[BCMA] Window Glass Replacement

[Moderated BCMA subscriber listserv.]

Hi Julianna,

Good questions - thanks for asking!

It sounds as if you might be new to managing an historic building.  If this
is the case, you should familiarize yourself with the "Standards and
Guidelines for the Conservation of Historic Places in Canada".  It
prescribes how we conserve buildings in Canada and contains the information
you need to become a sensitive steward of  an historic building.
Download the pdf at:
https://www.historicplaces.ca/media/18072/81468-parks-s+g-eng-web2.pdf
<https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwi32fvzjMPhAhURrZ4KHQ95CSAQFjAAegQIAhAC&url=https%3A%2F%2Fwww.historicplaces.ca%2Fmedia%2F18072%2F81468-parks-s%2Bg-eng-web2.pdf&usg=AOvVaw3qFJ7LB3c-JcThESDFC6wb>

More specifically about your window questions:

Be very careful about changes to your windows.  They are character defining
elements to every building.  Changes will be immediately visible, and
replacing heritage materials with modern equivalents will cause a loss of
heritage value and should therefore be considered a last alternative, if at
all.  Glass is particularly important, as it has become flatter over the
years and has a very different appearance in the 2020s than it did in the
1920s.  Sealed glass units are particularly bad, as they are slightly
concave and are immediately visible as modern elements.

Restoring old glass to a window in which modern glass has been used to
replace broken panes has an immediate positive effect in restoring heritage
value.

I have consulted on and worked on many heritage windows, and in the
Okanagan I have yet to see a window that needed significant repair.  Most
just need maintenance.  And from pictures I can find online, yours are
probably in a similar condition.  The most common problem is that the putty
has dried up, cracked and in some cases fallen out.  That leaves the glass
loose in the sashes, allowing air to leak between the glass and the sash.
If your windows rattle when you tap on the glass, they are in this
condition. Restoring the putty (linseed oil putty, not modern caulking)
will solve that problem, and greatly improve thermal efficiency.
Weatherstripping can be added between the sashes and frames to reduce air
leakage.

It is commonly thought that window replacement "upgrades" are needed to
improve the thermal efficiency of a building.  This is a myth propagated by
window salespeople and modern building enthusiasts.  In fact, tests show
that single pane windows in good repair with well-fitting storms are 80% as
efficient as modern windows, and that the cost of replacing windows cannot
be recouped from energy savings due to the short lifespan of modern window
systems (often only 25 years for a sealed glass unit, compared to the
almost 100 years already on your windows).  That is to say, by the time the
windows have saved their cost in energy, they will have to have been
replaced again.

Functioning windows that can be open or closed to regulate the temperature
of a building significantly reduce heating and cooling costs.  Closing the
windows and leaving the thermostat at a constant setting is an expensive
way of maintaining internal temperature.  Subject to the requirements of
your artifacts and archives, using your windows in their intended manner is
the most environmentally friendly thing to do.

If your artifacts and archives require added UV protection, the best
solutions for a heritage building is to add UV filter film to the inside
windows, or add an interior storm with UV filter glass.  Replacing wobbly
glass with flat UV filter glass will significantly impact the heritage
value of the building.

Interior storms are a useful way of improving the thermal efficiency of a
building.  They are uncommon and little known in North America, but widely
used in Europe, due to the ease of seasonal changes and conservation of the
heritage window system.  One advantage is that it is easy to make them with
good seals.  Whatever your window system, it is important that the best air
seal be on the inside window.  Having the best seal on the outside window
results in foggy or frosty outer windows and greatly advanced rates of
deterioration.  This is why it is essential that outer windows never be
caulked shut.

When you come to planning and making changes, ensure that your team
includes heritage expertise, as well as window expertise.  Without it the
heritage values of your building will be compromised.

I hope this is useful for you.  I welcome further questions

Regards,

Robin Digby
Digby Heritage Services.
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