We’re Cracked!

The Challenge of Fixing Foundation Flaws 

Foundation Problems (minor)Every building has a foundation, whether it’s above ground or below ground, concrete or wood.  A foundation is the first building element constructed and therefore it is very important to get it right.  Any errors or flaws will manifest, either relatively quickly for a major mistake or over time for a subtle error.

In Alberta, most heritage building foundations are poured-in-place concrete.  Some foundations are comprised of concrete blocks while others are comprised of a mixture of masonry units (i.e. fieldstones, cut stones and brick).  Now and again flaws such as cracks and spalling (the breaking or splitting of surface layers) manifest themselves.  It is not recommended to ignore these deficiencies as, depending on their severity, they can be repaired fairly easily.  If left unrepaired, the severity will increase.

Some foundation flaws/cracks are inevitable and often show up early once the building is finished and the full weight of the structure is at rest.  Others appear once the structure above and the ground beneath have fully settled.  Depending on the ground composition and the depth of the foundation (foundation depths vary, such as a full basement vs. a crawlspace), these settlement cracks will vary in size.  And finally, some cracks will suggest that something is wrong with the foundation but if addressed in a timely manner may still allow a reasonable/affordable correction to be implemented.

Foundations can also be damaged by water and seasonal frost heaving.  To minimise this damage, ensure that the grade slopes away from the building with sufficient drainage to move the water away.  Frost protection can be achieved by embedding the ground with high-density foam insulation to prevent the frost line from going under the foundation if it is less than four or six feet (1.2 metres or 1.8 metres) or by underpinning the foundation to a depth greater than the frost level in the area (this is usually at least 1.8 metres in Canada, which is one of the reasons why we tend to have basements).  If one has to dig that far down to protect the foundation against frost then one might as well as make it a usable space.

The Standards and Guidelines for the Conservation of Historic Places in Canada  contains a number of sections related to the conservation and repair of foundations: check out the general recommendations of “Structural Systems” (4.3.8) under “Guidelines for Buildings” and for material specific information read about “Masonry” (4.5.3) and “Concrete” (4.5.4) under “Guidelines for Materials.”  Depending on the type of structure and level of intervention, other sections of the Standards and Guidelines might also need to be reviewed.

The following images summarize some of the types of foundation cracks and the potential solutions that might be proposed:

Type of crack: Minor – surface only, usually located at higher stress points.
Type of crack (minor): surface only, usually located at higher stress points.
Proposed Solution: Minor  - Concrete patching, parging or an injected filler product
Proposed solution (minor): concrete patching, parging or an injected filler product.
Type of crack: Medium - showing signs of structural failure and weakness such as spalling.
Type of crack (medium): showing signs of structural failure and weakness such as spalling.
Proposed Solution: Medium - Containment – pour new foundation wall against the old to stop the structural failure.
Proposed solution (medium): containment – pour new foundation wall against the old to stop the structural failure.
Type of crack: Significant - structural failure has occurred and structure becoming increasingly unstable.
Type of crack (significant): structural failure has occurred and structure becoming increasingly unstable.
Proposed Solution: Significant - Full foundation replacement.
Proposed solution (significant): full foundation replacement.

Notes:

  • Minor and some medium types of cracks can usually be repaired by foundation specialists.
  • Some medium and all significant level cracks will require the services of a structural engineer.
  • Due to the specialty of the mixes and structural nature of foundations it is best to seek certified and experienced masonry/concrete professionals to help resolve the situation.

Ultimately, foundations perform a crucial function for our buildings.  Whatever problems occur they will begin to transfer to the rest of the structure if they are not addressed.  For designated provincial and municipal historic resources the costs incurred to address these issues, whether they be minor, medium or significant (including any engineering costs), would be eligible for grant funding through the Alberta Historical Resources Foundation’s Historic Resource Conservation program.

Written by: Carlo Laforge, Heritage Conservation Adviser.

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