Windows

Frost is in the air!

With winter coming some owners of historic places might be witnessing the formation of frost on their single pane wood windows and storms, most notably on the second storey. The reasons for this will vary and subsequently so will the solutions. Generally speaking, a little frost now and again should not harm the window frame but a more persistent formation will saturate the surrounding material and in the long run, potentially cause significant damage. Should this be the case, ignoring the situation is far from the recommended solution.

Frosty window. Note the closed storm window vent cover. During the winter it should be open.

So what is one to do?  The first step, as with any intervention on a historic place, is to develop an understanding of the problem.  What is causing frost to form on the window? The answer: warm moist air comes in contact with the cold glass and condenses, which then freezes on the surface. So how does one mitigate this? Should you let the house freeze so that the interior temperature matches the outside, or should you turn the house into an oven to eliminate any and all moisture in the air? Obviously, neither scenario is plausible.

So what is one to do – replace the windows?  Speaking from a heritage conservation perspective, replacing authentic historic windows would be the equivalent to someone shaving their head bald because they found a grey hair. Historic windows have, in my experience, proven themselves to be longer lasting than any modern window and can continue to serve their function with proper care and maintenance, while modern windows wear out and routinely need to be replaced.

As air moisture is the general cause of frosted windows, controlling it would appear to be the most appropriate approach. However, there is more than one way to control moisture during the winter. One can control moisture levels with a dehumidifier, or by preventing it from reaching the cold glass with weather stripping techniques. As well, one could better manage the presence of moisture with exhaust fans and insulation. Any combination of these efforts will help to reduce the frost on windows but it should also be noted that there are pre-existing systems that should be taken advantage of in regards to this problem.

Storm windows traditionally have three holes at their bases with a flap cover. During the winter, these should be open to let moisture and condensation escape. When bugs arrive with spring, close the flap. Double hung windows generally have locks where the sashes meet, use them to tighten the window and reduce air leakage.  Should you decide to proceed with a form of weather stripping, concentrate on the interior side of the window and allow the storm window to breathe. This will create a micro climate (similar to the ventilation in one’s roof), which should help prevent frost and therefore better sustain and protect the window.

Hopefully, the preceding information will be useful for those who might be dealing with frosty windows.  There are many articles on the Internet, which tackle this issue and propose similar, different and additional solutions ranging from “free to expensive”.  As a Heritage Conservation Adviser, my advice and that of the Standards and Guidelines for the Conservation of Historic Places in Canada, is to start with the minimal approach.  With any luck, that is all that will be needed.

Written by: Carlo Laforge, Heritage Conservation Adviser.

If you have any technical questions related to the conservation of your historic place, submit a comment in response to this post. We would be happy to prepare a response.

It’s bad to clad!

Property owners occasionally ask whether historic wood windows and trim can be clad in sheet metal to both eliminate maintenance and protect fragile historic material. As conservation advisers, we discourage cladding since it removes, in effect, a character-defining element from the building, and cladding raises maintenance issues of its own.

Tempting though it may be, simply covering up deteriorated areas can ignore the causes of deterioration, leaving underlying moisture or other problems to continue their destructive work within the structure.

Wood sills, as an example, may be weathered rather than actually rotted and can often be treated relatively easily and economically with wood epoxy repairs. Once repaired, the repainted wood is stable, rot-resistant and easily maintained.

Sheet metal cladding, on the other hand, takes skill to properly detail, fit, and install so that it drains properly. Once installed, claddings often rely on caulking to seal open edges. Caulking can attract dirt and, like the painted surfaces it conceals, needs to be maintained and periodically replaced. Perhaps most important, clad wood is no longer exposed to the drying effects of the sun and circulating air, so that if water does gets beneath the cladding, as it likely eventually will, deterioration can occur rapidly and unnoticed. Better the devil you know…

This isn’t to say cladding is always inappropriate: it may be a valid means of adding a weather detail missing in the historic element while minimizing impacts on heritage value. In general, though, it’s preferable to have an authentic original material that you can appreciate and easily maintain.

Written by: Fraser Shaw, Heritage Conservation Adviser.

Not Just a Pane: Historic Windows

 

Windows are an integral part of a building system. They transmit light, control heat flow, are a means of egress, frame exterior views, and are significant elements that contribute to the design of the building. Windows are complex units and are made up of many different components that can be decorative, functional or both. 

Why are historic windows important? 

Historic windows are often character-defining elements. Character-defining elements are the materials, form, location, spatial configurations, uses and cultural associations or meanings that contribute to the heritage value of a historic place and must be retained in order to preserve its heritage value. Furthermore, historic windows are elements that directly reflect a site’s craftsmanship and design and are usually constructed out of particular materials. They are usually quite detailed and in some instances retain original glazing units.

Left to Right: Beatty House, Rimbey; Cronquist House, Red Deer; Pine Lake Holy Trinity Church, Pine Lake

Common misconceptions about historic wood windows 

On a daily basis I field questions about the replacement of historic wood windows. A typical case is a historic site with historic windows that have not been looked at in some time and have deteriorated to some extent due to weathering. A common misconception is that replacement of these historic windows with a modern unit is cheaper and will increase the thermal efficiency of the building through higher R values. 

Research in performance standards for timber sash and case windows in Scotland has taught us that estimated costs including painting of window components, repairing damaged putty and re-caulking where necessary within a regular maintenance program eliminated the cost of a major restoration project every five years. Another thing to consider is that modern sealed units, when they fail are not maintainable and must be replaced outright. 

It is also interesting to learn that a single glazed window in conjunction with an exterior or interior storm window is comparable to a modern sealed unit. A single glazed window has an R value of 0.6 while a single glazed window with wood storm has an R value of 2.0. The top of the line triple glazed window with low E coating and argon has an R value of 3.5. Overall windows in general are thermally inefficient in comparison to a typical wall with 4” batt insulation that has an R value of 12. 

Planning for historic wood window conservation work 

When planning for any conservation work we always take the approach of minimal intervention. Preserving historic material and maintaining historic material is the first step and outright replacement, if necessary, is the last option. 

In most cases simple epoxy repairs to wood, adequate prepping of the wood surface (manual scraping), the application of an appropriate primer and brushed on layers of exterior paint is all that is needed to repair historic windows and to prevent deterioration.

For more severe cases, putty replacement, replacement of broken or damaged glazing, and dutchman (splicing in of new wood) may be required. 

Conclusion 

  • Historic windows have heritage value.
  • Historic windows have demonstrated good durability and maintainability.
  • Always assess and document each window before proceeding with conservation work.
  • Compile historic photographs and refer to the Statement of Significance in your planning process.
  • Minimal intervention should be the first approach.

Remember, you can save on costs and achieve the same thermal efficiency through conservation.

Written by: Ophelia Liew, Heritage Conservation Advisor