At least once per day, our appointment center receives a call requesting for us to replace their fiberglass insulation. We then explain to our caller why we do not recommend or install fiberglass insulation. Since it comes up so often we decided it was time to write an article about it. Fiberglass insulation is the most commonly used, and recommended, type of insulation on the market now and for many reasons. Fiberglass insulation is inexpensive and works in the vast majority of installation practices within the home. More than 90% of homes in the United States are lined with Fiberglass insulation. (Fuller, 2017).It is a mixture of fibrous glass that came into popularity with the declining use of asbestos. When installed properly is safe and rests between panels, sheetrock, and plaster. Here is where a bigger issue presents itself. According to manufacturing specifications, the correct installation of fiberglass insulation, has insulation covered on all 6 sides (as in a wall cavity). This is so the glass particles do not escape, and do not become fine particulate in the air of the home. However, this is not how insulation is installed in the crawlspace. The typical installation of subfloor insulation is as follows:
Insulation is placed inside the floor joists with the vapor barrier side (paper adhesive that the insulation is secured to) facing the interior side of the home. You are to not compress the fiberglass and allow it to expand completely to fill the rafter cavity. The fiberglass insulation is then held in place through the use of support wires below to secure the fiberglass insulation in place (Lipford, 2017).
While this all sounds well and good, there is a host of issues when installing fiberglass insulation in the crawlspace in this fashion.
This is due to a term known as “The Stack Effect”. The ground is constantly breathing. The ground takes in water during rain and evaporates back up into the atmosphere. This is the reason that we install a vapor barrier under homes, to keep the moisture down. Over the years this barrier inevitably rips, tears or becomes displaced, or even worse it was not installed properly at the construction of the home. (Which is common).
This condensation then moves up from the dirt floor crawlspace, and into the exposed fiberglass insulation. Over time this insulation retains enough moisture that it begins to sag. Once the insulation has sagged and fallen from the rafters a few issues can occur. Fallen insulation provides an air break. The entire point of installing insulation under the floor is to prevent cold air from the crawl space from entering the home from below. These gaps allow that cold outside air a direct path up through the floorboards, rendering the insulation useless. Once moisture has collected and these breaks occur, the moisture is able to reach organic material such as the paper backing of the insulation and the wood subfloor. This creates a perfect environment for mold to grow.
Mold in the crawlspace is an all too common problem that we see regularly in our daily inspections. Much of this is due to our current building methods. Homes are sealed up tight. Energy efficient windows and doors, sealed building envelopes and controlled home environments add to the stack effect. Air must have somewhere to go. It will continue to travel upward. The fiberglass insulation serves as a filter between the ground and your home. Think of furnace filters and car filters for a second. How do you clean them? You don’t, you replace them. Only you don’t replace your fiberglass insulation annually. It just continues to accumulate mold, mildew, debris, and worse yet rodents.
Torn crawlspace vent screens are the perfect avenue for rodents to come into your home to escape the elements. Fiberglass insulation provides a warm protected area for them to eat, live and reproduce. According to Basement Systems, rodents are attracted to crawl spaces because they are warm, damp, and protected from the elements. In addition, they are typically near food supplies (such as trash) and are not usually monitored frequently by homeowners. Crawl spaces supply plenty of entry points for pests, including gaps between the foundation and framing, spaces under doors, penetrations for wires and pipes, vents, and tunnels through dirt floors (Basement Systems, 2017).
Fiberglass insulation may be a solid choice for many areas of the home when it is installed according to engineering specifications, but for the crawlspace fiberglass insulation is absolutely the wrong choice. This insulation retains moisture, houses rodents, provides food for mold, and once damp provides no insulating value for your home. Before installing ineffective fiberglass insulation, review other insulating materials that would be better suited for crawlspace conditions and your home specifically.
Basement Systems (2017). Rodent Control in Crawl Spaces. Retrieved from https://www.basementsystems.com/crawl-space/crawl-space-rats.html
Fuller, J. (2017) Is insulation dangerous? Retrieved from https://home.howstuffworks.com/home-improvement/household-safety/tips/dangerous-insulation1.htm
Lipford, D. (2017). Is Hidden Mold at Home Making You Sick? Retrieved from http://abcnews.go.com/WNT/story?id=131638&page=1
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