  We present new radio continuum images of the edge-on starburst galaxy NGC
5775, from LOFAR (140 MHz) and the Karl G. Jansky Very Large Array CHANG-ES
survey (1500 MHz). We trace the non-thermal radio halo up to 13 kpc from the
disc, measuring the non-thermal spectral index and estimating the total
equipartition magnetic field strength ($\approx13\mu$G in the disc and
$\approx7\mu$G above the plane). The radio halo has a similar extent at both
frequencies, displays evidence for localized cosmic ray streaming coinciding
with prominent H$\alpha$ filaments and vertical extensions of the regular
magnetic field, and exhibits a boxy morphology especially at 140 MHz. In order
to understand the nature of the disc-halo flow, we extend our previous model of
cosmic ray propagation by implementing an iso-thermal wind with a tunable `flux
tube' (approximately hyperboloidal) geometry. This updated model is successful
in matching the vertical distribution of non-thermal radio emission, and the
vertical steepening of the associated spectral index, in a consistent
conceptual framework with few free parameters. Our new model provides the
opportunity to estimate the mass outflow driven by the star formation process,
and we find an implied rate of $\dot{M}\approx3-6\,\mathrm{M_{\odot}\,yr^{-1}}$
($\approx40-80$ per cent of the star formation rate) if the escape velocity is
reached, with substantial uncertainty arising from the poorly-understood
distribution of ISM material entrained in the vertical flow. The wind may play
a role in influencing the vertical gradient in rotational velocity.
