8. Crawlspaces Archives - Hammer & Hand

8.1 CRAWLSPACES: GENERAL GUIDELINES

sproutbox — Mon, 30 Sep 2024 07:16:41 +0000

Options:

1. New Construction: Conditioned Crawlspace with Insulated Slab (8.2)

Treating the crawlspace like a mini-basement with an insulated wall and slab is the highest performance crawlspace option.

2. Retrofit: Conditioned Crawlspace with Soil-Barrier (8.3)

This is the best retrofit option in crawlspaces that contain mechanicals or ductwork, or are interconnected with a conditioned basement.
Install a Sealed Seam heavy duty (12 mil) soil barrier to seal the space from water vapor and soil gasses.

3. Retrofit: Vented Crawlspace with Floor Encapsulation (8.4)

Acceptable option for crawlspaces without mechanicals or ductwork.
Install new plastic soil barrier with lapped seams. Heavy duty soil barrier with sealed seams optional.
Air space should be maintained between floor and spray foam if underfloor hydronic tubing is being used for radiant heat.

To Know Before Building or Retrofitting a Crawlspace:

Moisture management: all surface and ground water must be properly managed prior to sealing and insulating a crawlspace.
DO NOT route ductwork through unconditioned attics or crawlspaces. All water supply lines must be insulated even in a conditioned crawlspace.
Cleanup: crawl must be thoroughly cleaned of all dust and debris after construction is complete and any damage to the soil barrier must be repaired.

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8.2 NEW CONSTRUCTION: CONDITIONED CRAWLSPACE WITH INSULATED SLAB

sproutbox — Tue, 01 Oct 2024 20:56:10 +0000

We treat conditioned crawlspaces just like a very shallow basement. Please refer to 7.1 Basement, New Construction for a narrative of our approach.

Note: With appropriate detailing and maintenance, vented crawlspaces in new construction are also okay in many Pacific Northwest locations. For guidance, refer to 8.4 Retrofit Option 2: Vented with Floor Encapsulation.

A. CAPILLARY BREAK
B. MEDIUM DENSITY SPRAY FOAM (MDSPF)
C. FLUID APPLIED ELASTOMERIC MEMBRANE
D. DIMPLED DRAINAGE MEMBRANE WITH GEOTEXTILE FABRIC
E. 2” CONCRETE SLAB, “RAT SLAB”
F. HEAVY DUTY GEOTEXTILE FILTER FABRIC
G. WATERSTOP
H. CAPILLARY BREAK
I. 4” DRAINAGE PIPE, HOLES DOWN
J. 12 MIL REINFORCED SOIL BARRIER WITH JOINTS LAPPED, TAPED, AND SEALED

K. 2”-4” RIGID SUB-SLAB INSULATION (XPS OR EPS)
L. MINIMUM 4” LAYER WASHED AND CLEANED (NO FINES) CRUSHED STONE OR GRAVEL ALSO CONNECTED TO FOOTING DRAIN WITH PIPE/SLEEVES CAST INTO FOOTING
M. NOT SHOWN: IF RIGID FOAM INSULATION IS USED ON AN EXTERIOR WALL, PROTECT THE TOP WITH A COATING OR PROTECTION BOARD. BELOW GRADE, PLACE INSULATION BETWEEN DIMPLE DRAINAGE MAT AND ELASTOMERIC WATERPROOF MEMBRANE. FOAM MUST BE PROTECTED WITH DURABLE FINISH WHEN EXTENDED ABOVE GRADE.

Ventilation: Code requires 1.0 CFM of continuous mechanical exhaust for each 50 square feet. For example, a 1000sf crawlspace will need 20cfm of ventilation. Ideally this is provided by a Heat Recovery Ventilator (HRV).

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8.3 RETROFIT OPTION 1: CONDITIONED CRAWLSPACE WITH SOIL BARRIER

sproutbox — Wed, 02 Oct 2024 12:13:44 +0000

Note: As an option, insulation can be added below the soil barrier. Insulation cannot, however, be added in/below the floor system because this thermal barrier defeats the purpose of a conditioned crawlspace and can set up a dangerous condition where the mechanically vented crawlspace becomes cold enough to produce condensation.

a. MEDIUM DENSITY SPRAY FOAM (MDSPF)
B. STEM WALL
C. 12 MIL REINFORCED SOIL BARRIER WITH JOINTS LAPPED, TAPED, AND SEALED

Ventilation: Code requires 1.0 CFM of continuous mechanical exhaust is required for each 50 square feet. For example, a 1000sf crawlspace will need 20cfm of ventilation. Ideally this is provided by a Heat Recovery Ventilator (HRV).

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8.4 RETROFIT OPTION 2: VENTED CRAWL WITH FLOOR ENCAPSULATION

sproutbox — Fri, 04 Oct 2024 03:58:01 +0000

Vented crawlspaces are a great option provided that:
1. They are kept clean and dry (with proper site drainage)
2. Ventilation is kept open and free flowing.

By enveloping the bottom of the floor joists with the floor insulation/encapsulation the joists become thermally broken from the unconditioned crawlspace and protected from the risk of condensation and rot.

Do not install high density/closed cell spray foam in the joists as that would establish a vapor barrier in a dangerous location.

A. ENCAPSULATE FLOOR WITH LOW DENSITY SPRAY FOAM (LDSPF)
B. STEM WALL
C. 6 MIL POLYETHYLENE BARRIER WITH 12″ LAPPED SEAMS

R408.1 Ventilation

Minimum Net Area: 1 square foot for each 150 square feet of under-floor space area.
Minimum Net Area when soil barrier is installed with 12” lapped seams: 1 square foot for each 1,500.
Install vents within 3 feet of each corner of the building to encourage cross flow ventilation.

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