Building Movement

Question 1

What different types of building movement are you aware of?

Question 2

Outline subsidence and possible causes?

Answer 2

• Downward movement of foundations due to changes in ground conditions below the foundations.
• Possible causes:

o Volumetric changes in clay soils following long periods of dry weather.
o Volumetric changes in clay soils due to increased water uptake by nearby trees such as oak, willow, sycamore and ash.
o Soil erosion caused by a leaking pipe or drain.
o Mining subsidence due to failure of ground caused by mining.

Question 3

Outline heave and possible causes?

Answer 3

• Upward movement of foundations due to changes in ground conditions below the foundations.
• Possible causes:

o Volumetric changes in clay soils following long periods of rain.
o Volumetric changes in clay soils due to removal or death of nearby trees.
o Volumetric changes in soils due to freezing of moisture causing expansion.
o ‘Stress relief’ of deeper soil following removal of above layers of soil (such as occurs during construction of a basement).

Question 4

Outline settlement and possible causes?

Answer 4

• Downward movement of foundations due to compression of ground below the foundations.
• Possible causes:

o Natural settlement following construction.
o Weak-bearing soils whereby the foundation design and location is incorrect.
o Poor compaction of soil prior to construction.
o Differential settlement caused by disproportionate loadings and/or different foundations.

Question 5

Outline building fabric decay or poor construction methods?

Answer 5

Building fabric decay and poor construction methods can significantly impact a building’s performance and lifespan, leading to issues like energy inefficiency, moisture problems, and structural instability. These problems can arise from various factors, including poor workmanship, material failures, and inadequate design.

• Inadequate Insulation - reduced thermal efficiency
• Thermal Bridging - reduced thermal efficiency
• Air Leakage - reduced thermal efficiency
• Poor Workmanship
• Material Deterioration
• Moisture Problems
• Foundation issues - structural problems
• Lack of Maintenance - reduced lifespan of building elements

DWL Answers:
- Wall tie corrosion leading to horizontal cracking.
- Lack of lateral restraint leading to bulging walls and collapse.
- Roof spread leading to bulging walls and collapse.
- Sulphate attack in concrete ground slabs leading to bulging and displacement of walls.

Question 6

What guidance would you use when assessing cracking caused by building movement?

Answer 6

• BRE 251 – Assessment of damage in low-rise buildings.

RICS - Cracking and Building Movement 2004 (Publication)

Question 7

What are the different categories of cracking?

Answer 7

• Category 0 - Hairline cracks of less than 0.1mm in width which are classed as negligible.
• Category 1 - Largely internal cracks which are up to 1mm in width.
• Category 2 - Largely internal cracks which are up to 5mm in width. Doors and windows may stick slightly.
• Category 3 - Internal and external cracks which are up to 15mm in width (or several smaller cracks). Doors and windows may stick and service pipes may fracture.
• Category 4 - Internal and external cracks which are up to 25mm in width (or several smaller cracks). Doors and windows are distorted, service pipes may fracture, floors may slope, walls may bulge, possible loss of beam bearings.
• Category 5 - Internal and external cracks which are over 25mm in width (or several smaller cracks). Doors and windows are distorted, significant fracture of service pipes, significant bulging, significant loss of beam bearing and structural instability.

Question 8

What works are likely required for each category of cracking?

Answer 8

• Category 0 – 2 cracks are classified as ‘aesthetic’ issues. Remedial works including redecoration, external repointing and minor easing of doors and windows.
• Category 3 – 4 cracks are classified as ‘serviceability’ issues. Remedial works including external repointing, replacement of sections of wall, adjusting or replacement of walls and windows, repairs and replacement of services.
• Category 5 cracks are classified as ‘stability’ issues. Remedial works include significant structural stabilisation works, partial or complete rebuilding.