Home Fix: Dwight Barnett answers home-improvement questions. This week's topic is on insulation, ductwork and mold in a crawlspace.
Q: I inherited a concrete block building that was then converted into a home several years ago. Part of it has a crawlspace and part is on a concrete slab. The crawlspace is always damp, and the furnace ductwork is covered with a fiberglass insulation. A termite contractor recently found mold growth on the wood floors and under the duct’s insulation.
I was told that, beyond treating the mold, it would cost several hundred dollars more just to replace the insulation on the ducts. Is this really necessary?
A: Depending on the climate and the ducts’ location, it may not be necessary to insulate them.
First, determine where the ducts are. If they are in an unconditioned crawlspace or attic, then they literally are located outside the house. The ducts are exposed to the same cold, heat and humidity that exist on the outside. Insulating them is essential in colder climates, optional in milder ones and necessary in humid climates to prevent condensation.
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In all cases, the ducts need airtight seals at all joints, seams and takeoff points before the insulation is applied. If the ducts are inside the house but in a basement ceiling or between the first and second floors of a two-story house, condensation can form and leave water stains on the ceilings below. If the ducts are accessible, insulate them to prevent condensation.
Before applying insulation, make sure the ducts are not already insulated on the interior. Homes with electric heat more than likely have ducts that were insulated during the fabrication process. The insulation is glued inside the sheet metal before it is bent and formed to fit your specific needs. You can check the duct to see if it has an insulated lining on your furnace’s filter box.
Simply remove the filter and shine a flashlight inside the ducts. If you see bare metal, the ducts are not lined with insulation.
Before insulating the exterior of the ducts located in a crawlspace, check with local and state building officials concerning fire codes. The insulation may have to meet stricter standards when located in the crawl.
When installing exterior duct insulation, use a metallic tape to secure the materials. Although duct tape has a thousand and one uses, it does not hold up well on ductwork. For more information on duct wrap insulation, go to http://www.certainteed.com/resources/3036081.pdf.
Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Contact him at d.Barnett@insightbb.com.