2013 Higher Level Construction Studies Sample Solutions
Two safety features:
- minimum handrail heights shown on drawing,
- sphere diameter 100mm should not pass between openings in handrail (i.e. between balusters).
Every construction worker must have completed the Safe Pass training course. This course teaches workers about the basic safety issues they will encounter on the building site. This will help workers to identify the hazards and assess any risks they are exposed to on site. They will also learn about basic emergency procedures and what to do in the event of an accident. Workers who do specialised jobs (e.g. erecting scaffolding) must do additional training. This is called the Construction Skills Certificate Scheme. Only workers who have completed this training can do certain hazardous jobs on site (e.g. crane operation).
It is very important that all workers are aware and observant at all times on site. This begins with risk assessment - it is essential that a risk assessment is carried out on every hazardous task that is completed on site. This will allow for the identification of hazards and the taking of appropriate risk control measures. In addition, a Safe System of Work Plan (SSWP) should be used to ensure that tasks are being carried out in a safe manner. A SSWP should be signed off before work begins. This will help workers to see the risks involved in the work they are about to do and to take the correct safety control measures to prevent an accident.
It is essential that every worker is part of a team on the construction site. Younger workers should be paired with older, more experienced, workers who can 'show them the ropes' and help them to develop safe work practices. Working in teams protects workers because it spreads responsibility for safety across the team. This encourages each member of the team not to let the team down by working unsafely. Many companies offer bonus schemes to workers for 'accident free' days. Teamwork also improves communication and ensures everyone working on the site is aware of any particular hazards on a given day (e.g. a crane being moved or a trench being dug).
Using a ladder on a construction site:
Two possible risks include:
- a worker could fall from the ladder causing injury or death,
- the ladder could fall onto somebody below causing injury or death.
Safety procedures that should be observed include:
The ladder should be corrected secured to the structure/ scaffolding to prevent movement.
Fitting a window in the second storey:
Two possible risks include:
- a worker could fall from the scaffolding causing injury or death,
- tools, equipment or materials could fall from the scaffold causing causing injury or death to someone below.
Safety procedures that should be observed include:
A proper scaffolding should be erected by a CSCS certified worker. The scaffold should not be used until it has been signed off as safe to use by the qualified scaffolder.
When completed the scaffold should have:
- a proper guardrail with a minimum height of 800mm - this will prevent workers falling from a height.
- a fully decked working platform with a toe board - this will prevent tools, equipment and materials from falling onto workers on the ground below.
Three best practice guidelines when using electrical tools:
- cordless power tools should be used whenever possible - this greatly reduces the risk of electrocution,
- all corded power tools should be 110V - this reduces the likelihood of death in the event of a fault/ electrocution,
- all power tools should be double insulated and connected to a power source that is protected by RCD/ ELCB.
The sketch of the rear elevation shows a single storey flat roof extension to the home. The existing back door and small kitchen window above the sink have been replaced by three large glazed folding doors.
The extension extends the full width of the existing home - increasing the area of the ground floor by 50%.
The original ground floor rear wall of the home has been removed - facilitated by the installation of a load-bearing rolled steel joist. A similar joist is used to allow the internal wall A-A to be opened up. This creates a single unified space where the purpose of each space can still be clearly defined by the homeowner.
The use of large glazed folding doors links the interior of the home to the exterior and will provide a pleasant light-filled internal space.
It also allows for optimal solar gain; allowing the sun's heat and light to penetrate deep into the home. This will reduce the energy required to light and heat the home and will, consequently, reduce the carbon output of the home.
This open-plan design maximises the space available for the new kitchen/ dining/ living space. This gives the homeowner greatest flexibility in the layout and use of the available space. It also allows heat generated in the kitchen (e.g. cooking) or in the front space (e.g. stove) to permeate throughout the ground floor of the home.
Two design considerations for siting a solar collector:
- tilt angle - the solar panel should be installed so that it is at the optimum angle for solar irradiation,
- in Ireland, this is between 30 and 40 degrees,
- if the panel is too flat or too vertical the solar energy captured will not be maximised.
- azimuth angle - the horizontal angle measured clockwise from north,
- in Ireland a solar panel should face as close to due south as possible,
- in other words an azimuth angle of 180 degrees,
- this will maximise the solar energy captured by the panel.
In addition, to ensure maximum efficiency, the panel should be installed so as to avoid shading by nearby trees, buildings or other structures.
- wood is a sustainable energy source and is essentially carbon neutral,
- capturing solar energy to heat water reduces the energy demand and carbon emissions of the home.
- zoned heating is of limited practical value in a small building (e.g. a typical home) because the heat energy moves freely throughout the home (i.e. air movement), especially if the heating is on downstairs but off upstairs (i.e. hot air rises),
- wood fuel (e.g. pellets) varies in quality (e.g. moisture content/ calorific value) and must be sourced from a reliable supplier (e.g. WFQA certified supplier) to ensure the stove/ boiler operates optimally.
High performance window U-value data: window frame: 0.18 W/m2K / glazing 0.26 W/m2K
Traditional window U-value data: window frame: 0.32 W/m2K / glazing 5.30 W/m2K
- the high performance insulated window frame is somewhat better than the traditional window frame; it's U-value is 0.14 W/m2K lower,
- the high performance triple glazed unit is significantly better than the single glazing; it's U-value is twenty times lower!
The significant difference in the thermal performance of the windows will have a real impact on the comfort of the occupants of the home. A home with old single glazed windows will experience significant radiant asymmetry; the indoor spaces will be cooler during cold weather; a home with tripled glazed windows will be warmer because the internal temperature of the glazing will be higher.
There are two main impacts that the performance of these windows would have on the environment:
- energy consumption - the tripled glazed units will greatly reduce the amount of energy (i.e. fuel) consumed in the home,
- carbon emissions - the single glazed units will lose a lot of heat leading to more fuel consumption and carbon dioxide emissions.
Window / 350mm cavity wall detail:
Three features that contribute to the house having a low environmental impact:
- solar panels are a sustainable energy source,
- they are used to provide hot water to sinks and baths,
- this reduces fuel consumption, CO2 emissions and heating costs.
Large area of glazing to the facade:
- if this facade is oriented to the south the house will benefit from a high level of solar gain,
- this will reduce the need for fossil fuel based heating and lighting,
- this will reduce CO2 emissions and heating/ lighting costs.
- simple rainwater collectors are installed on the rain water downpipes,
- collecting rainwater from the roof will reduce the household’s demand for water,
- many everyday tasks can be carried out using rainwater (eg. car washing, watering plants),
- water meters are going to be introduced soon.
Modest in scale:
- a general rule of thumb is that there should be 25 to 35 square meters of floor area per person living in the home,
- for first-time buyers (e.g. a couple starting a family) a floor area of 100 to 125 square meters of floor area should suffice,
- such a modest sized house will strike a balance between providing adequate living space and the energy bills that the family have to pay.
Easy to modify:
- the needs of a young family change rapidly over time; as the family grows it is important that the home can be modified to meet the family's needs
- this means that internal walls should, ideally, not be load-bearing so that they can be easily moved and/or removed,
- the pitch of the roof should be steep enough to allow for conversion of the attic space into a living area (e.g. bedroom) if necessary,
- a downstairs living space (e.g. study) should be convertible to a bedroom should the need arise.
Proximity to services:
- it is essential that a young family is not overdependent on their car for everyday essentials,
- for example, services like school, shops, playground and so on should be within walking distance of the home,
- the home should also be close to public transport links (e.g. local bus service),
- proximity to services will reduce the use of the car and encourage sustainable lifestyles that do not contribute to global warming.
Two functional requirements of a foundation suitable for a dwelling:
- safely transfer the actions to the soil: the permanent actions (e.g. building load) and variable actions (e.g. people, furniture) must be safely transmitted to the ground,
- prevent subsidence: the foundation must spread the load evenly across the ground to prevent subsidence.
- strip is typically three times wider than the wall,
- wall is centred on strip,
- depth of strip is equal to width of wall,
- steel reinforcement used to improve tensile strength.
- extends across entire footprint of the building,
- spreads the load over maximum possible area,
- reduces load on subsoil,
- raft is thickened where load is concentrated under external/ internal load-bearing walls.
A strip foundation is suitable for use on a site with a moderately firm clay subsoil.
A strip foundation is preferable because:
- it is more economical being faster and easier to excavate, requiring less labour, will cost less to build,
- it has a lower environmental impact because it uses less materials; concrete and steel have a high embodied energy.
Three best practice guidelines for maximum strength of concrete:
water - cement ratio: this should be between 0.45 and 0.60. If too little water is used the hydration reaction will not be able to fully occur; if too much water is used the evaporation of the extra water will leave air voids in the concrete - both of these factors can affect the strength of the concrete.
compaction: it is essential that the concrete is properly compacted into place to drive out an entrained air bubbles. A 5% volume of trapped air can lead to a 30% decrease in the strength of the hardened concrete.
curing - the concrete must be kept at the correct temperature and humidity for 7 days after placement to ensure the target design strength is achieved. If the concrete freezes or overheats the water will not react properly with the cement (i.e. hydration) and the strength of the hardened concrete will suffer.
Window head: a stepped damp proof course (DPC) will exclude moisture above the window. Wind driven rain will not be able to transfer across the cavity because it would have to flow uphill to move across the DPC.
Window cill: the cill is wrapped in a DPC to prevent moisture soaking through the cill into the structure below/ behind. A second DPC protects the timber frame structure from moisture transfer.
Abutment: a stepped damp proof course combined with a lead flashing is used to ensure moisture is prevented from penetrating the roof wall junction.
Window head: a plastic damp proof course is used in this position. The advantage of this material is that is flexible, durable and easy to fit into place.
Abutment: a plastic damp proof course is used within the wall (i.e. to bridge across the cavity); a lead flashing is used to seal the roof-wall junction. The advantage of lead is that it is malleable - it can be readily shaped to fit the joint and it is durable.
It is essential that moisture does not penetrate to the inner timber frame leaf of the wall structure. While the timber frame structure is protected by a water resistance breather membrane/ wind layer it is still possible that moisture could get through gaps in this weathering layer. If the timber frame structure does become damp rot (fungal attack) or structural degradation could occur. Over time, this could lead to structural failure.
In general, a Passive House should be oriented so that the glazed façade is within 30° of south. This orientation will maximise solar gain as the sun tracks across the sky. This is especially important during the cold winter months when the sun angle is low and daylight hours are reduced.
It is possible to build to the Passive House standard on a site where the ideal orientation is not possible but it usually requires higher levels of insulation and very careful design of the fenestration to ensure maximum solar gain and minimum heat loss through the building fabric.
Thermal mass describes the ability of a material to absorb and store heat. A concrete floor is the most common form of thermal mass in a typical Passive House.
Thermal mass is a useful way of regulating indoor temperature. Solar gain through the windows is absorbed by the concrete floor. During the summer, this helps to stabilise the internal temperature and prevent overheating. During the winter solar energy absorbed by the floor helps to heat the home and reduce energy consumption
Primary energy demand:
Primary energy demand is one of the key energy performance evaluation criteria that a Passive House must meet for certification. Total primary energy demand must not exceed 120kWh/m2a. A typical passive house, built recently, would have a primary energy demand of between 60 to 70kWh/m2a.
How a mechanical heat recovery ventilation system works:
- Mechanical ventilation heat recovery is used in passive houses to provide a continuous controlled supply of fresh, clean air. This ensures that the internal temperature of the home is maintained at 20°C all year round.
- Moist, warm air (‘extract air’) is extracted from the kitchen, bathroom and utility room and drawn through a filter into the mhrv unit. At the same time, ‘outdoor air’ is drawn through a separate filter into the MHRV unit. The outdoor air passes through a fine filter to ensure dust, pollen and other contaminants are removed from the air - this provides better air quality than simply opening a window.
- In the MHRV unit, the ‘extract air’ and the ‘outdoor air’ do not mix - instead, they pass through a heat exchange unit. This unit is made up of a number of very thin metal or plastic plates. The heat in the extract air heats one side of each plate. The outdoor air passes on the other side of the plate and absorbs this heat energy. The outdoor is now warm and filtered and is now called ‘supply air’. The ‘supply air’ is pumped to the living spaces (‘supply zones’).
- During cold weather a post heater is used to raise the temperature of the incoming air to ensure a constant comfortable temperature of 20°C is maintained in the home at all times. During warm weather a ‘summer bypass’ is used to bypass the heat exchanger so the supply air does not cause overheating.
- A sound attenuator is used to ensure that noise does not travel between the bedroom and the dining room.
Two design considerations for location of the MHRV unit:
- energy conservation: ideally the MHRV unit should be located within the thermal envelope of the dwelling - this reduces the likelihood of heat loss through the supply air ducting from the MHRV unit to the living spaces, similarly, the unit should be located so as to minimise the length of ducts - supply and extract rooms should be grouped - for example, in the house shown in part (b) the extract rooms are grouped,
- maintenance: the unit should be located in an accessible area to facilitate routine maintenance - for example, the exhaust air filter and the outdoor air filter would typically need to be replaced annually. In major cities where air quality is poorer the filters may need to be replaced every few months,
- noise: the MHRV unit should be located where the noise generated by the fans will cause a disturbance - the Passive House standard requires that the sound produced by the MHRV unit does exceed 25 decibels,
- aesthetics: the MHRV unit is an appliance; like a washing machine or tumble dryer - it may be preferable to locate it in a utility room or within a cabinet in the kitchen.
“a large house built to passive house standards but remote from schools, shops or workplace”
Here the author is drawing attention to the contradiction inherent in building an energy efficient home in a rural area. While an energy efficient home will reduce the energy consumption and associated carbon emissions of the home, these benefits are cancelled out by the energy consumption and carbon emissions associated with excessive reliance on cars to get to and from the home to everyday facilities like schools and shops. I think the main point being made here is that sustainable living is about seeing life ‘in the round’ and not just measuring the energy performance of the home in isolation.
“the reuse of existing space”
This is a reference to the need to ensure efficient use of land resources. When the need for new homes arises the first reaction should not be to build on a green-field site. Instead we should be looking at brown-field sites in town and cities that are available for redevelopment. This will ensure the long-term viability of our towns and cities by avoiding the hollowing out of urban areas (i.e. the doughnut effect).
“appropriateness of scale”
This is a comment on the increasing size of new homes being built. The size of the average ‘starter’ home has grown. The Sustainable Energy Authority of Ireland reports that average floor areas of new houses grew from 130 square metres in 1990 to 190 square metres in 2011 (an increase of 46%). These new homes contain the same average number of people - family sizes haven’t grown. While the energy performance of homes has improved over this period, this has effectively been cancelled out by the increase in house sizes. So, the amount of energy being consumed overall isn’t falling. In future, it will be essential that new homes are designed to a more modest scale that meets the actual everyday needs of people. This will reduce the energy consumed and the carbon emissions produced.
Three guidelines to promote environmentally sustainable housing in Ireland:
- use natural construction materials:
- natural materials (e.g. stone, timber) should be used - natural materials are produced using cleaner processes that have a lower impact on the environment compared to unnatural alternatives - e.g. timber windows versus uPVC windows,
- use locally sourced construction materials:
- using local materials reduces the amount of transport involved, transporting heavy materials like roofing slate from China consumes huge amounts of fuel and causes greenhouse gas emissions, because they do not have to travel far, locally sourced materials have lower levels embodied energy.
- design houses to consume less energy:
- the building regulations is a minimum standard, if housing is to become environmentally sustainable in the future the standard of design will have to be much higher
- building houses to the Passive House standard will significantly reduce the energy consumption and the impact on the environment because it no longer be necessary to burn fossil fuels to create a comfortable indoor environment.