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Above Sheathing VentilationIn Tile Roof Installations

PAC PresentationSeptember 13, 2007

Jerry Vandewater

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Steep-Slope Assembly on ESRAat Oak Ridge National Laboratory

T 3

T 4

T 5

RH 1

HFT 1

HFT 2

HFT 3

HFT 4

HFT 5

Envelope Systems Research Apparatus

Winter Ra*H= 33,000

Summer Ra*H= 50,000Ridge Closed

Underside of Tile Instrumented for Temperature and Heat Flow Measures

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S-Mission Tile Reduce Daytime Heat Gain by 50 to 75% of Gain for Shingle Roof

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Note - the Cool Roof transfers much less heat into the living space.

Figure 25: Heatflux Through Ceiling Panel Over Several Days(Air Conditioning ON)

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Cool Roof (Roof E1) Thai Concrete (Roof C1)Ashpalt Shingles (Roof A1) Solar/10 (incident on roof)

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AtticSim Heat Flux Validation

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Florida Solar Energy Center

FSEC July 6, 1992 Report• Test Criteria

• Black asphalt shingles were used as a baseline comparison

• Test Conclusions• Counter batten system reduced ceiling heat flux

by 48%• Direct deck system reduced ceiling heat flux by

39%

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“THE COOL ROOF”

Light colored high profiled tiles, (if possible with reflective coating).Tiles laid on counter battensVentilation of the batten space at the eaves level and at higher level.Radiant barrier at rafter height.Roof space ventilation at eaves, ridge and gable.Insulation at ceiling or rafter height

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What makes a roof “Cool”?

High surface reflectivity

High emissivity

Air circulation – Above Sheathing Ventilation (AVS)

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California Climate Zones

• Climate Zones 9-15 represent greatest challenge for energy savings.

• Tile roofs most common new construction roofing material.

• Compare existing methods of installation to methods that employ enhanced air flow between the roof deck and roofing material.

• Analyze Above Sheathing Ventilation (AVS)

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Energy benefits of a tiled roofcompared with shingle roof(in climate 15 – El Centro)

- with/without insulation, radiant barrier & duct work

Scenario 1 – benefit 34% –1.Annual cooling energy only

Scenario 2 – benefit 31% –1.Annual cooling energy plus2.Annual heating energy

Scenario 3 – benefit 27% –1.Annual cooling energy plus2.Annual heating energy plus3.Annual duct losses

Scenario 4 – benefit 14% –1.Annual cooling energy plus2.Annual heating energy plus3.Annual duct losses plus4.Attic with insulation & radiant

barrier

0%

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Scenario 1 Scenario 2 Scenario 3 Scenario 4

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gy b

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f tile

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Scenario 1 Scenario 2 Scenario 3 Scenario 4

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Asphalt shingle roofTiled roof

34%31%

27%

14%

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Profile Comparison

Flat Tile

Medium Profile

S-tile / High Profile

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The role of air movement in the batten-spaceStudy conducted by Lafarge Roofing

Technical Centers

Tiles and slates are air permeable providing an air permeability of approximately 0.5% to 1% of the laid area. Complicated flow networks are found between tiles and underlaymentThe flow between tiles and underlayment will influence:

• The energy performance of the roof

• The wind loading on the tiles

• The driving-rain performance

• The dispersion of moisture

Outward acting pressuresover leeward slope

Separated wake(very unstable)Batten space flows

Area of separatedFlow near eaves

Streamlinedflow

Ridge

Eave

Eave

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Plan view of the roof showing air flows between tiles and underlayment

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A flat tile with limited Above Sheathing Ventilation meets the performance of the default construction.

The higher thermal mass of the tile also contributes to the benefit:

• Tile mass: 10.2 lb/ft2 Default construction: 1.7 lb/ft2

Improved ASV under the roof tiles reduces the annual energy losses - the tile roof is then always at least equal to the default construction

Improved ASV is achieved by:

• Elevating the roof tiles with counter-battens.

• Using profiled tiles instead of flat tiles.

• Increasing the ridge & eaves ventilation.

All of these improvements reduce the air flow resistance under the tiles and improve the energy benefits from ASV.

Limited ASV versus full ASV Main findings

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Above Sheathing Ventilation

As the temperature under the tile increases, the heated air rises toward the ridge, drawing cooler air into the system through the vented eave risers.

The heated air exhausts through the vented ridge assembly. The high profile tile allows more heated air to exhaust from beneath the cap tiles.

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Flat tiles attached direct to deck

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Complicated flow networks are found in both mono-pitch & duo-pitch roof types

The ventilation rate & heat benefits from wind driven air flows are broadly similar for both roof types.

Ridge

Eave

Eave

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rect

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Plan view of the duo-pitch roof

Plan view of the mono-pitch roof

Win

d di

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Ridge

Eave

Air movement in the batten-space; mono-pitch vs. duo-pitch

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Cut Away of Installed Raised Fascia Eave Treatment

Anti-ponding mechanism required at all raised fascias.

Minimal air intake at eave.

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Birdstop- supports first course, closes opening, weep holes provide drainage.

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Vented Eave Riser

Birdstop modified to increase airflow.

Protects against the entry of birds or rodents.

Prevents entry of blowing embers.

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Single Batten Installation

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Flat tiles on battens

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S-tile on single batten.

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Airspace beneath S-tile

Natural airspace along with air permeability of

installed tiles promotes air flow beneath and around

tiles.

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Natural Airspace

S-tile – direct deck

Medium Profile on elevated batten

S-tile on elevated batten

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Counter Batten on Low slope

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Counter Batten System

¾-inch vertical battens.

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Optimized Systems

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Typical Ridge Detail.

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Rollable Ridge Vents

Vents through perforated metal.

Vents through air permeable fleece.

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Standard vs. Cool Roof

Dark Colored Tiles

Asphalt underlayment

Direct to deck attachmentMinimal ventilation

Light Colored Tiles

Radiant Barrier

Counter battens

Balanced Ventilation