Insulation Basics – Weather Effects

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.

Wind Chill

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.

Rain Wetting Walls

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.

Summer Radiant Heat

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.


See Insulation for similar Posts

For Posts about Green Building see Sustainability


Insulation Basics – Double Glazing

Large single glazed windows are one of the biggest reasons for heat loss in a modern house.

It is also a major source of heat coming into the house in summer.

So what can you do?……………here is a comparison between single and double glazing.

Single Glazing
A single glazed window with an aluminium frame has a U value of around 7watts/degree C/m2 (an R value of 0.14 )

So if your house has got 30m2 of windows and its 5 degrees C outside.

You will be losing the following amount of heat through the windows if you keep the house at 20 degree C

30 x (20-5) x 7 = 3,150watts = 3.15kW/hour

For refrigerated cooling from 300C to 200C you will need the following amount of cooling to balance heat gain through windows:

30 x (30-20) x 7 = 2,100watts = 2.1kW/hour

Double Glazing

If you have double glazing with timber or uPVC frames you will reduce the U value to around 3 watts/degree C/m2 (An R value of 0.33 ).

For the same conditions as the above example the heat loss through the windows will be reduced to:

30 x (20-5) x 3 = 1350watts = 1.35kW/hour

For refrigerated cooling from 300C to 200C your heat gain through windows will be reduced to:

30 x (30-20) x 3 = 900watts = 0.9kW/hour

Other ways to reduce heat loss are

  • Reduce window size. As walls are better insulation than windows this can offer significant reductions in heat loss
  • Curtains or Blinds. Will provide similar performance to double glazing. . . but only during the time when they are closed.

Extra Benefits of Double Gazing

Improved Security: Its much more difficult, and noisy, to break in through a double glazed window.

External Noise Reduction The bigger the gap between glass the better the performance.

See Insulation for similar Posts

For Posts about Green Building see Sustainability


Insulation Basics – Vapor Barriers

When you are thinking about installing insulation you also need to think about Vapour Barriers.

Although I frequently saw mention of vapor barriers in books and articles it was a long time before I understood why there were needed……………. Here is my explanation:

  1. Warm air, inside the house, contains a lot of moisture (water vapor) which comes from people breathing, cooking, showers, flueless gas or oil heaters, and house plants.
  2. If this air is allowed to pass through the building structure it cools.
  3. As the air cools it can’t hold as much moisture and water condenses in the structure and in the insulation.
  4. The water can:
    • Waterlog the insulation reducing its effectiveness.
    • Cause rot in wood.
    • Cause corrosion, Particularly on the underside of a metal roof.

To stop the problems you put a vapor barrier………….Which is really an airtight barrier……….on the inside face of any insulation.

An Exception

You Don’t usually need a vapor barrier on the ceiling if you have a ventilated roof space as the air flow above the insulation will dry out any moisture in the insulation.

Cathedral ceilings  and flat roofs are a different matter and Do Require a vapor barrier as there is no ventilated space above the insulation.

Types of Vapour Barriers

Vapor barrier don’t have to withstand any pressure so they can be quite thin. Examples are;

    • Polythene sheet,
    • Reflective foil,
    • Foil backed plasterboard,
    • Water resistant painted surfaces,
    • Impermeable insulation such as sheets of polystyrene.

All joints and overlaps in the vapor barrier should be taped or glued to make sure no air gets through.

See Insulation for similar Posts

For Posts about Green Building see Sustainability

For more about Moisture Problems see this link: Condensation.


West, or East, Facing Windows

Well the first rule is to avoid West, or East, facing windows . . . or at least keep them as small as possible….and here is why:


West windows get direct sunlight from mid-afternoon to late in the evening in summer causing overheating.

East facing windows get sun from sunrise to midday.

This isn’t normally as bad because the house is cooler in the morning, but the heat built up during the morning does stay making the house hotter later in the day.

Because of the low angle of morning, afternoon and evening sun the over window shading that works well with North Facing windows will be inadequate for West and East facing windows.


In the winter there is minimal heating benefit with little or no direct sunlight getting into West or East facing windows.

In the last house we built the master bedroom full length windows all face west.

I would have preferred to decrease the size of the windows but the builder would not alter the size of the windows on the front. (They were quite happy to change all the other windows, just not on the front)


To shade, our west facing windows, we adopted the following three stage strategy.

  1. A highly reflective tint was applied to the window, by Tint-a-car. This had the immediate effect of lowering the temperature in the room by about five degrees on a sunny afternoon. Even the installer was amazed at the difference it made. Expect to pay around $50-60/m2,
  2. We planted shrubs in front of the windows to shade the bottom third of the windows and also provide a micro-climate to reduce heat loss in winter.
  3. We have fertilised and trimmed a couple of trees on the nature strip, in front of the house, to encourage dense foliage which now shades the window from mid afternoon to sunset.(see photo below)

For similar posts see Passive Solar

Choosing a House . . . A new E-book for only $4 to help plan your new house


Rooms over Garage

Will your new house have a bedroom above the garage?

If so you should check what the builder specifies in the way of Insulation between the garage and the room floor.

Although regulations quite often specify insulation on external walls they usually don’t consider above the garage.

Why this matters

In winter garages can get very cold, particularly if the garage door is left open.

In summer the garage can get very hot. . . more so if the garage door faces west and absorbs the afternoon sun..

This means that in both summer and winter the lack of insulation can make the room uncomfortable!

What You Can Do

Make sure you discuss with the builder the option of putting insulation in the garage roof before the ceiling is installed.

Doing it then is going to be much cheaper than trying to do it later.

Already built? . . . perhaps you could add Insualtion to the garage door.

Microclimate, And Why It’s Important To Your New House

A microclimate is a local atmospheric zone where the climate differs from the surrounding area.

The term can refer to areas as small as a few square feet (for example a garden bed) or as large as many square miles.

When we are talking about providing a microclimate for a house the things can do for are things like:

      • Providing shade trees to keep the summer sun out of the house, particularly on the west side where eaves don’t work as well. (see Photo)
      • Overhanging eaves, and verandas to keep the walls dry. (Once brick walls get wet winter winds cause evaporation which chills the brickwork speeding the loss of heat through the wall)
      • Providing shrubs and plants close to the walls to retain a layer of still air which slows heat loss in winter. The plants also help shade the walls in summer.
      • Soft leaved plants that can help reduce summer heat due to evaporation from their leaves.
      • Fences, bushes or trees to deflect or break up winter winds.


Have you provided a microclimate around your house?

For More post about the garden and finishing off a house see Settling In


What Size Rainwater Tank 3

Other postshave explained how to calculate:


From your calculations find out the month of lowest average summer rainfall which is likely to be the peak month of water demand.

Design Case 1

If each monthly average rainfall is above the estimated use for that month.

You will need a tank with around 10% more volume than required for  the peak month of use. (This allows for evaporation, and the water that’s unavailable because its below the tank outlet.)

Design Case 2

If the monthly average rainfall below the estimated use for that month.

For this case you will need to add the differences in volume between the expected use and the rain for each month leading up to the peak month to the amount in Design case 1 above.

When you have the expected storage volume you can then look at storage tanks.

Not enough room, or enough rain?………….. then you need to think about reducing your use or getting more collection area.

Bushfire Zone

If you are in an area with a bushfire risk you will need additional storage,

This needs to be in tanks that will be resistant to flame attack. (Concrete or Steel. . . NOT Plastic tanks)

See this post for more information:  Bushfire Reserve


Before choosing a tank look at Round or Slimline Tanks.


What Size Rainwater Tanks Do You Need – 2

How Do You Plan To Use The Water?

The most common uses for rainwater are for toilet flushing, garden watering and car washing.

Toilet Flushing

Basically a new duel flush Australian toilet will use 6 L for it’s main flush and 3L for it’s half flush.

Older toilets will use 9 L and 4.5L respectively.

Assuming two main flushes and 2 half flushes per person per day gives a monthly average usage between 540 – 810L per person.

For a family of four that’s between 2,160L and 3,240L of water.

If you are reading this in other country your numbers may be a bit different!

Garden Watering

This depends on the area that you want to water, whether you are watering an area or spot watering, and how often you want to water.

A reasonable summer months watering of an area would be the equivalent of 10mm a week, which would be 10L/m2 of garden watered so for each m2 of garden you need to store 45L/month. (To water say 200m2 of garden weekly would use 2000L which would add up to 9,000L per month)

You can see from this how much water can be used on the garden compared with indoors.

Approximatly 3 times the volume used in the toilet!

Car Washing

Washing a car using a pressure washer would probably only take about 30L so the monthly total per car for washing once a week should be less than 150L.

Rainwater is Sole Water Supply

Every family is different so its hard to predict your water use.

We are fairly careful, don’t water the garden,  only have 3 minute showers, use a front loading washing machine and only run the dishwasher when full.

All this means we use around 75L/person/day say 28kL/year.

The average usage in Melbourne with drought restrictions over the past few years has been about double that. . . so there must have been lots of people taking 30 minute showers!

Perhaps the best thing to do is monitor your water meter where you live now.

If your only supply is rainwater its worth checking with your Council if they have a minimum requirement.

Its also quite common for councils to require a bush fire reserve storage capacity for rural properties which can range from 10,000 litres to 20,000 litres depending on your State and location.

How Long Do You Want The Water to Last

Once you know the intended amount of useage, you can then find the total volume to supply a months usage.

For example: If a family of four was only using the water for toilet flushing and car washing a storage volume 3,500L (3.5kL) will be required for each months storage.

If the same family also wanted to also water 200m2 of garden 12,000L (12 kL) would be required for a summer month. (For Winter months there would be no garden watering so the storage would easily last for  several dry winter months..

As you can see the less garden watering you do the smaller the tank needs to be. . . or the longer you can survive  without rain.


Next step See What Size Rainwater Tanks 3

For similar posts see Sustainability


What Size Rainwater Tanks Do You Need – 1

With sustainability being a majot topic you may be thinking about a rainwater tank. . . but what size of tank do you need?

The bigger tank you get the cheaper the cost of storage per kilolitre (1,000L or 1kL) but you don’t want to buy one too big!

Not only will it cost more, but it will take up more space on your block.

How Much Rainfall is There in Your Area?

The first thing you need to do is find out what is the average rainfall for your area.

Remember that average rainfalls can change over quite small distances. (For example the rainfall in some Melbourne’s Western suburbs can be 30% lower than parts of the Eastern suburbs).

If you go to this web page and enter any Australian town it will give you the nearest weather stations.

For other counties try your national weather centre.

Once you have selected a weather station click on the get data button and you will get heaps of data. What you want is the mean monthly rainfall in mm.

This should look something like the table below, which is the rainfall for Werribee Racecourse, my local Weather station.



























Remember the above figures are the mean so for example one year there may be a summer thunderstorms and January may get 80mm of rain, the next year in a drought it may get no rain at all.

How Much Rain Will You Get ?

Now you need to measure the roof plan area that will be drained to the tank/s in m2.

Multiply the area in m2 by the rainfall in mm for each month and divide by 1,000 will give you the volume of rain in kilolitres.

For example; An 180 m2  roof in Werribee Household will get a mean of 97.6kL per year. (The bottom row of the table below shows the monthly means as well as the annual mean)










































The above totals are theoretical!

In practice you will usually collect 80-90% of these amounts.

This is due to losses through evaporation, and any first flush filtering systems.

The next question is how much water do you need?….To find out see Post 2 on this subject


For similar posts see Sustainability


Shading Northern Windows

In a post about Passive Solar I talked about shading North facing windows.

That doesn’t mean installing roller shutters, or blinds that pull down over the window.

Shutters and blinds tend to make the rooms very gloomy and depressing, and with good design are unnecessary.

The best methods of shading North facing windows are:

• Overhanging eaves
• A well designed veranda
• A pergola

How Much Shade?

For areas North of Brisbane its better to have  enough shade to keep the sun out of the house as much as possible.

For areas from Brisbane and South the keys are:

  • Keep direct sun off the window during the summer months of; December January and February.
  • Allow full sun to shine on all of the window in June July and August.


Keeping the summer sun out for areas South of Brisbane can generally be achieved by making sure the eaves overhang is 45% of the height (H) the shade is above the bottom of the glass.

The eaves, or other method of achieving shade, should also extend horizontally along the wall window 45% of H to either side of the window.

To minimise shading of the window in winter the shading needs to be around 20% of H above the top of the glass.

West and East Facing Windows

West and East facing windows are almost impossible to effectively shade in summer and get minimal benefit from winter sun.

Information on dealing with these windows can be found at: West and East Windows


For more Green Ideas see Sustainability