Crawl Space Insulation Myths
Some crawl spaces have insulation in the floor above and some do not. One reason for insulation in the floor above a crawl space is that the crawl space is cold in the winter due to the open vents.
But, because, fiberglass insulation is loose and air passes right through, it only works in a closed cavity. When it is between the joists in a vented crawl space, with the paper or foil side up, and the unfaced side down, it does not function.
Additionally, paper-faced insulation is mold candy - a term from Joe Lstiburek from Building Science Corp., www.buildingscience.com. Mold loves paper even more than wood.
Foil-faced insulation is supposed to be a radiant barrier. You put the foil face to the heated side. But you need to have at least a 1/2" air space in front of foil radiant barriers for them to reflect the heat. If insulation even has a radiant barrier, it is most often jammed up against the floor sheathing with no air space between the radiant barrier and the sheathing. Therefore, that element of the insulation is not working. Besides, such an air space creates a conductive bypass where air can flow on both sides of the insulation, rendering the insulation useless.
Mold grows on insulation because it has some organic material in the resin used to set the fibers. Also important to note, when fiber glass insulation is damp, it loses much of its insulation value.
Insulating is still a good idea. If you do it, insulate the crawl space walls along with your crawl space solution and use foam insulation. This can be rigid foam boards or, better, sprayed closed cell foam. While cellulose insulation is better than fiberglass, foam insulation is the best. If a plumbing leak ever happens, as it's bound to, insulation that won't get ruined and support mold growth is preferred.
Any foam insulation used must meet the ASTM 84E standard for a flame spread of 25 or less and smoke density of 450 or less. If not, it must be covered by another material – which is not practical. In general, white styrofoam beadboard does not meet the standard, but pink or blue foam boards do. If an inspector is unhappy with pink or blue board, you can use Dow Thermax – a polyisocyanurate foam board with foil on both sides.
Mold, Fungus and Rot
Mold has become a big issue in recent years. Mold is the subject of lawsuits, a terror to builders, subject matter for front-page writers, the reason for school closings, and the growth of a "new" industry – mold testing and remediation. With all this talk about mold, you might think it is new. You might think it is a complex issue. Mold is not a new or a complex issue.
First, let's talk about why mold is here in the first place. Mold has a purpose. Its purpose is to breakdown or eat dead organic matter. Without mold, plant and animal material would grow and grow and pile up and pile up.
Mold knows its purpose. If it's organic, dead, and wet, mold will eat it. Organic means it is a material that was once living, such as wood. Mold sends out its spores everywhere, which can lay dormant for many years. When we say "mold", we mean any mold or other fungi, of which there are many thousands of varieties.
Since mold spores are everywhere, and our building materials and contents of our homes (furniture, boxes, clothes, etc.) are made from organic materials, this factor cannot be controlled. The only one that we can control in our homes is the moisture.
Mold needs 70% Relative Humidity (RH) to grow; however this is a loose number. Some molds can grow at less RH. In many cases, like in a crawl space, the RH of the surrounding air, and the RH of the surfaces are two different things because of temperature differences between air and surfaces.
Mold likes processed organic fibers best. In other words it will grow on paper and cardboard first. Paper is like "mold candy". After that it will grow on fiberboard and chipboard, and then plywood, and finally on framing lumber. Sheetrock has paper on it.
Mold releases airborne spores or "seeds", which are so light they float on the slightest air currents, off to find more suitable places to grow. Most people are not allergic to mold spores, but some are. The higher the concentration of mold spores, the greater percentage of people who will be bothered by them.
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