2015 Higher Level Sample Solutions
Note: the timber frame inner leaf in this drawing is 150mm wide. The correct solution would show this as 200mm wide. Also a 60mm service cavity should be added.
Ease of access for everyone is ensured by:
- a level transition from the footpath outside to finished floor level inside the home
- 15 degree maximum slope on the concrete sill (item #4)
- maximum 15mm high door threshold (item #57).
The primary functions of an external wall are to provide shelter from the weather and to support the roof; it should:
- resist the actions of the weather (i.e. sun, wind, rain etc.),
- prevent heat loss from inside to outside,
- support the loads from the roof,
- support the loads from upper floors.
Three external wall types:
Full fill wide cavity masonry wall:
- cavity wall construction is the 'norm' in Ireland and is familiar to trades people,
- the materials used in this wall are similar to those used in typical cavity walls so they are readily available.
- a proprietary low conductivity wall tie (e.g. teplo tie) should be used - some builders may not be familiar with these,
- the increased cavity width means a high level of workmanship is required to ensure the wall is correctly built and the insulation is correctly installed so that it fully fills the cavity.
Externally insulated single leaf 'block on flat' masonry wall:
- quick and easy to build,
- can support heavier loads (e.g. concrete upper floors).
- there is a potential for interstitial condensation (dampness) in the masonry if the external insulation is reduced or removed for some reason.
Recommendation: I would recommend the single leaf externally insulated wall. This wall is more sustainable: it uses less blocks, it is cheaper and faster to build. It can support greater loads (i.e. permanent actions of floors/ roof). The 300mm external insulation ensures the entire structure is thermal bridge free; for example, the insulation can be dressed up over the window and door frames to reduce thermal bridging.
Building a single storey extension:
- the solar heat gained into the extension will be transferred to the rest of the home by convection of the warm air,
- because it is easier to access the new space from the existing dwelling it will be used more - making better use of the energy required to make it a comfortable indoor space.
- the extension makes the building very deep along the North-South axis - it will mean that the opportunity to open up the floor plan to allow heat/ light into the front (living) room will be lost,
- the outdoor garden area immediately behind the home, which has excellent solar exposure, is lost - this reduces the amenity value of the garden.
Building a detached free-standing space:
- it will be a quiet, peaceful separate space - ideal for use as a study,
- the construction process will not disrupt life in the home.
- as a stand-alone building, it will require more materials to construct,
- depending on the roof design, it will cast a shadow...
- on the remaining garden area (between the house and the study) making it a less enjoyable/useful outdoor space
- on the house in winter - reducing natural light to the kitchen.
Option B: a free-standing space (i.e. garden room) in the garden:
The glazed door and the windows on the north and south facades of the garden room provide a visual link to the garden. The south facing windows are higher to prevent direct glare on the occupant sitting at the desk during the day. The north facing windows are lower to provide a view of the garden which continues to the north (break line shown in plan above).
Advantages of designing a space that links with the garden:
increased sense of wellbeing from closer contact with nature,
engaging the senses – sound, touch, sight – full enjoyment from location
health benefits of ongoing exposure to natural light
encourages greater use of the garden.
The importance of respect for local character in the eco-refurbishment of an old house built in the vernacular tradition:
Every town has buildings of local interest, which are important elements of the heritage of their area. Most heritage buildings are significant because they represent the centre of human activities, a connection between people and places and an expression of local customs and traditions. The vernacular style reflects the traditions of the local area; the typical building forms, the materials used, the palette of colours and so on. When upgrading an old house built in the vernacular tradition it is important to be sensitive to these issues and retain the essence of the building's character so that its contribution to the architectural streetscape can continue.
The importance of breathable structure in the eco-refurbishment of an old house built in the vernacular tradition:
- Most heritage buildings have solid masonry walls comprising stone or brick bonded using a lime based mortar. This combination allows the wall to absorb and release moisture in response to environmental conditions (e.g. absorb and release rain water). When upgrading an old house built like this it is essential that breathable materials are used to ensure that the wall doesn't become damp. For example, cement based mortar/ render should never be used because it is not breathable and will cause an old wall to retain moisture and become damp leading to mould growth and possible structural degradation.
Upgrading an un-insulated traditional cut roof with natural slates:
- carefully remove existing roof slates and battens
- inspect roof joists for decay
- replace any decayed or damaged joists with treated timber
- install breathable roofing underlay
- install battens and counter battens
- reinstall original roof slates
- remove existing plaster (if present)
- install breathable quilted insulation
- install a breathable airtightness membrane to underside of roof surface and seal to wall
- install an insulated service cavity
- install plasterboard and finish.
Upgrading an un-insulated suspended timber floor :
- carefully remove existing floorboards
- inspect floor joists for decay
- replace any decayed or damaged joists with treated timber
- install netting between joists to support insulation
- install quilted insulation
- install a breathable airtightness membrane over entire floor surface and seal to wall
- reinstall the original floorboards.
The new house (U-value 0.12 W/m2K):
The building regulations house with a U-value of 0.21W/m2K:
To prevent the ingress of water at the window head in the wall of the new house... a stepped damp proof course (#13) is installed in the wall as shown.
The stepped doc prevents water crossing the cavity, because any water would have to flow up the surface of the doc and this is not possible.
Also, the window frame is usually sealed to the external wall with a flexible silicone sealant.
A 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, providing heat and natural light,
- this will reduce the need for fossil fuel (e.g.oil, gas, coal, peat) 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 (e.g. car washing, watering plants),
- reduces the costs associated with water use (i.e. metering).
- solar panels are a sustainable energy source,
- the solar water panels (on the right) are used to provide hot water to sinks and bath,
- the solar electricity (photovoltaic) panels on the left are used to generate electricity,
- these panels reduce energy consumption from unsustainable sources (e.g.oil, gas, coal, peat) and also reduce CO2 emissions and heating costs.
Compact form - heat is lost through external surfaces including the ground floor, the walls and the roof. The greater the surface area, the greater the heat loss. A simple house design that has a minimum of extensions or additions works best.
For example, having lots of dormer windows increases the surface area of the roof - this increases the amount of heat loss.
Flexible design - homes should be designed so that they are able to grow with the people living in them. As families increase in size or as people get older their needs change; the home should be able to respond positively to meet these changing needs.
For example, if the homeowner decides to work from home, it should be possible to extend the house or convert the roof space to create an office. So, it is important when designing a home to include a generous roof pitch so the attic space can be converted in the future if required.
The European Union Directive (2010/31/EU) on the energy performance of buildings requires that by 2021 all new buildings are ‘nearly zero-energy buildings’.
A nearly zero-energy building is defined in the directive as ‘a building that has a very high energy performance’ and states that ‘the very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby’.
This is achieved in two simple steps:
- reducing the energy demand of the building by designing better buildings and building better (more insulation/ more airtight),
- using solar panels (or other micro generation technology) to generate most of the energy required by the building.
Importance of designing NZEB for the 21st century:
- approximately one quarter of Ireland's energy is consumed by the residential sector,
- approximately one quarter of Ireland's carbon emissions are caused by the residential sector,
- the NZEB standard requires all buildings to be designed and built to a higher standard for energy performance,
this means every new building will be better insulated and require less energy to provide a comfortable indoor environment,designing and building homes to meet the NZEB standard will to reduce the energy demand and carbon emissions of the residential sector.
The insulation is installed on the slope. The roofing underlay (green) is breathable. An intelligent airtightness membrane (blue) is installed to the underside of the rafter. The roof structure is breathable. Ventilation is provided to the outer surface of the roofing underlay by installing a counter batten along the length of each joist. This allows air to circulate between the outer surface of the underlay and the underside of the slates.
The correct tilt angle (approximately 30° - 40°) is determined by the latitude of the home/ roof. The correct azimuth angle (approximately 178° - 182° (i.e. due south)) is determined by the site's longitude. However, these angles are usually predetermined by the slope and orientation of the roof onto which the panels are installed.... unless the panel is installed on the ground or a flat roof in which case a supporting frame is used and the optimal angle can be used.
Location of chimney/ fireplace:
locate centrally and/ or on an internal wall - high thermal mass of chimney breast allows heat to be stored and radiated back to adjoining spaces; works best in an open-plan layout,
compact design – locate chimney, hot press and bathroom close together.
Location of hot press/ storage cylinder:
locate hot water storage cylinder as close to the boiler as possible,
short pipe runs means less heat loss from hot pipes to surrounding air,
ensures quick heat up time – flow and return as short as possible.
A wide cavity full-fill insulation wall with thermal bridge free junctions:
At each junction, there is unbroken continuity of the thermal (insulation) layer. This ensures a thermal bridge free junction and prevents heat loss.
A thermal bridge occurs when the insulation layer is interrupted or ‘bridged’ by a material of higher thermal conductivity. In older houses thermal bridges have a negligible impact on the overall energy performance of the house because the main structural elements (i.e. walls, floors, roof) are poorly insulated. However, in energy efficient houses (e.g. passive houses) the impact of thermal bridges is very significant and can lead to significant heat losses.
Thermal bridges are usually a result of the building’s design: it’s structural design or geometry:
- construction thermal bridge - occurs where the structure penetrates the thermal layer offering a ‘path of least resistance’ to the flow of heat,
- geometric thermal bridge - occurs where the shape of the structure (e.g. a corner) reduces the amount of insulation in the external envelope. This usually results in a change in insulation thickness and is common at junctions (e.g. wall - floor junctions, wall-roof junctions, and around windows and doors.
Airtight building envelope:
Making a building airtight requires a contiguous airtight layer in the external envelope. The airtightness layer is usually on the inside of the envelope. It is absolutely essential that the airtightness layer is unbroken. This means that every junction (e.g. floor - wall, window - wall, wall - ceiling, etc.) is sealed to prevent air movement. Any penetration of the envelope must also be carefully sealed. For example, where drainage pipes for sinks and toilets and electrical cables pass through the building fabric the airtightness layer must be sealed to prevent air movement.
Space heating demand:
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 rooms - it does not include hot water heating or other energy needs. In the sketch (above) the radiator represents the space heating demand" - the extra heat energy that must be added to the home to bring the system into balance - in other words the extra heat needed (on the left) to balance the heat losses (on the right).
Thermal mass is the term used to describe the ability of a material to absorb and storage thermal (heat) energy. Heavy materials like concrete, stone and water have a high thermal mass. In this example (above) the concrete floor slab is acting as a thermal store... the heat energy from the sun is stored during the day and released later in the evening when the indoor and outdoor air temperatures drop.
Buildings that are designed to harness solar energy have the potential to overheat in the summer. Shading devices are used to control solar gain through south facing glazing during the summer. Permanent shading devices (e.g. brise soleil) that do not require adjustment by the occupant are preferable to those that do (e.g. shutters).
The extent of the shading required is determined by the building geometry and fenestration; tall windows/ patio doors will require a deeper shading device to provide shading all the way to the ground and so ensure solar gain is controlled in the summer months.