The following fact sheet is part of the About Your House — General Series

Before You Start an Energy Efficiency Retrofit — The Building Envelope

The building envelope is the outer layer of the building that separates the indoor living space from the outdoor environment, both above and below grade. It is made up of the walls, roof, foundation, windows and doors. The building envelope is an important part of many energy efficiency retrofit projects as many older homes have high rates of air leakage and building envelope areas that are not well insulated — and high space heating and cooling energy costs.

Like any renovation, retrofitting the building envelope requires careful planning. Before you decide to go ahead with the project, it is important to clearly identify the areas that you want to improve. Just as important is a thorough inspection of the existing structure so that any current problems can be corrected before you start the renovation.

Common Situations

Many homeowners experience houses that are cold, drafty or have high heating bills, especially on windy days during the heating season. The process of improving the energy efficiency of the entire building envelope can seem like an overwhelming task. An understanding of the principle that the house functions as a system (see the House as a System section) is critical for anyone undertaking a building envelope retrofit. Prioritizing the different aspects of the work and learning about viable retrofit techniques can help you to work through the many decisions that must be made.

To help you recognize problems and to plan an energy- efficiency building envelope retrofit, consider these important areas:

Structural problems
There may be structural problems. Any existing problems and damage must be repaired as part of the retrofit project otherwise your renovation, and all of your invested time and money, will be at risk.

There may be moisture problems in the existing house that must be identified and remedied to protect your renovation investment. Be aware that building envelope retrofit work may increase humidity levels in the building and you might have to install mechanical ventilation to compensate.

Heating and ventilation
Inadequate and inefficient heating and ventilation may be symptoms of a poorly performing building envelope.  Additionally, by adding insulation to, and increasing the airtightness of, the building envelope, the heating system may become over-sized. It may be advisable to consult with a heating contractor on the post-renovation heating needs of the house.

Finishes may be damaged from moisture problems associated with poor building envelopes.

Understanding the options available for upgrading the various elements of the building envelope requires research or professional help. CMHC recommends that you consult with a residential energy advisor and qualified, knowledgeable contractors to help you plan your energy efficiency building envelope retrofit.

House as a System Considerations

A house is much more than just four walls and a roof — it's an interactive system made up of many components including the basic structure, heating, ventilating and air conditioning (HVAC) equipment, the external environment; and the occupants. Each component influences the performance of the entire system. A renovation provides an opportunity to improve how your house performs.

Retrofitting the building envelope often results in a better insulated, more airtight building that is easier to heat and more comfortable to live in. However, reduced air leakage and heat loss may require changes to HVAC equipment in your house to keep things in balance.

Avoid Surprises

A retrofit of the building envelope should not be started until all decisions about construction details have been thought through. Thorough planning will help you to develop a realistic understanding of the work to be done and the costs involved. Here are some of the likely situations that people encounter. However, every situation is unique and you should hire a qualified residential energy advisor, home inspector, contractor or other professional to do a thorough investigation, find the problems and suggest the best solutions as a part of the overall renovation project.

Use the Building Envelope Retrofit Worksheet (PDF) to record the present condition, any problems related to the building envelope, proposed changes and preliminary costing.

Assessing the Building

Ask Yourself

  • What are the existing insulation levels of the various parts of the house?
  • How airtight is the building?
  • How energy-efficient are the windows and doors?
  • Is there sufficient ventilation?

Consider Your Options

  • Have a professional residential energy advisor undertake an assessment of your house. The audit should include a blower door test to determine the airtightness of the house and the locations of leaks. A professional audit will help you to prioritize your retrofit options. The audit will also help to identify ventilation needs required after a retrofit.

If you don't Consider Your Options

  • You may be wasting money on retrofit work that will have little overall benefit.
  • You may be unaware of important retrofit possibilities that have relatively short payback periods.
  • You may underestimate the post-retrofit ventilation needs in your home and end up with poor indoor air quality.

Structural Problems

Ask Yourself

  • Are there any structural deficiencies — such as sagging floors, cracked walls, etc. — in the existing house that needs to be repaired?
  • Are there any roofing, flashing, siding, basement or window and door problems that allow water into the house?

Consider Your Options

  • Carry out a complete inspection before you start. You may need to hire a structural engineer or a qualified home inspector.
  • Plan any needed work as a part of the renovation.
  • Use contractors that are familiar with energy-efficient construction practices to carry out repair work.

If you don't Consider Your Options

  • Unforeseen problems will lead to unexpected costs and delays during renovation.
  • Structural deficiencies can lead to cracked finishes, floor vibration, bowed or displaced walls, floors or roof structures and possible structural failure.
  • Any unresolved problems may occur again either immediately after the renovation is complete or years later. Having to re-do the renovation would be costly and disruptive.

Building Envelope Components

Ask Yourself

  • Can basement areas be air sealed and insulated in a way to avoid moisture and mold problems?
  • What options are there for improving the insulation and airtightness of the walls? Ceiling areas?
  • How can the energy efficiency of the windows and doors be improved? Should they be replaced?
  • What knowledge and skills are required to undertake the work?
  • Should the work be done from the inside or outside? Either will have implications on costs, disruption, and timing of the project.

Consider Your Options

  • Insulate basements on the outside, if possible — particularly if you have to excavate to deal with moisture problems. If this is not possible, insulate on the inside, as long as any pre-existing moisture or water leakage problems are addressed and dryness is guaranteed.
  • Add insulating sheathing to the outside of main wall areas, if possible. Fully insulating wall cavities is another, but more difficult, possibility. Insulate and air seal the joist spaces above the foundation wall .
  • Air seal any leaks between the house and attic. Then add extra insulation.
  • Air seal to eliminate drafts in all areas.
  • Repair, air seal or replace windows and doors.
  • Assess the skills needed for each task through discussions with your residential energy advisor or renovator.
  • Do some preliminary research on your options.

If you don't Consider Your Options

  • Poorly detailed work can lead to moisture and mold problems.
  • The potential to improve the energy efficiency of your home may be wasted.
  • Poorly insulated building envelopes can cause comfort problems in the home.
  • Improper practices can compromise the effectiveness of the work.
  • As energy costs increase, you won’t be protected against higher utility bills.


Ask Yourself

  • Is there any evidence of moisture problems in the existing building envelope? These can include water damaged finishes, water stains or visible mold growth on any surfaces, blistered or peeled paint, cracked or missing caulking and condensation on windows, wall or ceiling surfaces.

Consider Your Options

  • Determine the source of the moisture that is causing the problems. It may be from building envelope leaks, plumbing leaks or condensation on cold surfaces.
  • Solve the moisture problem — either immediately or as a part of the renovation project.
  • Clean up visible mold growth.
  • Insulate, air seal and use energy-efficient windows to provide warmer inside surface temperatures and prevent condensation problems that lead to moisture damage and mold growth.
  • Repair or replace all deteriorated finishes or structural components.
  • Provide ventilation and eliminate sources of moisture to control high humidity. Air sealing will usually increase indoor humidity levels so good, balanced ventilation such as that provided by a heat recovery ventilator is critical.
  • After the renovation, maintain caulking, grout and flashings to prevent water access to the building structure.

If you don't Consider Your Options

  • Unresolved water damage problems will continue and will lead to further deterioration of the building, including newly renovated areas.
  • Mold growth caused by excess moisture can be a source of serious indoor air quality (IAQ) and health problems.
  • Superficial cleanup or hiding moisture damage behind new finishes will allow deterioration to continue.
  • You may lose your renovation investment.

Heating and Ventilation

Ask Yourself

  • How efficient is the heating system?
  • Can the existing heating system be modified to meet the reduced demand after the retrofit work?
  • Is the retrofit an opportunity to install a more energy-efficient heating system?
  • Does the house have a ventilation system and will it handle the needs of the occupants after the retrofit?

Consider Your Options

  • Make sure that the heating system is reviewed by an HVAC professional who is aware of what insulating and air sealing work you plan to do. A “heat loss” calculation may be in order to properly re-size your heating system.
  • Seek professional help to determine ventilation options. Consider a ventilation system that includes heat recovery to save on ventilation-related energy costs.
  • Many existing furnaces are oversized. Choosing a new, properly sized furnace can lead to a smaller, less expensive furnace and possible gains in efficiency and lower operating costs.

If you don't Consider Your Options

  • An oversized or poorly installed heating system will not work efficiently in your newly retrofitted home.
  • Air sealing can reduce the amount of air needed by heating appliances and exhaust fans and can result in problems with the venting of combustion gases from the furnace, hot water tank or other fuel-fired appliance. Consulting with a knowledgeable contractor, inspector or professional can help ensure that the right provisions for make-up or combustion air are provided as a part of the renovation project.
  • Improper ventilation can lead to lingering odours and excess humidity.


Ask Yourself

  • What finishes such as paint, varnish, stains will need to be replaced during the retrofit work?
  • What skills are needed to properly install the finishes?
  • What finish options are available to minimize the impact on indoor air quality?

Consider Your Options

  • Do your research. There are many new and different products on the market that emit less pollutants into the indoor air.
  • Choose the product that meets your needs for water resistance, durability or cleaning.
  • Consider maintenance-free or low maintenance materials.
  • Determine the preparation and installation requirements for each type of finish.
  • Choose finishes that are environmentally friendly such as paints that carry the EcoLogo symbol or caulking designed for indoor use.

If you don't Consider Your Options

  • Selecting finishes that don’t match the use will yield poor results and require high levels of ongoing maintenance.
  • Improper preparation or installation of finishes will void the warranty.
  • Inattention to the ingredients in finishes may result in chemical off gassing that may compromise the indoor air quality of your home.


  • A well-executed building envelope retrofit will result in a warmer, more comfortable living space.
  • Improved airtightness and increased levels of insulation will help to reduce heating costs in the winter and air conditioning costs in the summer.
  • Repairing structural problems and leaks in the building envelope will prolong the life of your house and help to improve its value.
  • Added ventilation will improve the indoor air quality of your home.
  • Warmer interior surfaces will help to prevent condensation and mold growth.

Skills to Do the Job

A homeowner with good fix-it skills may be able to do some of the work on the building envelope renovations such as:

  • Removing old siding, window or door units.
  • Caulking or repairing of windows and doors.
  • Installing insulation and a vapour barrier.
  • Air-sealing the building.
  • Painting.

However, be aware that there may be hazardous material such as lead paint, asbestos and faulty electrical and plumbing systems that need to be dealt with by qualified professionals to ensure the remedial work is properly and safely done. Consider hiring a professional renovator to manage the project. If you are doing it yourself, you may still want to hire subcontractors to do work such as siding, basement insulation and installation of replacement windows. Installation of a ventilation system or modification of the heating system should be done by a qualified HVAC contractor.

Remember to obtain all necessary permits, get a written contract, ensure that workers use safe working practices and are covered by workers’ compensation. Protect yourself, your family and your home.

Costing Your Project

The cost of the building envelope energy efficiency renovation work will depend on the size, condition and original material of the existing building envelope, local labour and material costs and the extent of the work to be done. Costs of finishes and fixtures vary widely. A good budget checklist will help you to develop a realistic cost estimate for the project before you start.

Some of the items to include are:

  • Energy audit and assessment of the existing building envelope and house.
  • Condition inspection of the existing building envelope and house.
  • Permit costs.
  • Basement insulation and air sealing (including excavation and corrective landscaping if needed).
  • Insulation improvement and air sealing of walls and ceiling areas (including replacement of interior or exterior finishes, siding, etc).
  • Window and door repair or replacement (including surrounding trimwork).
  • Heating system adjustment or servicing (or replacement if age of system or change in heating load warrants it).
  • Ventilation.
  • Caulking and painting.
  • Waste disposal.
  • Contingency for unforeseen conditions.



Print(opens in a new window)