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daveh
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R-Value Confusion

09/28/2012 8:47 AM

New legislation has been introduced in South Africa defining the level of insulation required in a new building. Now, in order for a plan to be approved, the application must be accompanied by R-values achieved for walls, windows and roof structure. Prior to this, architects here tended to design empirically, particularly dwellings. Now, we all need to deal with terms like Thermal Conductivity and R-values. For a house roof in Cape Town, an R-value of 3.7 is stipulated. We are fully metricated, so obviously this figure is in Metric units.

I was most impressed to discover an insulation material (SPF) newly introduced here, having an R-value in excess of 6 per 25mm. The info is in the supplier's technical website literature, and endorsed by their associates, a huge US chemical firm. Being a suspicious cynic I decided to dig a bit, and it didn't take me long to discover - particularly from an informative Wikipedia article - that the material's R-value was being quoted in Imperial units, and its value in Metric terms is only about 1.05 per 25mm. When this was brought to the attention of the firm's owner, he conceded that Imperial R-value with no units given "can cause confusion". What an understatement!

My only reason for writing is to enquire from someone out there - hopefully an architect or engineer - if this sort of confusion is common? The Wikipedia article refers to 'ambiguity', but it seems to me that someone in the industry, particularly if backed by a large chemical firm, should be beyond this sort of thing. To me it either smacks of abysmal lack of education, unacceptable casualness or a deliberate attempt to mislead. Any opinions?
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Joshi
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#1

Re: R-Value Confusion

09/28/2012 9:11 AM

I think it is a deliberate attempt to mislead.
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Yahlasit
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#2

Re: R-Value Confusion

09/28/2012 9:12 AM

Eventhough I haven't gone thru the case you describe, I'd say it is a deliberate attempt to mislead, counting on a generalized costume to abandon any search of the second asterisk, and laziness to read the small letters.

It is unbelievable to think that they didn't pay enough attention to something from which totally depends their existence: Sales !.

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Yahlasit
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#3

Re: R-Value Confusion

09/28/2012 9:20 AM

Send us a picture of your locality that worth seeing, I can't travel much, but this forum is visited by people from around the globe and it would be nice to know places thru their posts.

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ozzb
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#4

Re: R-Value Confusion

09/28/2012 10:37 AM

Just about all the companies around the world do not specify what the unit of measure is.

If the R value is out of the norm we all should question it.

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redfred
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#5

Re: R-Value Confusion

09/28/2012 11:54 AM

While some people dislike the use of Wikipedia links because they can be modified by anyone, I find that this is more often an advantage because an error on wikipedia is quickly corrected. From that link you will see that the dimension difficulty of the R value of insulation is a known complication.

Around most of the world, R-values are given in SI units, typically square-metre kelvins per watt or m²·K/W (or equivalently, m²·°C/W). In the United States customary units, R-values are given in units of ft²·°F·h/Btu. It is particularly easy to confuse SI and US R-values, because R-values both in the US and elsewhere are often cited without their units, e.g., R-3.5. Usually, however, the correct units can be inferred from the context and from the magnitudes of the values. United States R-values are approximately six times SI R-values [2].

As for the complaint about sales and marketing, their job is to make sales for their company. The engineer or architect of a project has the due diligence responsibility to meet local building codes, not the sales department of any construction material. There has always been and always will be multiple standard unit systems used by different engineering systems. The value "h" in the Wikipedia clipping is the time unit of hours instead of seconds or the more universal Planck's constant. The engineer must know the difference.

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Yahlasit
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#6
In reply to #5

Re: R-Value Confusion

09/28/2012 5:08 PM

GA redfred, I recently had to infer the correct units myself, it was the pressure required to allow a negative (inwards) deflection of a flame curtain into an anealing oven, the engineer specified from .5 to 3 Psig. of pressure inside the combustion chamber, when that would be orders of magnitude over the .5 to 3 mmHg. required; I wrote him my concerns and after 3 days he corrected his requirement to mmHg.

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daveh
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#7
In reply to #5

Re: R-Value Confusion

09/29/2012 1:00 AM

Hi Redfred, your injunction for a practitioner to apply 'due diligence' is heeded. However as I said, the necessity to be aware of actual insulation figures is new in this country and the material is also new. It's described by the supplier as "Best insulation in the world". I don't fall for 'hype', but here's an extract from the extremely comprehensive technical website:

• Maximum aged Thermal Conductivity ('Lambda' ) of 0.028 W/(m•K)
• Aged Closed-Cell 'SPF' has an average R-value of 6 per 25mm thick.

Thermal Conductivity is expressed in Metric units; the R-value thickness is expressed in mm, not inches. What inference is any reasonable person expected to draw? In addition, the supplier's associate is probably one of the largest chemical companies in the world. One would surely expect one of their 'boffins' to have read the literature and offered correction. Lastly, as you say, "around most of the world, R-values are given in SI units". We've been fully metricated for about 40 years. What should one expect from locally-written technical info?? Frankly, I just give up!!!
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