Seasonal movement is a common issue faced by property owners, particularly in areas where soil conditions are reactive to environmental changes. This natural phenomenon can lead to a range of visible and sometimes serious consequences in and around buildings.
Issues with Seasonal Movement
As the seasons change between the dryer and wetter months, fluctuations in moisture levels within the soil can lead to expansion and contraction of the ground. This causes what is classified as seasonal movement, which often results in:
- Diagonal and vertical cracking in walls, particularly at corners of windows and doors or where the wall is naturally more weak.
- Displacement or leaning of walls and retaining walls, indicating uneven settlement or movement beneath the surface. Sometimes this results in horizontal cracking.
- Uneven paving or cracking in slabs, which can become safety hazards.
- Gaps between walls, ceilings, and floors, which may open during dry periods and close during wet seasons.
These issues can range from being merely cosmetic to significantly compromising the structural integrity.
What Causes It?
Several factors contribute to the occurrence and severity of seasonal movement, including:
- Inadequate Foundations: Foundations that are not designed or constructed to accommodate the level of ground heave will likely experience movement. Foundations that are too shallow and/or don’t have sufficient stiffness are particularly problematic.
- Clay Soils: Highly reactive clay soils, which swell when wet and shrink when dry, are a major contributor. The extent of movement depends on the type of clay; climate; and stormwater drainage conditions.
- Moisture Variations: Seasonal changes in rainfall and temperature can dramatically alter the moisture content in the soil. Activities such as watering the garden or maintenance issues such as leaking pipes, can exacerbate this issue.
- Trees and Vegetation: Large or high water-demand trees close to the home can influence soil moisture levels significantly. Roots extract moisture unevenly from the ground, which can lead to differential movement across the building footprint.
Understanding these causes is key to preventing and managing the effects of seasonal movement.
How to Reduce the Effects
While it may not be possible to completely eliminate seasonal movement, its effects can be greatly reduced through proactive design and maintenance:
- Correctly Designed and Constructed Foundations: New buildings should have foundations designed in accordance with site-specific ground investigations. This includes adequate footing depth and quantity of steel reinforcing bars to handle anticipated ground movement.
- Consistent Moisture Control: Maintain a stable moisture regime around the building perimeter. This may include controlled irrigation throughout the year, as well as providing concrete paving around the building to help reduce the impact of seasonal influences on the ground immediately adjacent the external foundations.
- Addressing Existing Problems: For existing structures, while we can’t change the foundations, we can mitigate the severity by managing contributing factors
- Drainage: Ensure proper drainage around the home. Pooling of water next to foundations should be avoided. Check for and repair leaking pipes or fixtures that might oversaturate the soil. This applies for stormwater; water supply; as well as foul water.
- Vegetation Management: Avoid planting large trees or vegetation with high water demand close to buildings. Existing problematic trees might require removal or root barriers to control their influence on the soil.
- Flexible Cladding over the walls: By covering the problem wall with a sheet of plasterboard, or a layer of render over flexible mesh, minor to moderate levels of imperfections could be hidden.
- Underpinning: If all the other measures have been exhausted, then at times underpinning could be the only solution left. The reason that this usually one of the final options is due to the relatively higher costs, and the lack of guarantee that it will address all the issues. At times, unpinning a problem area could just push the issue over to an adjacent location.
By implementing these strategies, homeowners and builders can reduce the risks and impacts of seasonal movement, protecting both the appearance and structural stability of buildings over time.
Visit the Geared website for more…
George Ramsay CEng MICE MFPWS
Director – Geared Consulting Partnerships
Chartered Structural & Civil Engineers l Party Wall Surveyors
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