  We analyze non-universal 5D standard model extension, where some or all of
the gauge and Higgs fields propagate in a flat extra dimension, while all other
degrees of freedom are localized on a S^1/Z_2 orbifold brane. From LEP data,
model-dependent bounds on the compactification scale M between 4 and 6 TeV are
derived. We analyze the correlations between M and the SM Higgs mass m_H.
Investigating the prospects at an e^+e^- linear collider such as TESLA, we show
that the so-called GigaZ option has the potential to improve the LEP bounds by
about a factor 2. At the center of mass energy of 800 GeV and with an
integrated luminosity of 10^3 fb^{-1}, linear collider experiments can probe
compactification scales up to 20-30 TeV and beyond, depending on the systematic
errors.
