[Greenbuilding] CF analysis of tearing down a house vs. renovation?

Alan Abrams alan at abramsdesignbuild.com
Tue Jul 23 07:49:10 MDT 2013


great topic, one I wrestle with as a remodeler, with projects often in
historic districts....

first, I'd suggest that the 1998 LCA should be re-evaluated in terms of the
current IEEC--if a new code compliant house is 50% more efficient than one
built in '98, than the 93% ratio is reduced accordingly.

IOW's, the more efficient the new house is, the greater the
*proportional*impact of the materials.  Even that assumes that we are
using the same set
of materials, extracted, manufactured, transported, and assembled in the
same way as '98.  Likewise, what are the more recent considerations related
to demolition or deconstruction, and reuse and recycling or landfilling.

another huge variable is looking forward...will a completely new dwelling
function longer than a renovated dwelling?  that introduces a host of
subsidiary issues, such the quality of lumber from, say, 1920, vs modern
plantation grown SPF.  I'd venture that the 1920 stock will be faring
better in 2113 than some stock milled in 2013--even if it is not exposed to
the weather.

(this is my big beef with preservation policy, that it is a "freeze-frame"
mentality.  It neglects the self evident facts, that what we desire to
preserve was the best of its *own* time; that what we are able to preserve
was constructed with durability--like old growth lumber, coated with
rot-preventing lead paint, etc)

to me, there is no way to generalize.  this question must be evaluated on a
case by case basis.

AA

On Tue, Jul 23, 2013 at 8:41 AM, John Straube <jfstraube at gmail.com> wrote:

> Love to hear the answer.  The difference in before to after energy use
> will be a major determinant of the answer.
> Attached is a 1998 LCA of a house in Michigan.  They found 93% of the
> ENERGY use over 50 years was due to operation, not embodied.  So materials
> and energy during construction is not that important in normal houses.  The
> question is, can you renovate to the same level of low energy performance?
> If that performance is quite low, embodied energy will be quote a large
> proportion.  If the building has a lifecycle of 75 or 100 years, then
> operation becomes more important.
> Complex question, but a worthy one!
>
>
> On 2013-07-23, at 8:29 AM, Matt Dirksen <dirksengreen at gmail.com> wrote:
>
> > I understand its "assumed" that tearing down an old house and building a
> new high efficient home is still going to have a higher CF than
> adding/renovation/energy retrofitting an existing home.
> >
> > However, can anyone point me to any carbon footprint analysis of
> something like this? (And yes, I fully understand its  an apples to oranges
> comparison.)
> >
> > Thanks much,
> >
> > Matt
> >
> >
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> John Straube
> www.JohnStraube.com
>
>
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-- 
Alan Abrams*
**certified professional building designer, AIBD
certified passive house consultant, PHIUS*
*certified passive house builder, PHIUS**
*Abrams Design Build LLC
*sustainable design for intentional living*
cell     202-437-8583
alan at abramsdesignbuild.com
www.abramsdesignbuild.com
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