Upgrading Windows in Heritage Buildings

Conserve Energy & Heritage at the Same Time

Climate change action is something everyone is concerned with today. The BC government has pledged to significantly reduce greenhouse gas emissions and energy consumption.  A new BC Green Building Code is coming that will require higher energy efficiency standards for both new construction and rehabilitation projects. Can heritage buildings measure up to these new demands without sacrificing the very qualities that we value in them?

Many energy upgrades (such as installing energy star appliances) do no harm to vintage buildings. Some, however, such as window replacement, can have a significant negative impact:

“We tend to take windows for granted. Yet we recognize that heritage buildings whose windows have been replaced have been diminished. The depth and thickness of frames and sills, the width and visual weight of sash components, the materials, the colour and the pattern of light reflecting off the glass—all complement and elaborate the architectural style, texture and age of a building. Much of this character is lost when windows are replaced with modern versions that lack these features.”

— Craig Sims and Andrew Powter:  Repair or Replace:  Windows in Historic Buildings - Arriving at a Sustainable Solution

The BC Heritage Branch recently hired a University of Victoria Engineering student to research and design window energy conservation solutions that would not harm heritage character. Here are some of her suggestions:

  1. Repair existing windows – frame, sash & glass
  2. Draft proof and insulate window frames (caulking & weatherstripping)
  3. Add  storm windows – interior or exterior
  4. Add heavy lined curtains
  5. Add insulated and reflective internal blinds

National Resources Canada (NRC) also offers these tips on repair, draft proofing and insulation to improve window energy efficiency:

If the window appears to be in good shape, it may be possible to improve airtightness by doing the following:

  • Adjusting or replacing the sash locks or adding more locks to large windows.
  • Repairing or replacing hinges on casement windows.
  • Ensuring that caulking, weather-stripping and paint are not interfering with the operation of the window.
  • Ensuring that weather-stripping is fully functional (i.e., it should be flexible, be properly located and make full contact between the sash and the frame.)

NRC provides specific advice on caulking and weatherstripping:

  • Air leakage can be reduced by applying a constant bead of caulking around the window trim, at the mitered joints of the trim and between the trim and the frame ... Caulking on the outside of a window should be done only after interior sealing is complete. If the exterior is caulked first, it can trap warm, moist air in the wall, which can, in time, damage the wall.
  • For older wood-frame windows, look for a good quality, self-adhesive plastic V-strip weatherstripping.

Ongoing maintenance is a very important part of the building use and care, and good window conservation is no exception. Windows in historic buildings have usually been in service for a long time – often 100 years or more – proving their durability, functionality and worth.  A good overhaul and retrofit will ensure their longevity and upgrade their functionality for another 100 years. This is more likely to provide long term solutions than inserting a replacement window and throwing out the original frame, sash and glass. Most of today’s manufactured replacement windows carry warranties of about 8-10 years and failures are usually not repairable.  Maintenance and conservation are very green behaviors.

Owners can also install storm windows that add an extra layer of glazing and insulation, bringing the energy rating very close to that of an energy star window. Historically, exterior storm windows were common on Canadian houses. They can be installed permanently or as a seasonal unit with a built-in screen and sliding sash.  When using an exterior storm window, the interior window should be sealed more tightly than the storm to prevent condensation between the two that can lead to deterioration of the sash and frame. 

Interior storm windows have the advantage of being more accessible and easier to install and remove. There are fewer problems with condensation; if condensation does occur it affects the storm and doesn’t lead to deterioration of the window frame and sash.

By using these ‘alternate compliance’ solutions, you can rehabilitate and upgrade your heritage building to the standards of the new BC Green Building Code while still complying with the best standards of heritage conservation.

For current news articles about Sustainability
» News : Sustainability

Read more about residential upgrades
» Tips for Upgrading Heritage Homes




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