Remedial Works For Roofing Defects Environmental Sciences Essay

Building defects also known as imperfections of a building which mean the building fail to fulfil the requirement of its function, performance, statutory of user and the building defect will show an evident within the structure, services, fabric or other facilities of the affected the building (Watt, 1999). Some examples of a defect are cracking, damage and deterioration of brick walls, sagging of roof, leaking and so on.

At the beginning of this chapter will outline the various types of building defects that occurred nowadays. Next will identify the potential causes of building defect included the defect to the roof, ceiling, floor, external and internal wall, and foundation. Appropriate remedy works will be carry out at the end of this chapter. The research will only emphasize on the defects that occurred in Malaysia.

2.2 Foundation

Introduction

Whenever a project begins their construction on a new building, it is essential to first assess where and how they will build the foundation. The foundation is a structure, most commonly made of concrete for homes. There are different types of foundation designs and each serves a different purpose and specific, but generally, the usage of a foundation is to transfer the weight of the structure and spread through the entire earth below.

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A good foundation can sustain the building and resist it against any physical forces cause by the subsoil. In addition, a good foundation can resist against chemical compound attack which readily contain in the subsoil and imposed various load into the ground with sustain and transmit safety in the sound of zero damage or defect to the building. (Douglas & Ransom 2007)

2.2.1 Soil Factors

Most soils consist of solid particles of varying shapes and sizes, mixed with water and, to a lesser extent, which air filling in between the gap. Soil originated came from various rocks, when the rocks gradually attack by weather, it will decompose and soften in place, which changes into soil, called residual soil. If the decomposed rock materials are washed away, usually by rainwater and streams, they are washed down to a lower area where they are deposited in valley bottoms.

Normally soil can be classified in two types:

Cohesionless soils- sand

Cohesive soils- silts, clays and peats.

2.2.1.1 Cohesionless Soils

Sand generally is considered as a favourable construction material, and usually favourable from the standpoint of foundation support, which do not need much foundation structure. As sand does not hold water, hence the materials may easily be washed away by water. Excavations in sand generally do not stand very well, as damp sand may temporarily stand steeper, even vertical, for short periods of time.

2.2.1.1 Cohesive Soils

Clay is very soft materials exude between the fingers when squeezed, it is composed of rock particles ground extremely fine. However, a chunk of dry clay is hard and difficult to break by hand.

Clay soil commonly keeps water in within a moisture contents in the range of 10 to 50% by weight. When water is withdrawn by drying, the clay will shrinks cracks and becomes very hard. Firm clay is a good foundation material. The excavations in firm clay usually stand well and steep, but if the banks are too high or steep, still there is a chance of landslide occurs.

2.2.2 Foundation Factors

Foundation defects, almost all the time, will related to soil movement apart from the material defects. Swallow foundation stability merely depends on the support of the soil, when the soil moves, most foundation will move together. Subsidence is a downward movement under applied load. The movement of soil may occur as uniform movement where the soils move as a wholesale, such movement may cause out smaller defect as the building settle uniformly.

The cause of subsidence may be as straightforward as the poor soil curing before any construction commend. Normally foundation and ground subsidence arise from the ground instability and changing in soil stress-state. Whereas movements due to a changing soil stress-state may leading to soil volume changes, cause by dewatering, vegetation problems or change of loading to the foundations.

Generally subsidence will be classified as three types:

Slope or tilt

Differential movement

Uniform settlement

2.2.2.1 Slope or tilt

This type of movement can occur when the foundation is distorted due to the soil movement or landslide at slope. The foundation and the entire structure that it attached to it will tilt, usually in a downhill direction. When tilting occur, it do not means that the foundation is not rigid enough to support the building, but when the soils below been moved or wash away, the foundation will moves as a unit with the soil.

In these instances, a foundation that experiences tilt many times does not have a lot of cosmetic distress (sheetrock cracks, brick mortar cracks, etc.) or structural distress (slab cracks). However excessive tilt will cause cracking because of the unbalanced gravitational forces on the superstructure but will not be too serious as compare to differential movement.

2.2.2.2 Differential Movement or Settlement

The differential movement or settlement means that the foundation moves more in one area than in another as a result of localised soil settlement. This is due to the foundation is not rigid enough to overcome the movement of the soils.

Differential movement will creates slab cracks, brick cracks, especially at the door and window level, as the opening area is the weakest part of the wall. Unfortunately, this is the most common type of foundation movement in expansive clay soils.

2.2.2.3 Uniform settlement

The definition of uniform settlement means that the foundation moves downward without tilting. This is the best settlement as even the foundation is not rigid enough to respond, but it will not generate any tilting or cracks at the wall. However, excessive uniform settlement may cause to the failure of underground piping or facilities, which the building load will damage piping underneath the building.

2.2.3 Remedial Work for Foundation Defect

When a building is facing settlement and cracking, the only method can be done is to strengthening the foundation. There are many types of remedy method such as:

Traditional underpinning

Pynford stools method

Jacked pile underpinning

Needle and piles

Root piles

Underpinning by mini-piles

Ground injection

Underpinning pad foundations or column bases by needle and piles

Underpinning floors

Among all of the repair method, only one will be selected according to the needs and recommendation by the structural engineer. Underpinning may be necessary when the building is facing uneven settlement, in which the uneven loading of the building, unequal resistance of the soil action of tree roots attacks or cohesive soil settlement. Increase in loading of the existing building also may need the foundation repair. This could be due to the addition of an extra storey or an increase in imposed loadings such as that which may occur with a change of usage to the building.

2.3Roof Defect

Introduction

A roof is an uppermost part of a building which protects the building and occupants against exposure to the weather. Generally, a roof not only protects primarily against rain, it may also protect against some climate factors such as cold, heat, sunlight and wind.

Flat roof is one type of covering of a building. It can be horizontal or nearly horizontal which in contrast to a slightly slope form of horizontal surface to allow water to run off into a gutter system. It is quite difficult to do survey or inspection on a flat roof unless there is an adjacent building surround to allows a view above the building.

A pitch roof is a roof made up of two angled pieces which meet in the middle, with gables at either end. Both side of the pitch roof is generally the same, although sometimes they maybe pitched at different angles for aesthetic reasons. (S.E, Smith, 2003)

Failure of roof can be in variety reasons such as poor construction, poor design and lack of maintenance. Thus, extensive repair works need to carry out to major failures.

2.3.1 Ponding

Roof ponding is cause by the excessive accumulation of rain water on a low-slope or flat roof. On the other hand, it is cause by the poor design of the roof slope.

Sometime, roof ponds can lead to the collapse of roof if nobody concerned about this problem for a long time. The adverse effects of roof pond included:

Deformation of roof deck

When water on the flat root cannot manage to runs-off in time, the density of water can cause the roof deflect into a dish shape which will hold more water and create a greater deflection.

The greater the stagnant water the greater the deflection on the roof. As the deflections on roof increase, it can cause damage to the structural of the deck.

Penetration of moisture into roof system through the roof membrane

The efficiency of thermal insulation of a roof can be reduced as moisture content penetrates into the roof membrane. In other hand, moisture also can cause damage to the structure, contents and occupants.

Growing of algae and fungi

The growing of algae and fungi will likely occur when stagnant water stand for a long periods on roof and may cause damage to the roof membrane. In addition, the growing of algae and other debris could block the drain and cause additional ponding on roof.

2.3.2 Sagging

Roof sagging can be found in both old and new building, it can be seen from the exterior of the roof. Sagging in roof tends to be caused by the faulty design of the roof struts and incorrect design of strutting beams.

The connection or bearing points of a rot timber roof frames can lead to an unbalanced forced which it is being imposed on the supporting walls, sagging may likely occur as the roof transfer loads.

2.3.3 Leaking

Roof leaks are the main cause of roof damage which caused by the poor design of the roof and extreme weather ability. Day after day, roof leaks may weaken the roof structure as well as destroy the stuff inside the building.

One of the factors that lead to leaking is inappropriate sloping area of the roof surface. Water on flat roof accumulates faster than it runs-off therefore form stagnant of water. As stagnant water accumulates on roof surface in a period of time, it may result in leakage problem.

Another cause of roof leaks is by the obstacles such as debris, leaves, moss and branches. Penetration of water block by the obstacles, as the rainwater downpipe cannot function properly and cause leaking on roof.

2.3.4 Remedial Works for Roofing Defects

Roof Pond can be repair by installing EPDM (Ethylene Propylene Diene Monomer) Rubber Membrane. It is a high-density rubber, durable, reliable and easy to install. Roof pond can be avoided if EPDM Rubber Membrane installed correctly.

The remedy work for sagging on roof is reconstructing the strutting beam of roof. It is necessary to replace a new structure if the roof sagged very serious and the new structure must be able to support the finishes.

It is very easy to repair an early stage roof leaks which is clear all the obstacles from the roof as it prevents easy flow of rain water. Besides, leaking can be repair by applying a new roof coating; it is often made after the roof damaged.

2.4 Wall Defect

Introduction

A wall is one part of the building’s structural system. The basic function of a wall is to protect the covered or otherwise conditioned interior spaces from surrounding environment. A wall should be able to control mass, energy and particulate flows such as water, air, smoke, odour, heat, light, noise, fire into the building. A wall can also act as partitions which separate the spaces in a building into rooms.

Other than that, a wall unit must be able to resist and transfer loads which imposed from suspended floors and/or roof. In other hand, a wall has to provide the functions such as support, control, distribution of services and aesthetic.

2.4.1 Rising Damp

Rising damp in a building can be identified by a generally horizontal although irregular pattern of dampness. This is commonly associated with the discoloration of inner surfaces, which may rise to 600mm above ground floor level. If rising dampness occurs, the DPC material may have failed or have been inadequately jointed. Alternatively, the DPC may have been bridged. This would allow dampness to move around the DPC upwards through the wall. (H.John, C.Geoff, 1997)

The cause of rising damp can be caused by the failure of linking between the DPC in the wall and DPM in the floor. The materials of DPC and DPM are different which commonly have different characteristic. If the DPC is above the DPM, dampness may move to another place which behind the skirting board. If the DPC is below the DPM, dampness can move through the floor and into the wall.

Dampness penetration through ineffective joint between DPC and DPM (Source: H.John, C.Geoff, 1997)

2.4.2 Wall Cracking

Cracks occurred in most of the building. Wall cracking can be in horizontal crack, vertical crack and diagonal crack. Cracking of wall can be due to variety reasons. Horizontal crack usually occur in any joints of the brickwork and can be found in at least several joints or may be in every joint. Vertical cracks are usually widest at the top, straight and gradually smaller to the bottom part of the building whereas diagonal cracks are often being widest at the foundation and end up at the corner of a building.

Typical cracking in wall

2.4.2.1 Ground movement

Settlement of building classified into two types, uniform settlement and differential settlement. When a building settle equally as whole unit, less damage will be suffer by the building as the settlement is almost the same and less crack cause. But if one side of the building settle more than the other side, these will cause several cracks develop along the wall especially at the opening area such as door and window, this is because openings area are the weakest part of the whole building.

Differential settlement is caused by the movement of soil underneath of the building which groundwater movement and wash away the soil below the foundation, which the foundation no longer able to support the building due to the running sand, local vibration effects and mining subsidence.

2.4.2.2 Sulphate attack

Sulphate attack is a chemical reaction between the sulphate salts in the bricks and portland cement in the mortar and water. The compound that is formed is called calcium sulphoaluminate which can cause considerable expansion, disintegration of mortar joints and distortion of brickwork. The first characteristic sign of sulphate attack is horizontal cracking of bed joint which will lead to expansion of the mortar.

2.4.2.3 Moisture movement

Moisture content of brickwork depends on whether the walls are internal or external. Bricks themselves vary in their ability to absorb moisture, they may absorb enough moisture to cause expansion in which case they would probably also dry very fast and shrink.

Excessive expansion and contraction can produce shrinkage cracks of the brickwork and plaster.

2.4.3 Remedial Works for Wall Defect

Damage by cracks in brickwall is usually not sufficient to affect the stability of a structural. Fine cracks are often ignored, however a wider cracks will generally require repair. It is recommended to cut out and rebond using a mortar similar to that in the existing cracks which passed through bricks or mortar wall.

According to H.J. Eldridge 1976, there is no easy solution since it is not readily possible to remove any of the materials needed for sulphate attack to place, Portland Cement, water or the sulphate. Removal of water is more likely and some slackening of the rate of attack can be obtained by attention being given to the drainage of the surface water around the building. Otherwise it may require piecemeal replacement of the foundations or underpinning.

2.5 Wall Finishes

Introduction

Wall finished is the most outer layer of a wall. The function of wall finishes is to protect the brick wall inside and act as aesthetic of a building. The common wall finishes are painting, plastering, rendering and tiling.

Defects of wall finishes can be caused by environmental factors, faulty design, construction factors and structural factors. Environmental factor is cause by the weathering effect such as wind, rain, and thermal cycle and UV radiation. Furthermore, faulty design is cause by the specification of material such as tile, adhesive or render. A construction factor is caused by the preparation of material and equipment whereas structural factors included spalling, cracking, shrinkage and settlement.

2.5.1 Blistering of Paint

Blister occurs on the surface of the upper layer of paint separates from the lower layer. It can be identified by small to medium size of bubbles form and usually happened in internal and external wall.

The formed of blisters are caused by the moisture in the wall. When moisture penetrates into unsealed walls, water moves through the paint from the wall into the internal room, thus pressure separate the paint from the wall.

On the other hand, excessive humidity can lead to blister or paint bubbles, either during application of paint or after the paint started to dry. Paint blister fill with water absorbed from the moisture in the air. Even recently applied paint that has already dried can bubble from excessive humidity. Poor ventilation contributes to the problem. (L. Philips, 1999)

2.5.2 Paint Peeling

Paint peeling is the most common paint problem. Painting over a poor paint surface such as being dirty, wet or shiny may lead to peeling of paint. Therefore, before applying a new coat onto both old and new building, dust and dirt should remove from the wall first.

In every building, poor maintenance or faulty of design may cause rain water penetrate through the coating of the external wall and cause defect the brick wall. Water which penetrates through the coating will patch in between the painting and internal wall can cause the paintwork or wallpaper to peel off. Water discharge piping should be imply to discharge the rainwater and prevent it from penetrate through the wall.

2.5.3 Remedial Works for Wall Finishes

Paint blister is due to moisture in wall so it is necessary to remove the water in wall. Besides, avoiding from direct sunlight when doing painting work and make sure the paint is completely dry.

Peeling of paint can be repair by repainting. There are few steps of repainting work:

Step 1: Scrape off peeling paint with a paint scraper.

Step 2: Lightly sand down the remaining paint edges to give the area a smooth finish. Wipe off with a clean rag or tack cloth.

Step 3: Apply a coat of primer and allow drying thoroughly.

Step 4: Apply the top coat colour. (Hjohnj, 1999)

2.6 Research Gaps

For this dissertation, the research gap will be the various type of building defects faced by the high rise building. In order to obtain the defects information, case study will be carry out and survey on a few resident within the condominium. The research will then proceed and identify the potential cause of defects. Lastly recommendation and remedy repair work will be determine and suggest in the conclusion.

By carry out this research, apart from identify the gaps, the researcher can learn more about the possible defects, as well as determine the root cause and remedial work. Thus prevent the possibility of defects occur while act as a guidance for further improvement in future.

2.7 Summary

As there were so many building defects occurred, it is necessary to find out the potential defects that might affect to the structural; study into the potential causes thus recommends suitable remedial works onto it. By review to the objectives of the project dissertation, in this chapter, the researcher has studied few types of building defects, identified the potential causes of defects and recommends the potential solutions for the defects.