Replies

1. 
   kevin_in_denver | Aug 17, 2011 01:41am | #1

   The answer is a simple heat loss calculation, comparing the zero heat loss of a common wall with the heat loss through an insulated wall with a couple windows.

   I'm going to pass on doing the calculation for you though, because of my opinion about the situation:
   A homebuyer faced with a decision between the two configurations, with all other things being equal, will always choose the detached single family residence. Even if he is convinced that the common wall will save him $300/yr.

   As windows improve and walls get thicker, this savings goes down, so the trend is moving toward the SFR.

   I apologize for offering opinion instead of fact.

2. 
   user-659915 | Aug 17, 2011 09:33am | #2

   Attached homes share more than common walls. This forum, reasonably enough, tends to focus on operational energy efficiency of the individual home itself, and as Kevin points out the differential energy advantage of the shared wall tends to fall away as insulation standards improve. From a holistic perspective however compact development of attached homes can offer many additional environmental benefits including more intensive land use (saving land for agriculture), reduced infrastructure requirements and better opportunities for shared local transport - carpool, bus, light rail, etc. (I say 'can' offer these advantages because they are by no means implicit in the model. I'm sure we've all seen attached home developments in inappropriate locations, far from important community resources such as education. employment and social life).

   Having said that, attached homes are not for everyone and as Kevin again rightly points out, few people will choose to build or buy one merely for a few hundred dollars a year in energy savings.

3. 
   user-869687 | Aug 17, 2011 03:24pm | #3

   When houses stand directly side by side (e.g. townhouses) there are various savings vs. detached houses, as mentioned here. It's important to consider energy used for transportation, in addition to the structures themselves. However, as density increases, certain building types have additional demands for resources. High-rise buildings use steel and concrete construction and add elevators and sub-grade parking structures, all of which are resource intensive.

   Apartment dwellers have lower heating bills and they don't waste gasoline on leaf blowers and weed whackers, but they also lose the opportunity to grow produce in the yard. An ideal density would be high enough for people to get around without gasoline, while still having the ability to grow food rather than buying produce that traveled a thousand miles on a truck. I would guess the sweet spot is attached dwellings in small clusters--duplex and fourplex wood structures, some mid-rise structures, no high rises. Walk Score should be 75+.