Rendered Foam Walls

This addendum was added to an original Post from 2014 as there has been a lot of publicity recently (late February 2019) about foam panels and certification has been removed from certain types of panels.

A particular issue for apartment blocks has been related to high speed spread across the surface of the panels to other flats.

On a standard house the render should protect the insulation from external flames. (If flames penetrate the plasterboard, from the inside, it is likely that the occupants will either have already evacuated, or be dead before the insulation ignites) n

Nevertheless you should review whether the potential risks from foam panels are acceptable to you.

Original Article

Rendered Foam walls are becoming much more common, particularly in the upper floor of 2 storey homes. They offer a real advantage in situations where it would be difficult to provide adequate suppport for a heavy brick wall (For example when the upper floor needs to be set back from the ground floor)

If you are worried about strength you need to be aware that the real strength of the house is in the frame. (see: House Construction – The Frame)


  • The Foam boards, which are manufactured with an external mesh face, are fixed to the frame with special galvanised screws that incorporate spreader washers.
  • Joints are sealed with a polyurethane foam and have mesh jointing tape.
  • External corners are reinforced with metal strips.
  • A minimum of 5mm of  acrylic render  is applied, normally in a three layer system.

Polystyrene Foam

There are 2 different types of foam used in this construction method:

  • Expanded polystyrene( EPS) – Good thermal performance but limited impact resistance/structural strength.
  • Extruded polystyrene (XPS) – Similar thermal performance and looks similar  but the production method is different which results in increased impact resistance and structural strength. Higher cost

Insulation values for the various board thicknesses are:

  • 50mm    – R 1.2
  • 75mm    – R 1.8
  • 100mm – R 2.4

Final Thoughts

Although there are some advantages in this system it does require careful detailing and construction otherwise leakage can occur damaging your house.

The advantage of masonry on the lower part of the house is that it is less likely to be damaged by the bumps and bangs of daily life. Once the wall is above head height damage becomes less of an issue and the rendered foam board should be fine.

I’d prefer XPS to EPS.

Although the insulation values are good the builder will most likely want to save the cost of the insulation batts in the frame. If you ask for the wall to include insulation batts you will have an exceptionally well insulated wall at very little extra cost.


For similar posts see Insulation

For more about house design see Choosing a House . . . A new E-book for only $4 to help plan your new house


Don’t Forget Curtains!

It’s well known a lot of heat is lost through windows.

With single glazing the Thermal Resistance, ‘R’ Value  is 0.16.

Although they aren’t considered in energy calculations (see this link: Energy Rating) curtains can significantly decrease the heat loss from a window.

They also improve the feeling of comfort.

Insulation Value

With different materials its not possible to give a definitive value for the insulation value of curtains  however there are some indicative values in this post.

An effective curtain can increase the ‘R’ value of the window to between 0.3 – 0.5.

Even with a double glazed window curtains will typically further reduce the heat loss. (‘R’ value increased from around 0.33 to around 0.6).

Effective Curtains

To be fully effective curtains must:

  • Provide a ‘seal’ around the window to stop air movement at:
    • Top – Pelmet
    • Bottom – Overlap window sill by at least 300mm, or down to the floor
    • Sides – Overlap edges of window by at least 300mm.
  • Use heavy close weave material, preferably lined.


What Does The Energy Rating Mean?

The ratings are calculated by a NatHERS (Nationwide Housing Energy Rating Scheme) computer simulation of an individual house design to estimate the thermal comfort.

The calculations are based on 69 different ‘Climate Zones” and allows comparison of different properties in the same climate zone.

The following table shows the Energy Load (heating,cooling, lighting and hot water) for various capital cities for each of the star rating band.

  6 Star 7 Star 8 Star 9 Star 10 Star
Adelaide 27 19 13 6 1
Brisbane 12 10 7 5 3
Hobart 43 31 20 9 0
Melbourne 32 23 15 7 1
Perth 19 14 9 5 1
Sydney 11 8 6 4 2

The values are in kilo watt hours/m2/annum.

I haven’t shown less than 6 stars as that is the minimum for new houses.

As you can see if you go all the way to 10 stars the energy load will be virtually nil.


If you are building a 200m2 house in Melbourne at the minimum 6 Star Rating your annual energy load will be:

200 x 32 = 6,400 kilo watt hours

By increasing the rating to 8 star the calculation becomes:

200 x 15 = 3,000 kilo watt hours

a significant reduction of more than 50%!


Air Locks

I am away in the UK at the moment.

As I have been travelling round I was remembering something I felt was very strange when I first got to Australia. . . . . . It was as soon as you went through the front door you were in the main living space of the house.

In the UK most houses have an enclosed porch like this photograph; or an internal space with a door to the inside (a vestibule)

These ‘Air Lock’ rooms can be important in helping keep heating and cooling bills down.


Advantages of ‘Air Lock’ Rooms

The advantages of Air Lock Rooms are:

  • Acts as a Buffer Zone slowing down the rate of heat trnsfer through the door and side panels;
  • Slows down the house Ventilation Rate by reducing drafts (air loss around a closed door);
  • Stops massive heat loss when a door is opened (as long as you treat it like a true air lock and always keep one door closed). . . .useful when you have people at the door you don’t want to invite in.
  • A useful security feature as wide windows allow you to check out callers that might be hiding out of the view of CCTV cameras.

Types of ‘Air Lock’ Rooms

As well as enclosed porches and Vestibules mentioned above other common ‘Air Lock’ rooms are:

  • Mud Room;
  • Laundry;
  • Enclosed veranda:
  • Sun Room/Conservatory.

If you are serious about saving energy perhaps you should think about ‘Air Locks’.


Garage Door Insulation

Most garages are too hot in Summer and too cold in Winter.

If you want to use the garage as a workshop . . or even a man cave, it will be much more comfortable if its insulated.

Maintaining a comfortable temperature in the garage also means  it makes a better Buffer Zone for the rest of the house

For most garages that are built as part of the house  it is relatively easy to put some insulation batts in the roof, but that still leaves the garage door!

Here is  how I insulated the garage door on the last house I built, in an afternoon.

DIY Garage Door Insulation

  1. Measure the door width and the height of the steel ‘C’ sections that make up the door. You will need enough Foil Board to fill all the sections. Foil Board can normally be ordered at your Big Box DIY store.
  2. When you pick up your Foil Board buy 3-4 cans of expanding construction foam.
  3. Cut the Foil Board into strips that are wider than the opening in the ‘C Section’ but can still be inserted into the section and drill holes in the foil board approx 1m apart. (Putting some masking tape around the holes will make cleaning up easier)
  4. Place the sections in the ‘C Sections’, foil facing outwards and hold them in place against the edges (I used duct tape.)
  5. Following the instruction on the cans of foam insert the nozzle through the holes and start to fill behind the foil board until foam comes back out of the holes.
  6. WARNING. Make sure you keep the foam away from any moving parts.
  7. Leave the garage door shut for a few hours to allow the foam to cure and then clean up and remove the duct tape.
  8. Even though the Foil board and Foam is light the door will now weigh several kgs more. This shouldn’t be an issue if you have an electric opener but with manual opening you will probably need to get the lifting spring reset. As this spring is under a lot of tension this is not a DIY job!

After doing this job I found the garage was much more comfortable . . . and the beer fridge didn’t have to work as hard!


For more posts see Insulation


Sisalation or Sarking

Sarking is the sheet material which can be put over the roof trusses before the final roof covering is installed.

It’s normally standard on a metal roof as it prevents condensation on the underside of a roof from dropping onto the ceiling below.

In the case of a tiled roof it helps with weatherproofing and keeps dust out of the roof space.

In bushfire zones it is mandatory for a tiled roof to have sarking.

The reflective sarking (installed reflective side facing down) does help in reducing summer heat being radiated into the roof space and can help to keep the house warmer in winter. (See Reflective Finishes for more information)

In addition to plain sarking you can get an insulation blanket with sarking attached. This offering some sound insulation, for rainfall, and extra thermal insulation.


See Insulation for more posts


Seaweed House

What do you think of this house?

Roof look a little unusual?

Well the roof, and the walls, are built using seeweed!

The seeweed provides a long lasting external surface, which as well as being a natural renewable resource, has great insulation values.

To find out more, with lots of pictures of a spectacular interior, see the website.


For more Unusual House Photos, and Fails, have a look at: What the………………….?


Understanding Ceiling Insulation

I frequently see comments like “Ceiling insulation is next to worthless in summer.”

I have even heard people say “With a hot roof space it will be overwhelmed.” and “After the sun has gone off it stops the house cooling down.”

Here is the truth:

  • All insulation works by slowing the rate of heat transfer. If the roof space is hot some heat will pass through to the room below. The insulation will slow the rate that the room heats up from the roof space.
  • Ceiling insulation isn’t enough to keep the room cool by itself. The room will still get hotter if heat is leaking in through poorly insulated walls and windows.
  • Ceiling insulation, by slowing the heat gain from the roof space, will reduce the cost of mechanical cooling.
  • In a well insulated conventional ceiling minimal residual heat remains in the plasterboard and ceiling insulation. The heat in the room is just hot air. The best way to remove the hot air is to open the windows when the air temperature outside is less than inside, or run the air conditioning.


See Insulation Basics – Ceiling Insulation to see the difference it makes.


Insulation Basics – Double Brick Walls

I have previously carried out a worked example of the insulation of a Brick Veneer Wall, so as a comparison here is double brick wall.

I have also shown (in brackets) the effect of using a hebel block in place of one of the brick ‘leaves’:


R value

Outside surface air layer


110mm brick


25mm cavity


110mm brick (*or 125mm Hebel Block)

0.08 (*0.81)

Plasterboard 10mm


Inside surface air layer


Total R value


U value = 1/R

1.96 (*0.81)

The heat losses or gains for 150 sq m (fairly typical external wall area) of this type of double brick  wall at 15 degrees above, or below, outside temperature will be:

Area x ‘U’ x temperature difference = watts per hour

150m2 x 1.96 x 15degrees = 4410watts per hour

Heating/Cooling Requirement = 4.41kw/hour

Using Hebel for one of the leaves will improve the heat loss as follows:

150m2 x 0.81 x15degrees = 1822watts per hour

Heating/Cooling Requirement = 1.82kw/hour

Still not as good as the 1.17 kw/hour of the typical brick veneer construction

Don’t forget heat is also lost through windows, ceilings floors and ventilation.


See Insulation for similar Posts

For Posts about Green Building see Sustainability



Condensation,  a minor inconvenience,  or a major problem?

A little condensation on windows is easily dealt with, . . . . . .  but heavy condensation in poorly ventilated corners can lead to mould damaging your walls, ceilings, or even your clothes.

Why does Condensation Occur

Condensation in a building occurs when warm air, containing water vapour, comes into contact with a cold surface.

As the air cools it can’t hold as much water vapour so the excess changes into liquid water which is deposited on the cold surface.

The  water usually appears as surface condensation as water droplets or water film on cold surfaces, typically windows.

Condensation occurring on cold walls and ceilings is a major issue as it is when mold problems start. Of particular risk are wardrobes on  an external wall as there is a cold surface and a lack of ventilation.

Sources of Water

Here are five main sources of water vapour in the home

  • People A typical adult will lose around 0.8L/day of water, half from skin evaporation, and half from breathing.
  • Bathrooms Not just the obvious showers and baths, its also those drying towels and bathrobes 
  • Kitchen – Kettles, Pans, dishwasher, and the microwave will add water vapour
  • Un-Flued Combustion – Portable Gas Heaters, Gas Hobs, Bio Ethanol Heaters, even Candles, all emit water vapour into the room as they burn.
  • Laundry – Unvented Tumble driers, Airing Clothes.
  • Evaporative Cooling – Because it is mainly used in summer less of a problem, but can be an issue on cold nights.

Preventing Condensation Damage

Action to prevent condensation damage involves looking at both insulation and ventilation.

Insulation. Additional insulation in walls or ceiling will keep those surfaces warmer which will reduce the risk of condensation damage in most rooms .

Ventilation In bathrooms and kitchens the more moisture laden air means that insulation by itself will not be enough. The moist air needs to be effectively extracted to prevent condensation being an issue. (Although I have previously posted about Heat Loss due to Ventilation some  ventilation is  needed throughout the house)

Role of Double Glazing

Double glazing is often suggested as an answer to condensation however this is not really the case. As the windows are now less cold there is less surface condensation on the windows, so it looks like the issue has gone away. The problem is that without removing the moisture laden air the risk of condensation on walls and ceilings is increased.

See this link to find out why I prefer a separate Extraction fan in the Bathroom: 3 in 1 Bathroom Heaters

To keep moisture out of the insulation materials see this link: Vapour Barriers