Insulation and Air Sealing
The insulation and air sealing of the structure work in conjunction to slow the transfer of heat through the assembly. Without one the other is almost completely ineffective. We prefer to install mineral wool in the wall, rim joist, floor, and rafter caviters. Mineral wool offers numerous advantages over other insulation products. The friction fit batts stay tight in the wall cavity and do not slump or sag . Mineral Wool is also fire resistant even at extremely high temperatures making it a code approved fire stop material. We often recommend using it in interior wall and floor cavities for fire safety as well as its fantastic sound dampening capabilities. Yet another benefit to mineral wool is that it is hydrophobic in nature meaning it does not absorb water. Many other insulation materials will become saturated in the event of water intrusion and decrease their performance. Mineral wool’s R-value will not be compromised by this.
The majority of the air tightness is achieved by the use of a primary interior air barrier inbound of the insulation. In northern climates there is risk for condensation during the cold seasons. Warm humid interior air makes its way into the wall cavity eventually condensing on the wall sheathing. Dehumidification and a properly installed air barrier is the best defense against the condensation. During this phase of construction the interior side of the exterior wall are wrapped with an airtight membrane. Every penetration and junction is meticulously sealed with the use of tape and sealant. This membrane is “smart” in the sense that it has the ability to change vapor permeance based on the environmental conditions around it. Passive standards of air tightness and insulation will be achieved following this process.
The rim joist is first sealed with a fluid applied air barrier. Then 12” of insulation of insulation is installed. On the inboard side of the insulation 1/4” plywood is installed with the edges sealed. This stops warm humid air form condensing on the cold rim joist. Plywood being permeable also allows for great drying potential.
This sloped ceiling assembly consists of 4 layers of mineral wool with the cavity R-Value totaling R-76. 2x12 rafters furred out with gussets gives the assembly an R-15 thermal break.
This garage ceiling assembly consists of 3 layers of mineral wool. The flanges of the I-joist were padded out with 1/2” foam to provide a snug fit without gaps. In this particular assembly using mineral wool is important to use because of the fire risk that is prevalent in a garage.
The primary air barrier in this wall assembly is on the interior. Having this on the interior side of the wall provides provides multiple benefits. It takes the primary air barrier out of the elements allowing the product to maintain its integrity for a much longer period of time. The other benefit of the interior air barrier is that it also acts as the vapor barrier. In northern climates it is crucial to prevent warm humid air from condensing on the wall sheathing in the cold months.
Insulation on interior walls is critical for reduction in sounds transmission between rooms and floor. Key area include bedrooms, laundry rooms, and offices. Mineral wool offers the added benefit of fire protection and can act as a code approved fire stop.