Building Design
Processes
From the outset the owner sought to build a ‘no frills’ home that optimized passive solar performance whilst also being cost-effective. The home is located in a cold climate where home heating amounts to on average 60% of annual energy use so substantial financial and comfort benefits were anticipated.
The owner undertook substantial market research when developing the house concept and spoke with many project home suppliers. The choice to build a project home was made to try and reduce construction and design costs. Having determined the style of house preferred the owner then worked with the supplier, Seedab Homes, to modify an existing project home design to their specific needs.
As the original project home design substantially met the owners requirements all cost increases from the base project home price arose from selecting more expensive fittings (e.g. windows) and increasing floor area. At the time of construction total $ per m2 for construction were comparable to the cost of standard brick veneer for a similar home design.
The house was built on a raft slab using internal tilt slab concrete walls with an outer brick skin. The 70mm wall cavity was insulated with 50mm rigid polystyrene and the slab edge also insulated with 30mm rigid polystyrene to the depth of the slab edge . This construction method performs substantially the same as insulated double brick yet was much cheaper to build.
The house is a rectangular shape with the long face running east to west. Northern glazing is maximized, representing 18% of Gross Floor Area (total glazed area is 27%). Southern glazing is minimised with no westerly and minimal easterly glass. Living areas and bedrooms are located on the northern side of the home and wet areas/service areas along the south side.
Solar ingress is further supplemented by north facing clerestory windows that run the length of the living areas. All of the windows in the house are double glazed with timber frames and high efficiency double window seals. Full length curtains with pelmets are fitted to all northern windows except the clerestory windows.
The features described above are common in many solar passive designs. The McCook home supplements these by a more unusual design feature in the inclusion of stub Trombe walls. These are low height freestanding walls built of a high mass material that are located on the inside of northerly facing windows. They serve to absorb and store solar radiation during the day to be released into the room at night. They work in much the same way as massive floors, walls or ceilings in a standard passive solar design, but have the advantage of not being shaded by furniture.
In the case of the McCook home most north facing windows are fitted with Trombe walls. The walls extend out from the sides of the room for variable lengths. This allows for access through some sliding windows and also the full height of part of the windows to be visible.
The trombe walls in this home are 750mm high, 150mm set back from the window and 130mm thick. They are made with the same tilt slab construction method as the internal walls. The sides of the walls that face the windows are painted with a black acrylic paint to improve heat absorption.
Hot water is supplied to the home through two separate instantaneous gas hot water systems. One system supplies the kitchen, laundry and main bathroom whilst the other supplies the master bedroom ensuite that is located at the other end of the house. The two units were installed to avoid the significant heat loss through long piping runs if using a single unit.