Understanding how foundations are built
Knowing when and understanding how foundations are constructed and sealed (damp proofed or waterproofed) to prevent water intrusion is an important first step in being able to evaluate and solve basement moisture problems. Prior to the I 920’s, foundations were most commonly constructed using limestone blocks or castin-place poured concrete walls and rarely had any type of damp proofing sealer applied or drain tile system installed. From the I920’s through the early I 990’s the majority of foundations were constructed using concrete masonry block. Over time, poured concrete foundations gained in popularity and today a majority of foundations are poured concrete. In the late 1950s, asphalt (tar) foundation coatings began being used to prevent water intrusion. However, this tar product is organic and hardens, cracks and deteriorates over time, allowing more water to enter the cores of block foundations. While rubber polymers have been added to improve elasticity, asphalt coatings are still used today as are several other spray-applied products. However, most of these products do not prevent the migration of moisture into a basement, they only slow it down. Prior to 1978, building code didn’t require drain tile or subsurface drainage systems and many foundations experienced water intrusion during heavy rain events and early spring thaws. However, when the new code requirements were implemented builders were forced to address the issue. Concerned that water would still get into basements, most builders constructing block foundations decided to knock holes in the cores of the block and install an interior drain tile system. Poured foundations would typically have drain tile installed around the exterior perimeter footing. Both methods carry water to a sump basket and a pump discharges the water to the exterior of the building. This was a major improvement in managing water flow.
Sources of moisture
There are three sources for basement moisture:
- Liquid water from rain or ground water
- Interior moisture sources such as moisture in concrete from construction unvented bath fans and clothes dryers, humidifiers and cooking
- Exterior humid air that enters a basement and condenses on cooler concrete floors and foundation surfaces
Here are some of the symptoms of moisture and water problems in open or unfinished basements and parking garages:
• Water trickling out of walls and on floors
• Damp or saturated concrete block on walls and at the base of the wall
• Condensation on cold foundation walls and floors in the summer
• Discoloration and flaking of painted walls and efflorescence or spalling of the foundation surface materials
Finished basements will have some of the same symptoms and often include the following:
• Damp, cool humid air
• Mold and mildew on finished surfaces such as sheetrock and wood framing
• Odors from carpet and tack strips and dark staining of vinyl floor coverings
• Warped and curled baseboard and flooring materials and staining of the bottom few inches of wood framed walls and interior door trim
Where Water Originates
Rainwater and Ground water
The majority of the water entering a below grade parking garage or basement comes from roof water runoff. One inch of rain falling on a 2000 square foot roof will yield 1250 gallons of water, which will saturate the soils next to the foundation and beneath the basement floor. Multiply that by several inches of rain at a time, like we experienced this year, and it’s not surprising to see signs of water. Excessive soil moisture can also raise the below grade water table, which is why perimeter drain tile systems are recommended even in sandy soils and basements built on a hill.
New construction concrete materials contain a lot of moisture and will take three to five years to reach equilibrium with its environment, depending on soil type. People generate moisture with activities such as showering, humidifiers, unvented clothes driers and cooking. Increased activity in finished basements, especially those with inadequate ventilation often experience even bigger problems.
Outside Air Ventilation
Many of us enjoy opening the windows for fresh air, but if that air is warm and humid, it will condense on a cool basement wall or floor. This will also cause beads of condensation to appear on the inside face of the polyethylene vapor barrier covering insulation in a basement that had “energy walls” installed by the builder.
How Moisture Movement Occurs
This method of movement allows air leakage through walls and floors, commonly referred to as the “stacking effect” and is created when warm air rises. This draws moist air in through cores in a block foundation wall, crack in floors and walls and open sump pits by creating negative pressure on the basement. To reduce this source of moisture, sump pits should have a sealed lid and all openings on the top of block foundation walls should be sealed. I would also advise that floor cracks and cold joints where the basement floor meets the wall be caulked.
Vapor Diffusion or Transfer
This is the movement of moisture in the vapor state through permeable materials and is the driving force of vapor pressure differential. This occurs when vapor diffuses (or migrates) from the wetter ground surrounding a foundation through the walls and floors to the dryer basement interior. Saturated soils create hydrostatic pressure around a foundation causing the moisture in the soils to migrate through porous walls and floors. The deeper the basement, the greater the pressure and all the more reason to install drain tile at the footing of a foundation where the pressure on the structure is greatest.
Basement Moisture Problems
Why Basements Get Wet and What To Do First
Start by identifying potential sources of basement moisture to help you reduce, control or eliminate the problem. Though none of these “solutions” alone will completely eliminate all sources of moisture in a basement, especially one that is damp proofed, you should see some improvement. Taking an incremental approach to solving moisture problems is often the most effective and least expensive approach to addressing the issue.
Internal Moisture Sources
Ventilation and Air Circulation:
Problem: Improper or inadequate venting of appliances, poor air circulation and ventilation, open sump baskets, humidifiers and cooking are some sources of basement moisture that should be addressed.
Solutions: Be sure that all appliances and bathrooms are properly vented to the exterior. Sump basket lids and discharge pipes penetrating the lid should be sealed to prevent moisture and Radon gas from being drawn into the basement when air exchanges occur. Once you have addressed these sources, dehumidification can be used to reduce humidity and odor in a basement. However, it is not a complete solution, and in some cases, moisture is drawn into the basement more rapidly. This can cause white chalky deposits, known as efflorescence, to appear on the basement walls and may cause future damage to interior finished materials.
External Moisture Sources
Gutters, Downspouts and Roof Water Runoff
Problem: A lack of or inadequate gutters and downspouts allow water to collect around foundation walls. Converging roof lines direct higher concentrations of water into valleys and the water often ends up collecting around stoops. Settled sidewalks and landscape designs that trap water next to the foundation will contribute to basement moisture problems. In many cases, sump pump discharges dump water next to the foundation.
Solution: Install oversized gutters with downspouts located every 40 – 50 feet of roof eave. Downspouts should discharge water at least 5 feet away from the foundation or to the outer edge of landscape edging, whichever is farther away. Extend sump discharges 4 – 5 feet away from a foundation with PVC pipe that has a positive pitch, and elevate the end to prevent it from becoming clogged or frozen. Corrugated flexible pipe should be replaced with PVC pipe before winter to prevent freezing and sump pump failure.
Improper Window Well Design and Maintenance:
Problem: Basement and egress window wells are magnets for water and when improperly constructed and maintained, can be major sources of basement moisture, especially in finished basements where the problem can go undetected for some time.
Solution: Drain tile connecting from the window well to the perimeter drain tile is the best solution. The window well should have a perimeter weed barrier installed to protect the rock against silting from the surrounding soils and the well should be filled to within 6 inches of the window sill or trim with clean ¾ inch rock to allow water to flow freely to the drain tile.
Grading and Landscaping:
Problem: Soils used to back fill around residential foundations is rarely compacted and inconsistently compacted in commercial construction. As a result, soils within 5 – 8 feet of the foundation and under stoops will settle slowly and unevenly. Shrubs and perennial plants can also create drainage problems as the roots grow and spread, causing water to flow toward collect next to the foundation wall. The settling often takes 30 – 40 years to reach compaction consistent with what existed on the site prior to construction. Water collecting on non-permeable polyethylene (black plastic) used to control weeds, directs even more water toward the foundation.
Solution: Periodically correct the grade to provide a 10% positive slope for at least 6 – 8 feet around the foundation and filling voids beneath stoops will reduce water intrusion. Shrubs and perennials should be culled or replaced as they outgrow the space they occupy. Replace black plastic with a breathable weed barrier to promote evaporation. Using wood chips without fabric and landscape edging is an even more effective solution.
Poured and Block Foundation Wall Cracks:
Problem: Poured and block foundations will usually develop cracks over time. Poured wall cracks are often referred to as hydration (shrinkage) cracks and can be found on most 8 inch thick walls over 20 feet long and where wall heights change, such as the side walls of a walkout foundation. Equipment getting too close to a foundation wall while back filling and excessive settling of soils during heavy rains can also cause cracking.
Solution: There are a wide variety of repairs that can be done to correct minor cracking on both types of foundations. Consult with a knowledgeable professional, and in cases where walls bow or severe cracking is observed, the services of a structural engineer may be needed.
Damaged or Ineffective Drain Tile:
Problem: Drain tile systems are prone to failure for a variety of reasons, including improper or poor installation, clogged or collapsed pipes, tree roots or improper connections to the sump basket. Forced Air heat ducts installed beneath a basement floor, especially in homes built before 1978 or homes where the drain tile system is installed higher than the duct work, will become the de facto drain tile system. This can allow water to collect in the ducts, creating potentially serious health issues from mold contamination.
Solution: In some instances, clogged, collapsed or improperly installed drain tile systems can be repaired if the problem area can be located. Finding the problem can be done using a miniature camera to “scope” the system. However, these problems are typically symptomatic of a much larger problem and rarely solve basement water problems permanently.
Solving water problems in Forced Air heat ducts will require removing the duct work and installing a drain tile system below the new heat ducts. This is an expensive repair and should be done by employing the services of an experienced foundation repair contractor and HVAC
contractor. Abandonment of the system in favor of some other heating and cooling source is another option and in many cases a better long term solution.
More Extensive Repairs For
Solving Basement Moisture Intrusion Problems
The old saying that “An ounce of prevention is worth a pound of cure” certainly applies here, so start by trying the previously mentioned repairs first. If the interior and exterior solutions don’t solve your problem, a more extensive and costly interior or exterior repair may be required. When deciding which repair is best for your particular situation, it will be wise to determine how the basement will be used. If the basement is going to be left unfinished, an interior drainage system may serve you well. However, if you plan to finish the basement, a much more extensive interior repair using a poly vapor retarder on the basement walls and floor, or an exterior repair is recommended.
Exterior Repairs and Drainage Systems
Though less common for residential properties because of the higher cost, making repairs and installing a complete waterproofing system on the exterior of a foundation is the most effective approach to solving exterior water intrusion problems. This requires landscape removal, digging around the foundation and installing materials commonly used on new construction foundations. This method of repair is most often used on commercial buildings such as offices or banks, underground parking garage and apartment/condo buildings where disruption of daily activities or relocating tenants would be prohibitive and expensive.
A properly designed repair will include making repairs to the structure, installation of a waterproofing membrane, foam insulation and a drain tile/drainage system that drains water to a sump basket and pump. Using a “free flowing” dimpled waterproofing membrane allows the foundation walls to breathe and provides a path for water to the drain tile that is covered with 12 inches of rock. Backfilling with pea rock or sand is preferred, but more expensive, and backfilling with excavated site soils is acceptable when a “free flowing” membrane is used.
Interior Drainage Channel: Above the Floor
The simplest and least expensive repair is a base board drainage channel glued to the floor at the base of the wall where water is collected and “channeled” to a sump basket. This will not solve the problem because water remains in the block cores and only lowers the water level to the top of the floor. This system should never be used if a basement is to be finished or floor coverings are going to be installed. My experience is that this method is most often installed by “do it yourselfers” and that it will eventually need to be replaced with a more effective system.
Interior Drainage Channel: Below the Floor on Top of the Footing
A more expensive but effective approach is to remove some of the floor, drill holes in the cores of the block and place a drainage channel on top of the footing. The drainage channel is connected to the sump basket using a drain pipe. Draining water out of the block cores reduces the water level and is an improvement over the above system. Because water collects in the blocks, it is important that the top of the block walls be capped and a poly vapor retarder be installed on the foundation wall. However, this repair does not address non granular saturated soils below the slab that can cause problems for flooring materials. If you plan to finish the basement and this is your choice for repairs, be sure the contractor installs the poly vapor barrier on the walls and floor and seals the joints and edges of the poly to prevent moisture transfer.
Interior Drain Tile System: Below the Floor
Unfinished Basement or Below Grade Garage
The most effective interior drainage system uses a fully perforated drain tile pipe installed around the inside perimeter of the footing and is connected to a sump basket with pump and sealed lid. The best drain tile is corrugated and has a series of 8 holes around the circumference, which allows water to enter the tile from all sides. This repair requires removal of 12 – 16 inches of floor, drilling holes in the block cores, trenching next to the footing and installation of filtering fabric in the trench. Drain tile is placed on the fabric, covered with washed rock and the fabric is folded over the rock (think taco) to protect the tile and rock from silt. A pre formed floor edging is placed at the base of the wall to protect the holes in the block and to allow water entering the blocks to flow freely to the drain tile. The exposed edge of the floor edging will need to be sealed to prevent Radon gas and moisture from being drawn into the basement when air exchanges occur. Placing the drain tile below the top of the footing and surrounding it with rock allows it to intercept rising ground water, something Drainage Channel systems don’t do as well. The foundation walls can be painted to improve appearance and maintaining a fresh look will require periodic repainting. Don’t expect this “waterproofing paint” to prevent moisture from entering the basement or garage and it should never be used as a substitute for a poly vapor retarder.
Refinishing or Finishing a Basement
I talk to people weekly that have finished a basement that had occasional water problems that have become much bigger after the work was done. Why basements get wet just isn’t something most people (and many in our industry) understand, so if you have a finished basement with water problems, you have some tough decisions to make. Water presents itself in two forms: Bulk water that gets your carpet wet and Vapor that condenses on cool surfaces and inside finished wall cavities. Selecting a repair that addresses both problems will be the best long term solution and your wisest choice. If your basement is finished, you will achieve the best results if you remove all of the materials attached to the perimeter foundation walls from floor to ceiling, returning on perpendicular interior partition walls one foot, install or replace the existing drain tile system and follow these recommendations for preparing the basement for finishing.
The preformed floor edging mentioned above will work well if you plan to use spray foam insulation in the wall cavities. Foam is a more expensive insulator but is an excellent way to seal the walls and prevent vapor diffusion or transfer.
A poly vapor retarder is installed behind the floor edging and secured to the walls from the footing to the top of the foundation. The joints and edges are sealed to prevent moisture from escaping into the future wall cavity where mold can grow undetected.
Finished Wall Surfaces
No interior poly vapor retarder should be used with either insulation. Applying an additional layer over the framing will create a “sandwich” effect and trap moisture in the wall cavity. The interior air barrier will be the finished wall material which should be sealed at the top and bottom plates and at all penetrations.
Though rarely done, it is advisable to place a poly vapor retarder and insulation on the basement floor before covering it with a moisture resistant plywood subfloor. In extreme cases, a dimpled plastic sheeting can be placed over the floor, covered with rigid insulation and tongue and groove plywood subfloor to create a vapor retarder and drainage layer on the floor. If using this method, consult with a HVAC contractor to determine how ventilating the area beneath the subfloor might be done.
Many homes built with unfinished basements do not have a HVAC system that is large enough or designed for the basement to be finished. Before proceeding, consult with a reputable HVAC contractor and work with them to make sure the existing system is adequate for your future finished space. If it is not, make the recommended changes and your family and your home will be more comfortable after doing so.
Selecting a Contractor
Do some research on your own so that you will be better equipped to understand the problem and ask the right questions. Knowing the answers to these questions will better equip you to make good decisions when hiring a contractor.
- Is the contractor knowledgeable, does he/she explain why you are having the problem and does the recommended repair address the entire problem or do they offer a “one size fits all” approach? EXAMPLE: Installing interior drain tile alone WILL NOT solve vapor or condensation problems.
- Experienced, reputable contractors will provide a detailed scope of work that explains the process and materials used. Will the contractor be using subcontractors? If so, what work will his/her employees perform? How long will the repair take to complete and will they start and finish the work in a timely manner? If you’re not comfortable with the answers you get, move on.
- Warranties vary widely so make sure the one offered covers the work to be done.
- Ask that the contractor’s license and insurance information be submitted with the proposal and ask how long the company has been doing the specific type of work you need done. Get references and CALL THEM. Call the Better Business Bureau and Minnesota Department of Labor and Industry to see if the contractor has had complaints filed against them.
- Make sure the proposed repair will solve your problem. Look for detail and a comprehensive scope of work that explains the process and materials used. Reputable contractors always provide this information because doing so reduces the chances for misunderstandings.
- Finally, make your decision based on VALUE, NOT PRICE. The contractor providing the most comprehensive solution for solving the problem, has a good reputation and provides a good warranty will be your best choice.
No two water intrusion problems are exactly the same and neither is the repair. Determining the root cause of the problem can often be difficult and consulting with a professional that specializes in and has a track record in solving these types of problems will serve you best.
In turn, they will educate you and provide solutions for you to consider that will properly address the problem. The more you understand the problem, the easier it will be for you to choose the best repair and the right contractor for solving the problem. Last but not least—-NEVER HIRE A CONTRACTOR BASED SOLELY ON PRICE AS YOU WILL RARELY GET WHAT YOU NEED.
John Lamoureux is Owner of and Advanced Waterproofing & Foundation Repairs, Inc. His expert teams have worked with housing coops, condo associations, apartment building owners, commercial and residential property managers and single-family homeowners in solving all types of basement water problems. For more info, go to www.advancedwaterproofing.net.
1996 – Construction Waterproofing Handbook
Mc Graw – Hill
John Carmody & Brent Anderson
1997 – 2006 – Moisture in Basements: Causes & Solutions
University of Minnesota