ASHRAE Journal - July 2021 - 54

COLUMN BUILDING SCIENCES
considered an occupiable or habitable space. In floodprone
and coastal regions, it is not recommended to
construct " not vented " and " conditioned " and connected
to the " inside " crawlspace foundations.
Floors above crawlspaces should be constructed above
the base flood elevation (BFE). The BFE should be at a
minimum 12 in. (305 mm) below the lowest horizontal
structural member.
Design and construct a crawlspace that controls flood
water by ensuring flood waters enter and exit the crawlspace
without causing hydrostatic pressure differences.
Water levels in the crawlspace should rise and fall at
the same rate as the water level outside so hydrostatic
pressures are equalized (Figure 9). Sufficient openings
need to be provided to control hydrostatic pressure. The
total area (size) of all openings serving the crawlspace
should be equal to or greater than 1 in.2 (6450 mm2) for
every 1 ft2 (1 m2) of crawlspace area. Vent openings typically
contain a screen or a louver to control the entry of
animals, and these screens or louvers can block the flow
of water. These openings should be distributed over the
entire perimeter.
Vented crawlspaces must keep air and vapor out of
the crawlspace floor framing. Figure 10 illustrates the
use of foil-faced rigid insulation under the floor framing.
The wood is warm and therefore dry-during both
winter and summer. The foil facing on the rigid insulation
addresses the vapor drive. The foil facing is an
exceptional vapor barrier (<0.1 perm). With the impermeable
rigid insulation, even relatively impermeable
floor coverings such as vinyl flooring and polyurethane
coated wood flooring work. The flow of vapor into the
assembly (vapor drive) is less than the flow of vapor out
of the assembly even with relatively impermeable floor
coverings.
Adding fiberglass cavity insulation in conjunction
with the impermeable foil-faced insulating sheathing
is a hybrid approach that uses the best qualities of both
materials. The optimum location for the air space is
above the cavity insulation-makes for warmer floors.
This is the same detail that should be used under bedrooms
over garages.
The rigid insulation also needs to be airtight. The
seams should be sealed with foil tape. Figure 11 illustrates
perimeter details. Again, pest and insect control is provided
by installing a protection board over the underside
of the rigid insulation.
54
ASHRAE JOURNAL ashrae.org J U LY 2021
FIGURE 12 Closed-Cell Spray Polyurethane Foam. If closed-cell, high density
spray foam is used and gets wetted by flood waters, it still will need its exposed
surfaces to be cleaned even though it is water resistant.
Cladding
Air Gap
Wood Based Sheathing Plywood or OSB)
Water Control Layer
Spray Polyurethane Foam (SPF)
Acrylic Latex Paint
Gypsum Board
Sealant
High Density Closed Cell Spray
Polyurethane Foam
Protection Board
Crawlspace Vent at Top of
Foundation Wall
Crawlspace Foundation Wall
Flood Vent at Grade
Ground Slopes Away
From Wall at 5% (6 in. per 10 ft)
Concrete Footing Below Frost Depth
Figure 12 illustrates an alternative approach-the use
of closed-cell, high-density spray polyurethane foam
(ccSPF). Such foam has a low vapor transmission-less
than 1.0 perm-and can be used with most floor finishes.
If closed-cell, high-density spray foam is used and gets
wetted by flood waters, it still will need its exposed surfaces
to be cleaned even though it is water resistant. It is
recommended that sill plates and rim joist framing be
treated to be decay resistant.
Where floods are concerned, it is good to be " high and
dry " -not a difficult situation and one where you were
able to control the outcome.
Bibliography
DISASTERSAFETY.org. 2021. " Protect Your Home From Floods. "
DISASTERSAFETY.org, a product of the Institute for Business and
Home Safety. https://tinyurl.com/5bpsjep7
FEMA. 2009. Homeowner's Guide to Retrofitting: Six Ways to Protect
Your Home From Flooding, Chap. 6, Wet Floodproofing. Federal
Emergency Management Agency. https://tinyurl.com/43jvybj4
http://www.DISASTERSAFETY.org http://www.DISASTERSAFETY.org https://www.tinyurl.com/5bpsjep7 https://www.tinyurl.com/43jvybj4 http://www.ashrae.org

ASHRAE Journal - July 2021

Table of Contents for the Digital Edition of ASHRAE Journal - July 2021

Contents
ASHRAE Journal - July 2021 - Intro
ASHRAE Journal - July 2021 - Cover1
ASHRAE Journal - July 2021 - Cover2
ASHRAE Journal - July 2021 - 1
ASHRAE Journal - July 2021 - Contents
ASHRAE Journal - July 2021 - 3
ASHRAE Journal - July 2021 - 4
ASHRAE Journal - July 2021 - 5
ASHRAE Journal - July 2021 - 6
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ASHRAE Journal - July 2021 - Cover3
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