Exterior Surface of Below-Grade Walls

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Description

A complete water management strategy is critical in order to keep the home from excessive moisture issues. Mold, rot, ruined insulation, poor indoor air quality (IAQ), and the potential for structural damage are all a result of excessive water entering the building envelope. While a home’s overall moisture protection strategy may include sump pumps and other technologies to help remove water, the primary goal should be to keep water from entering the home in the first place. Designs that include roof overhangs, gutters and downspouts that carry water away from the foundation, site grading away from the house, and other preventative steps will keep water from pooling around the home’s foundation (Ueno and Lstiburek 2011; BSC 2009).

See Final Grade for guidance on managing water drainage around the home’s foundation.

Moisture Infiltration in Below-Grade Wall

Figure 1 - Moisture Infiltration in Below-Grade Wall. Water saturated concrete, mineral stains on the wall, and standing water on the floor are obvious signs of moisture infiltration in below-grade walls.  Reference

Finishing the Exterior Surface of Below-Grade Walls that are Concrete

Most foundation and below-grade walls are constructed with concrete, concrete masonry, or insulated concrete forms (ICFs). Concrete products are porous, and unless treated, are not waterproof, allowing water to migrate into the building (BSC 2006). Telltale signs that concrete foundations have water issues include mineral stains, mold, wet (saturated) areas, and even puddles on the floor.

To ensure that concrete-based foundations and below-grade walls remain dry and water does not seep into the home, you must do the following (with each bullet described in more detail below):

  • Customize the below-grade poured concrete mixture to yield concrete that is more impermeable to water migration.
  • Cover the surface of all below-grade walls with damp-proof coating.
  • If installing below-grade insulated concrete forms, use manufacturer-approved materials for the damp-proof coating.

Customize Below-Grade Concrete Mixture for More Water Impermeability

Not all concrete is mixed to the same specifications. The overall strength of concrete and the ability to repel water can be adjusted depending on the ratio of water, cement, sand, and aggregate used. Concrete is compression rated using a pounds per square inch (PSI) measurement. Most mixed concrete will range between 3,000 PSI and 4,000 PSI, but greater strengths are available. The higher the PSI the more water resistant the concrete will be once it is cured.

Also, additives called admixtures can be incorporated into the concrete before it is poured that can alter curing time, improve freeze protection, and improve water impermeability. When determining the PSI and admixtures for concrete, it is important to make decisions based on climate and local building codes.

Because increasing the PSI and water impermeability of the concrete will also increase the cost of the material, you may consider increasing the PSI for only the foundation or below-grade walls and select a lesser PSI concrete mix for other parts of the house like sidewalks, parking areas, and patios.

Apply a Damp-Proof Coating to Concrete Below-Grade Walls

In addition to customizing the concrete mixture, you can apply a waterproof treatment, known as a damp-proof coating (as shown in Figure 2). Damp proofing is usually an asphalt emulsion that can be brush- or roller-applied, or may take the form of a spray-on coating, or closed-cell polyurethane foam.

A Below-Grade Foundation Wall with a Damp-Proof Coating

Figure 2 - A Below-Grade Foundation Wall with a Damp-Proof Coating. Customized concrete mixtures (more water impermeable) and damp-proof coatings help protect below-grade concrete walls from water absorption. Here a damp-proof coating is painted onto the concrete, which is covered with the secured ends of the plastic sheeting that is located under the concrete slab.  Reference

For poured concrete walls, a damp-proof coating can be applied directly to the surface; however, for masonry block walls and below-grade insulated concrete forms the surfaces must first be prepared.

Preparing Masonry Block Walls for Exterior Damp-Proof Coating

The surfaces of concrete masonry block walls must be coated with a layer of parging before damp-proofing can be applied. Parging is a mortar applied to the surface of a masonry wall to create a smooth, continuous surface free of holes. It will give the damp-proof coating something even to adhere to and form a flat plane.

The steps for preparing masonry block walls for exterior damp proofing are as follows:

  1. Mix parging material per manufacturer’s directions.
  2. Using a trowel, apply parging directly to the exterior of the masonry or rough surface wall, creating a smooth, even plane.
  3. Allow to dry, per manufacturer’s recommendations, prior to applying damp-proof coating.

Preparing Below-Grade Insulated Concrete Forms for Damp-Proof Coating

Below-grade insulated concrete forms (ICFs) are blocks or panels consisting of two layers of rigid plastic foam that sandwich a 4- or 6-inch layer of concrete (see Insulated Concrete Forms). ICFs require slightly more attention due to the possibility of trapping moisture between the concrete and the insulation. Refer to the manufacturer’s recommendations when applying any coating as some coatings may dissolve the foam form.

The steps for damp-proofing ICFs are as follows:

  1. Contact the manufacturer or refer to the manufacturer’s documentation to determine the appropriate damp-proofing material.
  2. Apply per the manufacturer’s directions.

Finishing the Exterior Surface of Below-Grade Walls that are Wood

The 2012 International Residential Code (IRC) allows wood foundation walls, although this is not considered a Building America best practice. If using wood as a below-grade wall, be sure to do the following for the exterior finish:

  • First, refer to local and national codes and Authority Having Jurisdiction (AHJ) instructions regarding the required preservative-treated lumber and moisture barrier for your climate zone.
  • Select the materials that meet all regulations and are recommended for below-grade construction.
  • Install per specifications.

The following overall steps are to be considered within the specific code and AHJ instructions.

  1. Install preservative-treated lumber for all below-grade walls. This lumber is immersed in a liquid preservative and placed in a pressure chamber to force the chemical into the wood. It is important to select wood for below-grade applications that has been pressure-treated with an appropriate and code- or jurisdiction-approved preservative for the specific climate zone and application.
  2. Ensure the lumber panel joints are sealed the full length with a caulking compound that produces a moisture-proof seal.
  3. Cover all below-grade lumber with a moisture barrier:
    1. Apply 6-mil-thick polyethylene sheeting or a self-adhesive waterproof membrane to the entire exterior side of the below-grade walls before backfilling.
    2. Lap the joints by 6 inches and seal with manufacturer-recommended adhesive.

    Note: Do not nail or otherwise puncture the sheeting as this allows moisture to contact the concrete.

The Exterior Finish as Part of an Overall Water Management Strategy

Finally, as shown in Figure 3 below, applying a damp-proof finish to a below-grade wall is just one important water management strategy in designing the below-grade wall (Ueno and Lstiburek 2011; BSC 2009). The overall strategy needs to consider many factors including national and local codes, climate zone, and insulation options (Aldrich et al. 2012; BSC 2002).

A Complete Water Management Strategy for a Below-Grade Wall

Figure 3 - A Complete Water Management Strategy for a Below-Grade Wall  Reference

Ensuring Success

Finishing the below-grade wall is one small part of a whole-house water management strategy that needs to consider many factors, such as national and local codes, climate zone, and insulation options.

Also, a wide variety of materials and methods are available to use when adding a damp-proof coating to the exterior of below-grade walls. It is essential to follow the manufacturer’s recommendations and requirements for any of the products used to finish the exterior surface of a below grade wall.

Scope

Water Managed Site and Foundation

Exterior surface of below-grade walls of basements & unvented crawlspaces finished in one of the two options:

Option A: For poured concrete, concrete masonry, and insulated concrete forms, finish with damp-proof coating.

Exterior surface of below-grade walls

  1. If installing below-grade poured concrete, the mixture can be customized to yield concrete impermeable to water migration.
  2. If applying a damp-proof coating to a rough surface such as concrete masonry block walls, coat all walls with a layer of parging prior to applying the damp-proof coating.
  3. Cover the surface of all below-grade walls with damp-proof coating.
  4. If installing below-grade insulated concrete forms, use manufacturer-approved materials for damp-proof coating.

ENERGY STAR Notes for Existing Homes:

Interior surface of existing below-grade wall (e.g., in a home undergoing a gut rehab) listed in Item 1.5a (above) is permitted to be finished by:

  • Installing a continuous and sealed drainage plane, capillary break, Class I Vapor Retarder (per Footnote 8) and air barrier that terminates into a foundation drainage system as specified in Fabric Filter at Drain Tile; OR
  • If a drain tile is not required as specified in Footnote 9, adhering a capillary break and Class I Vapor Retarder (per Footnote 6) directly to the wall with the edges taped/sealed to make it continuous. Note that no alternative compliance option is provided for existing below-grade wood-framed walls in Item 1.5b (below). 

Option B: for wood framed walls, finish with polyethylene and adhesive or other equivalent waterproofing.

Exterior surface of below-grade walls

  1. Install preservative-treated lumber and sheathing for all below-grade walls.
  2. Cover entire area with at least a 6-mil polyethylene sheeting and attach to the exterior side of the wall with the appropriate adhesive.

Training

Right and Wrong Images

Presentations

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Compliance

ENERGY STAR Version 3, (Rev 07)

Water Management Checklist, Water-Managed Site and Foundation. Exterior surface of below-grade walls finished as follows:

  • For poured concrete, concrete masonry, and insulated concrete forms, finish with damp-proofing coating.
  • For wood framed walls, finish with polyethylene and adhesive or other equivalent waterproofing.

Interior surface of existing below-grade wall (e.g., in a home undergoing a gut rehab) listed in Item 1.5a (Option A on Scope page) is permitted to be finished by:

  • Installing a continuous and sealed drainage plane, capillary break, Class I Vapor Retarder (per Footnote 8) and air barrier that terminates into a foundation drainage system as specified in Fabric Filter at Drain Tile; OR
  • If a drain tile is not required as specified in Footnote 9, adhering a capillary break and Class I Vapor Retarder (per Footnote 6) directly to the wall with the edges taped/sealed to make it continuous. Note that no alternative compliance option is provided for existing below-grade wood-framed walls in Item 1.5b (Option B on Scope page).

DOE Challenge Home

Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3. 

2009 IRC

Section R406.1 Concrete and masonry foundation dampproofing. Foundation walls that retain earth and enclose interior spaces and floors below grade must be dampproofed from the top of the footing to the finished grade.  Masonry walls must have at least 3/8 inch Portland cement parging applied to the exterior.  The parging is to be dampproofed per one of the following: 

  • bituminous coating;
  • three pounds per square yard of acrylic modified cement;
  • 1/8-inch coat of surface-bonding cement per ASTM C 887;
  • any material approved per Section R406.2; and
  • any other approved means. 

Exception:  parging of unit masonry walls isn’t required where a material is approved for direct application to the masonry. Cement walls are to be dampproofed using one of these methods or any listed in Section R406.2 for waterproofing. Section R406.2 Concrete and masonry foundation waterproofing. Where there is a high water table or other severe soil-water conditions are known to exist, exterior foundation walls that retain earth and enclose interior spaces and floors below grade to be waterproofed from the top of the footing to the finished grade. Walls to be waterproofed per one of the following:

  •  two-ply hot-mopped felts;
  • 55 pound roll roofing;
  • 6-mil polyvinyl chloride;
  • 6-mil polyethylene;
  • 40-mil polymer-modified asphalt;
  • 60-mil flexible polymer cement;
  • 1/8-inch cement-based, fiber-reinforced, waterproof coating;
  • 60-mil solvent-free liquid-applied synthetic rubber. 

Exception: organic-solvent-based products such as hydrocarbons, chlorinated hydrocarbons, ketones and esters cannot be used for ICF walls with expanded polystyrene form material.  Use of plastic roofing cements, acrylic coatings, latex coatings, mortars and pargings to seal ICF walls is allowed.  Cold-setting asphalt or hot asphalt to conform to type C of ASTM D 499.  Hot asphalt to be applied at a temperature less than 200°F. All joints in membrane waterproofing to be lapped and sealed with a membrane-compatible adhesive. Section R406.3 Dampproofing for wood foundations. Wood foundations enclosing habitable or usable spaces below grade to be dampproofed per R406.3.1 through R406.3.4. Section R406.3.1 Panel joint sealed. Plywood panel joints to be sealed full length with caulking compound capable of producing a moisture-proof seal. Section R406.3.2 Below-grade moisture barrier. 6-mil polyethylene film to be applied over below-grade portions of exterior foundation walls before backfilling. Joints in the film to be lapped 6 inches and sealed with adhesive.  Top edge of film to be bonded to the sheathing to form a seal. Film areas at grade level to be protected from mechanical damage and exposure by a pressure preservatively treated lumber or plywood strip attached to the wall several inches above finish grade level and extending approximately 9 inches below grade. The joint between the strip and the wall to be caulked full length prior to fastening the strip to the wall. Other approved coverings may be used. The film must extend down to the bottom of the wood footing plate but not overlap or extend into the gravel or crushed stone footing. Section R406.3.3 Porous fill. The space between the excavation and the foundation wall to be backfilled with the same material used for the footings; for well-drained sites, up to a height of 1 foot or ½ the total backfill height for poorly drained sites. The porous fill must be covered with strips of 30-pound asphalt paper or 6-mil polyethylene to permit water seepage while avoiding fine soil infiltration. Section R406.3.4 Backfill. The remainder of the excavated area must be backfilled with same type of soil that was removed.*

2012 IRC

Section R406.1 Concrete and masonry foundation dampproofing. Foundation walls that retain earth and enclose interior spaces and floors below grade must be dampproofed from the top of the footing to the finished grade.  Masonry walls must have at least 3/8 inch Portland cement parging applied to the exterior.  The parging is to be dampproofed per one of the following: 

  • bituminous coating;
  • three pounds per square yard of acrylic modified cement;
  • 1/8-inch coat of surface-bonding cement per ASTM C 887;
  • any material approved per Section R406.2; and
  • any other approved means. 

Exception:  parging of unit masonry walls isn’t required where a material is approved for direct application to the masonry. Cement walls are to be dampproofed using one of these methods or any listed in Section R406.2 for waterproofing. Section R406.2 Concrete and masonry foundation waterproofing. Where there is a high water table or other severe soil-water conditions are known to exist, exterior foundation walls that retain earth and enclose interior spaces and floors below grade to be waterproofed from the top of the footing to the finished grade. Walls to be waterproofed per one of the following:

  • two-ply hot-mopped felts;
  • 55 pound roll roofing;
  • 6-mil polyvinyl chloride;
  • 6-mil polyethylene;
  • 40-mil polymer-modified asphalt;
  • 60-mil flexible polymer cement;
  • 1/8-inch cement-based, fiber-reinforced, waterproof coating;
  • 60-mil solvent-free liquid-applied synthetic rubber. 

Exception: organic-solvent-based products such as hydrocarbons, chlorinated hydrocarbons, ketones and esters cannot be used for ICF walls with expanded polystyrene form material.  Use of plastic roofing cements, acrylic coatings, latex coatings, mortars and pargings to seal ICF walls is allowed.  Cold-setting asphalt or hot asphalt to conform to type C of ASTM D 499.  Hot asphalt to be applied at a temperature less than 200°F. All joints in membrane waterproofing to be lapped and sealed with a membrane-compatible adhesive. Section R406.3 Dampproofing for wood foundations. Wood foundations enclosing habitable or usable spaces below grade to be dampproofed per R406.3.1 through R406.3.4. Section R406.3.1 Panel joint sealed. Plywood panel joints to be sealed full length with caulking compound capable of producing a moisture-proof seal. Section R406.3.2 Below-grade moisture barrier. 6-mil polyethylene film to be applied over below-grade portions of exterior foundation walls before backfilling. Joints in the film to be lapped 6 inches and sealed with adhesive.  Top edge of film to be bonded to the sheathing to form a seal. Film areas at grade level to be protected from mechanical damage and exposure by a pressure preservatively treated lumber or plywood strip attached to the wall several inches above finish grade level and extending approximately 9 inches below grade. The joint between the strip and the wall to be caulked full length prior to fastening the strip to the wall. Other approved coverings may be used. The film must extend down to the bottom of the wood footing plate but not overlap or extend into the gravel or crushed stone footing. Section R406.3.3 Porous fill. The space between the excavation and the foundation wall to be backfilled with the same material used for the footings; for well-drained sites, up to a height of 1 foot or ½ the total backfill height for poorly drained sites. The porous fill must be covered with strips of 30-pound asphalt paper or 6-mil polyethylene to permit water seepage while avoiding fine soil infiltration. Section R406.3.4 Backfill. The remainder of the excavated area must be backfilled with same type of soil that was removed.*

*Due to copyright restrictions, exact code text is not provided.  For specific code text, refer to the applicable code.

More Info.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: April 2012

    Case study about energy efficienct new home construction that also incorporated moisture management techniques for durability in the damp Northwest climate.

References and Resources*

  1. Author(s): BSC
    Organization(s): BSC
    Publication Date: January 2002

    Report describing approaches to insulating basements in homes built to meet Energy Star.

  2. Author(s): Ueno, Lstiburek
    Organization(s): BSC
    Publication Date: January 2011

    Report about the fundamental concepts that must be understood at the planning or initial nspection of existing homes regarding surface and ground water management.

  3. Author(s): DOE
    Organization(s): DOE
    Publication Date: June 2013

    Standard requirements for DOE's Challenge Home national program certification.

  4. Author(s): EPA
    Organization(s): EPA
    Publication Date: June 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  5. Author(s): BSC
    Organization(s): BSC
    Publication Date: May 2009

    Information sheet about groundwater control.

  6. Author(s): Aldrich, Mantha, Puttagunta
    Organization(s): CARB, NREL
    Publication Date: October 2012

    Document describing good practices for insulating basements in new and existing homes.

  7. Author(s): DOE
    Organization(s): DOE
    Publication Date: December 2006

    Case study of new home construction in the hot-humid climate.

  8. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: October 2006

    Information sheet with methods for keeping basements dry, comfortable and contaminant free.

  9. Author(s): EPA
    Organization(s): EPA
    Publication Date: February 2011

    Guide describing details that serve as a visual reference for each of the line items in the Water Management System Builder Checklist.

Last Updated: 08/15/2013

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