The Challenge of Fixing Foundation Flaws
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:
- 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.