Design Considerations / Cost & Budget / Beyond the build
Running costs and life-cycle value
The builder's price is what a house costs to make. It isn't what the house costs to own. Over thirty years and more, the energy and water it uses, the maintenance it needs and the parts that wear out and get replaced add up to a large share of what you'll spend on it. Most of that is decided during design, and much of it can't be changed later.
Design ConsiderationsCost & BudgetAt a glance
Judge every decision over the life of the house, not just on the day it's built. Spend on what lasts the life of the house and is built over. Choose efficient equipment and make it easy to replace. Keep the maintenance simple.
- A house has four costs over its life: building it, running it, maintaining it and replacing the parts that wear out.
- The building envelope sets how much energy the house needs for heating and cooling, every year, for as long as it stands. It's very hard to improve later.
- Equipment such as heat pumps, hot water systems and appliances lasts around ten to fifteen years. Choose efficient models, and design so they're easy to reach and replace.
- Size counts twice: every extra square metre costs to build, then to heat, cool, clean and maintain.
- Eaves, robust materials and simple details cut maintenance for decades.
- Materials carry energy too. Build durably where it will last, and lightly where it will be replaced anyway.
Over the lifeFour costs, not one
A house costs money in four ways:
- Building it. The construction cost, paid once, at the start.
- Running it. The energy for heating, cooling, hot water, lighting and appliances, and the water it uses, paid every year.
- Maintaining it. Repainting, oiling, cleaning gutters, resealing and servicing, every few years.
- Replacing parts. Equipment, finishes and fittings that wear out, on cycles of ten to thirty years.
The first is visible and negotiated. The other three are spread thinly over decades, so they're easy to overlook while the design is being settled. Yet nearly every one of them is fixed by design decisions: the size of the house, how well it's insulated and sealed, which way the windows face, what it's clad in and what equipment goes in.
RunningEnergy and water
The envelope comes first. Insulation, airtightness, windows and shading decide how much heating and cooling the house needs, for its whole life. Equipment can be upgraded every fifteen years. The envelope, once it's built over, effectively can't. A house that needs little energy to stay comfortable will stay cheap to run whatever happens to energy prices or technology.
Then efficient equipment. Once the demand is low, a heat pump for heating and cooling, a heat pump hot water system and efficient appliances meet it with the least energy. An all-electric house can then be run partly or largely from solar on the roof.
Then size. Every square metre is heated, cooled and lit. A smaller, well-planned house uses less energy every year, before any other measure is counted.
Water. Efficient taps, showers and toilets, a garden planted for the climate, and a rainwater tank for the garden and toilets reduce what the house draws from the mains. Their benefit, like the envelope's, runs for the life of the house.
The Comfort & Energy guides cover each of these in detail. The point here is the order: reduce the demand first, meet it efficiently second, and generate your own energy third. The first step lasts longest and is the hardest to add later.
MaintainingDesign it out
Maintenance is easy to forget during design and impossible to forget afterwards. Much of it can be designed out.
- Eaves and overhangs. They keep rain and sun off the walls, windows and doors, which is where most exterior maintenance happens. Walls and window frames under good eaves weather far more slowly.
- Finishes that don't need repainting. Pre-finished cladding, masonry, and factory-coated window frames and roofing need far less attention than painted timber. Exterior paint usually needs redoing every seven to ten years.
- Timber outside, used carefully. Timber decks, screens and cladding look good and need regular oiling or staining, more often where they face the sun. Use them where they matter, and keep them out of the weather where you can.
- Simple roofs and gutters. Fewer valleys, box gutters and penetrations mean fewer places for leaves to collect and water to get in. Gutters you can reach safely are gutters that get cleaned.
- Access. A roof space you can get into, equipment you can reach, and taps and valves that aren't buried behind joinery make every future repair quicker and cheaper.
I design for standard construction methods partly for this reason. The trades know how to build, repair and maintain them, and the parts are easy to get, now and in twenty years.
ReplacingKnow what wears out
Some parts of a house last as long as the house. Others are replaced several times over.
| Part of the house | Typical life |
|---|---|
| Footings, slab, frame and structure | The life of the house |
| Insulation, built-in services and waterproofing done well | The life of the house, if it's built right the first time |
| Metal roofing | Around 40 years or more |
| Tiled roofs | Longer again, with repairs to flashings and bedding |
| Windows and external doors | Several decades, depending on the frame and the exposure |
| Kitchen and bathroom joinery | Twenty to thirty years or more, often replaced for style before it wears out |
| Exterior paint | Seven to ten years |
| Interior paint | Ten to fifteen years |
| Carpet | Around ten years |
| Heat pumps, air conditioners and hot water systems | Ten to fifteen years |
| Appliances | Around ten years |
| Tapware | Fifteen to twenty years |
These are typical figures, assuming regular maintenance. Exposure, quality and use all change them.
Over thirty years, the things with a ten- to fifteen-year life will be replaced twice or more. That has two consequences for design. First, there's little point spending heavily on a premium version of something that will be replaced anyway. Second, they should be easy to replace: equipment with room around it and access to it, standard sizes, and wiring and plumbing that allow for a different model next time.
The things that last the life of the house, and are built over, are the opposite. Get them right first time, because replacing them means pulling the house apart.
The energy in the materials
Running a house isn't its only energy use. Making, transporting and installing the materials takes energy too, and so does every replacement over the house's life. For a typical house, the energy in its materials, at construction and in later repairs and renovations, can be around half of everything it uses over fifty years. As houses become cheaper to run, the materials become a larger share. Build durably where a material will last the life of the house. Where it will be replaced anyway, such as a floor covering, choose something modest and light.
Weighing it upSpending now to save later
Most choices that lower running costs cost a little more to build. Asking whether each one will pay for itself in a set number of years is tempting, but the answer depends on energy prices and technology that will change many times over the life of the house.
A steadier test is the one used in Where to spend and where to save. If it's built over, lasts the life of the house and reduces the energy the house needs, it's almost always worth doing well now. If it's equipment, choose the most efficient model that fits the budget, and make sure it can be swapped for something better later. If it's a finish, keep it modest, durable and easy to maintain.
A house designed this way is cheaper to own and more comfortable to live in, for as long as it stands.
Applying it locallyCanberra and New South Wales
Canberra and the Southern Tablelands. Heating is the largest energy use in most houses, so the envelope matters more than anywhere else in the region. Frost, strong UV and big daily temperature swings are hard on external timber, sealants and paint, so favour pre-finished materials and keep timber under cover. Condensation control in walls and roofs protects the structure itself.
The NSW coast. Salt air corrodes metal quickly. Use corrosion-resistant roofing, fixings, flashings and window hardware suited to the exposure, and expect to rinse and maintain exposed metal. Wind-driven rain makes good eaves and well-flashed openings even more valuable.
Western plains. Summer cooling is a major load, alongside cold winters. External shading on the east and west, a well-insulated roof and light-coloured roofing reduce it every summer. Strong sun and dust shorten the life of exterior finishes, seals and outdoor equipment, so shade them where you can.