R-value

The Diminishing Returns of Adding Insulation

Posted on April 18,2015 by ab3 in conduction

If you're building a house and want to have a really good building enclosure, you need it to be airtight, handle moisture properly, and have a good amount of insulation. Ideally, you'd also consider the effects of solar radiation on the home, but for now let's just focus on the insulation. What exactly is "a good amount" anyway?

Stay Away from Foil-Faced Bubble Wrap

Posted on April 18,2015 by user-756436 in bubble wrap

Most brands of foil-faced bubble wrap are only 3/8 inch thick or less, and have an R-value of only 1.0 or 1.1. Since the product often costs more per square foot than 1-inch thick rigid foam rated at R-5, why would anyone use bubble wrap as insulation?

What’s the Definition of an ‘R-20 Wall’?

Posted on April 18,2015 by user-756436 in building code

Builders often talk about the R-value of their walls. But if a builder claims to have an R-20 wall, what does that mean? Building codes commonly include a table listing the minimum prescriptive R-values for walls and ceilings in different climate zones. For example, Table R402.1.1 in the 2012 International Energy Conservation Code (IECC) informs builders that the minimum prescriptive R-value for walls in Climate Zones 3, 4, and 5 is “20 or 13+5.”

Free Online Calculators for R-Values and Costs

Posted on April 18,2015 by ScottG in Ekotrope

A team of software developers is offering a free online calculator you can use to compare the thermal performance and cost of a variety of roof, floor, and wall assemblies. Ekotrope is part of a larger application of the same name that the company sells to residential designers. Nick Sisler, one of Ekotrope’s founders and a product development engineer at the company, said by e-mail that the full version of the software is accredited as a HERS rating tool.

In Cold Climates, R-5 Foam Beats R-6

Posted on April 18,2015 by user-756436 in EPS

Researchers have known for years that most types of insulation — including fiberglass batts, extruded polystyrene (XPS), and expanded polystyrene (EPS) — perform better at low temperatures than high temperatures. The phenomenon was described by Chris Schumacher, an engineer and researcher at Building Science Corporation, at a conference in 2011: “If you measure the R-value of an R-13 fiberglass batt, you’ll get different results at different outdoor temperatures. If the outdoor temperature rises, the R-value goes down.

Finding the Insulation Sweet Spot

Posted on April 18,2015 by ScottG in insulation thickness

Anders Lewendal, a builder in Bozeman, Montana, is wrestling with a familiar dilemma: What's the right amount of insulation to put in a house? "Our theory," he writes in Q&A post at GreenBuildingAdvisor, "is that too little insulation wastes energy and equally, too much insulation wastes energy. Where is the sweet spot in each climate zone?" To that end, Lewendal is proposing more performance testing.

Is R-Value Dead as a Dodo?

Posted on April 18,2015 by user-1048334 in air leakage

Once upon a time, house insulation meant an extra sweater — and stop your damn complaining. Men were men, women were women, and cats and dogs were cats and dogs, I assume. Houses included features to produce and retain heat, of course — things like double back-plaster walls and central chimneys. But until the 20th century, insulation barely existed in any formal sense.

FTC Cracking Down on False R-Value Claims

Posted on April 18,2015 by AlexWilson in exaggeration

Most of us want to do the right thing in improving the energy performance of our homes. We research energy-saving products like appliances and insulation. We search the internet or clip ads from the paper looking for products that will save us the most energy (and money). We look for the most R-value for the money. Well-meaning homeowners do this all the time.

Air Leakage Degrades the Thermal Performance of Walls

Posted on April 18,2015 by user-756436 in Building Science

For the past five years, researchers at the Building Science Corporation (BSC) in Massachusetts have been testing the thermal performance of a variety of wall assemblies as part of an ambitious project to develop a new metric to replace R-value. (I last reported on the project in my August 2011 article, A Bold Attempt to Slay R-Value.)

A Bold Attempt to Slay R-Value

Posted on April 18,2015 by user-756436 in Building Science

R-value is the poor stepchild of building science metrics. Although it is often essential for builders, designers, and engineers to know a material’s R-value, this useful metric is regularly abused, derided, and ridiculed for its shortcomings. “R-value doesn’t measure assembly effects: thermal bridges, air movement, thermal mass, moisture content — all of which can all affect thermal properties,” explained Chris Schumacher, an engineer and researcher at Building Science Corporation, at a summer symposium in 2009. “R-value doesn’t do a good job describing the entire system.”

Is There a Downside to Lumpy Attic Insulation?

Posted on April 18,2015 by ab3 in attic insulation

If your attic is going to have 50 bags of insulation blown into it, does it make much of a difference if it goes in flat or lumpy? One reason that I'm interested in the question is that my dissertation in grad school was called “Flat or Lumpy.” (Of course, it had the requisite incomprehensibility in the subtitle, with words like “heteroepitaxy.”) Those two words in the title, which cut to the heart of what my surface physics research was all about, also describe a property of insulation that's important in building science.

Air Leaks or Thermal Loss: What’s Worse?

Posted on April 18,2015 by ScottG in air leakage

Beefing up R-values and reducing air leaks are the twin rallying cries of builders focusing on energy efficiency. Regardless of the particulars of the house design, more insulation and fewer air leaks make houses more comfortable, more durable, and less expensive to heat and cool. No one seems to argue that point. But Al Cobb wonders which is more significant.

Energy-Efficient Garage Doors

Posted on April 18,2015 by user-756436 in garage door

If you’re shopping for a garage door, the door’s energy performance may not matter — especially if you don’t heat your garage. However, there are a few reasons why you might be looking for a well-insulated, draft-free garage door:

How Much Insulation is Needed?

Posted on April 18,2015 by AlexWilson in expanded polystyrene

Standard residential construction in much of the country is 2x4 framing with fiberglass insulation, achieving a paltry R-10 or so in the walls. If insulation is installed at all on the foundation walls, it’s rarely more than an inch thick, and insulation is almost never put under slabs. In Vermont, we typically do a lot better. Act 250, enacted nearly four decades ago, required developers to improve energy performance and that led to a widespread switch to 2x6 framing in home building.

Understanding R-Value

Posted on April 18,2015 by user-756436 in conduction

R-value measurements are subject to a fair amount of ridicule, especially by marketers of radiant barriers. As it turns out, however, the ridicule is mostly unwarranted.

Beware of R-Value Crooks

Posted on April 18,2015 by user-756436 in FTC

Scammers continue to use exaggerated R-value claims to peddle inferior insulation products, in spite of the existence of strong consumer protection laws. Year after year, naïve builders fall prey to Web-based marketing pitches for “miracle” products like “insulating” paint and 1-inch-thick R-10 foam.

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