Builders and homeowners are always looking for ways to save money. They also look to reduce anxiety about the resale value of their home. It has been a long time since concrete blocks had a serious competitor in the block foundation field, but foam is it. The manufacturers of solid foam blocks as a substitute for concrete claim a higher compressive strength and greater insulation at a slightly higher cost. Foam blocks are lightweight and fit together like Legos.
Foam blocks come in different types. First, there is the solid foam block; second, the preformed block with a foam exterior that is then filled with concrete. The third option is the traditional concrete block that uses foam additives to combine the advantages of both products. No one denies that foam has helped the quality and strength of foundations, and regardless of which option you choose, concrete is never eliminated, as it must be used at least as mortar and sealant.
The solid foam block can come in any shape, color or size, and it is less porous than concrete and absorbs less water. The compressive, as opposed to impact, strength of the foam is greater than concrete, and it has excellent thermal properties. One of the more important advantages of the foam block is its consistency. Concrete loses strength as it gets older. At the same time, each foam block is identical to every other. Concrete has the disadvantage of being less consistent.
Foam and Concrete
Most foam manufacturers make the foam box that is filled with concrete. Concrete's lower price can be used with the better strength and insulation of the foam block. Foam blocks, whether filled with concrete or not, are easy to assemble and stack. They are lightweight and easy to handle. Foam has the distinct advantage of leaking less, since the foam, whether the filled or solid block, absorbs little water. Since most codes require at least two levels of insulation in the foundation wall, the foam block is the best bet, since it already contains two layers of foam with concrete inside. Adding to the benefits is the ability to use foam additives, such as insulators or waterproofing, to the poured concrete for even more strength and insulation.
Foam's disadvantages are several. First, fewer builders and contractors know how to work with the foam. Most of them are used to concrete, and so asking them to work with different blocks might slow down the work. Second, it is more expensive. Third, it is new, so there has not been a lot of experience with 30-year-old houses with this insulation. Long term disadvantages, as of 2011, have yet to be fully understood. The result is that many builders are hesitant to use them, and home buyers do not want to hear that the foundation is made from what they may associate with “Styrofoam.” Lastly, it is petroleum based, and will fluctuate in price with the price of oil.
Concrete has the advantage of being a known quantity. Builders are used to it, and you can prepare for foundation problems 30 years down the road because concrete's qualities are very well known. It is a powerful insulator, and so the foam, while superior, might not be worth the higher price. Foam blocks seem to be stronger in terms of compressive strength and consistency, but the lack of experience with the material can be worrisome to home buyers, especially over long periods of time.
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