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Demolishing or Modifying Existing Construction Structures

Construction
By Paul Netscher | Read time: 3 minutes

From time to time contractors have to demolish existing structures, either completely or partially, to enable new structures to be built. This work is inherently dangerous, and if it’s not done correctly could result in the remaining structures or surrounding property being damaged, and even people getting injured or killed.

Usually, large demolition work must be done by licensed contractors, but often projects involve smaller demolition works which are tackled by less experienced people. In fact, sometimes contractors have to demolish newly completed work because the work was substandard of poor quality and didn’t meet the project specifications because the client changed their mind, or the designer made a mistake. Some of these demolitions are done with little forethought and planning, sometimes with inappropriate equipment, often done hurriedly so that impacts to the construction schedule are minimised.

Precautions before demolition

To prevent accidents it’s important that certain precautions and steps are implemented before any demolition work begins. These include:

1. Ensure all service lines and pipes have been terminated

Live electric cables are dangerous. Damaged water pipes can flood the project, or possibly leak underground undetected. Ruptured gas pipes can lead to explosions.

2. Make sure that the right structures are demolished

For example; in 2016 the wrong house in Sydney Australia was demolished. The contractor arrived at what they thought was the correct address and proceeded to demolish the house, instead of the house next door which they were supposed to demolish. A very expensive and embarrassing mistake. It pays to always double check and also to ensure that there is adequate supervision in place.

3. Hazardous materials should be identified and where possible removed

Not only are these materials hazardous to work with but they can contaminate all of the demolished materials and parts of the construction site which can cause bigger problems and costs to clean up.

4. All permits and permissions must be in place

Many jurisdictions require demolition contractors to be licensed.

5. Check that there aren’t any restrictions

Heritage structures can’t be demolished.

6. Ensure that items that are to be salvaged have been removed

7. Protect the surrounding properties and structures from dust and debris

8. Prepare a risk assessment and safe work procedures

9. Have the right equipment and trained operators

10. Barricades

Barricade the areas where demolitions are happening and keep unauthorised people out of the area.

11. Cleaning

Clear demolished material as quickly as possible to make the area safe.

12. Plan

Plan the work so that demolitions are done in the correct sequence therefore equipment can safely reach parts that have to be demolished, and so that structures aren’t left standing which are unsupported or weakened; they could collapse in an uncontrolled manner on top of people, equipment or other structures.

13. Warnings

Provide adequate warnings to those around the demolition work who could be impacted by the demolitions.

14. Dust suppression

Ensure there is adequate dust suppression systems in place to minimise dust.

15. Complete dilapidation surveys

For large demolitions it is advisable to complete dilapidation surveys of the surrounding structures to record all existing cracks and defects. This will ensure that the demolition work can’t be blamed for damaging structures and buildings when the cracks were already pre-existing and weren’t a result of the demolitions.

Precautions before partial demolition

Often existing structures have to be partly demolished and openings cut in them. In addition to the checks above it’s also necessary to:

1. Engineer

Have an engineer check the structure to determine that the modifications won’t impact its structural integrity.

2. Structural support

As directed by the engineer, install permanent structural supports and beams, and where necessary temporary props and bracing.

3. Inspection

Not remove temporary props and supports until the replacement structures have attained sufficient strength and have been inspected by the engineer.

4. Dimensions & Drawings

Check that the areas to be removed are carefully and clearly marked out. On more than one occasion only a line has been marked and the portion on the wrong side of the line has been taken out. Doublecheck dimensions and drawings.

5. Equipments

See that appropriate equipment is used. Equipment that is too large or powerful may damage the remaining structures because of excessive vibrations and impacts.

6. Overloading structures

Not overload the structure by using equipment that is too heavy for the structure, nor should rubble from the demolitions be allowed to accumulate in heaps on, or against, the remaining structures.

7. Pre-cutting

Ensure, where possible, that areas to be broken out are pre-cut along straight lines to separate them from the remaining structure. This not only allows for neater joins and less damage to finishes but also lessens the risk of the remaining structure being damaged by vibrations and forces exerted on the parts being demolished.

8. Removing parts

Always ensure that only the parts to be broken and demolished are removed. Removing larger portions of the structure not only creates unnecessary additional work and costs, but it could also weaken the structure, resulting in structural damage or even causing its collapse.

Conclusion

Always take care when demolishing structures, no matter how minor the work is. Accidents happen easily. All demolition work is potentially dangerous. Demolition work must be properly supervised at all times.

Have you had demolition work go wrong? What happened?

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