Title: The effect of a reflective underlay on the global thermal behaviour of pitched roofs
Authors: Roels, Staf ×
Deurinck, Mieke #
Issue Date: 2011
Publisher: Pergamon Press
Series Title: Building and Environment vol:46 issue:1 pages:134-143
Abstract: The influence of the emissivity of a roof underlay on the global thermal behaviour of sloped roofs is
investigated. Five well-insulated pitched roofs have been constructed in a test building. The five roofs
have a south-west and north-east-oriented pitch and differ in long wave emissivity of the underlay. All
roofs are equipped with thermocouples and heat fluxes sensors to evaluate the thermal response of the
roofs to the climatic conditions. Both summer and winter conditions have been measured. In addition to
the in situ evaluation, a laboratory experiment was set-up to evaluate the influence of the emissivity of
the underlay on the summer behaviour of a sloped roof under fixed boundary conditions. With thermocouples
and heat flux sensors at different heights in the roof the effect of the reflective foil on the heat
gain to the inside could be evaluated. The measured data are compared with a simple numerical model
that accounts for the buoyancy effects in the ventilated cavity between tiles and underlay. Laboratory
experiments and simulations revealed that a low emissivity of the underlay decreases the heat gain to
the indoor environment, but that due to the thermal stack flow in the air cavity underneath the tiles, the
advantage of a reflective foil mainly plays a role in the bottom part of the roof. In the in situ measurements
it was found that workmanship, airtightness and wind and thermal stack effects are much more
important and disturb the possible benefits of using a reflective underlay.
ISSN: 0360-1323
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Building Physics Section
× corresponding author
# (joint) last author

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