Just Enough Science To Understand Your House In A Heatwave (Pt.3)

How to design for your climate

This is part of a three part article called “Just Enough Science To Understand Your House In A Heatwave”.

To put this article in context I’d recommend you start here at the beginning.

In this section I’ll explain what you and your architect can do about it.

Night Purging

Removing all the stored heat overnight

AKA no, it’s not the latest Netflix horror

The best way to avoid the accumulative affects of heat build up over a few days is to purge all of the heat it gained during the day. The diurnal cycle in the South West of WA (remember, the temperature range between the hottest and coolest part of the day) gives us a great opportunity to cool our house overnight.  If we can get rid of all the heat gained each day of a heatwave we can reset the temperature back to below our thermal comfort range, which means its starting from a relatively low temperature each day of a heatwave. 

Not only do we get cooler temperatures at in the evening, we often get cool breezes too. If we open up our houses to let that breeze in, it helps a great deal in cooling our house. Even better if we can take advantage of cross ventilation. This means that air enters one side of the house and can exit the other side of the house. This way it takes the hot air out (through convection). This is another textbook passive solar design move.

However, if we forget to open our windows (or can’t), and our houses are designed like labyrinths so the hot air can’t find its way out, we have little chance of purging all that heat.

Your house hasn’t been able to remove days and days of heat build up so you’re copping the affects of thermal lag, thermal gain and a lack of night purging all at once. This triple whammy is the crux of why trying to go to sleep on night four of a heatwave is so rough.

You might have seen a pattern emerge above. Contemporary double brick homes are among the worst offenders here. They absorb more heat, release it at night when you’re trying to sleep and, the way many of them are designed means that we can’t get a good cross-breeze going at night.

Resisting the Heat

While heat transfer is somewhat inevitable, we can help our home out by giving it a fighting chance.  Building it out of materials that have good insulating properties will go a long way to resisting the heat.  Remember, you’re looking for materials with a high R-value. If you’re dealing with an existing house, your best options are insulating the roof with batts.  If you’re building a new extension opt for building materials that lend themselves to insulation. A framed wall system like a reverse brick veneer allows you to pack insulation into the wall cavity.

I was a bit too young for this show, but I remember thinking it was a bit weird at the time

Northern Exposure

If you’re starting from scratch you have the added benefit of being able to orientate your building the “correct way”. The impact of this can’t be understated. It is the cornerstone of solar passive design.  If you can minimise the amount of western and eastern glazing and open your house up to the northern sun, you will go a long way to managing the long stretches of summer days in a heatwave.  There’s too much on this to cover in this article, but reach out to me, check back here soon, or give it a bit of a google.

Plant a Tree or Put up a Blind

It might take a few summers to really make an impact, but a deciduous tree is a great asset to keeping your house cool.  It will provide shade in the warmer months. It will then drop its leaves in winter so that it is letting all that warm sun in.  Take some time to plan out the location of the tree to make the biggest impact.  You want it to be shading your house in the hottest part of the day – especially if you have living rooms and bedrooms to the west and north of your house.

An external blind is also a great way to keep the direct sun’s rays off your window and keep it out of your house.  Although having internal blinds helps a little, having the blind on the outside keeps out solar radiation and keeps the outdoor temperature lower (the little pocket under the shade).

So that’s a fairly deep dive into the way your house gets hot in a heatwave and a few things you can do about it. I’m always looking to add more useful information in these articles.

If you have any questions or want to know more about how to design your house to better manage heatwaves, follow the links to contact me.