Construction Techniques For Cantilever Concrete Foundation Wall And Rib Raft Floor System

Building a Cantilever Concrete Foundation Wall

Using your free hand, sketch and label a typical section of a cantilever concrete foundation wall with reinforced concrete slab on ground. Identify the following elements in your diagram:

Figure 1: A wall cross- section (Student own)

Identify five (5) installation processes in the construction of a Rib Raft Floor System

1. Removal of topsoil and leveling: this involves clearing vegetation and grabbing shallow plats from the ground; per the design levels, the ground may also be cut or filled with selected fill material to level and compacted. The ground is then compacted.
2. Blinding: it is the construction of a thin layer of concrete that helps obtain a flat and smoother ground. Aggregates may be used with compaction too.
3. Damp proofing: the ground is covered with a damp proof membrane such as polythene, hot bitumen, mastic, etc.
4. Laying the rib raft ribs. Thin accordance to structural engineer design, the ribs are constructed using various formwork materials such that to form ribs at a given spacing (Guide, 2018)
5. Reinforced concrete. The reinforcement steel is cut, bent, and fixed using binding wires or welding. The concrete is poured, vibrated, and worked to the desired finish (Shabbar, 2010).

1. Moisture absorption: Moisture in timber causes swelling of surfaces when the water occupies the inter grain spaces and cells. Additionally, water above 20% moisture content increases the chances of attack by insects and fungi (Nunes & Cruz, 2018). This lowers the lifespan and aesthetic value of the cladding.
2. Face splitting: timber being a natural material with cells, its properties change with environmental conditions; in cladding, the exposure determines the behavior of wood in swelling in water, shrinking, and cracking when dry. The properties vary from timber to timber, therefore, affecting the choice of timber weatherboard. According to TDCA (2022), splitting involves the method of cladding fixation. Some wood requires specific fixation methods, such as ring shaft nails in softwood to reduce the chances of splitting. Also, some timber needs to be predrilled, with pilot holes as prevention against.
3. Longer cladding timber boards will move more due to thermal movement, and as a result, they require expansion joints or allowances in their construction, while shorter ones may not require such provisions (Brookes & Meijs, 2008).

1. Roof ridges and valleys: where roof planes intersect at hills and valleys, the joints need to be sealed against water ingress. This is essential because the different angles at which the plane meet do not allow for water-tight joints, and flushing is helpful to prevent water (Chudley and Greeno, 2006). 
2. Between roofs and vertical walls: since the walls and ceilings are made using different materials, the joints require flushing. 
3. Sill flashing: in fixing windows and doors, spaces between the frame and wall will likely allow water and airflow; flashing is necessary to seal them.
4. Pipe flashing: where pipes go past walls. Since the drilling is not similar in size and shape of the pipe, the empty spaces are flashed with a filling material. 

 A bond is the pattern in which bricks and blocks are laid. Different types of bonding systems exist in the construction of buildings. Compare with diagrams, three (3) bonding systems used for brick and block walls. (6 marks).

Stretcher bond: the pattern is made of stretchers only where they are joined such that the joint is a third or a quarter of a brick of the preceding layer (The constructor, 2022).

English bond: The pattern is made of both stretchers and headers. The headers are joined such that their joints in their course, are centered within the stretcher blocks.

Explain three (3) purposes that bonding is desired to achieve in brick and block work (3 marks).

1. Bonding forms the aesthetic value, especially when they are not plastered.
2. Bonding determines the strength and stability of a wall. For instance, the English bond is weaker than a stretcher bond (Civiconcepts, 2022).
3. The bonding influences the number of blocks required in a wall. The Flemish bond, for example, requires more blocks than stretcher blocks.

The bricks do not have sufficient strength to carry heavy loads therefore the house is limited to two storeys. The unbonded brick are therefore unsuitable for load bearing walls.

1. Verandah post in the ground: Coat the timber with a waterproof layer of chemicals that seals the timber from water. It is also essential to apply anti-insect on the wood to reduce the risk of attack.
2. Wall framing weather-exposed: Timber exposed to weather requires treatment against water using oil-based paint or chemical treatment that prevents water ingression.
3. Deck piles in-ground: for such permanent use of timber, it should be pressure treated where it is treated with preservative blown through it under high pressure to prevent fungal growth, insect attack, or decay.
4. External wall framing E2/AS1 cavity cladding: The surface should be treated against insect attack and laminated to minimize environmental factors such as rain and sun hence swelling and shrinkage, respectively. They should also be kept dry (Murphy and Frost 2004).

The performance of wall cladding depends on their degree of exposure to rain and weather. There are three known exposure classifications. In your own words, compare using diagrams, two (2) exposure classifications in accordance with NZS3604 (6 marks).  

1. Closed conditions: the conditions are fully protected by cladding and there is minimal exposure to climatic conditions
2. Sheltered conditions: these are conditions that prone to attack by winds and moisture but do not experience direct rainwater.

Figure 2: Exposure conditions (figure 4.3 (b) in New Zealand Standards 3604: 2011)

Design features and the owner’s aesthetic and performance expectations usually have a major influence on the choice of cladding material. However, for each particular building location and style it is also important to consider the cost of the material to be used. Compare two (2) cost implications of timber and brick wall claddings in the construction of small residential buildings (4 marks)

1. Timber cladding is cheaper to construct in cutting and fixing. It uses handy tools such as hand saws and hammers to cut and join timber pieces (Forsythe, 2017). Additionally, timber is less costly to furnish in color and texture. Timber cladding lasts longer (durable) hence lowering the cost for maintenance and reinstallation of new cladding.
2. Brick wall buildings: brick is a poor heat conductor that helps preserve heat in the building cost, lowering the amount required to maintain thermal comfort in the building – cooling and heating expenses. Bricks require little maintenance than painting and maintaining the main structure.

(b) Wall underlay must be installed to form a water-resisting drainage plane that stops water getting to timber frames. Describe three (3) functions of wall underlay according to ES/AS1 (6 marks)

Water lay forms the channel through which the water flows downwards in vertical walls preventing horizontal movement into the timber or insulation.

The water lay gets wet and temporarily stores water before it evaporates. The waterway should be made of water-resistant materials that do not deteriorate with water exposure.

(a) The inclusion of drained and vented cavities will not stop water leaking through a cladding but will help to remove water. Explain two (2) reasons why drained and vented cavity is important during the installation of wall claddings (4 marks)

The vented cavity helps to remove moisture from the wall. Some steam still ingresses into the wall through windows, doors, and other openings, even with cladding. The vapor accumulates in the cavity and is allowed out through vents. Some water may be from the subfloor cavity that gets into the cavity (Gharpedia, 2022).

The cavities improve the comfort of the structures by enhancing thermal insulation sound insulation and enhancing the durability of the internal leaf of the wall.

1. Wall ventilations: should have ventilations spaced along their spans. The ventilations allow for moisture or vapor to escape from the cavity.

Figure 3: A breather membrane within a wall for moisture movement (Property health check, 2022)

1. Flashing: At the joint of the wall to the foundation, joints and wall penetrations should be flashed with sealant to drain away water from the walls.

Figure 4: flushing wall at joint

1. Drain at the cavity: The bottom of a wall with cavity a drain to take away unwanted water within the cavity is installed.

Figure:5  drain at the cavity

1. The external walls of all buildings should be designed and built according to the basic concepts of managing water on walls knows as ‘4Ds’.

1. Deflection: the concept demands that buildings deflect away water from joints and walls, e.g., roof eaves deflect farther away from the wall. Some walls are also non absorbers to keep away moisture from them (Hazleden, 2022). Claddings should also slope away from walls.
2. Drainage: Walls need to have drainage channels that allow unwanted water to get away from the exterior of the walls at the earliest time. This includes drainage structure at the bottom of the wall and flashing in windows, e.g., In window sills.
3. Drying: Walls need to allow air movement through the wall cladding and behind them because evaporation occurs in the drying process.
4. Durability: The cladding system must be of excellent quality and effective in handling water without deteriorating its efficiency.

The 4D concept (Students’s own)

1. Compare two different cladding systems in terms, appearance, availability, durability, construction time and weathertightness (10 marks)

(a) Wall linings should not be fixed in place until the moisture content is at a level recommended by the lining manufacturer or required by NZS3602 (20% max.). Discuss three (3) effects of fixing linings too early in building construction (6 marks).

The construction material may contain water content (over 20%) which deteriorates the lining installed. For instance, walls painted too early peel off or remain wet months-long after painting. Soluble lining materials such as gypsum may dissolve in the moisture of undried walls.

Lining a building too early is fertile ground for the growth of fungi, algae, and insects along the walls. 

The structural stability of the building may be at risk when the lining is done before they develop strength. For instance, uncured mortar in brick walls may be weaker in compressive strength therefore unsuitable to carry lining load at early stages (the United States. Environmental Protection Agency. Indoor Environmental Division, 2013). 

(b) Before fixing internal lining in residential buildings, some final checks are required. Discuss the two (2) checks that should be made (4 marks).

1. The surface texture: the check requires that before lining the surface. To form an even surface, the bumps should be scrapped off and any low points filled with mortar, fillers, etc.
2. Structural soundness. The buildings are checked for cracks and defects in the structural elements before lining. Items found with defects should be repaired before lining. 

Discuss five (5) things that need to be taken into consideration to minimize the penetration of driving rain through windows (10 marks)

1. Flushing: it is sealing with a sealant material any openings between the window frame and wall- in head flashing and jamb flashing.
2. Drain water away from the window by using roof eaves and window sills above the window to direct rain away from the window. The building should also be exteriorly clades to safeguard the structure from the rainwater (United States Environment Protection Authority, 2013).
3. Use of water-resistant materials which are non-porous to allow capillary water movement from the external surface into window surfaces and consequently into the building
4. Foam sealant: they are applicable where the windows have gaps like cracks that allow water ingress and the sealant blocks the water entry.
5. Using weatherstrips: these are tapes fixes along the frames of windows and window frame. The weatherstrips are water absorbers and they soaked water from the window, they could be replaced when soaked.

1. GIB aquiline is water-resistant and prevents water movement from wet areas to structures like walls and floors where water is undesired- in all its forms, such as liquid and vapor. 
2. The GIB is stable in its structural properties and does not bend easily; therefore, they reinforce the strength of the floor to carry finishing materials such as tiles by resisting buckling or bending. 

(b) All new domestic construction must be insulated to comply with the requirements of the Building Code. Discuss three (3) requirements that must be considered during the installation of insulation in residential buildings (6 Marks

1. Leakages: the insulations should be airtight with no weak areas for leakages at all. It is implemented by careful workmanship and constant checks.
2. Energy efficiency: the insulation in residential buildings needs to consider the cost of installing maintaining the insulation and cost effects of insulation on thermal comfort in the buildings.
3. Continuous Insulation: the insulation should be monolithic with most minor breaks and overlaps, often weaknesses. Where not possible, the joints should be flashed to eliminate any loopholes in the insulation.

References Lists

Brookes, A. J., & Meijs, M. (2008). Cladding of buildings. Taylor & Francis.

Civiconcepts, 2022. Types of brick bonds. https://civiconcepts.com/blog/types-of-brick-bonds

Chudley, R. and Greeno, R., 2006. Building construction handbook. Routledge.

Forsythe, P.J., 2007. Improving timber cladding for builders and designers.

Garpedia, 2022. Cavity Wall: Its Purpose, Advantages & Disadvantages.                        

https://gharpedia.com/blog/cavity-wall-advantages-and-disadvantages/

GIB Aqualine, 2007. GIB aqualine Wet area systems https://www.gib.co.nz/assets/Uploads/LiteratureFile/System-Brochures/Aqualine/GIB-Aqualine-Wet-Area-Systems-Brochure-2007.pdf

Guide, D., 2018. + RIBRAFT® X-POD®.

Hazleden, D.G., 2022. A decay risk model for wood frame walls using the 4Ds with special reference to New Zealand. Journal of Building Engineering, p.104070.

Martins, A., Vasconcelos, G. and Costa, A.C., 2017. Brick masonry veneer walls: An overview. Journal of Building Engineering, 9, pp.29-41.

Murphy, C.P. and Frost, G., 2004, November. The New Zealand building code: Changes to timber treatment. In Proceedings of the 38th International Conference of Australia and New Zealand Architectural Science Association, Launceston, Tasmania.

Shabbar, R., Noordin, N., Dawood, E.T. and Sulieman, M.Z., 2010. Comparison between ribbed slab structure using lightweight foam concrete and solid slab structure using normal concrete. J. Concr. Res. Lett, 1, pp.19-34.

TDCA, 2022. Cladding Fixings. https://www.tdca.org.uk/timber-cladding/cladding-fixings/

The Constructor, 2017. Types of bond brick masonry. https://theconstructor.org/building/types-bonds-brick-masonry-flemish-english-wall/11616/

United States. Environmental Protection Agency. Indoor Environmental Division, 2013. Moisture control guidance for building design, construction and maintenance. US Environmental Protection Agency.

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