Insulating Ductwork Between Floors: What You Need to Know

Learn how to properly insulate your home's ductwork between floors with this comprehensive guide! Find out what you need to know about measuring insulation thickness, sealing air leaks, installing thermal barriers & more.

Insulating Ductwork Between Floors: What You Need to Know

If the ducts are inside the house but on the roof of a basement or between the first and second floors of a two-story house, condensation can form and leave water stains on the ceilings below. To prevent this, it is advisable to insulate the ducts if they are accessible. However, if the basement walls are sealed and insulated, it is not necessary to insulate the ducts if the basement is cold. On the other hand, if the basement is too hot, insulating the ducts is recommended. To find out if you have enough insulation in the attic, measure the thickness of the insulation.

If your size is smaller than the equivalent of R-30 (around 10 to 13 inches), it could be beneficial to add more insulation. Before doing so, make sure to seal any air leaks and make any necessary roof repairs and other necessary repairs. Properly insulating cathedral-type ceilings will allow the roof temperature to be kept closer to room temperature, which will provide an even distribution of temperature throughout the house. Cathedral-type roofs must leave space between the roof of the roof and the roof of the house to achieve adequate insulation and ventilation. This can be achieved by using lattice beams, scissor frames, or sufficiently large beams.

For example, cathedral ceilings built with 2 x 12 inch beams have space for standard 10-inch blocks (R-30) and ventilation. Cathedral-type ceilings without ventilation (warm roof design) are also an option. The warm roof design allows more insulation to be installed in the roof cavity, since the need for a ventilation gap is eliminated. It is important that the roof cavity is fully isolated from the conditioned space below to prevent moisture ingress and roof degradation. Insulating a slab in an existing house can be expensive and annoying, but if the slab of the house is cold, it is possible to dig around the perimeter of the house and install insulation, usually a foam board. In most parts of the United States, insulating the outer edge of a slab can reduce heating bills by 10% to 20%.Checking the functioning of the ducts is the first step in deciding whether insulation is needed or not.

To do this, perform a visual inspection and then turn on the central air conditioner and check for leaks. Plastic can become brittle over time and affect the R value, which measures the installation level. Some leaks will need to be repaired before beginning with insulation. Nowadays, it's a good decision to choose this alternative. Generally, a cavity in the ground is not deep enough to accommodate both a supply duct system and a return duct system if they must cross one over another.

While adapting ducts to an existing floor cavity is likely to be unrealistic due to lack of access, it is possible and advisable to install thermal and air barriers at any accessible edge of the floor cavity that contains ducts. Small inaccuracies in duct construction are common and can increase the vertical dimensions of the ducts above what is allowed in a well-designed floor cavity. If a higher than expected air leak is measured, use a duct test fan to slightly pressurize the ducts in the floor cavity. When existing ducts cross an intended edge of a conditioned floor cavity and extend partially into an adjacent ventilated attic, enclose this space around each duct with thermal and air barriers to extend a portion of conditioned floor cavity. When accessible, cavities with joists that function as air distribution channels should be abandoned and replaced with properly sized, well-constructed and sealed ducts that have adequate support. In addition to checking for leaks in ducts, thermal images of them under normal operating conditions can be useful for locating leaks both in ducts and in floor cavities.