foundation types

insulating concrete forms

Insulating concrete forms.

For each foundation type – basement, slab-on-grade, and crawlspace – there are several construction systems and products from which to choose:


  • Cast-in-place concrete
  • Concrete or masonry blocks
  • Insulating concrete forms
  • Precast concrete
  • Permanent wood foundation

    Most of these foundation systems can be designed to meet necessary structural, thermal, radon, and moisture control requirements. Your whole-house systems approach, including the climate, will help determine your choice.


    It's also important to determine how the foundation will be insulated.


    Cast-in-place concrete

    Cast-in-place concrete construction involves setting up removable forms for the pouring of concrete foundation walls. It's a common method for all three types of foundations – basement, slab-on-grade, and crawlspace.


    Rigid foam board insulation is usually placed between the removable forms and held in place with a system of non-conductive ties. Then concrete is poured on either side of the foam. Steel rebar is also generally used to add strength to the wall. Once the concrete has cured, the forms can be removed and reused as many as 3,000 times with minimum maintenance.


    Concrete or masonry blocks

    Another common foundation system is the use of concrete or masonry blocks. When using blocks for a foundation wall, the block cores should be filled with insulation. Filling the block cores with high-pressure foam works better than most other block-filling methods, such as poured-in insulations like polystyrene beads and vermiculite.


    Foam inserts for the block cores are also available. These are installed as the blocks are mortared into place. Some concrete block manufacturers attempt to increase the thermal resistance of their product by adding materials such as polystyrene or wood chips to the concrete mix. Even though the block cavities and special block designs can improve a block wall's thermal characteristics, it doesn't reduce heat movement very much when compared to insulation installed over the surface of the blocks, either on the exterior or interior of the foundation walls.


    Insulating concrete forms

    Insulating concrete forms (ICFs) serve as both foundation structure and insulation. They are basically forms for poured concrete walls that stay in place as a permanent part of the wall assembly. The forms, made of rigid foam insulation, are either pre-formed interlocking blocks or separate panels connected with plastic ties. The left-in-place forms not only provide continuous insulation but also a backing for drywall on the inside.


    Although all ICFs are identical in principle, the various brands differ widely in the details of their shapes, cavities, and component parts. Currently, about one-third of all ICFs sold are used in residential basements.


    Precast concrete

    Manufacturers construct precast concrete foundation walls or panels off-site. Most of them are preinsulated as well with rigid foam board. But additional insulation of your choice usually can be added inside the wall cavity to achieve a high R-value. The panels typically come in lengths of up to 16 feet and in standard heights of 4, 8, and 10 feet. Once constructed, they're transported to the building site. A crane is needed to lift them in to place.


    Precast concrete panels not only can provide for high R-values, but also structural integrity and termite protection. They minimize air infiltration, as well.


    Permanent wood foundation

    Permanent wood foundation (PWF) construction is similar to wood-framed exterior wall construction, with some exceptions. Because PWF walls are used in below-grade applications, all lumber and plywood is pressure-preservative treated for decay and termite resistance.


    Any type of insulation product can be used with a PWF. But there are some indoor air quality issues in regards to the preservatives used to treat the wood. Wood foundations also don't have the same structural integrity as concrete foundations.


    In the event of bowing, cracking, or buckling walls, a foundation repair contractor should be contacted.