Garland Aim High Columbia-roof - Building Science Corporation€¦ · 11/8/2011 · Joseph Lstiburek – Roofs 29 Building Science.com – Roofs 30 Green Roofs • Green roof acts

Building Science Roofs

John Straube, Ph.D., P.Eng

presented by www.buildingscience.com

This presentation

•  Roofing – Low-slope – Pitched – Membrane, metal, etc.

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–Roofs 2

Roofs

•  Roofs are significant proportion of the area of low-rise buildings – Significant to total cost – Major area for heat loss / gain – Low-slope membranes usually need

replacement every 15-25 yrs. •  Wide range of membrane choices •  Insulation on top or bottom of membrane •  Green roofs = organic ballast

Building Science.com Enclosures No. 3 /

Building Science 2008

Joseph Lstiburek – Roofs 4

Garland Company Aim High Seminar: Part II November 8, 2011

Straube © buildingscience.com 1 of 16



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Roofs 8



Inverted Roof

•  Pros: –  Preferred approach –  Exterior insulation

eliminates thermal bridges

–  Protects membrane •  Cons:

–  Added weight of ballast

–  Can only use XPS

Building Science 2008 Enclosures No. 9 /

Exposed membranes

•  Pros: –  Lightest weight –  Wide variety of

insulation and membranes

•  Cons: –  Exposed membrane!

Building Science 2008 Enclosures No. 10 /

Building Science – Roofs 11


“Money spent on roof slope is one of the best bargains in the construction business” Wayne Tobiasson, CRRL






– Roofs 15

•  Why fully adhered?

Building Science

– Roofs 16



Low-level air barriers

•  Roof membranes can be air barriers •  In practise, a deck level air barrier is more

reliable, easier to control – Other benefits include secondary roof during

construction and re-roofing


Roofs 17 Building Science – Roofs 18

A cheap air barrier


Combine multiple penetration at doghouses


Avoiding penetrations is always best




– Roofs 21

Building Science.com Roofs 22

Rain leaks at parapet Air leaks everywhere Heat leaks everywhere






Parapets



White roofs: the coming storm

What air barrier

White roofs

•  Lower heat gain: great! •  Reduce stress on exposed roof membranes •  But: Reduces drying out of roof •  Thus: Require better moisture control!

– Air barrier – Construction moisture






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– Roofs 30

Green Roofs

•  Green roof acts as thermally massive, low solar absorption surface – Not insulation

•  Save energy compared to black roof of same R-value

•  White roof with more insulation is less expensive alternate

•  Don’t feel good

Building Science 2008 Green Buildings No. 31/51

“Perfect” Green Roof

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Fully-adhered membrane!



Energy: Dirt is not insulation

Building Science.com 33

Source: Ray, S., Glicksman, ASHRAE Buildings XI 2010

20 R10 30

Stormwater Management

Building Science Green Buildings No. 34/51

NRC Roof Test Ottawa, Canada ¾” (19 mm) rainfall over 6.5 hrs 150 mm soil over membrane


Green Roofs

•  To save energy, use white roofs with lots of insulation

•  Soil does store lots of stormwater – Retention mats can do the same

•  Likely cleans water somewhat •  Likely absorbs particulates

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Sloped roofs

•  Basic Physics are the same •  Slopes allows non-waterproof materials to

be lapped “shingle fashion” •  Air – vapor impermeable insulation needed

OR ventilation of the sheathing

•  Air leaky roofs require more ventilation



Building Science Corporation

Vented Pitched Roof Types

•  Vented Attic –  Insulation/air barrier at ceiling plane

•  Cathedral Ceiling –  Insulation/air barrier at roof plane


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– Roofs 42

Building Science.com

Simple Vented Cathedral Beware Air leaks! Ventilation path?

Hard to Vent

Building Science.com – Roofs 44




Limitations of Ventilated Cathedral


Limitations


Pitched Roof Types

•  Unvented Cathedralized Attic – As cathedral but no venting above

insulation •  Unvented Cathedral






Roofs 49

Building Science

– Roofs 50


Temperatures in Georgia Roof Surface Temperature Distribution - Comparison of Different Roof Strategies (w/ ZIP)

(2005.04.11-2005.11.07)

0

200

400

600

800

1000

1200

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Temperature (°C)

Hou

rs a

t Tem

pera

ture

Attic, Poorly VentilatedAttic, Well VentilatedCathedral, VentilatedCathedral, Unvented









Building Science 2008 Airflow Control No. 55/79

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Garland Aim High Columbia-roof - Building Science Corporation€¦ · 11/8/2011 · Joseph Lstiburek – Roofs 29 Building Science.com – Roofs 30 Green Roofs • Green roof acts

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