House sheathing
Hi . I come here to write a question ( by re reading there is more than one ) as I haven’t found tradies around me that know the answer.
I would like to first thank Green Building Advisor for the amount of information you have provided along the years , i have learnt so much from this website among others and feel ever so grateful that people like you take the time to share their knowledge .
I live in Australia and work in renovation . I did half a year in residential new construction and am always on the look out when I see a building site . I must say that it is sometimes very hard to relate to what i learn from a website like GBA because the way buildings are built here seems really different then what i see on GBA.
One difference and that is my question is: why do American houses brace the entire house with OSB or ply panel? I’ve never seen that here and all houses are just braced with metal stripe braces on the wall and the roof .
can you guys explain why that is ? i wonder that because although the sheathing if taped offers a first air barrier and quite a good one but it also creates so much more tension when it comes to flashing details and water management as these products are so sensitive to moisture .
another thing that i notice here is how different our approach to flashing is . It’s all based on metal flashing ( majority of roofs are coruagated iron ) , very little seriousness is given to the house wrap ( called sarking here or sizelation ) on the wall and roof as being the actual water control layer . It seems here it’s just something you have to put on your roof and, oh well if it’s not taped on the seams or at the top and bottom, she will be right anyway .
Same for windows flashing , there is no peel and stick flashing tape here ( never ever seen any peel and stick product on a building site, don’t even mention liquid applied flashing ) , no sloped pan , no nothing. Anyway if someone has ever been to Australia and can explain me why our building industry seem so far removed from your that would be great .
( one last thing , although the building code of Australia asks for a “as tight as possible building” , there is no airtightness requirement in Australia , nor any registered builder i have talked to know what a blower door test is or how to rate airtightness ( nor do they really know what airtightness is ) . I’m renting in a house that i would say hit the 30.ACH50 with all the holes everywhere and i would say that it is the norm here , people live in very uncomfortable houses but everyone seem to just get along with it . )
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Houses in North America were built with little regard to air-sealing and insulation until quite recently. The impetus for change was the direct result of trying to minimize energy costs in a much colder continent than Australia, where I would imagine the more benign climate means there isn't as much reason to pay attention to efficiency.
North American construction more closely resembles that in Northern European countries with similar climates and abundant sources of timber. Similarly, from what I've seen Australian houses more closely resemble those found in southern Europe - which of course make some sense.
To me the upside of building in your climate is the close connection between the interior and surrounding lot you are able to get. The response to the Australian landscape by architects like Glenn Murcutt seems both appropriate and very beautiful.
There is no doubt that a great way to avoid sheathing rot is to not have wood sheathing. One can get an easy to seal exterior with foam + tape, diagonal bracing and no wood sheathing. It is done here in the USA. But no idea why this design isn't more popular.
User-7081215,
Can you tell us your name? (I'm Martin.)
In an article called "Wall Sheathing Options," I wrote:
"Builders who install a continuous layer of rigid foam insulation on the exterior side of their walls often install the foam over OSB or plywood sheathing. However, it’s also possible to skip the OSB or plywood, and to install rigid foam as the only sheathing material on the wall. The main advantage of this approach is that the rigid foam provides a continuous layer of insulation that interrupts thermal bridging through the studs. It’s also an affordable approach, because you don’t need to install any OSB or plywood."
Most builders prefer to use OSB or plywood, however, because it makes siding attachment easier, and is stronger in areas subject to high winds or earthquakes.
Malcolm gave a good analysis of the situation in Australia, which sounds a lot like the situation in southern California in the 1960s. If the weather is mild, who cares about air tightness?
Housewrap and roofing underlayment (sarking) don't necessarily need tape at the seams, even in a well-built house. Usually, the air barrier is elsewhere. If seams incorporate laps, gravity prevents water intrusion.
Plywood or OSB makes for a structure that can withstand earthquake forces and high wind. The strap bracing was used in California until real earthquakes demonstrated it did not work very well. You can follow the increasing code requirements that follow earthquake events. Also testing of shear walls & roof diaphragms have been done in the lab to verify the design strengths & design values. see ----W260 Research Report 158: Performance of Wood Structural Panel Shear Walls Under Cyclic (Reversed) Loading---- on the http://www.apawood.org site most every thing wood design related.
I know you have a lot of problems down there with little critters eating your wood too. I’ve seen many pictures of the termite (?) treated wood that is blue. Perhaps the steel bracing has the advantage of requiring less treated wood panels? I’d assume the treatment process makes the wood a lot more expensive, similar to our fire retardant treated (“noncom”) plywood here that is maybe 2-3 times more expensive than regular plywood.
As others have said, North America in general is much more concerned with insulation in the colder climate to keep heating costs down. Construction has many different requirements depending on the region. I suspect Australian building codes probably are more strict regarding insect control than codes here where the cold weather helps to limit the spread of destructive insects.
Bill
Okay , thank you very much for all the answers .
I wanted to add that i live in the south west which is considered Warm temperate . Our winters drop to 3 - 4 Degree C at nigh with a lot of rain and are summer can reach the 40s. Yesterday afternoon was 38 , 39.5 in the house .
Although it may be considered mild i can tell you that it is mighty uncomfortable , we are obliged to fly out of the house during the day and during the winter i have to chop so much timber to keep the place comfortable its dreadful as our forest have already been demolished from their original state and that although i only cut dead wood , these trees are much needed for the mammals and birds to nest in .
Tasmania is considered an Alpine climate zone and temperature can drop -5 -10 there is still no requirement in Air tightness there. People in Tasie have just the biggest pile of wood fire in the whole country ^^.
It just seems that Australia because of its mines and forest still choose to counter act the inefficiency of its building by using mass amount of fossil fuel .
Relating to the Sheathing it seems that your sensitivity to earthquake and high wind has led you to use the panel for sheathing where as here it may not be needed .
We do have a real termites sensitivity here and our frame are all blue , which may have led us also not to use the panels as that would be a real weak spot .
In response to Martin's Comment , i knew of using only rigid foam its just that here the idea of using external insulation hasn't reach the country and is still an Alien idea . Expect for the Passiv House Institut of Australia most builders here build without knowledge of airtighness , thermal bridges etc probably again because we can counter that with the use of a lot a energy .
I see and i hope that Australia will follow America in increasing its standards on building as the price of energy is getting unbearable for people.
Kevin,
I live in the Pacific Northwest which is a lot milder than the rest of Canada. Given that, when I moved here I was surprised to find a lot of the older houses are uncomfortably cold and drafty, when if they had been built the way it was common to do in the rest of Canada they would have performed really well. Maybe there is something about living in a temperate climate that reduces the impetus to build efficiently, even though it is much easier to do?
I've seen a few very appropriate and efficient houses designed by Australian architects. Hopefully their methods will gain more widespread acceptance among mainstream builders. Here the main driver of efficiency seems to be improved building codes. Without them I doubt there would be much incentive to improve the quality of new housing.
My favourite Australian design site:
https://www.lunchboxarchitect.com
one more little things i wished to say to agree with Malcom Taylor is that Australia abundant space offers a real opportunity for people building in the country to have a lots of land and space to build houses blended within a natural environment .
>"...why do American houses brace the entire house with OSB or ply panel?"
For one thing, it's relatively inexpensive in the US, and effective.
Except for higher elevation locations, the coolest states in Oz run less than 1500 HDDC (base 18C), making it comparable to US climate zones 1 - 3, which is cooling dominated.
http://www.bom.gov.au/jsp/ncc/climate_averages/degree-days/index.jsp
http://www.ccma.vic.gov.au/soilhealth/climate_change_literature_review/documents/organisations/csiro/MelbourneEDD2008_2012.pdf
>"Tasmania is considered an Alpine climate zone and temperature can drop -5 -10 there is still no requirement in Air tightness there. "
In US climate zone 4A & 4B a daily HIGH temperature of -5C is a common wintertime event, in US climate zone 5 a daily high of -10C isn't rare. In zone 6 the January mean temperature is lower than -10C in many locations, in zone 7 there are whole weeks that exceed that temperature.
The monthly mean MINIMUM temperature for July in random locations in Tasmania run between -2C - +2C. eg:
http://www.bom.gov.au/jsp/ncc/cdio/weatherData/av?p_nccObsCode=38&p_display_type=dataFile&p_stn_num=091022
http://www.bom.gov.au/climate/data/
That'e very mild compared to most of the US & Canada.
Air tightness counts a lot for comfort and energy use in zone 4-8 than it does in zones 1-3. When the outdoor temperatures average below 0C for weeks on end the indoor air becomes dry & uncomfortable, and has health consequences as well.