ASHRAE Journal - April 2020 - 20

TECHNICAL FEATURE

Basement Depth (ft)

insulation requirements are
FIGURE 4 Temperature contours for warmest and coolest months.
desired. Foam board insulaAugust
tion is slightly shimmed off
°F
0 ft
62
65.00
the foundation to accom60
61.75
65
58
modate any foundation
58.50
56
5 ft
water leakage and to enable
55.25
54
moisture removal behind
52.00
52
the insulation.
The plywood or fiberFebruary
0 ft
°F
board floor (Figure 8b)
40
65.00
42
continues the sealed wall
58.67
44
46
"cavity" envelope with
52.33 5 ft
48
4 ft × 8 ft (1.2 m × 2.4 m)
50
46.00
51
sheets that are sealed at
55 56
52 53 54
39.66
joints. 1 in. × 4 in. (25 mm
15
10
5
0
5
10
15
Distance From Centerline (ft)
× 102 mm) wood sleepers
support the subfloor. The
sleepers themselves are supported on spaced sill plate
FIGURE 5 Inner concrete surface average monthly wall temperatures (°F).
gasket shims to prevent the wood from touching the
0
concrete slab and to allow air and water movement (if
Month 10
2
98
there is flooding) beneath the sleepers. The subfloor
7
1
4
3
has aluminum foil paper (shiny side down giving an R-4
6
12 5
1
11
insulation value) over the sleepers, which themselves
are supported on spaced and folded sill plate gasket
2
"shims" on the slab to allow air and water to pass underneath if there is foundation leakage. The sleepers can
3
be replaced by dimpled plastic sheets, dimples down, in
which case the R-4 insulation value is lost and there is no
Winter
4
Spring
need for the aluminum foil. Further, if dimpled plastic is
Summer
used, the ability is lost to safely accommodate basement
Fall
flooding from a foundation leak or a sewer backup.
5
There is a standard water drain within the floor system
Temperature 52°F
and one on top of the subfloor system. Any water enter6 Seattle
ing the envelope will be removed by evaporation and, if
a lot of water exists, also by drainage. Note that all drain
7
P-traps should be periodically topped up with clean
40
45
50
55
60
65
water. To do this in the subfloor, run a tube to the drain
Temperature (°F)
under the subfloor from a tap off the hot water tank supexhaust rate is too low (less than 10 Pa at 85 cfm), leaks
ply pipe, for example.
A continuous duty blower exhausts the envelope air to are searched for using a smoke pencil and sealed.
Once deemed acceptable, the drywall and baseboards
the outdoors. The blower exhaust rate is controlled by a
three-speed fan control set according to the reading of a are installed and the floor finished as desired with hardwood, carpet, tile, etc. The system then undergoes final
differential pressure gauge measuring the pressure differential between the basement and the sealed envelope commissioning, and the minimum ventilation rate is
set for summer and winter. Emissions from basement
in units as small as 2 Pa (0.04 lb/ft2).
The sealed envelope is precommissioned prior to the
sump pits normally connected to perimeter weeping tile
drywall going up, and if the depressurization versus
flexible drainage irrigation pipe around the outside of
20

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ASHRAE Journal - April 2020

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