In my last post, I explained how the energy conservation provisions found in Chapter 11 of the International Residential Code (IRC) provide options for designers and builders when it comes to energy code compliance.
Since energy codes were introduced in the 1970s, they’ve provided different ways to design and build a home’s thermal envelope to provide for conservation, as well as other methods of creating effective use of energy that are all sufficient to meet the performance goals established by the International Code Council. Though there have always been options, the options have evolved.
The prescriptive methods for energy code compliance (including the R-value alternative, U-factor computation, and UA alternative) were explained in the last post. These straightforward requirements outlined in the IRC are generally simpler methods than the compliance paths I’ll discuss here.
In this post, I will explain the performance path and the Energy Rating Index, or ERI, but only a basic overview. That’s because these methods require third-party evaluations and significantly more detail about the house’s design, location, orientation, equipment, airtightness, on-site energy generation, and more to be evaluated for energy code compliance. While they may require more detailed information and the work of third-party professionals, they also offer much more design flexibility and choice.
No matter which path you take to energy code compliance, the 2021 IRC includes a section of “additional efficiency package options.” Here designers and builders face another set of choices. I will discuss this section of the energy code in this issue as well.
Performance path and energy costs
When measuring the results of something, you need to have a metric for comparison. For my route to the retail store, the metric of success is whether I arrived. But when measuring the path of energy code compliance, there is…
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5 Comments
Thank you for this informative piece. Roofers, I will take this opportunity to ask a question not about the article content but rather the roof: i notice the roof shown has asphalt shingles on higher facets vs metal standing seam covering porch. On New England houses this pattern is or has become popular. Im curious why ? Why wouldnt builder spec same cladding for all facets? If entire cladding is standing seam, upfront cost is higher but reroof can be delayed almost perpetually. If all asphalt, upfront cost lower but reroof needed sooner. Lower facets of roof get water shedding from higher ones. Why the asphalt / standing seam combo ? Why not be economical now and get all asphalt OR blow the big bucks now for 100% standing seam ? Thank you
am,
It's entirely a design feature to add some visual variety to the house, and include what is seen as a higher quality finish. Like the photo, around here it is invariably a small porch roof or dormer. Leaving the main roof as shingles both saves money, and allows the house to fit in with its neighbours.
Thank you Malcolm
It's common on old homes here in New England to have metal on the roof at the eaves only, as an attempt at alleviating ice dams, which are pervasive and destructive on older homes. The thought is that snow will slide more easily from a metal roof than from a shingled roof. A architect I used to work with called them "fingernails" and I've used that term ever since.
Similarly, with the idea that metal sheds snow better than asphalt shingles, many lower-sloped roofs, and/or roofs that other roofs dump their snow onto, get metal roofing as well.
In most cases, metal roofing is significantly more expensive than asphalt roofs, so the metal is used only where needed.
My experience is that metal doesn't actually shed snow much better than asphalt, at least the wet, sticky snow we usually get, but that's another matter.
Standing seam metal does seem to contain leaks from ice dams or just melting snow better than shingles. I'll include a photo of a porch addition I designed, on the north side of the main house and with tall evergreens shading the west side, so the inside corner doesn't see sun all winter, and snow presumably piles up. My clients also just liked the pizazz of a copper roof. Normally I would make that kind of porch roof lower-slope but I wanted all of the snow-shedding I could get.
Because these are traditional patterns, many people here like the contrast--similarly to how in other places (and increasingly here) people like facades with a lot of variety, changes in cladding and window sizes, etc..
Thank you, Michael, for the helpful explanation. A stunning porch !
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