Polystyrene Cladded House

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Regs

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Snowflake

#500565 1-Aug-2011 21:09

Nikoftime: Would you buy a house with polystyrene cladding?
Timber frame, wrap, cavity, polystyrene and then plaster.
Is it the general perception that this is potentially leaky and if yes, why would it be more prone to leaks than any other form of cladding?

Even if the house were 100% OK, i'd still be hesitant. If you go to some open homes, you'll see double or triple the number of potential buyers looking at timber weatherboard or brick homes than you see at plaster homes these days. Lower demand must equal lower prices and longer time to sell.

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grant_k

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#500572 1-Aug-2011 21:28

Regs:
mattwnz: However I believe building products only have to last a certain number of years under the building code. I think it is only about 10 to 20 years.

Surely that cant be true, or there must be exceptions for certain types of products. I'm pretty sure i remember my building consent for extening the house in Auckland to have a requirement that I build a structure with a minimum life of 50 years. Pretty hard to do that with building products that have a 10 or 20 year life...

Regs is correct -- in most cases. 50 years is the usual time period specified, but there are exceptions.

About 18 months ago, we managed to sell our house which had been reclad with monolithic cladding. It originally had weatherboards, thus had wide eaves, and had never leaked. However, we were part-way through the renovations at the time the leaky building crisis blew up in 2002. Had I known then what I know now, I would never have touched monolithic cladding in any way, shape or form. We wanted to modernise the house, and get away from the weatherboard look, in favour of a plastered look. The basement was concrete block, so we had that plastered over too, so the top and bottom storeys looked the same.

The trouble is that a concrete block basement hardly moves, whereas a timber-framed upper storey does. With Harditex sheets butted end to end, and plastered over, it is almost impossible to avoid cracks after a few years. In our case, there were no balconies on top of other storeys, just one big one over a driveway, so even if the fine cracks did leak, any water would run out the bottom, and onto the concrete below. Sure enough, cracks did appear, but the plastic building wrap prevented any water ingress, as was proven by invasive testing with a moisture meter.

We had to go through 2 determinations with the Department of Building & Housing before Auckland Council would sign off our house. Even then, the weathertightness period (with specified routine maintenance) was only specified as 15 years, rather than the usual 50.

In light of this experience, I would never again want anything to do with a house that uses monolithic cladding. Linea weatherboards may look a little bit old-school, but that design has stood the test of time, and will probably still be around in another 100 years. My preference would be brick cladding, but sometimes that can be very expensive, especially on a double-storeyed house.

Monolithic cladding comes in various forms:

- Polystyrene (as has been mentioned above)
- Harditex sheet (like Fibrolite/Cement board, but thicker)
- Other proprietary designs which are variations on the two options above

They all have this problem of butted joints which need to be plastered over, rather than lapped sheets like weatherboards use. Butted joints are a ticking time-bomb unless you put silicone between the sheets, however UV limits the life-span of that approach as well. It's a really bad idea, no matter which way you look at it.

mattwnz

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#500949 2-Aug-2011 18:15

Regs:
mattwnz:? However I believe building products only have to last a certain number of years under the building code. I think it is only about 10 to 20 years.

Surely that cant be true, or there must be exceptions for certain types of products.? I'm pretty sure i remember my building consent for extening the house in Auckland to have a requirement that I build a structure with a minimum life of 50 years.? Pretty hard to?do that with building products that have a 10 or 20 year?life...?

Actually different products have different durability requirements. If you read the NZ building code at, it lists the durability requirements http://www.dbh.govt.nz/UserFiles/File/Publications/Building/Compliance-documents/B2-Durability-amendment-7-April-2011.pdf

Some elements are required to last at least 50 years, but many elements must last at least 15 years, and others at least 5 years.

In that PDF if does show that non structural wall cladding must last no less that 15 years.

In general it appears the house itself should last at least 50 years, but elements on it may need to be replaced during that time.

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