Concrete block and poured concrete are both common choices for home foundations. Both types of concrete are relatively cheap and a worker with a minimum of training and skill can install them. Most do-it-yourselfers are capable of building their own concrete foundation. However, choosing between the two can be difficult. Despite the features they have in common, concrete block and poured concrete each have their own benefits and disadvantages.
According to the Concrete Network, poured concrete costs around $75 per cubic yard as of 2008. This material makes up most of the cost of any concrete project. Other poured concrete costs include forms, reinforcing materials and finishing. Conventional 8-inch concrete block costs about $1.30 per block or $1.46 per square foot. Aerated autoclaved concrete, or AAC, a lightweight material that can be up to 80 percent air, costs about $2.30 per square foot, according to the National Association of Home Builders.
Most concrete foundations provide relatively little insulative value on their own. According to Inspectapedia, concrete slabs have an insulation value (R-value) of between .08 and .3 per inch, or about 2.5 for a conventional 8-inch wall. According to Colorado Energy, an 8-inch concrete block has an insulative value of about 1.1. Eight-inch AAC blocks have an R-value of about R-10. You can insulate concrete blocks after installation by filling the voids with foam or other materials. Purchasing pre-insulated blocks can provide R-values up to 20. Poured concrete foundations can include insulation material in the forms, or you can install it later.
Laying a concrete block foundation requires fewer special tools and materials than building a poured concrete project. Concrete block requires only mortar and a trowel, while poured concrete needs special forms and reinforcing materials to hold up. However, poured concrete is much easier to use when the foundation curves or has another special shape. Blocks are best for structures with sharp corners and straight walls.
Block and mixed concrete may not be equally available at all job sites. According to This Old House, poured concrete resists water pressure and soil weight better than block, but you can't use it if the nearest cement plant is more than 90 minutes away. Mixing concrete on site is one option, but it requires more equipment and skill. Some specialty concrete blocks and forms may also be difficult to obtain or increase the cost of the job. For instance, while AAC block is lighter and cheaper to transport, few U.S. factories produce it, which can make shipping prohibitive.
- This Old House: Block Vs. Concrete; Tom Silva
- Concrete Network: Concrete Price Considerations -- Cost of Concrete
- National Association of Home Builders: Autoclaved Aerated Concrete
- Concrete Homes Magazine: Building Your Concrete Home; Carole McMichael
- Colorado Energy: R-Value Table
- Inspectapedia: Table of Insulation Material R-Values & Other Materials' Insulating Properties