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Wall energy performance upgrade strategies?

I'm planning to remodel my home and seriously upgrade its energy performance.

The house is a single-story, 2000 sf, 1950s brick-veneer ranch in Dallas, TX (zone 3a?). It is very poorly insulated/sealed and windows are single-pane aluminum sieves. The foundation is pier and beam; the crawlspace is vented.

At best the bricks need re-pointing; at worst they need to be rebuilt to deal with cracks, no flashing at the foundation, no weep holes, etc. Behind the bricks there is about a 1" air gap, and the outside surfaces of the 2x4 walls are sheathed with a 1/2", often crumbling/cracked gypsum-board material. Roof is 1:12 slope, 2x8s. Interior ceilings are dropped to create a low partially accessible attic. Forced air hvac, that I'd like to downsize considerably, maybe switch to minisplits.

To begin, I'd like to address the walls and I'd appreciate feedback on strategies for improving them. We are living in the house, so to the extent possible I'd like to improve the walls from the exterior with minimal disturbance of the interior. Later, I plan to strip the 2x4 walls from the inside and add more insulation. In all we're talking about 2000SF of walls, including about 500sf of window area. I'll be doing the work with another helper and there is no provision for heavy lifting equipment.

My plan is to remove the bricks; this will leave about 5-6" of clear space over the perimeter foundation wall outside of the unsheathed 2x4 wall and rim joists. With this in mind I'm considering 3 strategies:

1. Attach "curtain wall" 4" or 6" EPS or PUR SIPs to 2x4 framing. This sheathes the 2x4 wall, insulates and provides a nailbase for the rainscreen siding in one step. I haven't worked with SIPs before, but if I can get panel sizes that 2 guys could handle I think it's feasible. Could do an RTA kit or blanks. I do not need to match exact window locations, so I like the idea of a kit. I also like less waste and site labor.

2. Install 1/2" sheathing, then 4" nailbase. Provides sheathing, insulation and nailbase, but in 2 steps. More waste and site labor (cutting to size, window bucks), but also more flexibility to deal with unforeseen issues.

3. Install 1/2" sheathing and 2 layers of 2" polyiso. Again more waste, cutting to size, window bucks, but offers flexibility and can do it myself. Biggest downside to me, no nailbase. I remodeled part of the house like this already and had to do a lot of time-consuming tweaking and shimming to get nice straight runs of siding. Between variations in foam panel thickness and the squish-factor, I've got some reservations about doing it again, unless I find efficient work-arounds. That said, I have no personal experience with the manufacturing tolerances of SIPs nor nailbase; they may not be much better.

I'll be getting some material costing estimates in soon. This, combined with wall performance will obviously be centrally important to my decision, but even so, if you have any preferences, gut-reactions, experience working with any of the proposed methods, or other ideas, I'd be grateful to hear them.

Best,
Andrew

Asked by Andrew Thompson Zone 3a
Posted Mon, 12/03/2012 - 18:24
Edited Tue, 12/04/2012 - 08:39

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2 Answers

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Andrew,
All three approaches sound good to me, so really this comes down to your budget and your work preferences.

You might want to price out the three options, because that information may tip the balance in favor of one option.

I'm surprised that you had trouble getting the siding to be co-planar when you installed exterior rigid foam on a previous wall. Most builders don't have significant problems in that area, so there may have been something unique about the house you worked on that led to the problems you describe.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 12/04/2012 - 08:44

2.
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Thanks Martin. Glad they all pass the smell test.

Old houses are wavy, and I probably should have used wider furring strips in my rainscreen to minimize compression. My siding was also very labor intensive: a 2-1/2" exposure clapboard. Nevertheless, a big issue was poor manufacturing consistency of the polyiso panels themselves. As I recall, the 3/4" polyiso that I was installing varied from about 3/4+ to nearly 15/16". Great for R-value, bad for trim. Some times sheet to sheet, some times in the same sheet. This made it a royal pain as I had designed and built the wall components around the nominal 3/4 thickness. Shims and tweaks made it ok, but it took time. I feel a rant about the manufacturing quality of many building materials coming on, but I will resist.

Back to my wall question. Given my climate zone, how much insulation is enough? All things being equal, more is better, but there are diminishing returns, both in terms of performance and ROI. I'm willing to pay more than I might get back in energy savings in many years, in order to do the job right and waste less energy, but there are limits: I can't afford to pay double for 3% performance gain.

In my case would this point to using the EPS in place of PUR sips, for example? I'll know a lot more when I have some hard R and $ numbers to juggle, but perhaps there are articles/posts that address weighing these types of trade-offs...?

Cheers,

Answered by Andrew Thompson Zone 3a
Posted Tue, 12/04/2012 - 18:57

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