In this section several typical crawl space wall sections are illustrated and described.
Figure 3-8 shows a typical vented crawl space with insulation placed in the floor joists above the space. In Figure 3-9 insulation placed outside the foundation wall of an unvented crawl space is shown, while Figures 3-10 and 3-11 show insulation placed inside the wall of an unvented crawl space.
Included in this group of illustrations are variations in construction systems and
approaches to insulating the rim joist area.
Numbers that occur within boxes in each drawing refer to the notes on pages 53 and 54 that follow the drawings (see Figure 3-7).
The challenge is to develop integrated solutions that address all key considerations without unnecessarily complicating the construction or increasing the cost. There is no one set of perfect solutions; recommended practices or details often represent trade-offs and compromises. The purpose of this section is to show and describe a variety of reasonable alternatives. Individual circumstances will dictate final design choices.
EXAMPLE OF NOTES CORRESPONDING TO CONSTRUCTION DRAWING:
1. Insulation protection: Exterior insulation materials should not be exposed above grade.
They should be covered by a protective material — such as exterior grade plastic, fiberglass, galvanized metal or aluminum flashing, a cementitious coating, or a rigid protection board — extending at least 6 inches below grade.
2. Surface drainage: The ground surface should slope downward at least 5 percent (6 inches) over the first 10 feet surrounding the basement wall to direct surface runoff away from the building. Downspouts and gutters should be used to collect roof drainage and direct it away from the foundation walls.
Figure 3-7: System of Key Numbers in Construction Drawings that Refer to Notes on Following Pages
Figure 3-8: Vented Crawl Space Wall with Ceiling Insulation
RIM JOIST
PRESSURE-TREATED SILL PLATE 11
CRAWL SPACE VENT AT TOP OF FOUNDATION WALL 21
GROUND SLOPES AWAY FROM WALL AT 5% (6" IN 10 FT) 2
EXTERIOR SIDING SHEATHING
CONCRETE FOOTING 8 REINFORCING (OPTIONAL) 19 BATT INSULATION BETWEEN FLOOR JOISTS WITH VAPOR RETARDER ON TOP 20 1/2-IN. ANCHOR BOLTS AT 6 FT. O. C. MAX. 12 CONCRETE
FOUNDATION WALL 13 CONTINUOUS VAPOR DIFFUSION RETARDER (GROUND COVER) 18 INTERIOR FINISH MATERIAL VAPOR RETARDER
INSULATION IN 2 x 4 WALL SUBFLOOR
7-IN.
MIN.
24-IN. 17
Figure 3-8 illustrates a vented crawl space with a concrete foundation wall. The insulation is placed between the floor joists over the crawl space. The crawl space floor is at the same level as the
surrounding grade resulting in no major drainage concerns.
Figure 3-9 illustrates an unvented crawl space with a concrete masonry foundation wall. The exterior insulation is covered by a flashing at the top. There is no limit to the thickness of insulation that can be used with this approach.
The crawl space floor is below the level of the surrounding grade. A perimeter drainage system is shown.
CONCRETE FOOTING 8 REINFORCING (OPTIONAL) 19 EXTERIOR SIDING
SHEATHING FLASHING COVERS TOP OF INSULATION PROTECTION BOARD, COATING 1
RIGID INSULATION 5 RIM JOIST
GROUND SLOPES AWAY FROM WALL AT 5% (6" IN 10 FT) 2 LOW PERMEABILITY SOIL (OPTIONAL) 3
DRAINAGE MAT, INSULATING DRAINAGE BOARD, OR GRANULAR BACKFILL (OPTIONAL) 4
FILTER FABRIC ABOVE GRAVEL (OPTIONAL ON SIDES AND BELOW) 6
COARSE GRAVEL (OPTIONAL)
4-IN. PERFORATED DRAIN PIPE WITH HOLES FACING DOWN (OPTIONAL) 7
1/2-IN. ANCHOR BOLTS AT 6 FT. O. C. MAX.
EMBEDDED 7 TO 15 IN. AS REQUIRED BY CODE 23 FILLED BLOCK CORES OR BOND BEAM 22 CONCRETE MASONRY FOUNDATION WALL 14 VAPOR RETARDER 18 INTERIOR FINISH MATERIAL VAPOR RETARDER
INSULATION IN 2 x 4 WALL SUBFLOOR
CAULKING (OPTIONAL) 9 PRESSURE-TREATED SILL PLATE 11
GASKET UNDER SILL PLATE
8-IN.
MIN.
24-IN. 17
Figure 3-9: Unvented Crawl Space Wall with Exterior Insulation
Figure 3-10: Unvented Crawl Space Wall with Interior Insulation
EXTERIOR SIDING SHEATHING
DRAINAGE MAT, INSULATING DRAINAGE BOARD, OR GRANULAR BACKFILL (OPTIONAL) 4
FILTER FABRIC ABOVE GRAVEL (OPTIONAL ON SIDES AND BELOW) 6
COARSE GRAVEL
4-IN. PERFORATED DRAIN PIPE WITH HOLES FACING DOWN (OPTIONAL) 7
1/2-IN. ANCHOR BOLTS AT 6 FT. O. C. MAX. 12 RIGID INSULATION 15 CONCRETE
FOUNDATION WALL 13 VAPOR RETARDER 18 RIGID INSULATION MAY EXTEND HORIZONTALLY ON FLOOR (OPTIONAL) INTERIOR FINISH MATERIAL VAPOR RETARDER
INSULATION IN 2 x 4 WALL SUBFLOOR
RIM JOIST (OPTIONAL CAULKING ABOVE AND BELOW RIM JOIST) 9 PRESSURE-TREATED SILL PLATE 11 GROUND SLOPES AWAY FROM WALL AT 5% (6" IN 10 FT) 2 LOW PERMEABILITY SOIL (OPTIONAL) 3
CONCRETE FOOTING 8 REINFORCING (OPTIONAL) 19 BATT INSULATION RIGID INSULATION CAULKED AT ALL EDGES FORMS VAPOR RETARDER (OPTIONAL) 10
8-IN.
MIN.
24-IN. 17
Figure 3-10 illustrates an unvented crawl space with a concrete foundation wall.
Rigid insulation is placed vertically on the interior.
There is no limit to the
thickness of insulation that can be used with this approach.
The crawl space floor is below the level of the surrounding grade. A perimeter drainage system is shown.
EXTERIOR SIDING SHEATHING
DRAINAGE MAT, INSULATING DRAINAGE BOARD, OR GRANULAR BACKFILL (OPTIONAL) 4
FILTER FABRIC ABOVE GRAVEL (OPTIONAL ON SIDES AND BELOW) 6
COARSE GRAVEL
4-IN. PERFORATED DRAIN PIPE WITH HOLES FACING DOWN (OPTIONAL) 7
1/2-IN. ANCHOR BOLTS AT 6 FT. O. C. MAX. 12 VAPOR RETARDER EXTENDS ABOVE GRADE ON WALL (OPTIONAL) 18 CONCRETE
FOUNDATION WALL 13 FIBERGLASS INSULATION WITH VAPOR RETARDER ON INSIDE 16
INTERIOR FINISH MATERIAL VAPOR RETARDER
INSULATION IN 2 x 4 WALL SUBFLOOR
RIM JOIST (OPTIONAL CAULKING ABOVE AND BELOW RIM JOIST) 9 PRESSURE-TREATED SILL PLATE 11 GROUND SLOPES AWAY FROM WALL AT 5% (6" IN 10 FT) 2 LOW PERMEABILITY SOIL (OPTIONAL) 3
VAPOR RETARDER 18 CONCRETE FOOTING 8 REINFORCING (OPTIONAL) 19 BATT INSULATION VAPOR RETARDER SEALED TO SUBFLOOR AND FLOOR JOISTS 16
8-IN.
MIN.
24-IN. 17
Figure 3-11: Unvented Crawl Space Wall with Interior Insulation Figure 3-11 illustrates an
unvented crawl space with a concrete foundation wall. Batt insulation is placed vertically on the interior wall and extends horizontally onto the perimeter of the floor. The crawl space floor is below the level of the surrounding grade.
A perimeter drainage system is shown.