Wall Insulation

Walls are responsible for around a third of all the unwanted losses or gains of heat and cold in a typical home. Wall insulation may save you hundreds of dollars per year in heating and cooling bills (and your household will be more comfortable and produce less C02, helping fight climate change)..

Wall insulation is often underestimated in favor of attic insulation. But due to their much larger surface, walls and their insulation is typically more important for comfort and energy savings than the attic and ceiling. The only disadvantage is... the much higher cost (at least twice the cost of attic insulation).

Types of wall insulation

The type of wall insulation depends on the type of walls. Wood-frame walls should include cavity insulation, but also insulated sheathing over the outer walls, behind the siding. Solid walls should be insulated either on their exterior or on their interior faces (see: Exterior vs. Interior Solid Wall Insulation).

Image, Cavity Wall Insulation: Energy Saving Trust

Demanded R-values in walls

Whatever the thickness of your walls or your climate zone, wall insulation is never too little to get lower energy bills. Deficits on the wall insulation isn't restricted to old buildings. As a rule, modern ones also have too little insulation. See: Official Recommended Insulation & Climate Zones.

Types of walls and insulation

Pay attention to the type of walls you have. Most homes have either wood frame or masonry walls (veneer walls), or a mix of these two types. In terms of structure they can be solid or cavity walls...

As said before, solid walls (masonry…) demand exterior or interior insulation over their surface, behind the siding, while most wood frame homes demand both cavity wall insulation (the insulation of the gap between the two wall layers) and insulated sheathing.

New methods of wall insulation (for new homes) use new technologies/materials such as SIPs (Structural Insulated Panels) and ICFs (Insulated Concrete Forms).

Check the type of wall

To know the amount of insulation in wood frame walls, you may inspect their inside using some basic methods: see Simple tests to inspect the existing wall insulation.

If you don’t know whether your brick walls correspond to solid or cavity walls, check the brick pattern. Solid walls have alternate shorter bricks, that is, bricks set at right-angles to the rest. And the walls are also typically thinner than cavity walls: a cavity wall is around 12 inch/30 cm wide while a solid wall is around 9 inch/23 cm wide. In other terms, solid walls involve a 9 inch/23 cm header brick without a cavity, while cavity walls involve two 4.5 inch/12,5 cm bricks and a 2.5 inch/6,3 cm cavity.

Costs

Wall insulation is more expensive and more difficult to install than the ceiling-attic insulation. The costs and the economics of wall insulation depend on several elements: the type of wall, the existing insulation, climate, etc.

Cavity wall insulation around $1,50 per square foot is common. Wall sheathing and solid walls insulation may involve amounts of at least $1,500 - $2000 (medium-sized homes), without considering stuccoing, painting or other costs. But these are mere references.

Cavity insulation and insulated sheathing

Cavity wall insulation is often insufficient. Insulated sheathing is also very important in wood and steel-frame homes, to avoid thermal bridging and the related energy-inefficiency.

See: Insulated Sheathing Basics

Solid walls

Solid walls aren’t energy-efficient without insulation. See: Solid Walls Insulation.

Types of materials used in wall insulation

See:
Cavity Wall Insulation Basics
Insulated Sheathing Basics
Materials for Solid Walls Insulation

Required Insulation Levels (R-values)

Wall insulation requirements depend on climate. See: Insulation requirements and climate zones.

Reflective insulation

In hot climates, reflective materials (foil-faced paper, polyethylene bubbles, plastic films and cardboard) can also be used with advantage in walls. See: Reflective insulation.