Building physics isn’t rocket science. It’s physics, or more specifically it’s about heat and water: the movement of heat from a warm space to a cool space, and making sure water (as a liquid or vapour) doesn’t cause problems. This isn’t something that needs to be guessed at – we can calculate with a great deal of precision how much heat moves from a warm house to the cold outdoors. It’s science. And not just science but the physical sciences (not fluffy stuff likely social or political science!).

Whether you’re designing a new home or a major renovation it’s not too hard to do some calculations to run the “what-if” scenarios like:

• What happens if I replace my single glazing with double glazing? What about if I were to go all the way to triple glazing? Am I saving anything?
• What if were to upgrade my ceiling insulation? Would that do much?
• How about if I were to reorient the home, or put more windows facing north/east/west/south?
• How deep eaves should I have? And do I really need external blinds to keep the sun out in winter?
• What if I’m worried about all the complications and cost with building really airtight and instead reckon it’d just be easier to go reasonably tight without pushing too far? Are there diminishing returns? What’s the optimum?

These calculations can readily be done in a building energy model like FirstRate and AccuRate (for the standard Australian NatHERS star-rating system) or, far better, in a well validated, internationally recognised tool like the Passive House Planning Package (PHPP). A simple model can be built within a day or two and then very quickly be used to test any number of permutations. This has got to be much, much cheaper than taking a guess, building, and then being disappointed with the outcome.