in existing homes) but can be stopped by applying an exterior waterproofing membrane.
When applied to an existing home, the process begins by excavating the foundation wall but is done on new construction after the foundation has cured and before it is backfilled.
The installation begins by covering the entire wall to a point above the backfill line with a heavy coating of an asphalt-modified polyurethane material. The coating can be sprayed but is done most effectively with a trowel.
When the coating has cured it forms an impermeable barrier against water, even water under pressure from the surrounding oversaturated soil. The installer can then attach heavy-duty, dimpled plastic drainage board that will protect the membrane and channel rain and groundwater downward, away from the foundation. Insulating material to help cut the chill in the basement can also be applied.
Exterior waterproofing membranes are often augmented by installing exterior drain tile.
Exterior Drain Tile – Drain tile is one of the most useful methods of basement waterproofing and is an easy installation when a home is under construction.
Again, when exterior drain tile is installed in an existing home, excavating and cleaning the foundation are required. In new construction, the installer begins by clearing some space next to the outside edge of the foundation footings. Washed gravel is then poured into the opening and leveled to form a bed.
Lengths of perforated PVC pipe are then fitted and joined around the perimeter of the foundation and laid on top of the gravel bed. The piping is wrapped in a “sock” of filtration fabric and connected at both ends to a sump pump. Another layer of gravel is poured and leveled on top of the pipe; the installation is complete and the foundation can now be backfilled.
The exterior drain tile will alleviate the lateral pressure caused by saturated soil and accumulate the ground water that would cause it. The ground water then flows to the sump pump for discharge from the foundation.
The combination of an exterior waterproofing membrane and exterior drain tile creates a double safeguard against a wet basement but there is still one step a new homebuyer can take to ensure complete protection.
Interior Drain Tile – Interior drain tile is designed to relieve the pressure under a foundation and prevent seepage through cracks that may develop in the basement floor or through the cove joint between wall and floor.
In an existing home, installation begins with removing a strip of the concrete basement floor around the perimeter and excavating next to the footings. In new construction, installation takes place before the basement floor is poured.
The installer begins, as in the exterior process, by clearing space in the soil next to the foundation footings and pouring in washed gravel to form a bed. The pipe used in interior drain tile is flexible, corrugated plastic, also perforated, to avoid creating right-angle pipe joints in tight inside corners. This pipe is also encased in a filter sock and connected at both ends to a sump pump basin. Another layer of washed gravel is added and the gravel bed is leveled to prepare for the pouring of the basement floor.
The interior drain tile will alleviate hydrostatic pressure under the foundation and carry the ground water off to the sump pump for disposal.
Of course, when installing either interior or exterior drain tile in a new home, a sump pump with a properly sized basin is an essential part of the waterproofing system. Homebuyers should be sure that the pump is of good quality and sufficiently powerful to move water quickly up to and out of the designated discharge opening.
A battery or dual-powered backup sump pump is also a good idea, particularly in areas prone to heavy storms and/or power outages.
These basement waterproofing techniques are a specialty and are typically not installed by general contractors. A new homebuyer, or the builder, will need the advice and assistance of an experienced basement waterproofing contractor that has created dry basements in both new and existing homes.
At U.S. Waterproofing, we have been in the business of dry basements since we were founded in 1957 and have grown to become one of the country’s largest companies in our industry. We have worked on both existing homes and new construction for more than 300,000 satisfied customers so why not contact us (or ask your contractor to call) when you’re building a new home? Our advice is free.
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