NOTE: Make sure you read the first three posts (in order!) before tackling the rest, or it could be confusing: Post 1 is Designing the future, Post 2 is Setting up the problem, and Post 3 is Estimating basic requirements.


Friday, October 13, 2006

Breaking down energy needs: Insulation (Part 1)

An often-mentioned number in home building is “R-value” or “R factor”. The R-value is a measure of a material’s resistance to heat transfer and is used to compare different types of insulation. It is calculated using the thermal conductivity constant, k:

R = [thickness (in inches)] / k
k = [BTU * inch]/[ft^2 * hours * ˚F]

Insulation must be treated as a whole-structure concept. Just as the amount of insulation in your home means little if you leave your door wide open, using very high-R material in the walls may provide little return if you use low-R windows. It’s all in the rate of heat transfer.

The following table provides some common measurements for R-values compiled from various sources. A few things to note: R-values are calculated under ideal laboratory conditions and may vary considerably “in the field” (more on this later); these R-values are valid for wall, roof, or floor calculations; R-values for green roofs can be complicated and will also be discussed later.

MaterialR-value per inch thicknessR-value per unit
Gypsum0.6 – 0.9
Hardwood (oak, maple)0.91 - 0.94
Softwood (fir, pine)1.3
Fiberglass3.0 – 3.8
Brick0.1 – 0.2
Asphalt shingles0.44
Aluminum/Steel Siding 0.61/panel
Loose cellulose2.8 – 3.7
Loose fiberglass2.2 – 4.0
Loose rock wool3.1
Loose vermiculite2.2
Molded polystyrene3.6
Extruded polystyrene3.6
Polyurethane foam5.6 – 6.2
Sprayed cellulose3.0 – 4.0
Carpet (with padding) 1.2 – 2.1/layer
Air (3/4” – 4”) 0.9
- Single 0.76 – 1.1/unit
- Double 1.2 – 2.2/unit
- Triple 1.3 – 2.6/unit
- Double, low emissivity 1.3 – 2.9/unit
Cement mortar0.2
Vinyl 0.05/layer
Soil (fine, 20% moist)0.08

Coming up next: The Fallacy of R-value Tunnel Vision

Oswego University


At 9:10 AM, Blogger DJEB said...

More and more great resources keep arriving on this site. Great stuff.

Hopefully I will have some time soon to throw some stuff your way.

At 3:41 PM, Blogger PeakEngineer said...

Thanks djeb. I checked out your permaculture blog -- great stuff. Now that's a great resource. I look forward to talking more with you in the future.

At 11:37 PM, Blogger Blue Girl, Red State said...

Good stuff here. I'm pretty political, but I have been a working scientist for 20 years. I just left a career in laboratory medicine to pursue a doctorate in climate science, so the things I had an understanding of before are really popping now, as knowledge catches up with interest.

At 11:49 PM, Blogger PeakEngineer said...

Good luck on doctorate, blue girl, that's a tough field. Stop back when you have time, we could use your expertise as we develop things here, such as designing with global warming in mind.

At 6:43 PM, Blogger Blue Girl, Red State said...

I am the geek who drove around with the bumperstickers that said Everyone has Avogadro's Number and Honk if you passed P-Chem. No one ever honked.

Hey, I wrote a post today dedicated to basic conservation, since I reviewed previous energy posts and realized I have given it short shrift.

My husband is an Electrical Engineer. We inherited some tiberland in north Missouri and built an energy efficient two-bedroom half-earthen dwelling that is powered by three windmills. It is heated with radiant floors and solar panels, and the water is heated with a tankless electric unit.

At 12:46 PM, Blogger DJEB said...

I am happy to announce that PeakOilDesign is now linked to Permaculture Reflections.

At 5:00 AM, Blogger PeakEngineer said...

Cool, djeb. I finally remembered to link up to your site as well.

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