Closed Crawl Spaces & Sealed Attics

Applied Building Science TeamShaun HasselBruce Davis

Understanding the Problems and Solutions

Session Overview

• Definitions• Group Activity• Facilitated Discussion• Selected AE Research and Case Studies

Resources are at www.crawlspaces.org

Overview• If someone is going to build a house on a crawl space,

why would they want to close it? Why wouldn’t they want to close it?

• If someone is going to construct a house, why would they want to seal the attic? Why wouldn’t they want to seal the attic?

• If they do decide to utilize one of these approaches, how should they do so?

What is a ‘Closed’ Crawl Space?NC Code Definition

A foundation without wall vents that uses air sealed walls, ground and foundation moisture

control, and mechanical drying potential to control crawl space moisture. Insulation may be located at the floor level or at the exterior walls.

Why call it “Closed”?Unvented vs. Sealed vs. Conditioned vs. Closed

What is a ‘Sealed’ Attic?2006 ICC Residential Code

Unvented conditioned attic assemblies are permitted under the following conditions:

1. No interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly.

2. An air-impermeable insulation is applied in direct contact to the underside/interior of the structural roof deck.

3. In warm humid locations with asphalt roofing shingles: A 1-perm or less vapor retarder is placed to the exterior of the structural roof deck; that is, just above the roof structural sheathing.

4. In Zones 3 through 5 (all of NC), sufficient insulation is installed to maintain the monthly average temperature of the condensing surface above 45°F (7°C). The condensing surface is defined as either the structural roof deck or the interior surface of an air-impermeable insulation applied in direct contact with the underside/interior of the structural roof deck. For calculation purposes, an interior temperature of 68°F (20°C) is assumed. The exterior temperature is assumed to be the monthly average outside temperature.

Group Activity

Provide: • Reasons to utilize ‘your’ approach• Obstacles to overcome

Break into four groups, each representing an approach: vented crawls, vented attics,

closed crawls, & sealed attics.

Crawl Space “Owners”

• Builder• Owner• Installer• Code Official• Pest control• Grading/Drainage• Foundation

• Insulation• Plumbing• Electrical &

Mechanical• Gutters• Landscaping• Information

Services

Attic “Owners”

• Builder• Owner• Installer• Code Official• Framer• Roofer• Drywaller

• Insulation• Plumbing• Electrical &

Mechanical• Gutters• Information

Services

Ducts: 55-65 F

H2O pipes: 55-65 F

Floor:65-70 F

Framing:70-78 F

85 F60% RH70 F DP

73 F90% RH70 F DP

The Crawl Space Ventilation Myth

2004 Crawl Space Characterization Study

2004 Characterization Study• 67% of crawl spaces had WMC > 19%• 22% had wood rot NOT caused by plumbing leaks• 24% had wood rot caused by plumbing leaks• Typical 6” x 12” hole to the house• Stack pressure and HVAC driving forces• Very high bioaerosol levels: Crawl spaces are MADD!

99%100%100%> 70%

72%74%56%> 90%AugJulyJuneCrawl RH

The Princeville Project

• NETL, 2001-05• Bill Warren, Cyrus Dastur

• Technology Assessment• Characterization Study• Field Demonstration• Hygrothermal Modeling

Princeville, NC Field Study SitePrinceville, NC Field Study Site

Phase II: June 2003-June 2004

Wall ventedR-19 Floor

ClosedSealed linerR-19 Floor

ClosedSealed linerR-13 Wall

Wall ventedR-19 Floor

ClosedSealed linerR-19 Floor

ClosedSealed linerR-13 Wall

Closed Crawl Space Supply Air Duct

10

20

30

40

50

60

70

80

Jun-03 Jul-03 Aug-03 Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04

Dew

Poi

nt (F

)

Phase II Crawl Space Dew Points

Wall Vented ClosedOutside

Phase II Crawl Space Relative Humidity

Wall Vented ClosedOutside

30

40

50

60

70

80

90

100

Jun-03 Jul-03 Aug-03 Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04

Rel

ativ

e H

umid

ity (%

)

Phase II Average Wood Moisture Content

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Aug 2003 Oct 2003 Dec 2003 Feb 2004 Apr 2004 Jun 2004

Woo

d M

C (%

)

Vented + R-19 Floor Closed + R-19 Floor Closed + 2'' Foam on Wall

Seasonal Energy Use and Savings

0

1

2

3

4

5

6

7

8

9

Jun-Aug '03 Sep-Nov '03 Dec '03-Feb '04 Mar-May '04

Thou

sand

skW

h

Vented + R-19 Floor Closed + R-19 Floor Closed + 2'' Foam on Wall

-18%-15%Annual

Closed with Wall Insulated

Closed with Floor Insulated

Season

-28%-19%Spring

+4%-10%Winter

-10%-5 %Fall

-36%-22 %Summer

Princeville Study Conclusions

• CCS provides improved moisture control• CCS delivers significant energy savings with

either floor or wall insulation• CCS is feasible to install and maintain• Performance was achieved with designs that

isolate the crawl space from the living space

Healthy Homes, Healthy Lives• What is the connection between housing, health,

and the construction process?

• High Performance Homes (20) – Closed crawl – Enhanced air filtration– Tight envelope– Properly installed insulation– Minimal duct leakage with outside air ventilation

• Versus Code Built Homes (16)

Doing the right thing wrong

Key Design and Installation Issues

• Combustion safety

• Fire safety

• Radon control

• Mold control

• Moisture control

• Pest control

• Drying

• Insulation

• Performance verification

• Worker Safety

Download AE’s Introduction toClosed Crawl Spaces at:

www.crawlspaces.org

The ‘Spray Foam’ House

• A ‘typical’ production house in the Southwestern United States – slab, stucco, ceramic tile shingles, ~ 1700 sq. ft, gas heat with A/C

• Spray foam blown in the unvented attic and walls

• EFL house with right sized HVAC unit with minimal duct leakage (< 3%) and fresh air ventilation

• Sensors throughout the attic, exterior walls, and living space

YTD Hourly Mean Attic Space Conditions

Y Attic T-Stat

45

50

5560

65

70

7580

85

90

Tem

p (*

F)

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1/20

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Date

YTD Difference Between Attic and T-Stat

-5

-3

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9

11

Atti

c M

inus

T-S

tat

02/1

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Date/Time

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p (°

F)

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Date/Time

One Week Hourly Temperature Average Attic vs Thermostat

Y Attic T-Stat

7

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9

Woo

d M

oist

ure

Con

tent

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Y Bedroom OSB Roof OSB

YTD Daily Wood Moisture Readings for Bedroom vs. Roof Locations

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160

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p (°

F)

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Y Outdoor NE Roof OSB NE Roof 1.5'' Below OSBNE Attic Space T-Stat

24-Hour Hourly Mean NE Roof Deck Profile

‘Sealed’ Attic Case Study

• An unvented attic in the Southeastern United States

• Built on a closed crawl space• Utilized fiberglass insulation in

combination with manual air sealing techniques – caulk guns & cans of spray foam

Outdoor air at 90o and 70% RH

There is No Silver Bullet

Product

TrainingDesign

Process

Successful implementation requires: