Effect of roof colour on indoor temperature and human comfort levels, with implications for malaria control: a pilot study using experimental houses in rural Gambia

October 2021
Majo Carrasco‑Tenezaca, Ebrima Jatta, Musa Jawara, John Bradley, Margaret Pinder, Umberto D’Alessandro, Jakob Knudsen and Steve W. Lindsay

Background: In rural sub-Saharan Africa, thatch roofs are being replaced by metal roofs. Metal roofing, however,
increases indoor temperatures above human comfort levels, and thus makes it more likely that residents will not
use an insecticide-treated bed net (ITN) at night. Whether the colour of a metal roof affects indoor temperature and
human comfort was assessed.
Methods: Two identical, experimental houses were constructed with metal roofs in rural Gambia. Roof types were:
(1) original bare-metal, (2) painted with red oxide primer or (3) white gloss, to reflect solar radiation. Pairwise comparisons
were run in six, five-night blocks during the malaria season 2018. Indoor climate was measured in each house
and multivariate analysis used to compare indoor temperatures during the day and night.
Results: From 21.00 to 23.59 h, when most residents decide whether to use an ITN or not, the indoor temperature
of a house with a bare metal roof was 31.5 °C (95% CI 31.2–31.8 °C), a red roof, 30.3 °C (95% CI 30.0–30.6) and a white
roof, 29.8 °C (95% CI 29.4–30.1). During the same period, red-roofed houses were 1.23 °C cooler (95% CI 1.22–1.23) and
white roofs 1.74 °C cooler (95% CI 1.70–1.79) than bare-metal roofed houses (p < 0.001). Similar results were found
from 00.00 to 06.00 h. Maximum daily temperatures were 0.93 °C lower in a white-roofed house (95% CI 0.10–0.30, p
< 0.001), but not a red roof (mean maximum temperature difference = 0.44 °C warmer, 95% CI 0.43–0.45, p = 0.081),
compared with the bare-metal roofed houses. Human comfort analysis showed that from 21.00 to 23.59 h houses
with white roofs (comfortable for 87% time) were more comfortable than bare-metal roofed houses (comfortable for
13% time; odds ratio = 43.7, 95% CI 27.5–69.5, p < 0.001). The cost of painting a metal roof white is approximately
31–68 USD.
Conclusions: Houses with a white roof were consistently cooler and more comfortable than those with a bare metal
roof. Painting the roofs of houses white is a cheap way of making a dwelling more comfortable for the occupants and
could potentially increase bed net use in hot humid countries.