[Greenbuilding] new houses vs. retrofitting existing houses.

[Corwyn]

Greetings,

I wrote this up for a friend, and thought it might benefit from broader 
distribution.

Thank You Kindly,

Corwyn

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Looking at the academic question of new houses vs. retrofitting existing 
houses.

A house consumes several types of energy, embodied energy in the 
construction and renovation, and ongoing energy to keep it comfortable 
for its occupants, and energy to disassemble it and dispose (in whatever 
manner) it constituent parts.  The most energy efficient house will be 
the one which minimizes the sum of those three energies.

I will leave aside discussion of any current house, and assume we are 
starting with nothing but a desire to live as energy sparsely as possible.

The construction energy of a currently existing house is in some sense 
paid already, so we will ignore it.  That leaves renovation energy 
against building energy.  I often take money as a  first order proxy for 
energy.  It doesn't work if there is specific obscuring going on, but it 
makes thing simpler.  So for a high level look, you can compare the 
price of a new house to a comparable retrofit.  Since much of the work 
of retrofitting an old building will consist of removing existing 
insufficient materials and replacing them with more efficient ones, 
houses which already need to have those materials replaced will be 
better candidate for retrofitting.  Ripping apart a up-to-code 2005 
house, to make it appropriate for 2012 fuel prices, while a powerful 
statement, seems a bit wasteful of materials.

Disposal energy can be considered equal, if you assume that either way 
you are going to use the most environmentally friendly materials you can 
find.  Disposal of existing materials during the process of the retrofit 
will of course need to be considered now.

As far as ongoing energy is concerned, a retrofit of an existing house 
can be made as efficient as a new house, but it requires more effort. 
It also tends to require more high embodied energy insulation (like 
foams).  The best foams are still 30 times more energy intensive to 
create than cellulose insulation.  There do exist old buildings with 
large cavities, ready to accept huge amounts of cellulose insulation 
(i.e. over a foot thick), but they are fairly rare, and probably 
expensive to buy.  There may be reasons why you might not be able to 
meet the efficiency levels of the best new houses in an old house, so 
that would need to be taken into consideration.  There is NO reason not 
to build the most efficient new house you can.  For every $100 you save 
in monthly energy bills you can afford to put $16,500 more into the 
house, and keep the same overall monthly expenditures (if energy prices 
remain constant, ha!).

Air sealing is another issue, in the average house in Maine, roughly 
one-third of the heat loss is through air leaks. In building a new 
house, or retrofitting an old one, air sealing is mostly a matter of 
careful attention to detail (although there are some tricks to avoiding 
problem areas which are doable in new houses).  The problem in old 
houses is access; the air sealing needs to happen at a single contiguous 
surface across the entire structure to be most efficacious. This means 
getting into the guts of the building somehow (although it is likely 
this will need to be done anyway).

Other considerations:

* A new house can be made to sit on the most efficient location on a 
site, and in the best orientation, for solar access.  This just isn't 
possible with an existing house (though, of course, many are already 
sited that way, our ancestors weren't completely dim).

* A new house can be (but rarely are) made in such a way that it will 
respond to changing demands made on it, with minimal disruption.  "Open 
Built" is a way of constructing a building such that elements which need 
to be replaced more frequently, are installed such that they can be 
replaced without destroying elements with longer lifespans.

* The advantage of new houses being perfectly suited to you is 
overstated in my opinion,  circumstances change, best if the house 
adapts, rather than being perfectly suited to a lifestyle you no longer 
live.

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-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.greenfret.com/
topher at greenfret.com
(207) 882-7652