Whirlybirds

Some things to think about before installing a whirlybird on your container

Conventional houses are built with a ventilation system that, at least in theory, will draw outdoor air in through the outfit. This air is supposed to be drawn through the attic of a house in such a way that the warm, moist air rises and exits through the whirlybird and other ventilation. If the attic of the house isn’t sufficiently sealed from the living area, the ventilation will pull conditioned air from the house. This causes heating and cooling units to work harder, driving up energy costs. This is also essentially what will happen in a container home, unless you have built a gabled roof structure on top of your container.

Condensation is one of the most difficult challenges to overcome when converting a container into a dwelling. The metal heats up and cools in a cycle that all but guarantees condensation on the inside walls and all the problems that come with it. Proper ventilation is one of the key ways to manage this problem and maintain a comfortable, healthy home.

It’s all about the dew point

Put simply, dew point is the temperature at which the air is saturated. If the dew point is 18ºC, and the temperature of your container wall is 17ºC, condensation will form on it. If the surface temperature of your wall is 10ºC, a lot of condensation will form on it.

This is what makes condensation in a container so difficult. But what if I just heat the top part of the wall a little bit? That might work, but you will pay for that dearly, not just in creating a custom-built heating system for your container walls, but the energy cost to run it.

The top of my container is its roof

A home in Costa Rica solved this problem by using windows that are placed just beneath the roof line. This allows air to blow through the container, which promotes ventilation of warm, moist air through the vents in the roof. The net result was a cooler home and reduced humidity in the container.

An alternative solution

If you are still in the planning stage of your container home, you can drop your ceiling by about 20cm and insulate it either with foam spray or mineral wool insulation. Make sure you construct the ceiling in such a way that it will hold the additional weight of the insulation, and seal the space of from the living area below. You can mimic the soffit ventilation you find on a conventional home by cutting holes extending down the sides of the container and covering them with mesh. This venting can then be covered with a protective steel guard that will keep the rain and snow out while allowing the free flow of air into the space. For a 12 meter container, two whirlybirds, properly installed, along with two other passive vents should be all you need to eliminate the condensation problem.

When in doubt, consult with a pro

If you’re not sure about how this will all work, consult with an architect and/or contractor who has experience building container homes. This way, you will have peace of mind.

Whirlybirds need to be considered as part of a complete ventilation solution that efficiently moves air through the container, keeping its moisture level down.

Dehumidifiers and desiccants

If you keep your container home closed up with the air conditioning on, you can use a dehumidifier to pull excess moisture out of the air. There are also bags of dessicant you can purchase, which will absorb moisture.

Whirlybirds or not, ventilation in a container is tricky. You have to consider several factors, such as climate, relative humidity, and how windy it is. Ventilation must be approached with the whole container in mind, with the aim of efficiently removing warm, moist air.