Except in houses with attic spaces that are permanently accessible, the best time for a homeowner to make improvements to thermal insulation is often when doing major renovations—for instance, a bathroom or basement remodelling. Upgrading insulation, however, is a delicate procedure that requires knowledge and skill: there are best practices to be followed, and some materials are more appropriate than others depending on which part of the building is to be insulated.

In an attic, the most common technique is to blow in loose-fill insulation over the existing insulating material. When doing so, take care not to obstruct the soffit vents, which are located under the overhang of the roof deck.

Exterior walls
The most common method of upgrading exterior wall insulation is from the inside, by installing rigid-board insulation on the warm side. This will reduce the interior space slightly, but the operation increases the insulating value and airtightness of the walls without need for major demolition. The joints between the panels must be thoroughly sealed, and a vapour barrier installed per the specific characteristics of the product used (to prevent moisture infiltration and condensation).

To insulate foundations, it is also standard practice to proceed from the inside. Rigid boards are installed directly against the concrete wall, or batt-type insulation can be added between the studs lying against the foundation walls. Careful, though: fibreglass batt insulation must never come in contact with concrete. The best way to insulate the band joist—the joist that runs all the way around the floor structure and rests on the foundation sill—is by spraying in polyurethane foam. This is also the most effective method for insulating concrete foundations along their full height (basement walls or crawlspace sides).


Choosing the right type of insulation

Selecting the right material is the key factor. In residential renovation, the four most commonly used types of insulation are batt-type, loose-fill, rigid-board and spray foam.

  • Batt-type insulation provides an easy and inexpensive way to fill cavities in walls, floors and attics. For optimum performance, batts must not be compressed.
  • Loose-fill insulation provides good coverage on irregular surfaces in attics. Spread by hand or blown in with a machine, it fills in uneven areas, and sits around the frame timbers in a homogenous layer with no joints. It can also be injected into cavities and hollow walls that are inaccessible, through holes that are later patched over.
  • Rigid-board insulation is flat and compact, and comes in various thicknesses. It provides an uninterrupted thermal barrier along the surfaces of walls and ceilings (and even floors, in the case of high-density polystyrene).
  • Polyurethane foam, blown in on-site by professional installers, adheres firmly to surfaces and fills in the slightest cracks and crevices, creating an airtight, continuous barrier.


Characteristics of materials

The R value (as well as its metric-system equivalent, RSI) of an insulating material is a ranking of its effectiveness. The higher the value, the greater the material’s resistance to heat flow.

Loose-fill and batt
Cellulose fibre

  • Loose-fill only; R value 3.5/inch.
  • Fine particles, flows between nails and wires better than wool insulation.
  • Treated with borax to improve its resistance to fire, humidity and parasites.
  • Low cost.
  • Environmental considerations: non-irritant, non-toxic, made from recycled paper products, locally manufactured.

Fibreglass (often called “mineral wool” insulation)

  • Loose-fill, R value 3.0/in., batt, R value 3.2/inch.
  • Non-flammable, but local building codes’ and manufacturers’ clearance standards must be met.
  • Protective clothing, glasses and mask must be worn when installing.

Mineral fibre (also referred to as “mineral wool” insulation as well: beware of confusion!)

  • Loose-fill, R value 3.3/inch, batt, R value 3.5/inch.
  • Better suited to basement use than other fibres because of its water resistance characteristics.
  • Fireproof product, ideal for use around chimneys.
  • Environmental considerations: preferable to fibreglass if the home’s occupants are overly sensitive.

Expanded polystyrene (Type II)

  • R value 4.0/inch.
  • Rot- and mould-resistant.
  • Flammable; must be covered with an approved fireproof material.
  • Environmental considerations: contains 98% air; is recyclable and re-usable; contains no products harmful to the ozone layer such as hydrofluorocarbons (HFCs) or hydrochlorofluorurocarbons (HCFCs).

Extruded polystyrene*

  • R value 5.0/inch.
  • Same non-flammability and mould-resistance characteristics as expanded polystyrene, but greater insulating efficiency thanks to its structure of closed cells containing refrigerant gas.
  • Environmental considerations: less eco-friendly than expanded polystyrene.

Polyurethane and polyisocyanurate (foam board)*

  • R value 6.0/inch.
  • Contains refrigerant gas and is typically covered with a reflective aluminum foil facing (see below).
  • Less resistant to compression than polystyrene.

Wood fibre

  • R value 3.3/inch; available in ½-inch thicknesses (R value 1.6).
  • Environmental considerations: made in part from recycled materials, formaldehyde-free, locally manufactured.

Blown-in polyurethane foam*

  • R value 6.0/inch.
  • Rot- and mould-resistant.
  • High cost, but this is offset by long-term effectiveness.
  • Environmental considerations: made from natural oils and recycled plastic.

The foil-face option
Some insulation, such as expanded polystyrene, foam panels and wood fibre, can be covered with a reflective foil face.

  • This substantially increases thermal resistance, provided that the insulating material is covered with gypsum wallboard mounted to lengths of wood or metal (called “furring strips”) laid horizontally and spaced 16 inches centre-to-centre. The layer of air between the foil face and the wallboard plays an essential role in heat reflection.
  • The foil face contributes to the wall’s airtightness (air/vapour seal) and acts as a vapour barrier if its joints are properly sealed.

*Factor to consider: if sufficiently thick, these insulating materials can act as vapour barriers.

How much insulation is needed?
The mandatory thermal resistance standards for new buildings and newly constructed portions of existing buildings were recently revised. In most Quebec municipalities, they are R-41 for the roof space, R-24.5 for above-ground walls and R-17 for foundation walls.

When renovating, if the target values can’t be achieved because of lack of space or poor access to cavities, you should at least come close to them. It’s better to take as many possible small steps as you can than not to take any big steps because you deem them impossible.