Insulation Basics – Weather Effects

Author: Brian October 20, 2021

When you are considering how much heat you will gain in summer, or lose in winter its not just the outside temperature you need to think about.

It’s actually the surface temperature of the outside wall, or window as it can be different to the outside measures air temperature.

Here are some thoughts on how weather can change the thermal performance of your new house exterior.

Although people normally talk about wind chill with respect to clothes it applies to buildings as well.

Typically the most affected surfaces are windows.

For an exposed windy site the R value of the windows can be 25% lower than on a sheltered site.

Things such as changes to the micro-climate of you house will reduce wind chill.

Once a wall gets wet the rate of heat loss to the outside in winter will increase due to evaporation cooling the wall.

This affects porous surfaces such as brick and wood more than impermeable surfaces like steel.

For a typical brick wall a moisture content of 5% can lower the termperature of the outer skin by around 25%.

The most effective way of avoiding this by keeping the walls dry is to have at least 450mm wide eaves.

Have you ever felt a brick wall after the sun has been shining on it for a while?

The radiant heat absorbed by the wall can make the wall surface 5-10 degrees hotter than the surrounding air.

If you are doing calculations for air conditioning this can make a difference to the required cooling capacity of the unit.

So keeping the summer sun off the north and west facing walls with wide eaves, verandas or pergolas will help keep your house cool.