Wall Insulation Systems

Fiberglass Insulation Solid State Home Inspections

The exterior walls of our home act as a buffer between our desired conditions inside our homes and the actual weather conditions outside our homes. Walls need to be able to resist winds, rains, mechanical damage, and changes of temperature in order to keep occupants safe and comfortable. 

The standards for keeping a home warm and dry have evolved over the last century in modern construction. Increasing energy costs to heat our homes have spurred invocations in building methods and the energy efficiency of wall insulation systems. The energy savings from improved materials and building practices not only reduce energy costs to heat homes, but make it more practical to use lower levels of heat sources, including heat pumps, which in the past may not have kept up with energy losses on cold days.

Insulation Materials

In order to provide increased insulation value (also called 'R' values) to homes, exterior wall cavities are filled with insulating materials. To be most effective, the insulating material needs to completely fill all the voids in the wall cavities as any voids will reduce the effectiveness of the insulation costing home owners additional heat bills as well as lowering comfort when sitting near the wall with missing insulation.

Wall insulation products face two challenges to great insulation values:

  1. Limited Space - Exterior walls are commonly made with 2x4 construction. This only allows a gap of just under 4" of space in the wall cavity for insulation. To overcome this, there are some building materials used on the outside of homes that have R value that add to the total R value of the wall system.
  2. Vertical Orientation - Gravity and vibrations in the home will try and pull insulation product down in the wall over time. The insulation material must resist this downward force for the lifetime of the home as it is not common or practical to re-insulate exterior walls unless there is a major renovation underway.

In British Columbia where we are based, home building grants from the Provincial Government encourage home owners to improve wall insulation to R-12 Levels however other government jurisdictions require or encourage levels up to R-20. Common insulation products are:

  • Fibreglass Batt Insulation - Probably the most common material in wall insulation with R3-3.5 value (approximately R-12 in a 4" wall cavity)
  • Mineral Wool Batt Insulation - Similar in application to the Fiberglas batts but provides slightly better soundproofing levels. R2.8-3.7 which provides a similar R-12 in a 4" cavity.
  • Fibreglass or Cellulose Loose Fill - Installation of loose fill systems is more complex than batt installations but may be a time saver for experienced builders. R3-3.7 values provide the same R-12 levels in a 4" wall cavity as batt installations.
  • Polyurethane Spray On - This insulation requires the most skilled installation but provides improvements in insulation R values and is an air and vapour retarder. R values are 5-6 which can achieve an R20-24 in a 4" wall cavity.
  • Other Systems - There are other insulation products found more commonly in commercial applications like wall board systems and other variations and applications of the materials above. Builders will tend to use the insulation system that achieves desired R values for the lowest square footage cost. For home owners of existing buildings, the key is the R level of insulation, not the material itself.

Wind Barrier

In order for wall insulation to be effective, it needs to stop the transfer of energy between the inside and outside. Any air movement that passes through the wall will render the insulation value at zero as the air will simply carry the energy transfer past the insulation.

Exterior wall assemblies will include an air barrier to restrict air movement through the wall cavity. This is best accomplished at the exterior and commonly is a building paper or other membrane attached to the wall shearing, just below the exterior siding material. Most current building standards call for homes to be 'air tight' so all wall penetrations require extensive caulking and sealing to prevent air flow past the insulation.

Moisture/Vapour Barrier

If you have ever left a glass of cold water on a counter on a warm day, you will have noticed water droplets forming on the outside of the glass. This is a high school physics process called condensation. Warm air can carry more moisture than cold air. When warm air cools at a cold surface, the air can no longer hold the moisture level it could when it was warm and it deposits the moisture on the cold surface. 

As our homes are typically warm and moist on the inside and cool on the outside, condensation can form in our wall cavities if we don't add a moisture barrier to the wall system. This is most often accomplished using a sheet of plastic just behind the drywall on the warm side of the home. If we didn't install this moisture barrier, moisture that forms behind the walls could cause rot and mould growth and eventually compromise the structure of the home.

In air conditioned homes, the opposite flow of warm/cool air from outside to inside may require a moisture barrier on the outside wall of the home (the warm side) rather than the cool side. Unfortunately for homes that have both heating and cooling cycles, it is not possible to have moisture barriers on both sides or the wall will not be able to release any potentially trapped moisture. In these cases, a compromise is made with the moisture barrier being on the side most highly required.

Thermal Bridges

A thermal bridge is a material that may conduct heat or cold through an insulated system. The most common thermal bridge in residential homes is the studs in a wall cavity. Wood studs 'bridge' between the warm and cool sides with no benefit of insulation. For a 2x4 wall with studs every 16 inches, this could mean that 12.5% of the exterior wall is made up of thermal bridges. Two methods of mitigating wall stud thermal bridges are to use 24" stud spacing when structural building tables allow, or the use of exterior insulations to provide some type of insulation value over studs.

Other types of thermal bridges include windows, doors, vent exhausts, and other building penetrations like pluming. There are various insulation techniques that can be implemented to provide some protection to many of these thermal bridge points.

What Do Home Inspectors Look at With Wall Insulation?

Home inspectors are at a disadvantage when it comes to wall insulation systems as walls are typically covered by interior and exterior finished during construction. Some exterior wall systems like vinyl cladding may allow for an inspection of building paper or membranes but it can be very difficult (or not possible) to determine the types, amounts, or correct installation of insulation in the wall systems.

Forward looking infrared (FLIR) camera systems can provide some visibility to the performance of exterior wall insulation systems. FLIR cameras read the heat signatures of surfaces and can indicate to inspectors differences in heat levels which may indicate performance of insulation. There are a few drawbacks to this system through:

  • Home Inspections done to industry standards do not require the use of this specialized tool
  • FLIR Camera systems are very expensive. Minimum costs are around $1,500 and 'better' systems can cost as much as $5,000
  • When exterior temperatures have less than a 10-15 degree Celsius differential to indoor air temperatures, the heat losses may not be detectable (or may not be signifigant enough to make any assumptions from the results). With indoor temperatures typically around 20 Celsius, FLIR cameras work best in cold conditions below 5 Celsius. In our market of Greater Vancouver, days below 5 Celsius are rare making rendering poor FLIR results much of our year.

The best locations for inspectors to investigate wall insulation are in unfinished basement areas that may give visibility to the rim joists or wall assemblies from below.

Final Thoughts

There are two ways to keep a home warm. First, we can apply a small amount of heating energy and insulate the home very well. Second, we can compensate for poor insulation with additional heating energy. For older homes, retrofitting insulation can be very expensive and disruptive to the home with a long pay back period for energy savings. However, if there are major renovations taking place, considering an improvement to exterior wall insulation could save owners money in heating costs long term and help keep a safe home warm and dry.

By James Bell - Owner/Operator of Solid State Inspections Inc.