dow xps foam baord insulationDo I need to insulate the basement?

Current building codes require foundations to be insulated. Conventional thinking was that foundations did not need to be insulated since they are primarily below grade and not subjected to the full load of outdoor temperatures. Unfortunately for most homeowners paying high energy bills, that conventional thinking was wrong. Insulating the basement or crawlspace walls of a home is a crucial step in lowering energy bills.

One of the preferred products for insulating foundations is Dow XPS extruded polystyrene foam, commonly called “blue board” in the trades. It is available in several thicknesses and R-values. It can be installed on the exterior of the foundation walls, but in order to be effective, needs to be installed to the full height of the wall which means protecting the above grade portion. Two common methods are to install a product like Nudo Groundbreaker or Protecto Bond. There are also some scratch coat materials which are troweled over the insulation like a stucco coating.

I thought code says I need a fire barrier?

Those are all viable options, but perhaps the most sought after option is to insulate with foam board on the INSIDE of the foundation wall so you don’t have to worry about the above grade exposure. The problem with that application has always been that the foam board needed to be covered with a “thermal barrier” or “flame spread barrier” like drywall in order to meet local fire codes.


That’s right, the good folks at Dow have had their material tested and approved for installation on the inside of foundations, including living spaces, without the requirement for drywall. There are other reasons to cover it with drywall, but it does NOT need to be done at the time of construction. So BUILDERS, you can now foam the basement to meet the code requirements without trying to sell a full finished basement to the homeowners.

Here’s what you need to know:

This ONLY applies to DOW foam, not other manufactured brands of foam or insulation products.

You will likely meet some “resistance” from your local code officials, but DOWNLOAD THE CODE REPORT and look for the sections described below

  •  Application without Prescriptive Thermal Barrier: Section 4.2.1 of our code report permits the installation of Dow STYROFOAM™ insulation without a thermal Barrier in Attics, Crawl Spaces, Basements and buildings of Use Group U when the conditions of Table 1 are met. Table 1 lists all the various types of STYROFOAM products available. Note 1 on Table 1 specifies most of our Type IV and X products can be installed without a thermal barrier up to 3” thick.
  •  Application without Prescriptive Ignition Barrier: Section of our code report permits the installation of Dow STYROFOAM™ insulation without an ignition barrier in attic and crawl spaces when the conditions of Table 1 are met. Note 4 on Table 1 points out most of our Type IV and X products can be installed without an ignition barrier up to 3” thick. Storage in the attic or crawl space is irrelevant because the Specific Approval (full scale NFPA 286) requirements have been met.

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