On this forum we sometimes hear recommendations for very high levels of insulation.  In the case of deep-energy retrofits, the costs for this action can be quite high.  Martin Holladay of Green Building Advisor has a discussion at GBA forum that summarizes deep-energy retrofits of four 100-year-old homes (one a duplex) in Utica, NY, and points out that those retrofits averaged a cost of $89,783 for each living unit.  The retrofits saved an average of 393 therms of natural gas annually for each living unit, having a value locally of $647, for a simple payback period of 139 years. 

Mr. Holladay points out that if the same amount of money ($89,783) were spent on solar PV systems for each unit, that amount would purchase a 20 kW system with an annual electrical production of 22,401 kWh worth about $3,248, or about 5 times the energy saved by the retrofit program.  Maybe not quite a fair comparison since the homes hopefully were more comfortable and livable after the retrofits and included new roofs for two homes, but it does challenge our standard adage of "conservation first, solar second."  The conservation efforts must be evaluated for practical economic return.  I should point out that the $4.50/W assumed for the PV systems is the going retail rate for installed systems without any rebates.      

I think there is some validity, but I also noticed that some of the materials used were very expensive - e.g. Serious windows. Without looking in great detail I can't say this for sure, but my gut tells me they could have gotten the same results at a miuch lower cost than what they spent.

Also, there are some expenses in this that are not directly related to energy savings, like new siding to replace the stuff stripped off. In my mind, these types of costs should probably come off.

jerkylips-

I agree. On 100-year-old houses you can find a lot to repair. So maybe reduce the energy part of the retrofit values to only 75% of the total, but that is still $67,000 per living unit. I would also agree that some of their choices may have been more appropirate for rich guys wanting bragging rights about their technology than for low-income folks trying to squeek by. I think that was part of the point being made by Martin Holladay. Since I am a fan of solar PV systems, I also thought it was interesting that he compared the "insulation versus PV," although PV systems may not have worked on those houses, and may not be appropriate for the neighborhood.

They break the deferred maintenances out away from the rest of it in a slide toward the end of NYSERDA's deep retrofit contractor training slides, (worth looking at, for some of the construction details.) See p.143 of 144.

In most of the units retrofitted the "Above Grade Wall (AGW), windows, windows, doors" line is on the order of half the total cost, and I'd expect half of that at least half of that line would be just in super-performance windows.  (A quickie analysis of what a pretty-good but lesser windows with photovoltaics + mini-split heat-pumps against the condensing gas combi + super-windows might have been worth a back-of-napkin analysis were all things equal, which they're not. Cost for the mechanicals would have been comparable, but the offset in energy cost from PV paid for by the price differences of the window may have made enough of a difference in some cases, but probably not in all.)

On a cost per occupant basis the multi-family unit (DRP 3-4) looks atrociously expensive ($144K) until you subtract out the deferred maintenance, and end up with $59K/unit (~$119K total) for the efficiency upgrade aspects for 7 total occupants.  Except for the 2-person single-family house the efficiency aspects of the rehabs comes in at about or under $20K/occupant.

The total cost & breakdown is comparable to a full-gut rehab + deep energy retrofit (DER) on a 3-family I've been advising on locally.  Without state & federal subsidy just making code-min R would have been more expensive than what the fully subsided DER is turning out to be, so it didn't take much convincing to push the owner/developer in that direction once I made him   aware of the available subsidy.  (The "before" picture was quite the wreck-in-progress, but gladly it wasn't blown down by the last hurricane.)  By the time he's $200-250K into it (including the purchase price of the property) it going to be pretty damned nice for a rental compared to most local stock, and capable of housing 8-10 people comfortably, with VERY low (tenant-paid) utility costs.