Full Basements Should Be Insulated and Protected From Water

Bird's eye view

Green basements are comfortable and healthy

Most basements have dampproofing and a footing drain, but they can still be damp, clammy, and musty. Green basements go farther with a full waterproofing system, better footing drains, and foam insulation. With warm walls, moisture doesn't condense so basements don't get moldy.

See below for:


Key Materials

Waterproofing is better than damp-proofing

Basement walls need to stop groundwater from getting in. There are a number of products that can be applied to foundation exteriors, including asphalt-based damp-proofing, spray-on waterproofing coatings, dimple mats, and plastic membranes that shed water. Water-resistant coatings (damp-proofing coatings) by themselves do not make a wall waterproof. Bentonite, a type of clay, is sometimes used as one component in a basement waterproofing system.

Design Notes

Is building a basement worth the effort?

Basements take a lot of energy and resources to build. There are several situations that may justify the extra expenditures. For example, if a home needs storage space, basement space may be cheaper to build than above-ground space.

Sometimes it's more comfortable underground. No matter where you live, there will be some part of the year when the temperature deep underground is more comfortable than the air temperature. Creating conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. underground may take some of the load off of your heating or cooling system, depending on where you are and what season it is.

Frost lines require you to dig deep anyway. In a cold climate, you have to protect the foundation from damage caused by frost heaving. If your footings need to be several feet below grade, it's probably worth it to create a full floor with usable living space, instead of a less functional crawl space.

A hillside home has a few advantages. A hillside can shelter a home on some sides while offering sunlight and accessibility on others. Depending on how steep the site is, there could be two or more ground levels instead of just one. In a cold climate, an earth sheltered home should face south to take advantage of passive solar heating and to shelter the north side from winter winds.

Builder Tips

Keep water at bay and encourage drainage

  • Control runoff from the roof with a system of gutters and drains, and pitch the grade away from the house to keep water away from the foundation wall.
  • Virtually all building codes require the installation of subsurface perforated drain pipes around the perimeter of the foundation at the footing; these pipes drain either to daylight or to a sump that can be pumped out. Go here for more about foundation drains.
  • To reduce hydrostatic pressure against foundation walls, use coarse granular backfill that allows water to pass through. Using clay-rich expansive soil can cause problems.

  • The Code

    The code

    The International Residential Code, in section N1101.6.1, includes requirements for the protection of above-grade exterior basement insulation.

    Foundation drainage requirements are covered in section R405.1, which states, "Drains shall be provided around all concrete or masonry foundations that retain earth and enclose habitable or usable spaces located below grade. Drainage tiles, gravel or crushed stone drains, perforated pipe or other approved systems or materials shall be installed at or below the area to be protected and shall discharge by gravity or mechanical means into an approved drainage system."

    Illustration:Code Check Building 2nd Edition.
    click to buy .


    Basement windows don’t have to be energy drains

    Those bargain-priced metal window frames typically cast into a concrete basement wall are energy sinks that should be avoided. The metal frames are a conduit for heat and cold, and the single layer of glass results in a performance standard well below that of windows installed elsewhere in the house.

    It makes more sense to specify a window that meets basic performance criteria: double-glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. with low-e coatingVery thin metallic coating on glass or plastic window glazing that reduces heat loss through the window; the coating emits less radiant energy (heat radiation), which makes it, in effect, reflective to that heat; boosts a window’s R-value and reduces its U-factor. for a low U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. , and a non-metallic frame clad in aluminum or vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). for low maintenance and good thermal performance.


    Concrete-block Basement Details
    Concrete-Basement Details


    Any basement design should specify air-barrier details. The most critical basement areas for air sealing are:

    Airtight sump lid
    Incredible as it sounds, the stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season. in many houses is strong enough to pull air into the house through a sump. The solution is an airtight sump lid (available at Shelter Supply.

    Rim joist
    The rim joist area should be sealed with spray polyurethane foam or individual rectangles of rigid foam insulation. Fiberglass batts don't stop air, so they allow moist interior air to contact the cold rim joist, where moisture can condense.


    LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. 1/2 point available under MR2.2 (Materials & Resources) for fly ashFine particulates consisting primarily of silica, alumina, and iron that are collected from flue gases during coal combustion. Flyash is employed as a substitute for some of the portland cement used in the making of concrete, producing a denser, stronger, and slower-setting material while eliminating a portion of the energy-intensive cement required. More info or slag as replacement for 30% or more of Portland cement in foundation.

    NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. Under Ch. 6 — Resource Efficiency: up to 4 pts. for recycled-content (fly ash or slag substitution for Portland cement in concrete) (604.1).


    Invest in a waterproofing system

    Basement foundations should be insulated to minimize energy losses and should be protected from water infiltration. Even if a basement is not intended to be used as a finished space, it's best to assume that it may be finished in the future. That's why it's a good investment to upgrade from damp-proofing to a true waterproofing system when the basement is built. It's always cheaper to perform this work at the time of construction than years later, when landscaping is in place and excavation is difficult.

    For information on ways to improve a damp basement, see Fixing a Wet Basement.

    Types of basement foundations

    Full foundations that create usable basements can be built in a number of ways: formed-in-place concrete walls or concrete block on footings are the most common. Insulated concrete forms (ICFs) and precast concrete panels are two newer options. Although it's possible to build basement walls with treated wood lumber on footings of compacted gravel, all-wood foundations are rarely installed.

    Insulated concrete forms

    The most common type of ICF is made from inner and outer layers of rigid foam insulation with internal cavities that are reinforced with steel and filled with concrete. The forms are light, easy to handle, and quick to assemble. The foam provides an efficient thermal barrier. ICFs can be used to build above-grade walls as well as basements. ICFs can also be made from recycled polystyrene or wood chips combined with cement.

    Treated Wood. Foundations made from treated lumber can be less expensive than building with concrete or concrete block. Despite their novelty among many builders, these foundations have a long history of reliability. Regular carpentry crews can erect them, and wood foundation walls can be set on a gravel base rather than a concrete footing. All of that helps make construction simpler, and sometimes faster, than a concrete foundation. Also, framed walls are easier to insulate and wire than concrete. Structural insulated panels with a treated-wood exterior are a similar option.

    Precast concrete.
    Like wood foundations, precast panels can be erected quickly without the need for concrete footings. They consist of an outer panel of concrete and top and bottom plates connected by concrete studs. One advantage of these systems is that most include integral insulation.



    When the basement will be used as a home office, bedroom, home theater, or other living space, it has to have windows that are big enough to be used as emergency exits. Local codes may vary, but the requirements listed in the International Residential Code include these provisions:

    Windows must measure at least 24 in. high and 20 in. wide and have a minimum net clear opening (not including the frame) of 5.7 sq. ft.

    Windows must be operable from the inside, without the use of keys or tools.

    The sill must be no more than 44 in. from the basement floor.

    If windows open into a well, the floor must be at least 9 sq. ft. with a minimum dimension of 36 in.

    A permanent ladder or steps must be provided if the well is more than 44 in. deep.

    A metal or plastic well can be installed during construction or as a retrofit to meet code requirements for egress basement windows. In addition to providing emergency access or escape from below-ground living areas, the wells provide a lot more natural light than standard basement windows.


    Many concrete basement foundations are probably stronger than they need to be. A typical foundation wall 8 in. thick rests on a 12-in.-wide footing that distributes the load evenly. Because of the enormous compressive strength of concrete, it’s very unlikely the house will fall down. But it takes a great deal of energy (and greenhouse gas emissions) to manufacture cement, so it pays to reduce the amount of concrete in a foundation wall if possible.

    Building codes are based on assumptions about the bearing capacity of the soil beneath the footings as well as the weight of the structure. Calculating the loads more precisely, along with testing soils on the site, may allow thinner foundation walls, lowering costs and consuming less material.

    This is the approach advocated by Fernando Pagés-Ruiz, a builder in Nebraska and author of Building an Affordable House (The Taunton Press, 2005). Among his many suggestions are using fly ashFine particulates consisting primarily of silica, alumina, and iron that are collected from flue gases during coal combustion. Flyash is employed as a substitute for some of the portland cement used in the making of concrete, producing a denser, stronger, and slower-setting material while eliminating a portion of the energy-intensive cement required. More info (a by-product of coal-burning power plants) to replace some of the more expensive cement in the concrete; specifying concrete with lower load-bearing capacity where appropriate; and replacing wire mesh and steel reinforcing bar with synthetic and steel-fiber additives.

    The point is to design foundations for the load and soil conditions on the site, not a conventional standard that may not apply. Although Pagés-Ruiz doesn’t always bill his suggestions as "green," his cost-saving measures are all about resource conservation, which is very green.

    Where radon is a hazard, the crawl space can be safely vented by installing perforated plastic pipe in gravel beneath the polyethylene ground cover and running the stack up through the roof.

    For more information, see All About Radon.


    All About Basements

    Fixing a Wet Basement

    How to Insulate a Basement Wall

    All About Radon Renovating your Basement

    Image Credits:

    1. Charles Lockhart
    2. Charles Bickford/Fine Homebuilding #190
    3. Paddy Morrissey, Code Check Building 2nd Edition
    Tags: , , , , , , ,
    Jul 15, 2010 3:10 PM ET

    Response to Andrei
    by Martin Holladay, GBA Advisor

    Your question was answered some time ago in the Q&A section:

    Click the link to find out more information.
    In summary, here are your options for protecting the above-grade portions of exterior foundation wall insulation:
    1. Pressure-treated plywood.
    2. Fiber-cement panel siding.
    3. Cementitious coating (stucco) -- either reinforced with fiber, or installed over fiberglass mesh, or installed over metal lath.
    4. Insul-Cap vinyl covering from Wisconsin Poured Wall Products ( Muskego, WI).
    5. Ground Breaker fiberglass covering from Nudo Products (
    6. Insul-Guard 2 fiberglass covering from Diversified Composites (
    7. Surface-bonding cement.
    8. Perma-Bond Complete (foam plus factory adhered cementitious coating) from
    9. FP Ultra Lite panels (factory coated foam panels) from Styro Industries (
    10. Protecto Bond peel-and-stick membrane (

    Jul 5, 2010 8:03 PM ET

    External Insulation of existing basement foundation
    by Andrei Sosnovsky

    I'm planning on waterproofing of basement foundation walls and adding new weeping tile. I though it would a good idea to add rigid foam insulation since foundation walls are exposed anyway. What's a good way to protect and finish the above grade portion of rigid foam? After reading multiple articles I still can not seem to get a clear answer. Any ideas? Location - Toronto, Canada.

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