Best way to insulate a crawl space

There are several methods to insulating a crawl space.  Some can be efficient, and others can be detrimental to the environment of the crawl space.  Do your research before choosing the insulation method that is right for your home.  In harsh winters, a properly insulated, conditioned crawl space can save a homeowner 15% to 20% in energy savings.

To determine the best way to insulate the crawlspace under your home, a homeowner must identify all the current airflow, foundation, and moisture problems within the crawlspace.  Since not all crawlspace construction and potential problems are the same, I am going to outline some factors to take into consideration before insulating your crawlspace.

Question: Is your crawlspace above the ground level of the outside soil, or is your crawlspace below the ground level of the outside.   This factor is going to weigh into potential moisture problems, and possibly how you address insulating the perimeter walls.

Answer: Above Grade Crawlspace – If this is your crawlspace, you are less susceptible to water intrusion through the foundation and dirt floor of the crawlspace.   This crawlspace can be sealed with an appropriate encapsulation/conditioned system, and the walls insulated with either 2" rigid foam board or spray foam insulation.  The most efficient would be to spray foam the walls and bandboard with spray foam after the crawlspace floor and bottom portions of the walls is properly sealed with an encapsulation liner.

Answer: Underground Crawlspace – This is the type with the most problems. Before insulating this type of crawlspace, it is imperative to research all potential problems in the crawlspace.  These are often built without proper drainage methods in place to prevent water intrusion into the crawlspace via the foundation walls or ground floor.  In these crawlspaces, an external or internal drainage system, downspout extensions, or re-grading the soil around the home may be necessary before attempting to properly insulate the crawlspace.  Mold is a common occurrence in below grade crawlspace, and must be remedied prior to encapsulating the crawlspace.  The best way to insulate these crawlspaces is to first install an encapsulation liner on the foundation walls and ground, and permanently seal all air leaks and vents from allowing air intrusion into the crawlspace.  Once this is done, the most effective insulation method is to install 2" rigid foam insulation on the walls and along the band board.  Spray foam is not recommended on the walls due to the trapping of potential moisture into the sills, joists, and band boards.  Spray foam can (but not always) lead to dry rot in the wood structural components that are attached to the external foundation wall.

Question: Is your crawlspace foundation a solid poured foundation wall or block and mortar foundation?

Answer: Solid Poured Foundation –  These foundation walls are the least susceptible to water intrusion, and are the best candidates for spray foam insulation; however, the crawlspace floor should always be sealed with a durable encapsulation liner prior to insulating with spray foam.  If it is a below grade crawlspace and remains dry year round, spray foam could be applied to the walls as well.  In cases where there is a high water table in the soil, it is not recommended to spray foam these walls.  If there is any water intrusion at all, it is recommended to first address the water intrusion completely or use the encapsulation/conditioning with 2" rigid foam board insulation method.

Answer: Block and Mortar Foundation – This foundation type is the most susceptible to water intrusion, and need to be properly waterproofed prior to any crawlspace insulation installation.  If at all possible, it is best to manage the water intrusion from the outside footing and walls.  This can be accomplished with proper footing drainage, waterproofed foundation walls, positive grading, and downspout extensions.  Once the crawlspace is determined to remain dry, the crawlspace can be insulated with spray foam or rigid foam board.  In all cases an encapsulation system is required.  If the crawlspace is below grade, rigid foam board insulation is recommended over spray foam.

Guest post by: Larry Ralph, Indiana Crawlspace Repair

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I love what I do! Highly insightful, analytical and creative, there is nothing I love more than helping you find the right solution for your real estate transition. My mission is to serve my clients with honesty and integrity, exceeding their expectations in service and support… and to help others by donating a portion of every transaction to Habitat for Humanity.

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