INSULATION
When it comes to insulation, the building code does a pretty good job of setting sufficient requirements. The biggest consideration, then, is typically what material to use, especially in the tricky situations that come with insulating older structures. Cost, floor space, toxicity, and sustainability are all important factors to bear in mind.
MATERIALS
FIBREGLASS: Since insulation became commonplace after World War II, fibreglass has led the market for most applications. It still remains the most cost-effective and practical material for most new builds. However, though it is recyclable, it is not biodegradable, and it can irritate the skin and lungs through contact. These factors not withstanding, we generally specify this material expect where conditions or client direction merit otherwise.
MINERAL WOOL: Mineral wool has been developed as a closely cost-competitive alternative to address some of the limitations of fibreglass: it is more heat and water resistant, which make it ideal for fire-rated or older walls that are less water-tight. It is also firmer, and can be installed as an alternative to plastic foam boards. Regarding environmental concerns, it has the same issues as fibreglass and is more energy-intensive to make.
CELLULOSE: People have experimented with a number of organic materials to arrive at a cost-effective alternative to conventional insulation. The most successful has been cellulose fill. It’s made primarily of recycled paper-products and treated to make it fire and insect resistant. The most practical application is in unconditioned attic spaces.
HEMP: For walls and other applications, hemp batts are becoming an increasingly popular sustainable option, though it comes with a premium: typically 30% or so more than more conventional fibreglass. Because of budget concerns, we will only specify this material if a client instructs us to do so.
FOAM BOARD: For applications where boards are necessary for installation—over exterior wall sheathing or under slabs—plastic foam “rigid” insulation is the most economical option. Though recyclable, it is not bio-degradable, and it is toxic if ingested. Mineral wool is a more environmentally and fire-resistant alternative, though it is more costly.
SPRAY FOAM: The highest performing form of insulation is closed-cell plastic spray foam. It is typically used in wall assemblies and roofs where it also doubles as an air and vapour barrier. It’s a bit more expensive than fibreglass or mineral wool and comes with several environmental concerns: it’s toxic if airborne so it must be enclosed; it’s not recyclable or biodegradable; and since it sticks to the surfaces it’s sprayed onto, it makes those materials unsalvageable as well. For these reasons, we generally limit the use of this material to situations that merit it’s unique performance properties.
INSULATING OLD BRICK WALLS
It wasn’t until the mid-twentieth century that insulation became common in buildings. And though insulation adds comfort and energy savings, if not detailed correctly it can promote mould growth. This is especially difficult to manage in old buildings with brick bearing walls, where water and water vapour were expected to migrate through the assembly. Unfortunately, in this situation there is no perfect retrofit solution, but there are two effective methods are commonly employed.
Both insulation methods rely on installing a new frame wall (preferably wood if allowed by compliant) built on the interior side of the brick. This and the drywall over it replaces the original lath and plaster that would have been installed directly against the masonry. The highest performing option for insulation to is to then fill the stud cavities with closed-cell plastic spray foam, which achieves a high insulation value as well as a tight air and vapour barrier. On the downside are all of the environmental concerns mentioned above. In fact, in historic preservation circumstances, this is typically not allowed because of its irreversibility.
As an alternative, house wrap (Tyvek) can be installed on the backside of the brick to serve as an air and water barrier. Mineral wool can then be installed in the stud bays. To allow for water vapour trapped in the assembly to migrate out, a “smart” vapour retarder is installed behind the drywall, which adjusts its permeability based on relative humidity conditions. The assembly is somewhat less tight than spray foam, and to save floor area, we don’t typically build it out to meet the insulation level required by code for new structures. However, this method still represents a significant improvement, and it carries several environmental benefits in addition to being less costly. Therefore, we typically specify this unless directed otherwise by the client.
