Polystyrene walls vs Brick

We have been suggested to specify polystyrene rendered external walls rather than brick rendered walls as polystyrene is cheaper and has better energy efficiency.

Are there any downsides anyone knows of to Polystyrene walls, or has anyone any experience of these in their own houses?

Thanks

Simon

If you want energy effeciency, build either a reverse brick veneer or a full brick house. Rendered polystyrene would come a poor second to these two, but would be better than a brick veneer house from an energy effeciency basis.

not sure how the cost and durability of rendered polystyreen compares to brick veener, reverse brick veneer or full brick. It would have to reduce the house price by more than 5% for me to consider it since there are unkown risks.

Apparently the cost of rendered polystyrene is 50% of the cost of rendered brick, mainly because you don't have to employ a brickie!

And also apparently it gives a 4.5 energy rating compared to 3.5 for brick veneer.

But durability may be a concern.........

Simon

I wonder what 50% of the external wall costs translated to when considering a whole house.

I'd be worried the a ball kicked against the wall would dent it or that a fire would be disasterous. Polystyrene may have it's place but it will never be in my house.

If you want insulation go with Timbercrete, mud bricks or straw bale. Stay away from anything that burns with very noxious fumes.

Just my opinion.

Polystyrene is known to release fumes for many years on and I would not be building with it.
I've used it lots as floatation in my early kayaks (1970s) and it does eventually break down if exposed to air and water.
OK rendered will be different and straw is in a similar area - how will it perform in the hot Australia climes as part of a house? Muhc hotter than the traditional areas these material are used - Time will tell.
More details here.
http://inventors.about.com/library/inventors/blpolystyrene.htm

Steve

Steve,

Got any links, sources, etc about outgassing from expanded polystyrene ? I've been unable to find any conrete info on this.

Chris

Is this not really old information?
I did admittedly get my information from builders, but they definitely said that modern building methods were more energy efficient than double-brick. They said they were still happy to take my money, because the bricks cost more & they make more money, but it wasn't what they'd choose to use for that purpose.


Do we know it's actually the same stuff?
There was a thread only a week or two ago about it, and I have a recollection someone saying that the stuff used as part of wall-panels wasn't the same stuff you find in ... well, in old kayaks.

Again it's not something I know anything about, however things do change from time to time & going off old information isn't necessarily going to get the right answer.

Didnt you read the three little pigs when you where younger??

Brick have stood the test of time. I think even rodents could eat the poly wall.

Anyone who thinks a double brick house will perform better than a poly clad house is sadly misinformed.
A standard double brick wall has a total R value of 0.73.
By using a standard 90mm timber frame clad with 75mm poly and R 2.5 batts you can get that wall up to R 4.5 or R 5.0- way better than the double brick mud huts you get in Perth.
Outgassing of poly over the last few years too has been improved out of sight - you only have to check the specs of most of the board manufacturers to see.

Stewie

Me personally I am not really concerned which has better efficiency. I am looking at longer term reliability and performance of the structure. I think many other might shave similar views.

It really depends on the type of house you have..
If you are on a flat block, I would want a brick house as it will stand over time and no need to worry about it.
If on a slope like mine, I would go for poly. It is easier to repair if anything goes wrong on the outside vs a big crack in the brick wall on slope is hard to fix.

For poly, you can really think of it as timber alike. You can have that replaced later much easier than bricks.

Everyone is looking at the thermal resistance (R value) and ignoring the other important aspect, which is thermal mass (C value). If you want to have a thermally comfortable house with no airconditioning or artificial heating then you want to maximise R x C.

For a full brick house you get moderate R (about 1.5) and very high C (about 800). This gives an RC value of about 1200.

For a polystyrene house you get very high R (about 7) and poor C (about 1). This gives an RC value of about 7.

In practice, other materials in the construction will close this gap, however the full brick house will still have an RC value at least 20 times better than a polystyrene based build.

What benefits do you get as a consequence? Take a look at: http://www.boral.com.au/Bricks/bricks-thermal-mass.asp

If you live in a temperature climate (any part of Australia other than Tasmania and distinctly above Brisbane then it pays to smooth out the diurnal temperature variations.

Interesting thread. I think the only question I have is:
Figure 2 in Casa2's link shows that Cavity brick is the worst in terms of energy consumption and insulated cavity brick is the best. Are most new dwellings built with cavity brick insulated or not?

EDIT - Just reading further on this I think CSR are perhaps a little bit more balanced in their perspective:
http://issue2.csr.swwwipe.com/understan ... insulation

Especially here from the above link:
* CSR Building knowledge is not suggesting houses should be built with a 200mm cavity; that would be too expensive. The traditional practice of leaving only a 50mm gap is insufficient to achieve excellent thermal performance in very hot and cold conditions. Designers need to consider larger cavities to enable increased insulation R values for better performing cavity brick walls.

In NSW robbie, BASIX would make you install some form of insulation I'm sure. In the other states especially WA I don't think they do from what I've read meaning there are still thousands of homes being built over there that are still inefficient. The big problem with installing some form of insulation in there like 20 - 30mm foilboard is that it would have to be installed as the brick walls are being built - threading it over brick ties etc and as you probably know a 5% damage to most forms of insulation leads to a 50% reduction in its efficiency. Knowing how rough most brickies are I'd see this as a big problem.
Pumped in insulation into the cavity would come with its own set of problems too.
From your blog I see you are building a brick home - brick veneer ?
What did BASIX make you do regarding insulation ?

Stewie

Hey stewie

yes we are building brick veneer with R2.0 insulation in the walls and R3.5 in the ceilings + a 50mm anticon under colourbond (i'm not really clear if this has any significant insulation properties) and 2 whirlybirds. From memory for us to meet basix they just required R1.5 for walls and 2.5 for ceilings - happy for someone else to correct me. If reverse brick veneer was a standard offered by our builder I would most probably have gone for something like that.

I didn't want to go on about it but the more I read on the brick cavity insulation prepared by Newcastle Uni the more I questioned it - the report appears to be done with (or perhaps commissioned by a brick company) and the test house had a 200mm insulated cavity and from memory were solid clay bricks whereas most bricks tend to have holes through them. Further the results did not provide a full list of dates, only a short summer period and then just combined season figures. There might be a lot of merit to it don't get me wrong and again please set me straight if I am, I'm just trying to make some sense out of it but I could only find snippets of it not the complete report which I would think brick companies would be very willing to put forward if it was as black and white as they seem to suggest. Thermal mass does definately play a part but when faced with the real cost of getting the benefit from it I'm not convinced that it is a realistic proposition cost wise for most building a new house in the burbs - perhaps if it was more widely adopted the cost would come down.

My Dad did this for his small house in WA. He was able to do most of the work himself (he does have building experience, has built 3 houses himself prior to this). The poly bricks are filled with concrete. The energy performance has been great so far, no need for airconditioning and minimal underfloor heating.
It's pretty hard, you'd have to throw a brick at to dint a wall. I don't think rats can chew through concrete but I could be mistaken.

What you are having is similar to our proposed build although upstairs we are going for 75mm rendered poly as our external wall. Downstairs probably replacing standard bricks for eco brick which has a much higher thermal rating. Both levels 90mm studs, cavity and R2.0 or 2.5 batts.
The anticon will definitely help keep your roof space cooler in summer as will the whirlybirds. Good choice.

Yes, a 200mm cavity would mean a total wall thickness of 110 + 200 + 110 = 420mm - real good for tight suburban blocks. Ok if you're in the country on acreage.
Like you allude to I'm a bit skeptical when it comes to studies and reports that don't cover all the variables - it makes me think why ?

TinaG , were the blocks he used Zego ?
I've seen a few homes done with them and they looked pretty good.

Stewie

I don't recall the brand sorry Stewie, they were from Melbourne I believe