Almost all homes have insulation of some sort, but are usually under-insulated, or insulated with such low-quality insulation that it is actually useless. Insulation has to be installed over 100% of a surface to be effective, as gaps and voids reduce the effectiveness of the insulation exponentially. Upgrading insulation R-values will usually have a dramatic effect on energy savings throughout the year, as it will allow the home to stay cooler during the summer and warmer during the winter.
Older Home’s Subfloor Insulation
In older homes; generally built before 1960 the subfloor of the house was constructed of 1×6 Douglas fir boards over 2×4 floor joist spaced 16 or 24 inches on center or 2×6 tongue and grove boards over 4×4 beams spaced 32 or 48 inches on center.
After this type of subfloor was installed in some cases a second floor was laid down after the home was weatherized. This could be a 5/16 hardwood floor, tile or another type of material that created an air-barrier between the second floor and the subfloor.
Some subfloors just received carpet that did not create any air barrier; these floors can contribute to a large amount of air infiltration because of the wood shrinking, creating gaps in the floor assembly over time.
It is generally known in the home performance industry that 40% of the air entering the home comes from the crawlspace. This presents issues; poor air quality, moisture, and unconditioned air entering the living space.
Adding fiberglass batt insulation on this type of floor system, to help prevent heat loss, will not stop the infiltration but the fiberglass insulation will become like a filter; the insulating value of insulation will be degraded.
The best way to deal with this type of board floor assembly is to apply spray foam or install rigid foam board between the floor joists, seal the foam board to the subfloor, and use gun foam where the foam board meets the joists, on all seams.
Choosing this option will increase the job cost, but it is a more effective way to deal with air quality and moisture control as well as providing a more effective R-value to the assembly.
Even if you choose to go with this system always mitigate the bulk water issues surrounding the home as well as installing a vapor barrier in the crawlspace. When you install fiberglass insulation on this type of floor system you are missing the opportunity to install an effective air barrier.
Building Envelope Leakage / Air Sealing
One common complaint within a home is the presence of“drafts”. We completed a blower door test to pressurize the house, which provided us with information about the presence and intensity of drafts and air leakage. A healthy home should have 0.35 ACH, which is the same as replacing 1/3 of the house’s air every hour. A higher ACH means the house is draftier than recommended, which wastes energy and brings in dirt, dust, and outdoor contaminants. A lower ACH means that the house is sealed tightly, and mechanical ventilation is recommended to ensure healthy air.
Due to the extensive duct leakage throughout the duct system, the home as a whole could not be pressurized to determine leakage. In order to reach the recommended 0.35 ACH, the home needs to be sealed to at least 3332 CFM50. Sealing the home tighter than this is still a good idea, but at that point mechanical ventilation will need to be added.