SA Affordable Housing January / February 2017 // Issue: 62 | Page 16
COVER STORY
GRAPHS FOR ANNUAL ENERGY USE OF THE DIFFERENT TYPES OF MATERIALS
280mm cavity clay brick + insulation
3500
270mm cavity clay brick
3087
220mm clay brick
3000
140mm hollow concrete block
Light steel frame (SABS 517)
2500
2428
Timber frame (SABS 10 082)
2164
2000
1904
2054
1953
1623
1505
1500
1464
1282
1055
1000
749
827
10821066
1009
1012
887
853
734
725
590
496
479
454
500
945
868 862
786
1244
1135
1079
379
296
218
2
0
2
40m2 House KZN
2
40 m2 House GT
2
40m2 House WC
2
40m2 House FS
2
40m2
House LM
2
40m2
House NC
The study found that high density walling systems (clay brick) consistently result in lower annual energy use even without
additional insulation.
WALL TYPES
Six wall types were analysed
1. Double (internal and external) clay brick solid wall
(nominally 220 thick, plastered).
2. Double clay brick cavity wall with air cavity (nominally
270mm thick with an uninsulated 50mm air cavity).
3. Insulated double clay brick wall (nominally 280mm
thick, with 30mm extruded polystyrene insulation in
the 50mm cavity).
4. 140mm hollow core concrete block (150mm thick with
a single external layer of plaster and bagged internally).
5. Light steel frame, externally clad with 9mm fibre
cement board to SANS 517 (nominally 145mm thick
with 0.2mm polymer vapour membrane, 20mm
orientated strand board and 0.8mm steel studs.
Internal wall of 15mm gypsum board with 75/100mm
fibre sound insulation).
6. Timber frame to SANS 10 082 clad with external shiplapped tiles or weatherboard (nominally 145mm thick
with 20mm orientated strand board and internal
cladding of 15mm gypsum plasterboard).
A wall lifespan of 40 years was estimated, although not all
the walling types have been shown to have this lifespan.
US housing lifespan is taken at 32 years and influenced by
the use of timber frame and lightweight construction
systems in the American housing market.
CLIMATE ZONES
South Africa has six major climate zones. Energy use varies
depending on the location of the building – warm climate
zones use more air-conditioning and ventilation, cold
climate zones need heating.
14
JANUARY - FEBRUARY 2017
AFFORDABLE
SA HOUSING
High rainfall areas need to deal with humidity and
condensation. Lighting requirements have seasonal
variations.
Temperatures and other parameters used in the study
are acknowledged averages for that zone. The
measurements were based on the residents living in
reasonable ‘thermal comfort’ which is between 19 and 25˚C.
ANALYSIS OF THE RESULTS
The low density walling systems (timber and steel frame)
show a trend towards higher annual energy use even when
they have low U-values. High density walling systems (clay
brick) consistently result in lower annual energy use even
without additional insulation.
The results showing the variation of heating and
cooling energy modelled for the three building typologies,
can be summarised as follows:
BEST (LOWEST) ENERGY USE
• Residential buildings (all climate zones, all sizes):
thermally insulated 280mm clay brick cavity walling
• Non-residential building (climate zone 1): 140mm
hollow concrete block walling
• Non-residential building (climate zones 2-6): 220mm
solid clay brick walling
WORST (HIGHEST) ENERGY USE
• Residential buildings (all climate zones, all sizes):
140mm hollow concrete block walling
• Non-residential building (climate zone 1): timber frame
walling
• Non-residential building (climate zones 2-6): light steel
frame walling