Canadian Underwriter

Rethinking the Retrofit

July 31, 2013   by Jason Guihan

Print this page

Amid the rising cost of home heating in our harsh and diverse Canadian climate, more homeowners and building operators are considering various building envelope and energy retrofit and upgrade options with the goal of reducing heating and cooling costs. These energy retrofits, sometimes designed and executed without the proper understanding of basic building science principles, can lead to catastrophic outcomes for the owner. This can also place the insurer and/or claims professional in a challenging situation when resultant damage is presented in the form of a property claim.

As a specialist in assessment and remediation of property damage, we have often been retained to assess water damage and mould issues at a property only to conclude that the observed damages are directly linked to the improperly executed application of such measures under the guise of more efficient energy performance. Unfortunately, what was done in the spirit of improvement actually leads to degraded building performance and health.

To avoid such outcomes, it is critical for the insured (and more importantly the contractor) to give careful consideration to the original design and construction of the home (i.e. brick and plaster walls, brick veneer, wood frame construction, etc.) as this dictates the best option for the building envelope energy retrofit.

Consider the following example that illustrates how an energy retrofit implemented for all the right reasons can lead to unwanted outcomes. The owner of a beautiful turn-of-the-century brick veneer detached home decides to add blown-in insulation (i.e. loose fill fiberglass, cellulose, blown mineral wool fiber, etc.) to all un-insulated exterior wall cavities in order to reduce heating costs in the winter months. We can assume that the wall assembly consists of vertical wooden members with wood sheathing on the exterior, plaster and lath wall finishes on the interior and no vapour barrier behind the plaster and lath wall finishes.

Prior to the application of the new insulation into the exterior wall cavities, the structure and building envelope were operating as an interactive system consisting of various components (i.e. structural components, heating, ventilating and air conditioning (HVAC) equipment and the occupants). Each component is integral in how the structure operates in the context of how the whole building deals with energy and moisture transfer from the interior to the exterior.

An example of this ‘interactive system’ concept would be the movement of moisture laden air in the winter months from the interior through the exterior walls by means of passive air leakage and vapor diffusion. Before the introduction of the blown-in insulation, such moisture laden air produced by taking showers, cooking, breathing, etc. would have previously entered the exterior walls through hairline wall cracks and receptacles and would have been able to migrate towards and be directed to the outside. In the past, construction practices saw exterior walls built with little regard for vapour transmission and air leakage and heat loss. This approach was fine for an era when heating costs and energy efficiency were less of a concern. In this sense, the building envelope essentially acted as a passive ‘sieve,’ allowing moisture laden air (and the heat carried within it) to freely wick to the exterior while providing a modicum of insulating performance.

Although the above mentioned energy retrofit created a better insulated building envelope, it also resulted in less moisture laden air being able to escape through the insulated exterior walls. The moist air from within the home would now potentially enter the wall cavity and condense when it comes into contact with any portions of the blown-in insulation or wall structural components that are below the dew point (i.e. temperature at which water vapour condenses back to liquid form). Even worse, if the insulation installation is uneven throughout the wall cavity (i.e. gaps within the insulation), the moisture laden air could potentially reach the exterior sheathing (that is now at a decreased temperature because the added insulation is keeping the heat from the interior of the house from reaching the exterior sheathing). This further increases the risk of condensation and mould/mildew growth or wood rot.

Consider another example of a common energy retrofit option that is preferred by homeowners not only for the perceived energy savings, but also the additional living space (not to mention valuable rental income) — the internally insulated finished basement. The insured will often perceive a home with an insulated/finished basement to have higher value, but may be unaware of the potential damage to building materials occurring just behind the freshly painted walls.

To create a livable space in the basement, owners of existing structures have two options. One is to insulate the foundation walls externally. This option is rarely used because of the elevated cost associated. This leaves the more cost effective option of insulating the basement foundation walls from the interior. In order to provide a surface for wall finishing materials to be installed, the most common method is to add stud wall framing on the inside of the house foundation walls. This method involves the construction of a wooden stud wall frame against the foundation wall that is insulated with fiberglass batt insulation and then covered with a vapor barrier. Wall finishing materials in the form of drywall are then attached to the wooden stud wall frame.

A potential flaw with this type of construction is that moisture can migrate into the newly installed wall cavity from the exterior of the foundation if it is not properly damp or waterproofed (i.e. through ground water leakage, capillary pressure, etc.) or from the interior of the finished basement (i.e. diffusion, air leakage, etc.). This moisture becomes trapped between the foundation wall and the vapor barrier potentially resulting in mould growth and the decay of the wooden stud wall frame.

As we know, this is often followed by the homeowner contacting their insurer expecting that remedial costs and subsequent restoration work will be covered under their insurance plan only to learn that seepage and water ingress over time are excluded. This situation is further aggravated when some form of water leak or flood causes the wall cavities to be inspected, only to reveal the pre-existing non loss-related damage from the moisture ingress over time.

It creates an interesting debate as to whether the contractor and/or the design professionals retained to complete the energy retrofit and renovation should be blamed for the resultant damage. The extent to which the various parties involved can be held liable would depend on the individual role they were contracted to fulfill and would be subject to the requirements of the Ontario Building Code and the applicable best practices. The determination of liability in these regards would generally be done by a legal professional as part of the claims review and litigation process.

The insured could have avoided the resulting damage with a little research and understanding of the implications of adding insulation to an existing structure that was previously working as an “interactive system.” In the first example, a simple upgrade to the capacity of the existing HVAC system to remove excess airborne moisture should have also been included. In the second case, an alternative insulating method (e.g. a layer of rigid foam insulation against the foundation wall or water seal) could have avoided the resultant damage.

As building envelope and energy retrofit options become more common and resultant damage from improper installation become more prevalent, the insurance industry will require the tools to identify and delineate the related damages. They also need to have the insight to find the right resources in the early stages of such claims. It is our belief that forensic engineers and building scientists play a key role in
such solutions, which, when combined with an informed claims professional, will serve to avoid unnecessarily costly claims and litigation.

Jason Guihan, B.A. Tech., is an environmental technologist with the forensic engineering firm Giffin Koerth Inc.