For a good academic discussion of housing as a consumption good and as a component of an investment porfolio, see
http://www.socsci.uci.edu/~jkbrueck/course readings/flavin-yamashita.pdf
"Simply by virtue of its magnitude, housing
plays an important role in both the consumption
bundle and the asset portfolio of the household.
This role is complicated, and made more interesting,
by the fact that most consumers choose
to hold a single level of residential real estate to
satisfy both the consumption demand for housing
services as well as the portfolio demand for
housing, rather than use rental markets to disentangle
the two aspects of the problem. To the
extent that the household?s holding of real estate
is determined at least in part by its consumption
demand for housing services, the consumption
demand for housing places a constraint on the
portfolio problem. Using PSID data and the
Case-Shiller repeat sales transactions price data,
the paper estimates the risk and return to ? nancial
assets and residential real estate, and calculates
the optimal portfolios and constrained
mean-variance ef? cient frontiers for various
values of the housing constraint.
The model implies that households which are
ex ante identical, in the sense that they have
identical preferences toward risk and identical
perceptions of the risk and return to different
assets, will nevertheless hold quite different
portfolios of ? nancial assets because each
household is optimizing their portfolio subject
to a constraint on housing, and this constraint
varies across households."