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Continuous insulation vs. insulation batts

Hi, I am in Australia and our study in insulation is quite inferior to some of the overseas studies. I was wondering if anyone had seen or performed a study on the differences in insulation properties of continuous insulation in the form of rigid panels vs the non continuous insulation in the form of Insulation Batts?

I am particularly interested in the effect of having gaps where the frame or studs can act as a thermal bridge or even downlights can create air leakage. Our energy calculation software does not take this into account in it's energy efficient ratings but I suspect it should. Interested to hear people's thoughts on this.

Regards, Jamie

Asked by jamie harrison
Posted Wed, 12/18/2013 - 21:31
Edited Thu, 12/19/2013 - 06:30


1 Answer

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Building scientists have long recognized that a continuous layer of rigid foam insulation or mineral wool insulation performs better than strips of insulation installed between wood or steel framing members. It's a shame that your energy modeling software is so primitive.

Here are some issues to consider:

1. Fiberglass insulation (and other similar examples of batt-type insulation) is hard to install well. Flaws and gaps degrade the thermal performance of most batt installations. For more on this issue, see Installing Fiberglass Right.

2. Framing members can make up 25% to 30% of the area of a wood-framed wall. Wood framing has a lower R-value than insulation; steel framing is even worse. For more information on this issue, see Whole-Wall Thermal Performance.

3. In addition to the thermal bridging of studs and other framing components, building envelopes also have thermal bridging at penetrations, windows, chimneys, etc. While these types of thermal bridging are harder to address with rigid foam, they must be taken into account by energy software. For more information on thermal bridging, see:

Thermal Bridging

What is Thermal Bridging?

The Building Envelope

Thermal Bridging Calculation

4. You also raise questions about air leakage. This is an entirely different subject, but any energy modeling program that doesn't include some type of air leakage calculation would be surprisingly primitive. For more information on this issue, see:

Air Leakage Degrades the Thermal Performance of Walls

Questions and Answers About Air Barriers

Blower Door Basics

Answered by Martin Holladay, GBA Advisor
Posted Thu, 12/19/2013 - 06:27
Edited Thu, 12/19/2013 - 06:35.

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