2012 Higher Level Construction Studies Sample Solutions
Two functional requirements of a dwelling designed for lifetime use, include:
- there is a level approach to the door with a clear level zone 1500mm x 1500mm,
- a 1200mm deep cover or porch provides protection from the weather,
- all door hardware (bell, letter box, handle, lock etc.) is located in a zone between 900mm and 1200mm above ground level to ensure ease of access for a wheelchair user,
- the cill at the entrance has a maximum fifteen degree slope and the threshold height is a maximum of fifteen millimetres - these design features ensure that it is easy for a wheelchair user to gain access to the home.
- an outside light should be provided,
- the door should have a clear width of 800mm,
- there should be a 300mm clear space adjacent to the leading edge of the door.
internal corridor layout:
- the layout of a house should allow everyone to move about easily,
- it should enable people using wheelchairs or walking aids and parents using strollers to manoeuvre easily through doors and to turn around,
- a 900mm wide corridor is recommended,
- the entrance hall should incorporate a 1500mm turning circle.
Accessible shower room - the layout should be as simple as possible to maximise the amount of unobstructed space available to the wheelchair user. The design should provide a clear 1500mm turning circle. There should also be a clear area of 700mm x 1200mm in front of both the toilet and the wash hand basin. Ideally a ‘wet room’ design should be used. Alternatively, a flush finish shower tray can be installed for easy access.
Preferred location for the bathroom items:
- access to the window is unobstructed by furniture, storage cupboards etc.,
- the window should be positioned in the wall so that the bottom of the window is a maximum of 900mm above floor level,
- this will allow the wheelchair user to easily open and close the window.
- the shower area is located in a corner to provide solid wall fixing for grab rails,
- this will also contain water to a single area of the room,
- the bathroom is a wet room where the entire floor area is tiled (with a slip resistant tile),
- the floor is gently sloped (1:60) to a drain in one corner,
- a detachable shower head should be fitted.
- the toilet is located in the corner,
- the centre line of the bowl a distance of 500mm from the adjacent wall to ensure adequate space for transfer from the wheelchair,
- a clear area 700mm by 1200mm should be provided in front of the toilet.
wash hand basin:
- there should be clear knee space under the basin to allow a wheelchair user to wheel right up to the basin,
- a clear zone for approach 700mm by 1200mm should be provided in front of the basin.
- grab rails are installed to facilitate transfer from the wheelchair to the toilet or shower area.
Redesign of the ground floor layout to allow increased penetration of sunlight to the interior:
Upgrading the thermal properties of the external walls:
triple glazed window installed in the insulation layer to reduce thermal bridging at the window wall connection
graphite enhanced EPS external insulation on 225mm concrete external wall - thickness to suit eaves overhang (e.g. 100mm min.)
proprietary render finish
A NSAI (National Standards Authority of Ireland) certified external insulation and finish system would be ideal in this situation. The insulation is bonded to the wall and a proprietary render is applied. Careful detailing is required around window reveals to ensure the insulation is weather tight. Only SEAI (Sustainable Energy Authority of Ireland) registered suppliers and installers should be used. Unlike dry-lining, external insulation poses a much lower risk of interstitial condensation occuring in the wall. The insulation will reduce heat loss and ensure efficient use of energy. This will reduce heating costs and carbon dioxide emissions.
A septic tank is a very basic treatment system that separates solid waste from liquid waste. The solid waste collects in the tank while the liquid waste flows through the tank and into the percolation area where it is allowed to percolate (seep) into the soil.
A septic tank is essentially a settlement chamber, where solid waste is held and later removed for disposal:
- the wastewater effluent enters the tank through a T piece to avoid disturbing the scum layer,
- most of the solid waste settles in the primary settlement chamber,
- the solid waste is broken down to form a sludge by anerobic bacteria,
- the sludge is periodically removed for disposal off-site,
- the liquid flows through to the secondary settlement chamber where small suspended solids settle,
- the liquid then flows out of the tank to the percolation area.
The percolation area is the most important component of a septic tank treatment system because it provides most of the treatment of the wastewater effluent.
The percolation area must be located in an area of the site with a suitable subsoil. A suitable subsoil will hold the water long enough for the contaminants in the wastewater effluent to be broken down by biological, physical and chemical interactions.
The following design criteria must be met:
- slope of percolation trench 1:200
- diameter of pipes 100 mm bore, perforated (typically at 4, 6 and 8 o’clock) smooth wall PVC drainage pipes with perforations of 8mm diameter at about 75mm centres along the pipe,
- width of trench 500mm,
- distance between trenches 2m,
- distance between percolation pipes 2.5m,
- pipe laid in trench filled with 8-32 washed gravel.
Cross section of percolation trench:
- the trench is filled with 300mm of clean gravel,
- the 100mm pipe is laid,
- the trench is backfilled with 150mm of gravel,
- a geotextile is laid above the gravel,
- the trench is backfilled with topsoil.
The gravel ensures that the wastewate effluent can freely drain into the subsoil and also provides a medium for initial treatment of the effluent.
Three reasons why a site may not be suitable, include:
- the subsoil may be too cohesive (e.g. clay) to allow for adequate percolation,
- the site may be too small to meet the criteria for minimum distances from the house,
- the site may be located too close to a watercourse (e.g. stream/ river).
A concrete ground floor designed to meet Passivhaus standard should have a U value of less than 0.15 W/m2K. Most houses built to passive house standard would have a U value of around 0.08 to 0.12W/m2K.
Three features of the design that reflect the sustainable ideal of doing more with less for longer, include:
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,
- this will reduce CO2 emissions and heating 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.
- 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.
The importance of each of the following when designing an environmentally sustainable dwelling house:
orientation of house:
- one facade of the house should have approximately 25% glazing - this facade of the house should be oriented 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 the daylight hours are reduced.
flexibility of design:
- a well designed house will be adaptable to meet the needs of the occupants as their life circumstances change. For example, as a family grows and more bedrooms are needed it should be possible to convert the attic space. Similarly, if an elderly member of the becomes less mobile it should be possible to provide sleeping space on the ground floor level. Open plan living spaces like that shown in the house in part a) allow greater flexibilty in terms of how the space is organised and used.
sourcing of materials:
- locally sourced materials (e.g. stone, timber) should be used - using local materials reduces the amount of transport involved - this reduces the embodied energy of the materials,
- timber should be preferred to concrete because timber has a lower a lower embodied energy and is easily renewed through planting,
- natural materials should be used wherever possible. For example, cellulose (recycled paper) or sheep’s wool insulation can be used. Also, timber (sourced from a managed forest) instead of uPVC windows and doors.
The correct wiring layout for two electrical sockets in a ring mains circuit for a domestic electrical installation:
- a 2.5 mm2 twin and earth double-insulated cable must be used,
- a separate ring main circuit must be provided for every 100m2 of floor area,
- no limit to the number of sockets,
- radial spurs are allowed from 50% of sockets - max 2 sockets per spur.
Safety features to ensure that the circuit is safe for all users:
- each socket is connected to the yellow & green coloured earth cable,
- this cable is connected from the distribution board to a steel bar buried in the ground outside,
- if there is a fault in the circuit the current will take the path of least resistance through the earth cable to the soil outside thereby preventing electric shock.
- a circuit breaker is designed to cut off the supply to the circuit if a certain amount (rating) of current flowing in the circuit is exceeded,
- a ring main circuit would typically have a rating of 35A (amps).
Two strategies that would ensure the economical use of electricity in the home, include:
- a large portion of the electricity used in a typical Irish home is used to provide lighting,
- switching to energy efficient light bulbs (e.g. c.f.l. or l.e.d.) will significantly reduce the amount of energy consumed,
- a 21W compact fluorescent lamp (c.f.l.) will provide a similar level of light to a 100w traditional incandescent lamp,
- installing movement sensors on outdoor lighting will reduce unnecessary energy consumption
- many appliances (e.g. dishwashers, washing machines, etc. ) have a lifespan of over ten years,
- choosing ‘A’ rated appliances will reduce energy consumption over time,
- most appliances consume around 25% when they are in standby mode,
- turning appliances off instead of leaving them in standby mode will reduce energy consumption,
- many appliances (e.g. dishwashers, washing machines, etc. ) have an ‘eco mode’ setting that ensures the appliance uses less energy,
- using ‘eco mode’ whenever possible will reduce energy consumption.
The importance of careful design detailing in improving the airtightness performance of a dwelling house:
Airtightness is a key component of energy efficient home design because houses lose a lot of heat when warm air leaks out of the house. The aim of making a building airtight is to seal the external envelope (floors, walls, roof, windows & doors) to prevent the unwanted movement of air. Achieving a high level of airtightness is important for the energy efficiency of dwellings and the comfort of the people living in the home.
Careful design detailing ensures that there is a continuous airtightness layer throughout the structure. This layer is usually on the inside of the structure. Wall, floor and roof surfaces are reasonably easy to make airtight. The real challenge is the connections between these surfaces.
The key areas where careful design detailing is required for airtightness include:
- the connection between the floor and wall surfaces,
- the wall roof connection,
- the joint where internal and external walls meet,
- the internal reveal where the window/ door frame meets the wall,
- all areas where services (e.g. pipes, cables, etc.) penetrate the structure.
The materials and techniques used vary according to the structural system used.
wall floor connection:
- the timber frame wall is faced with oriented strand board (OSB),
- the OSB is the airtightness layer,
- the board joints are taped to ensure airtightness,
- the board is taped to the concrete floor slab to ensure continuity of airtightness layer.
- the timber frame wall is faced with oriented strand board,
- the board is the airtightness layer,
- the board joints are taped to ensure airtightness,
- a strip of airtightness membrane is taped to the window frame and the OSB surface
- ideally, a certified airtight window should be used.
- a passive house must should have a compact form. A compact form is a simple house design that has a minimum of extensions or additions. Because heat is lost through external surfaces, the greater surface area, the greater the heat loss
- compactness describes the relationship between the surface area of the home and its volume. In passive house design, the goal is to achieve a ratio of 0.7 or less; in other words to have a large volume enclosed by the smallest possible area
- two houses with identical floor areas (and hence volumes, assuming equal heights) can have very different compactness ratios.
- higher density housing like terraced houses and apartments provide much better compactness ratios than individual houses because they have less surfaces exposed to the outdoors.
The key factors necessary to achieve the required indoor environment in a passive house include:
- air temperature (vertical/ horizontal/ place to place)
- vertical: air temperature stratification should not exceed 2°K, (measured from ankles to head when seated),
- horizontal: radiant asymmetry, usually between a window and an opposite wall, should not exceed 4.2°K,
- the temperature difference from place to place should not exceed 0.8°K,
- air movement
- air movement (i.e. draughts) within a dwelling can create a cooling effect on the occupants,
- air velocity should not exceed 0.8m/s,
- air quality
- indoor air must be clean (i.e. free of dust, pollen and other airborne irritants)
- this is achieved by filtering the incoming air with a filter quality of at least F7 (an air filter that has an average efficiency of 80%-90% on particles 0.4 microns),
- relative humidity
- the relative humidity of the indoor air should be in the range 35% to 55%, this is the optimal range;
- to prevent respiratory illnesses and the growth of mould, dust mites and other viruses and bacteria,
- to avoid air that is uncomfortably humid or dry that might cause irritation of the eyes, nasal passages or skin,
- surface temperature
- the temperature of internal surfaces (e.g. walls, ceilings, windows) should not fall below 12.6°C,
- this is to prevent condensation forming on the surface,
There are three criteria that a passive house must meet for energy performance:
- space heating demand ≤ 15 kWh/m2a
- the space heating demand is the energy required to maintain an indoor temperature of 20°C all year round. Space heating refers to the heating of the indoor spaces. It does not include hot water heating or other energy needs.
- heating load ≤ 10 W/m2
- the heating load is the energy required to maintain an indoor temperature of 20°C on a given day. The heating load must not exceed the amount of heat that can be supplied to the house via the fresh air required for good indoor air quality (≤ 10 W/m2).
- When designing a passive house the heat load is calculated on two sample days; a mild overcast day (high temperature, low solar gain), a cold clear day (low temperature, high solar gain). Whichever calculation produces the greater heat load is used when designing the house. Doing this ensures the house will perform adequately in a ‘worst case scenario’. It is usually the mild, overcast day that creates a higher heat load, because on a cold clear day the benefit of solar gain outweighs the drawback of a cold temperature.
- primary energy demand ≤ 120kWh/m2a
- The primary energy demand is the total energy consumed for all requirements (i.e. space heating, water heating, ventilation and electricity). Primary energy is the term used to describe all of the energy required to deliver usable energy to the home. This includes the energy consumed during extraction, conversion, transport and so on. In Ireland the primary energy conversion factor for electricity is currently 2.58. This means that for every unit of electricity energy consumed in the home, 2.58 units of energy have to be produced.
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, warm air.
- 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 from one space to another - this is particularly important for bedrooms.
There are three main requirements that a mhrv system must meet:
- supply requirement:
- 30m3/hour/person of fresh air must be supplied,
- extract requirement:
- kitchen 60m3/hour
- bathroom 40m3/hour
- toilet/ store/ utility/ ensuite 20m3/hour
- air change requirement:
- the system must be balanced for the entire dwelling to ensure that a minimum air change rate of 0.3 air changes per hour is achieved.
Advantages of passive house construction:
- low energy consumption - a typical passive house uses 75% less energy than a similar house built to building regulations standards,
- comfort - passive house construction provides a consistent level of comfort (a constant comfortable temperature of 20°C is maintained all year round),
- economical - a typical passive house significantly cheaper to ‘run’ than a similar house built to building regulations standards,
- reduced environmental impact - lower energy consumption means that passive houses have a much smaller carbon footprint than houses built to building regulations standards.
Disadvantages of passive house construction:
- lack of experienced workforce - a very high level of workmanship is required on site - every member of the construction team must understand what is required to achieve passive house standard and ensure that their work is of the highest possible standard,
- training - tradespeople and designers need to be trained to ensure they are competent to achieve passive house standards.
“A sustainable ethos in building will require the consideration of environmental implications associated with design, construction and operation of buildings and neighbourhoods; and greater emphasis on the improvement of existing buildings. Most buildings are used for several decades, and many survive for centuries. As the community’s principal physical asset, getting good value requires that the building’s full life cycle be considered, avoiding short-sighted attempts to merely minimise initial cost.”
In this excerpt the authors make the following points:
“A sustainable ethos in building will require the consideration of environmental implications associated with design, construction and operation of buildings and neighbourhoods...”
By this they mean that a holistic view of the impact of cresting homes will have to be taken in the future. This will involve taking into account the impact of a home throughout the building’s lifecycle.
- what impact will there be on the natural environment during the construction phase; - for example, will the construction process disturb the natural level of the water table or contribute to pollution of local watercourses,
- what effect will a building have on the environment during its operation; - for example, will the home generate greenhouse gases by burning fossil fuels or will the location of the home contribute to environmental pollution by encouraging home owners to travel exclusively by car.
“...greater emphasis on the improvement of existing buildings”
Here the authors are drawing attention to the fact that there are hundred’s of thousands of dwellings already built in Ireland and that it is vital that these homes are upgraded to reduce their energy consumption.
To do this the following things need to be done:
- retrofitting of insulation in roofs and walls,
- replacement of old draughty windows with modern airtight double or triple glazed units,
- installation of airtightness barriers to reduce heat loss through air movement,
- upgrading of heating systems by installing thermostats and controllers to reduce unnecessary wastage,
- changing old incandescent light bulbs with low energy bulbs.
“As the community’s principal physical asset, getting good value requires that the building’s full life cycle be considered, avoiding short-sighted attempts to merely minimise initial cost.”
The point being made here is that is it often more environmentally sound to think about the long term implications of a decision being made when a home is being designed and built, rather than just focusing on short term cost savings.
- installing a higher quality insulation product in floors, walls and roofs,
- selecting tripled glazed airtight windows over cheaper windows,
- deciding to use natural or recycled materials like sheep’s wool insulation or hemp insulation so that they can be more easily disposed of or reused after the end of the building’s life.
Three guidelines for environmentally sustainable buildings include:
- 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.