[MassHistPres] new vinyl vs historic wood/storm windows

[Russel Feldman]

Thanks for passing this interesting study along, Dennis.  It's one of the more thorough analyses I've seen.  

For those that are interested, I've a few comments as we take up the issue both from a policy standpoint and as designers/specifiers/builders/owners/regulators considering specific projects. 

1. The study assumes that existing historic windows are in good working order and require no investment.  This is a rare circumstance.  Another and possibly more useful way to consider this might be to pose the question: How much investment in repair and restoration would make the system perform equally from a life cycle standpoint, all other things being equal?  I've reworked the figures and balanced out the different performance findings for North, East/West and South exposures and conclude that, based on this study's assumptions and modeling, the differential is about $470 per window.  In other words, it's fair to say that if one is to compare a new vinyl replacement versus whether to restore an historic window and install a new storm, it makes economic sense to restore the window if the restoration expense falls below $470.  (It makes sense for many reasons, of course, but this offers a way to assess the price that might be paid for preservation.)

2.  I agree with Dennis's observation that a 35 year life for double glazed unit overstates the life cycle benefit of the new window.  In our experience (>21000 windows and counting!) I'd recommend a replacement cycle of 20-25 years at the most.

3. There is no consideration of the sash counterweight wells.  Restoring existing sash necessitates keeping the uninsulated wall cavities for weights of course, which decreases the energy performance of the restored window relative to the replacement alternative.  Similarly, there is no consideration for the capital expense of foaming the cavity in a replacement scenario.  We have assessed this on a variety of projects and recommend insulation when there's an opportunity to do so.  This is particularly valuable in wood frame construction but we've found it worthwhile in stone and brick systems as well.  This aspect of the study understates the relative energy performance of a vinyl replacement.  

4.  There is no consideration of additional environmental impacts of the two alternatives: the energy embedded in the existing window versus the landfill impact of disposal, or the materials consumption, energy and transportation cost of fabricating new vinyl windows.  Setting aside the materials consumption, pollution and landfill factors and just framing the issue around energy and life cycle, the National Trust promulgates some statistics that suggest embedded energy can be a very significant factor.  This aspect of the study therefore overstates the energy benefit of a vinyl replacement.

My general impression is that, from the standpoint of preservation advocacy, the study errs by understating the energy and life cycle benefit of preservation.  That's OK: I'll be pleased to use the $470 per window budget as a good point of reference and I applaud the thoroughness and rigor of this effort.

Russ Feldman


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-----Original Message-----
From: masshistpres-bounces at cs.umb.edu [mailto:masshistpres-bounces at cs.umb.edu] On Behalf Of masshistpres-request at cs.umb.edu
Sent: Tuesday, April 24, 2012 12:00 PM
To: masshistpres at cs.umb.edu
Subject: MassHistPres Digest, Vol 74, Issue 19

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