Why isn’t a thick layer of quality insulation sufficient on its own? How can “air leakage” negate the effects of even the thickest insulation layers? What should be considered to ensure installed insulation provides maximum effectiveness?
Often, after attic renovations and the installation of entirely new, high-quality insulation, the results are drastically worse than before the renovation. In such cases, it is almost certain that something was done incorrectly, or a seemingly minor step was overlooked. The most common mistake made by untrained workers during attic renovations is inadequate sealing.
Related Articles:
INTERNAL WALL INSULATION: A FEW ADVANTAGES AND MANY DRAWBACKS
EIGHT COMMON QUESTIONS ABOUT HOME INSULATION
STYROFOAM OR ROCK WOOL: WHICH INSULATION IS BETTER?
Sealing achieves the effect of hermeticity, preventing air movement through the roof structure, also known as “air leakage.” This is accomplished by installing special vapor-permeable membranes that retain water and air but allow moisture to pass through, thus preventing condensation.
Proper Insulation Installation is More Important Than Its Thickness
When it comes to “air leakage,” membranes have a completely different role. When insulation is installed within the roof structure, whether it is rock wool, glass wool, or EPS boards (commonly known as Styrofoam), it is crucial to follow all steps, including the installation of a vapor-permeable membrane. Without it, air could freely move in areas where the insulation does not fully adhere to the roof structure, rafters, or walls.
Temperature differences, which occur both in summer and winter when insulation is most needed, intensify air movement. When there is a cold temperature on one side of the insulation and a warm temperature on the other, air will naturally flow to equalize these temperatures.
The Best Insulation is Useless Without Stopping Air Flow
During winter, this manifests as cold air being blown into the room. This allows cold air to bypass the thick insulation layer, rendering it ineffective. Installing a vapor-permeable membrane creates a barrier, forming an air cushion around the insulation, preventing cold air from easily finding a way into the room. This maximizes the potential of the insulation. Besides temperature differences, the “air leakage” effect is also intensified during windy conditions.
Experienced craftsmen often illustrate this effect with a clothing example. If you go outside on a cold, windy day wearing a thick wool sweater, the wind will cut through, and you will feel cold because the sweater’s coarse weave allows air to pass through. Although the same sweater keeps you warm indoors, it is inadequate insulation outside.
Simply adding a thin synthetic raincoat over the sweater will block the wind, allowing the sweater to keep you warm as expected. Clearly, going outside in just the raincoat would also leave you cold. Therefore, the combined effect of both garments is necessary, just like with insulation.
Special Attention Required for EPS Boards
Air leakage losses due to poor insulation installation can be as high as 30%, regardless of the insulation layer’s quality. The worst effect occurs with EPS boards (Styrofoam), as they can never fill every corner and edge completely. With glass wool, these losses are smaller because it is soft and can be pushed into every corner, making the structure more snug.
However, regardless of the insulation type, proper installation of the membrane, its overlapping, and careful sealing with high-quality reinforced self-adhesive tape is crucial, even though it may initially seem like an insignificant detail.
Photo: Knauf, Rockwool