Last week I expanded on the concept of passive design using the example of Earthships in the desert environment of New Mexico, USA. The point of the article was not that we should all start living in Hobbit Homes made from old tyres filled with earth, but that passive design is a great approach to housing all around the world, including right here in the Manawatu.

We can have passive design without tyres, and as a matter of fact it can look very much like the homes we already inhabit.

A well-designed passive solar home in Palmerston North could easily cut its winter heating budget by more than half compared to an equivalent home poorly design and laid out. That is a significant savings on power along with increased comfort in the home. But staying warm in winter is only half the story of passive design.

We know that summer temperatures can get on the uncomfortable side here and that many homes overheat due to poor design and inadequate ceiling insulation. The good news is that in many cases we can take a lesson from the tropics and use cross-ventilation to cool our homes without the need for air conditioning.

I have traveled to Nicaragua on a number of occasions and was surprised at first to learn about passive design in tropical regions. Instead of orienting homes on an east-west axis to maximize solar gain in winter as is the practice in most places on Earth, homes are built along a north-south axis to maximize the cooling effects of cross breezes. Of course this also means that ample windows allow those breezes to pass through indoor living spaces and cool the occupants.

A distinctive design feature in Nicaragua’s colonial architecture is a slatted wooden vent above the front door. This allows constant cross ventilation through the structure – provided there are open windows opposite the door – while maintaining security by leaving doors closed at times.

Wide eaves, high ceilings and light construction are also aspects of tropical architecture. But in my opinion the main lesson we can take is cross ventilation. Most homes in the Manawatu can benefit from cross ventilation that is either passive or active.

Passive ventilation works well for homes with windows on opposite walls and few or no obstructions between them. It also works well when the wind is blowing.

But some homes are long and L-shaped, or have curving hallways, or abut another home one on or more sides, or are sheltered from the wind. In these cases, active cross ventilation means opening windows at opposite ends of the structure and using an electric fan to push air out one window, which draws cool, fresh air in through the other.

Yes, you read that right. Using the fan as an exhaust is the best strategy for active ventilation for cooling. In many countries there is a product you can buy called a “window fan.” But any fan will do providing it does not fall out the window!

Peace, Estwing