metal roofs damage assessment - haag global · 2014. 4. 14. · • astm g60 andg90applies0.60 0.90...

Metal RoofsDamage Assessment

Seminar Handout

TM

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About Haag Haag is a worldwide diverse firm encompassing forensic engineering, construction consulting, and research and testing. Haag offers outstanding educational programs and publications. Haag handles all aspects of civil, structural, mechanical, electrical, metallurgical, construction defect, slip/fall, and transportation cases. Haag has been in business since 1924 and we continually strive to be the best.

Instructor Profile

Carlos Lopez, Ph.D, E.I.T. Ph.D. Civil Engineering

M.S. Civil Engineering

B.S. Civil Engineering Carlos Lopez graduated from University of Florida with a B.S., M.S., and Ph.D. in Civil Engineering. Currently, he is a member of the American Society of Civil Engineering, the American Concrete Institute, and the American Association for Wind Engineering. Carlos has been with Haag Engineering since 2012 and has inspected and assessed damage to hundreds of roofs. His primary areas of consulting are structural evaluations and general damage assessment. ©Copyright 2014 by Haag Engineering Co. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from Haag Engineering Co., 4949 West Royal Lane, Irving, TX 75063.

Metal Roofs Damage Assessment

© 2013, Haag Engineering Co.1

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Metal Roofs Damage AssessmentMetal Roofs Damage Assessment

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Metal Roofing References‐• NRCA (National Roofing Contractors Association)

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Metal Roofing References‐• MBMA (Metal Building Manufacturers Association)

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Topics:

1. Product description and manufacturing

2. Installation and roof details

3. Problems‐manufacturing, design/installation, weathering, and mechanical

4. Damage assessment‐ hail and wind

5. Repair methods

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1. Product description and manufacturing

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Advantages of metal roofing‐

• Durable‐‐warranties to 50 years

• Wind resistant

• Hail resistant (Class 4)

• Fire resistant

• Insect resistant

• Lightweight‐‐100 to 200 lbs/sq (compare asphalt shingles‐‐240 to 400 lbs/sq)



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Disadvantages of metal roofing‐

• First cost can be high

• Steeper roofs cannot be walked on

• Common problems with details at penetrations

• Can be noisy with changes in temperature, and rain and hail

• Can be difficult to repair‐‐many systems are interlocked

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Types of metals‐

1. Naturally weathering metals

2. Metallic‐coated steels

3. Protective coatings

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1. Naturally weathering metals

• Aluminum

• Copper

• Lead

• Stainless steel

• Zinc

• Lead‐coated copper

• Terne‐coated stainless steel (terne is lead and tin, or zinc and tin)

Copper panels

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Copper‐

• A malleable metal that can be formed easily

• Oxidizes from brown to green colors (patina) over time.

• Nominal 16‐20 ounces per sq ft

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The patina of copper over time‐

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2. Metallic‐coated steels

• Aluminized steel

• Aluminum/zinc (Galvalume®)

• Galvanized steel

• Terne metal

Galvalume®-coated steel



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Galvanized steel‐

• The most common coating for steel panels

• Steel is hot dipped in molten zinc (~1,000 ºF)

• Zinc is metallurgically bonded to the steel

• ASTM G60 and G90 applies 0.60 and 0.90 oz. per sq. ft. to the steel (G90 is ~1 mil thick)

• Zinc is water soluble and “sacrificial” protection

• Sometimes distinguished by bold spangle

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Galvanized steel‐

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Galvalume‐coated steel‐

• Invented by Bethlehem Steel in 1972

• Steel hot dipped in mixture 55% aluminum and 45% zinc

• Greater corrosion resistance than galvanized

• Normally bright finish and small spangle

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Galvalume‐coated steel‐

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Spangle‐

Galvanized Galvalume

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3. Protective coatings

• Fluoropolymer (PVDF: Kynar 500® and Hylar5000®)

• Siliconized acrylic and polyester

• Pearlescent and metallic additives

• Clear‐coat finishes

• Laminates

• Anodizing

Fluoropolymer paint



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Paint application‐

1. Individual panel spray

2. Continuous coil coat

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Paint application specifics‐

1. Clean steel‐‐remove dirt and oil

2. Chemical conversion (prep) coat

3. Prime coat ~0.25 mil, then heat cure

4. Top coat ~0.75 mil, then heat cure

5. Total paint thickness is ~1 mil

21Paint application‐ 22

Manufacture of panels‐

1. Panels from sheets

2. Panels from coil stock

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1. Panels from sheets‐

• Panels bent to form profile in brake

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2. Panels from coil stock‐

• Panels are cold formed in a roll former

• Coil is coated/painted before rolling

• Panels can be roll formed in a factory or in the field by portable equipment

• Steel coil is bent to form profile by a series of 20 to 25 dies in a factory; by 7 to 8 dies in the field



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Factory roll former‐

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Dies bend coil stock‐

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Portable roll former‐

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Panel profiles‐

1. Flat

2. Corrugated

3. Raised rib

4. Standing seam

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1. Flat profile

• Used on flat surfaces, vertical walls, as well as conical or curved surfaces of spires, domes, and cupolas

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1. Flat seam

• Not soldered

• Soldered



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2. Corrugated profile

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3. Raised rib profile

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4. Standing seam types‐34

Standing seam attachment

• Fixed clips

• Expansion (moveable) clips

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Standing seam installation‐36

Mechanically seamed‐

• Hand seams

• Tongs

• Electrical roll former



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Snap together‐

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Types of metal roofing systems‐

1. Architectural panels

2. Structural panels

3. Metal shingles or shingle panels

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1. Architectural panels‐

Copper architectural panels

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2. Structural panels

1. Water barrier (hydrostatic)

2. Often slope <3:12 (low slope)

3. Often Standing seams >1‐1/2” tall

4. Often Non‐curing and non‐skinning sealant (butyl) tape within seams

5. Span between structural supports, normally purlins

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Structural panels‐

Frames/purlins

Painted steel structural panels

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Structural panel seam tape‐

Butyl tape within standing seam



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3. Metal shingles and shingle panels‐

1. Water shedding

2. Slope >3:12 (steep slope)

3. Interlocked or overlapped

4. Applied over structural decking with underlayment

5. Press‐formed to mimic multiple asphalt or wood shingles, tiles, or slates

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Paint + granules application‐

• Steel shingle panel

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Metal shingles and shingle panels‐

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Thinking about metal…

• Expect large expansions or contractions with changes in temperature

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Thinking about metal…• Expect oil‐canning (distortions in the flatness of the metal)

• Inherent in flat panels

48Oil‐Canning Mitigation...• Identify problems with coil prior to installation

• Do not use roofing pans wider than 18”

• Use heavier‐gauge metal

• Use minor ribs or striations in pan profile

• Use lower gloss finish

• Apply architectural panels over solid deck rather than over foam insulation or existing roofing materials

• Account for thermal expansion and contraction

• Maintain on‐site roll forming machines in good working condition



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2. Installation and Roof Details

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Architectural panel application‐

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Architectural panel valley detail‐52

Structural panel application‐

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Structural application‐54

Structural panel eave detail‐



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Small penetration (soil stack) detail‐Avoid placement in standing seams

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Large penetration (curb) detail‐

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Drill screws‐

• Elastomeric washers form water-tight seal

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3. Problems ‐Manufacture, Design, or

Installation

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Galvanized coating problem‐60

Too shallow for drainage‐



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Panel slippage due to missing fasteners‐

Upslope edge Down slope edge

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Screw missing‐

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Improper fastener installation‐

Over-torqued Skewed

Under-driven Missed purlin

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Improper fastener installation‐

Over-driven screw

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Scupper too high (panel closure along eave flooded) ‐

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Non‐standard detail‐



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Dead valley‐68

Gutter too small‐

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Ridge misaligned‐70

Non‐standard termination at vertical projection‐

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Counterflashing missing‐72

Small penetrations non‐standard‐



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No flashing at stack penetrations‐74

Small penetration details‐

Stack dams runoff Stack does not impede runoff

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No crickets at large penetrations‐76

Large appurtenance not supported by structure below‐

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Abutting roof systems require special details‐

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3. Problems‐Weathering



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Galvanized steel stack corroded away‐80

Coating deteriorated‐

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Coating deteriorated‐82

Environmental problems‐

• Acid rain

• Salt spray

• Bird droppings

• Process chemicals

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Red rust on galvanized steel after zinc is depleted‐

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Manufacturing processes‐

Acid etching

Stacks atop roof



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Manufacturing processes‐86

3. Problems‐Mechanical

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Cripples are buckles in upper troughs of panels‐

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Mechanically caused dents in panels‐

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Abrasions in panel due to seamer‐90

Scratches in panel‐



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Cuts precipitated corrosion and peeled paint‐

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4. Damage assessment‐Hail

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Functional damage–

1. Reduction of water‐shedding capability

2. Reduction in expected long‐termservice life

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Functional hail‐caused damage to metal roofing‐

• Rupturing the metal

• Disengaging a lap element

• Disengaging a fastener

• Disrupting the protective surfacing (if present)

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Thresholds for functional hail‐caused damage to metal roofing‐

• Steel panels > 2‐1/2” (64 mm)

• Aluminum panels > 1‐1/2” (38 mm)

Hard hailstones, perpendicular impacts, and materials in relatively good or mid‐life conditions

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Importantly‐

• Dents in metal are not functional damage

• Hail‐caused dents do not appreciably thin the metal

• Factory‐applied coatings are not debonded or broken by hailstone impacts



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Rupturing the metal‐98

Rupturing the metal‐

Inside out corrosion (from the building interior)

Corroded thin panel broken by hail

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Disengaging a lap element‐

Obvious gap in roofing

100Disengaging a lap element‐

Gap in seaming tape within lap seam

101Disengaging a fastener‐ 102

What size hail dented this painted steel panel roof?



Stone-coated Steel Panels103

Class 4 Impact Rated

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Hail-caused dents stone-coated steel panels

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Stone‐coated Steel

Overview – Granules missing where dented by hail

Close view of dent

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Hail-caused dents stone-coated aluminum panels-

Note that dents did not align with peeled surface coating

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Factory coatings are tough‐

Analysis of material within dents described as "dirt"

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Factory coatings are tough‐



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Disruption of Protective Coating

Hail‐caused fractures in field‐applied paint on terne‐coated steel.

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Hail‐caused spatter marks on galvanized steel panels‐

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Hail‐caused spatter on Galvalume®‐coated stell panels‐

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4. Damage assessment‐Wind

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Functional wind‐caused damage to metal roofing‐

Direct wind‐caused damage

• Tearing panels from roof slopes

• Disengaging a lap element

• Disengaging a fastener

Indirect wind‐caused damage

• Rupturing the metal

• Disrupting the protective surfacing (if present)

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Where to look for wind‐caused damage‐

• Look high since wind speeds increase with height

• Look where wind is deflected away from the structure since these are areas of greatest negative pressures (uplifts)

• Greatest negative pressures (uplifts) are generated at windward eaves and corners, and leeward sides of ridges



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Painted steel architectural panels torn from windward slopes‐

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Panels could be lifted by hand with little effort, note nail at finger‐

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Only one small nail secured clip‐118

Painted steel architectural panels failed, note screws were too small‐

Specified Installed

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Painted steel structural panels torn away along windward eave‐

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Painted steel structural panels torn away and steel purlins buckled from wind uplift‐



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Painted steel structural panels torn away at failed overhead doors‐

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Painted steel structural panels failed, note only one screw per clip‐

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Galvalume® steel structural panels uplifted and standing seam disengaged‐

Underside of deformed panels

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Structural panels “unfolded” from clip‐

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Wind speed increases with height and greatest uplifts occur at windward edges and corners‐

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Indirect wind‐caused damage(impacts by wind‐borne debris)‐



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5. Repair methods

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Repair v replacement‐

• Assess hail‐ or wind‐caused damage

• Identify damaged panels

• Cost repair, cost replacement

• Make economic choice

• The complexity of many repairs will require bids by contractors

• Most systems can be repaired

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Repairing a hole or tear in a metal panel‐130

Repair structural panel‐

Metal Roofs: Repair131

Permanent repairTemporary patch

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Structural steel panel re‐cover (overlay)‐



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Questions?

Thank you!

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metal roofs damage assessment - haag global · 2014. 4. 14. · • astm g60 andg90applies0.60 0.90...

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