Lakeside House, North Manly

A Passive House in an Active Environment

Introduction

rsz_1hazell_house_side_viewAs land becomes scarcer in our major and regional cities, lots with ideal solar access will become the exception rather than the norm. We must be able to design passive solarbuildings on these lots, to ensure they are naturally comfortable and have minimal negative environmental impacts. This project stands on a coastal site with less than ideal orientation, and which is flood affected - these characteristics combined to impose difficulties which required some unusual responses. But as time goes by, many of these design responses will become commonplace.

The house was designed to reflect a timeless Australian style, at home in both the climate, and the culture of the Australasian region. It is essentially a timber framed weatherboard building with a corrugated steel roof, and has enclosed elevated concrete ground floor, with some internal brick walls for added thermal mass.

The client’s brief was for a simple unpretentious building that was honest to its intended function. Unlike most project homes which are styled to boast and shout about the owner’s supposed class and success in the world, this was to be a home which simply went about its job of nurturing life without pomposity or falsehood.

The Site

The new house was designed for a lot with its long axis 45° west of north, which made achieving perfect solar access challenging. The layout was arranged to share winter solar access to the north, and the view of the lagoon to the west and south. Bringing the lounge and the study forward from the garage, enabled the house to be orientated withan “average to north”, since true north was 45° off either axis. The site is mainly level.
Plants were selected for the landscape design which require virtually no additional watering (being endemic to the locality) and site porosity was maximised. To reduce the amount of the site covered by driveway, a turntable was used to eliminate a whole turning area.

Material choices

The selection of materials and construction systems were based on a balance of thermal performance, embodied energy, operational energy, and minimal construction cost.
Envirotecture policy is to create as much house as possible for minimum dollars, but unlike our traditional project home colleagues, we do not put invoice price at the top of the list - it is balanced against the other longer term impacts. The final choice came downto high mass living areas, with low mass elsewhere, and as much high performance insulation as possible.

Timber

This material is always at the top of the list for sustainable building design - it is renewable, has low embodied energy, can be constructed into highly insulated envelopes, and is very flexible. It is also very economical. Timber wall framing was the default on this project, with some high mass internal walls. The 1st floor bedrooms havea timber floor, using Hyne I-Beams for long stiff spans with minimal timber consumption.
External decking was LOSP treated hoop pine, which is a significant improvement invisual character and style, and dimensional stability, over radiata, in exposed situations.
Rainforest species were specifically prohibited from the site, and no old growth local hardwoods were used. The ground floor living areas have bamboo direct fixed to the concrete slab - this is dense enough to provide a thermal connection to the slab, and issustainably harvested, and is also extremely hard wearing.

Floor

rsz_hero_shot_hazell_houseBeing in a flood basin means that the local council have minimum floor levels approximately 1m above natural ground. Additionally the land is compacted swamp,and geotechnical investigation showed that any conventional slab or footing system would need 20m deep piers. To avoid deep piering and yet still achieve thermal mass in the floors, a truly floating slab was designed, comprised of two slabs 900 mm apart and parallel to each other, linked into a bi-directional girder by reinforced concrete blockpiers at spacings of approximately 2m. This ultra stiff 900 deep raft sits on natural ground with no deep beams in the lower slab - it is in fact like a gigantic elephant’s foot. The loadings are so low it literally floats across the top of the swampy layers of peat below ground.

Decks

The house has two decks, one being a large outdoor living area for the family on the ground floor, and the other a private retreat off the main bedroom on the 1st floor. Both decks allow views south to the lagoon, and to benefit from cool southerly breezes straight off the water in summer.

Flood levels

Council required than any development in the flood basin not reduce the available volume - a wise means of ensuring that flood levels do not creep higher and higher as time goes by. To this end they require that all subfloors be open to allow the ingress and egress of floodwaters. However, open subfloors are not good at maintaining constant temperatures in a floor, even with a suspended concrete slab. To enclose the subfloor, the team at Envirotecture and NB Consulting Engineers, used data suppliedby Manly Hydraulic Laboratory to demonstrate that floodwaters could be transferred in and out of the subfloor without it actually being open in the conventional sense. The subfloor walls are sealed and insulated, allowing thermal connectivity between upper floor level slab with lower ground level slab, and providing most of the thermal comfortthat comes with conventional slab on ground construction in this climate zone. To allow the flow of floodwater, an external grated sump at ground level is linked to another sump inside the subfloor slab, allowing the rising water in and out of the subfloor space, without disturbing the flow of the water or the connection of thermal mass from the earth’s crust to the house.

Thermal mass

Thermal mass is provided by any substance with the ability to absorb and redistribute warmth or coolth. Water has high thermal mass, as does concrete, brick and stone, andceramic tiles etc. Passive design uses thermal mass to advantage by allowing internal spaces to be exposed to it, thus throwing heat off to it when conditions are warm, and borrowing heat from it when things cool down. As well as the concrete slab on theground floor, additional thermal mass has been provided here by brick internal spinewalls. These were constructed from Austral’s SlickBrick for its strength and economy, and its 90mm thickness - consistent with the thickness of the adjacent timber studwork. The brick work was rendered with 2 coat white set plaster - the building’s only real traditional finish, which blends perfectly with the humble plasterboard used elsewhere.

Windows

Throughout the house, a combination of casement and awning windows have been used to achieve effective cross ventilation. Casement windows have been used on the north west, north east and south west sides of the house to catch the prevailing breezes. While on the south east facing walls, awnings were used to increase options for breezes during rain. Windows in the office, living and dining areas extend to floor level.
Not only does this allow more light into the rooms but also maximises the amount of insolation to the thermal mass in the walls and floor. All windows and external doors have double seals to eliminate air leakage. External glazing is single clear glass, rather than double glazed, which would have improved thermal comfort but was eliminated by budget constraints. The coastal climate removes most of the extremes from the annual temperature range, which allows this compromise not to cause much detriment to the performance of the house. Had the site been just a few kilometres inland this compromise would have had more noticeable negative impacts.

Ventilation

The floorplan has been designed to allow cross ventilation to every habitable space.
There are almost constant cooling breezes available to the site, and full advantage has been taken of these. Surrounding buildings were taken into account when breeze paths were determined, so as to reduce the amount of noise carried into the house, especially at night. One advantageous by-product of the increasing building density of the neighbourhood was the construction of a row of townhouses between this site and a busy main road, effectively providing a sound barrier. Fanlights have been installed above all internal doors which can be opened or closed when required, allowing privacy and ventilation at the same time. Ceiling fans have been used extensively for highly effective low energy cooling.

Shading

1 metre wide eaves are used throughout, except for the south side nearer side boundaries. These large eaves help keep the summer sun out during the warmermonths, while still allowing the lower winter sun to penetrate the house and warm the thermal mass. This enables the most basic tenet of passive solar design to be achieved despite the difficult orientation - it’s the secret of making the house warmer in winter and cooler in summer. Roller awning blinds are used on the main deck to keep low afternoon summer sun at bay.

Skylight

A skylight has been installed in the walk-in robe to allowing natural light into the room.
This not only makes it more convenient, it is a natural way of discouraging silverfish, which are photo phobic. The skylight has a double glazed timber frame, ‘low e’ coating and anargon filled cavity. The 'low e' coating minimises radiant heat flow through glass, while the argon filled cavity acts as a barrier to conducted heat, and prevents condensation. This makes the skylight an effective light source without unduly affecting the temperature ofthe room.

T3 energy system

The roof has been fitted with a hybrid photovoltaic - space heating - water heating system. The roof-integrated panel array combines PV panels with a unique system of reclaiming the heat given off them which is otherwise wasted. It produces a peak output of nearly a kilowatt, and at the same time sends heat to either the house directly, or to a heat storage bank mounted high in the garage. In this bank a series of ‘heat beads’ (“phase change medium”) can store the heat for later distribution through insulated ducting to the living areas. The system is controlled by a unique computer chip mounted in a simple to use panel in the Lounge Room. The system also contains the primary hot water absorption panels. The hot water tank is located in the roof space, close to the collectors, and has an instantaneous gas back-up.

Insulation

Insulation is a big part of achieving an effective and efficient habitation. A conventional “anticon” blanket has been laid directly below the roofing sheets. Between the rafters, a double layer of Concertina Foil Batts with an air gap of around 20 mm between each, were installed to resist radiant heat flows. Heat flow in far exceeded heat flow out due to the immediate coastal climate and low altitude, therefore foil is the most appropriate thermal barrier. For the walls, a baggy foil sarking was placed between the weatherboards and the timber framing - this fixed with definite bagging or pushing in between studs, thus creating an extra air gap between it and the external cladding. An extra single layer of double sided foil was placed in the centre of the stud frame, throughout the walls. Where 1st floor walls are enclosed by ground floor roof, a further double layer of foil was installed to the wall frames.

Water

The house harvests its own water supply, storing roof water in a 26,000 litre concrete tank built under the garage floor. Because rainwater is always cold, it is important that it not be stored in close contact with living areas. The tank was constructed like a swimming pool with a concrete lid on it. The access hatch is sealed, and the owner has constructed a simple float on the garage wall to indicate level. A small high efficiency 240 volt pump supplies the house at a constant pressure. Minimal filtration is required on this site, due to the clean atmospheric conditions and lack of overhanging trees. Town water is available as a back up. Water efficient taps and appliances have been fitted, including a frontloading washing machine which delivers superior results to most top loaders.

Fridge venting

Apart from air conditioners and electric storage water heaters (thankfully missing from this project), fridges are the biggest consumers of power in a normal house. To improve the efficiency of the fridge here we included direct venting from the clean subfloor. This is via simple hole in the floor, fitted with vermin-proof mesh, and an outlet above the overhead cupboards to the external wall. It has been estimated that venting fridges inthis way improves their efficiency by up to 25%.

Coda

The owners are very happy with the house, and how it relaxes in the environment and the climate. With a gross floor area of 270 sq.m it is not small, but still bucks the trend toward big houses. The design response to the site issues is typical of how the building industry will have to intelligently deal with a changing environment. If the NSW Government pushes ahead with “type approval” of mass housing designs, we will need to be very sure they can be tuned to respond to demanding sites, or we will have allowed the status quo to regress, not progress.

Dick Clarke is the principal of Envirotecture, is Past President, and Director ofSustainability with the Building Designers Association of NSW.

Building Notes:

The Site

  • long axis 45° west of north: imperfect solar access challenging.
  • layout arranged to share winter solar access to the north, and the view of the lagoon 
    to the west and south.
  • orientated with an “average to north”.
  • landscape designed for little additional watering and site porosity maximised.
  • turntable used to eliminate a whole turning area, minimise site coverage.

Material choices, materials and construction systems selected on balance of:

  • thermal performance,
  • embodied energy,
  • operational energy,
  • optimal construction cost.
  • construction cost balanced against other longer term costs and impacts.
  • high mass living areas, low mass elsewhere, and as much high performance insulation 
    as possible.
  • major windows & doors would have performed better if double glazed. 
    Timber

Always at the top of the list for sustainable building design:

  • renewable,
  • low embodied energy,
  • can be constructed into highly insulated envelopes,
  • very flexible,
  • economical.
  • timber wall framing is the default,
  • some high mass internal walls.
  • 1st floor bedrooms have a timber floor, using Hyne I-Beams for long stiff spans with
    minimal timber consumption.
  • external decking is LOSP treated hoop pine,
  • better visual character and style, and dimensional stability than radiata.
  • rainforest species specifically prohibited from the site,
  • no old growth local hardwoods were used.
  • ground floor living areas have bamboo direct fixed to the concrete slab
  • dense enough to provide a thermal connection to the slab,
  • sustainably harvested,
  • hard wearing.  

Floor

  • flood basin: council minimum floor levels approximately 1m above natural ground.
  • site is compacted swamp: geotechnical investigation showed conventional slab or footing system would need 20m deep piers.
  • to avoid deep piering and yet still achieve thermal mass in the floors, a truly floating slab was designed:
  • comprised of two slabs c.900 mm apart and parallel to each other,
  • linked into a bi-directional girder by reinforced concrete block piers at spacings 
    of approximately 2m.
  • ultra stiff 900 deep raft sits on natural ground with no deep beams in the 
    lower slab - like a giant elephant’s foot.
  • loadings are so low it literally floats across the top of the swampy layers of peat below ground.
  • insulated subfloor walls isolate the airspace between slabs, provide thermal connection to ground temperatures (good in Sydney).
  • still allows flood water to come and go under the house.

Flood levels - council required that the house not reduce the available volume of floodwater

  • a wise means of ensuring that flood levels do not creep higher and higher as development increases and displaces the volume of the basin.
  • require that all subfloors be open to allow the ingress and egress of floodwaters.
  • but open subfloors do not maintain constant temperatures in a floor, even with a 
    suspended concrete slab.
  • to enclose the subfloor, Envirotecture and NB Consulting Engineers used 
    data from Manly Hydraulic Laboratory to show floodwaters could move in and out of an enclosed subfloor.
  • subfloor walls are sealed and insulated,
  • allowing thermal connectivity between upper floor level slab with lowerground level slab,
  • providing most of the thermal comfort.
  • to allow the flow of floodwater, an external/internal sumps are linked,
  • allows the rising water in and out of the subfloor space,
  • does not disturb the flow of the water or the connection of thermal mass from 
    earth to house.

Thermal mass

  • provided by any substance that can absorb and redistribute warmth or coolth.
  • additional thermal mass provided by brick internal spine walls.
  • constructed from Austral SlickBrick:
  • strength and economy,
  • 90mm thickness consistent with the adjacent timber stud walls.
  • rendered with 2 coat white set plaster.

Windows

  • combination of casement and awning windows.
  • casement on the north west, north east and south west sides of the house to catch the prevailing breezes.
  • on the south east side, awnings are used to increase options for breezes during rain.
  • windows in the office, living and dining areas extend to floor level.
  • allows more light into the rooms
  • maximises the amount of insulation to the thermal mass in walls and floor.
  • all windows and external doors have double seals to eliminate air leakage.
  • external glazing is single clear glass, rather than double glazed,
  • would have improved thermal comfort
  • but was eliminated by budget constraints,
  • relatively cheaper now.

Ventilation

  • floorplan designed to allow cross ventilation to every habitable space.
  • consistent cooling breezes available to the site.
  • surrounding buildings were taken into account when breeze paths determined,
  • to reduce the noise carried into the house, especially at night.
  • fanlights above internal doors allow privacy and ventilation at the same time.
  • ceiling fans used for effective low energy cooling.

Shading

  • 1 metre wide eaves used throughout
  • except for the south side nearer side boundaries
  • and Northern corners to allow correct average shading angles.
  • eaves help keep high summer sun out during the warmer months,
  • still allow lower winter sun to penetrate the house and warm the thermal mass.
  • roller awning blinds on main deck to keep low afternoon summer sun at bay.

Insulation

  • conventional “anticon” blanket directly under roofing.
  • between rafters two layers of “Concertina Foil Batts” with an air gap of 20mm between 
    each,
  • to resist radiant heat flows.
  • walls have foil sarking between weather boards and the timber framing
  • this fixed with definite bagging in between studs, creating an extra air gap.
  • extra single layer of double sided foil placed in the centre of the stud frame.
  • where 1st floor walls are enclosed by ground floor roof, a 2nd layer of foil in the wall
    frames.

Water

  • harvests its own water supply in a 26,000 litre concrete tank under the garage floor.
  • rainwater is always cold, so must not be in close contact with living areas.
  • tank constructed like a swimming pool with a concrete lid on it.
  • access hatch is sealed,
  • a simple float on the garage wall indicates water level.
  • small high efficiency 240 volt pump supplies the house at a constant pressure.
  • minimal filtration required on this site, due to clean atmosphere and no overhanging
    trees.
  • town water is available as a back up.
  • water efficient taps and appliances have been fitted.

Fridge venting

  • fridges are big consumers of power in a normal house.
  • improved efficiency by direct venting from the clean subfloor.
  • via simple hole in the floor, fitted with vermin-proof mesh
  • and outlet above the overhead cupboards to the external wall
  • estimated that this improves fridge efficiency by up to 25%.

 

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