Concrete Block versus Poured Concrete Foundation Walls

The Pros and Cons of Concrete Block and Poured Foundations

By Mark J. Donovan

When building a home or home addition, the question frequently comes up on whether concrete blocks or poured concrete should be used in constructing the foundation walls. Both have advantages and disadvantages.

Concrete Block Wall Foundation Advantages

Standard concrete blocks are sold as 16” x 8” x 8” in length, width and height, respectively. Their true dimensions are 15 5/8th x 7 5/8th x 7 5/8th in length, width and height, respectively.

The slightly reduced actual measurements are to allow for mortar to yield the 16” x 8” x 8” finished dimensions.

Standard concrete blocks contain hollow cells designed to support rebar / steel reinforcing rods, as well as poured concrete/mortar, to maximize wall strength. Besides the standard size concrete block there are a number of alternative sizes, shapes, textures and color tones to choose from.

Concrete blocks for building foundation walls are large compared to standard brick. As a result, foundations built with concrete blocks can be constructed more rapidly than one might initially think.

Concrete block walls can be constructed by homeowners with some basic masonry knowledge and back strength. The basic masonry knowledge can quickly and easily be obtained via a number of resources. The back strength: that may take a little longer pending your specific genes and age.

If the concrete blocks are properly filled with concrete and rebar during the wall construction, a very large thermal mass is created. This large thermal mass provides for an excellent high thermal and acoustic insulation factor in the walls.

Differential Settlement Causes Unstable Foundations

Concrete Block Wall Foundation Disadvantages

Concrete block walls can look somewhat ugly if they are not parged or stuccoed on the outside wall surface. Parging or Stuccoing the outside wall involves the process of applying a thin layer of mortar to the outside concrete block wall to produce one smooth flat finish surface. The mortar can be tinted to achieve different colors.

As mentioned earlier, standard concrete blocks are heavy. So if considering a Do-it-Yourself foundation project, keep this in mind.

If concrete block walls are not filled with concrete and rebar they can be weak and structurally unsound. In addition, they will have a limited insulation factor.

Just as with poured concrete walls, it is imperative that a concrete block wall be installed on a proper concrete footing. In addition, a perimeter drain is critical when building a foundation wall with concrete blocks. Due to the seams associated with concrete block construction, foundation walls are more susceptible to water leakage.

Poured Concrete Foundation Wall Advantages

Poured foundation walls can typically be constructed much more quickly than concrete block based foundations, thus saving both time and money. The complete process of installing concrete forms, pouring the concrete, and breaking the forms down can take as little as 2 or 3 partial days of work.

Poured concrete foundations are usually 6-10 inches thick and joint-free, unlike concrete block walls. Consequently they are considered to produce stronger and drier foundation walls, critical for basement walls.

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Poured concrete foundations provide for highly flexible floor plans. Jogs in the foundation walls are easily constructed using pre-fabricated concrete forms.

Poured Concrete Foundation Wall Disadvantages

Poured foundation walls usually can not be performed by a homeowner. Large pre-fabricated forms are required to first be installed, sometimes requiring the use of small cranes and unique fasteners.

Regardless of whether you choose concrete block or poured concrete for building your foundation walls, be sure to apply a waterproof sealer to the outside surface to help prevent leakage. Also install rigid insulation on the outside of the walls before backfilling to maximize the insulation factor of your concrete foundations walls.

For more help on building a home addition, see’s Home Addition Bid Sheets. Our Home Addition Bid Sheets provide you with the knowledge and information on how to plan a home building project, and what to look for when hiring contractors. They also include detailed cost breakdown tables and spreadsheets for estimating your own new home construction building costs.

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