Metal roofing examples (C) Daniel Friedman How to Diagnose, & Repair Roof & Structure Noise Problems in Buildings

  • NOISE TRANSMISSION in ROOFS - CONTENTS: Building roof or other structural noise transmission: causes, cures, and detection methods for indoor noise pollution coming from outside through the building roof. Roof noise transmission: comparing metal roof noise levels to other roofing materials. Roof noise insulation and roof noise isolation techniques. How to build a quiet building under an airplane flight path, near airports or near highways. Roof booming noises, roof creaking or groaning noises
  • POST a QUESTION or READ FAQs about building roofs & noise or sound transmission or noises coming from roofs themselves
  • REFERENCES
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Roof & building structural noise transmission &control, causes & cures:

How does exterior noise (rain, hail, highways, aircraft noise) transmit through a roof to the building interior and how can we soundproof building roofs for a quiet building interior?



Green links show where you are. © Copyright 2017 InspectApedia.com, All Rights Reserved.

These articles discuss building noise control: how to inspect, diagnose & cure noise or sound problems in homes or commercial buildings.

Information is provided about auditory (hearing), visual, historic, medical, or other clues of building condition that explain various sounds heard in buildings. We also discuss methods of sound or noise control in buildings during construction or as a building retrofit.

Roof & Structure Noise Transmission & Structural Noises in buildings: Sources, Causes, Remedies

Metal roof installation (C) D Friedman

Are metal roofs more noisy than other roof covering types?

Metal-covered roofs in modern building installations are not necessarily noticeably noisier than other roof covering types - depending on the choice of type of metal roofing, underlayment, roof decking, fastener method, and roof insulation method. Therefore when investigating a specific roof noise complaint it makes sense to first understand how roof noise is transmitted to the building interior and second to check the most-common roof noise sources such as thermal movement, fastener errors, undelayment errors, or rain and hail noise transmission through or around insulation to the building interior.

The metal roof home shown in our photo (left, courtesy Galow Homes), was installed on a New York home and used solid metal plywood roof decking.

The roof framing support is comprised of I-joists, and the roof cavity is insulated with blown-in foam. During heavy rain, from inside the space below the roof, we could hear only a very muted sound of rainfall on the roof surface and in our opinion the sound level was not different than under an asphalt-shingle roof of similar design and use.

Nevertheless, reader questions & comments (see our roof noise FAQs below) as well as our own field experience make clear that some metal roofs and some roofs covered with other materials can be very noisy and at some buildings there are serious occupant complaints about roof noise levels observed at roofs of various designs and materials.

How is Roof Noise Transmitted into a Building?

Regardless of their source, roof noises are transmitted into buildings by two methods.

  1. Airborne Sound: Sound waves traveling through air move between building areas - such as through open windows, doors, or stairwells.
  2. Mechanically transmitted sound: When sounds move through solid building components such as floors, ceilings, walls, framing, carrying sound from one area to another the sound transmission is referred to more technically as impact insulation class transmission or IIC sound transmission.

Metal roof, Key West FL (C) Daniel Friedman

Certain building configurations, such as occupied attics or under-roof areas with cathedral ceilings, low slope or flat roofs, and metal roofed buildings may transmit noises to the building interior through the roof sheathing and building framing.

Where roof-transmitted sound reduction is most sought is in buildings located close to high noise areas such as under the flight path to airports.

Our photo of metal roofed homes (left) shows two older houses in Key West, Florida.

A Catalog of Types of Roof Noises & Sounds

Roof noises may be described as those attributed to an obvious source: the patter or even the roar of falling rain or hail, popping and cracking noises (perhaps due to thermal expansion and contraction of roof coverings, metal roofing, or roof structure), and transmitted noises from other external sources such as low-flying aircraft or nearby trains or auto & truck traffic from a nearby highway.

Very loud roof "booming" noises may be heard in cold climates when water freezing on a flat or low slope roof becomes cold enough to fracture.

Other noises sometimes attributed to building roofs are actually traced to other building components on or near the roof, such as antennas, wires, cables, signs, and roof-mounted equipment.

Role of Roof Covering Material in Noise Transmission

Choice of roof covering affects roof noise: Choices of roofing materials can reduce roof transmission of sound to the interior, including use of bituminous or asphalt shingles, or more effective, higher-mass roofing materials such as roofing tiles of clay or concrete. Metal roofing can be sound-transmission reduced by installing the metal roof over plywood and solid foam insulation. Keep in mind that roof skylights are likely to increase sound transmission through roofs.

Green roofs reduce roof noise transmission: One of the benefits claimed for "green roofs" is that by virtue of their stiffness and high mass, green roofs provide very good resistance to sound transmission from outside the building. Quoting:

Green roofs can provide a higher [noise] transmission loss than the additional ceiling element and improve [sound] transmission loss throughout the full architectural frequency range, specifically desirable in residential occupancies below aircraft flight paths. the field testing conducted on two 33 m2 low profile extensive green roofs indicated an increase of 5 to 13 db in [sound] transmission loss over the low and mid frequency range (50 Hz to 2000Hz) and 2 dB to 8dB increase in [noise] transmission loss in the higher frequency range relative to the transmission loss [sound transmission resistance] of a reference roof. - Connelly & Hodgson, [1]

Connelly & Hodgson reference Dr. Ben H. Sharp, an expert in sound transmission through structures who developed sound transmission theory and who proposed (Sharp 1973) improvements to roof sound transmission resistance thorough roof/ceiling assemblies that combined increased mass with low stiffness.

Accurate diagnosis of the source of roof noise transmission is important in deciding what remedy may work best. For example, check during rainfall to accurately determine the loudest sound source - you might find that more noise is transmitted to the building interior through skylights than through the roof surface itself.

Below at our roof noise FAQs we suggest investigative steps useful in diagnosing and thus curing annoying roof noises & sounds.

Metal Roof Noises & Roof Underlayments

Metal roofing examples (C) Daniel Friedman

Depending on installation details, metal roofing can transmit rain noise into buildings at levels exceeding 70 dB (equivalent to street traffic noise).[2]

Noise generated by the roof covering material itself may be a factor where metal roofing is installed, particularly if the metal roofing is not properly insulated and if its connections to the roof deck fail to secure the material properly, including providing an allowance for movement. A 10-meter metal roof panel can easily have 8 mm. of thermal expansion over its length. (NZSteel Company 2005)[6].

Quoting from another source: :

Enkamat underlayment and composites made with Enkamat reduce sound levels from 9.5 to 13.5 decibels compared to a metal roof directly over a weather barrier fabric.

When the entangled filament underlayments were combined with a gypsum ceiling and thermal insulation the sound reduction further increased to 21.5 decibels. When considering that a sound reduction of 10 decibels is perceived by the human ear as cutting noise levels in half, a reduction of over 20 decibels is significant. (Colbond 2011 [2])

As we explain at METAL ROOF EXPOSED FASTENER FLASHING

One frequently cited disadvantage of metal roofing is that it generates a noticeable noise when struck by rain, hail, or even dropping acorns. If installed directly to purlins with no roof sheathing, the noise might be heard in the building interior. However, when installed over a solid substrate, with normal levels of insulation, the noise should not be noticeably different than with other roofing types.

Noise From Thermal Expansion in Metal Roofs

The metal roof expansion data given here is adapted from the New Zealand Steel Company's metal roof installation manual cited at the end of the table.

Metal Roof Expansions by Colour & Roof Panel Length

Roof Colour Range Expansion in 8 Metre Length Expansion in 12 Metre Length Expansion in 18 Metre Length Comments
Light  5 mm 7 mm 11 mm  
Medium 6 mm 10 mm 14 mm  
Dark 7 mm 11 mm 17 mm  

Notes:

These expansion amounts are based on 0.01 mm / m / °C for Zincalume® and steel roof panels.

Sources:

  • Ellen, C. H., C. V. Tu, and W. Y. D. Yuen. "Theory for thermally induced roof noise." Journal of Structural Engineering 111, no. 11 (1985): 2302-2319.
    Abstract:
    This paper presents a theoretical analysis of thermally induced noise in sheet metal roofs. A quasi‐static model of the roof behavior is developed based on roof support batten frictional forces constraining the thermal expansion and contraction of the sheeting. As a result, in‐plane stresses, set up in the sheeting, build up until the static frictional force limit is exceeded at one of the fasteners. At this point the sheeting slips over the batten at that fastener, the local frictional force is reduced to the dynamic frictional force limit, and a redistribution of in‐plane stresses and fastener forces occurs. The redistribution can cause an overload of an adjacent fastener frictional force to exceed its limit, thereby inducing another slip. The sequence will continue until all frictional forces are below the static frictional force limit. The change in deflection pattern of the roof accompanying each slip is used to estimate the noise generated. With the assumptions that the curvature strain is small relative to the thermal strain, the coefficients of friction at each batten are identical and the batten spacing is uniform, the theory may be used to derive considerable detail of the slip cascade pattern and to determine expressions for the rate of noise bursts, for the necessary temperature change to cause a roof to change from “heating” to “cooling” cycling, and for the impulsive noise level.
  • Fisher, James. "Expansion joints: where, when, and how." In NASCC Proceedings, The Steel Conference, Montreal, Canada. 2005.
  • Garden, George Kirby. "Thermal considerations in roof design." In Canadian building digest 1-100, p. 4. National research council of canada, 1968.
  • Meyers, Larry R., Richard S. Koziol, Dennis K. Johnson, And Norbert V. Krogstad. "laboratory Testing Of Low Slope Standing Seam Metal Roof Application." In Proc., 4th Int. Symp. On Roofing Technology, Pp. 144-152. Nrca/nist, 1997.
  • Movement, B. Thermal. "Rigidly fasten metal roof panels to structure at one and only one location for each panel." Allow remainder of panel to move freely for thermal expansion and contraction. Predrill panels for fasteners 1: 07411-8.
  • Panels, Standing-Seam Roof. "Fasten to purlins with concealed clips at each standing-seam joint." Install clips over top of insulation. Crimp standing seams with manufacturerapproved motorized seamer tool. Rigidly fasten eave end of metal roof panels and allow ridge end free movement due to thermal expansion and contraction.
  • Roof, C. "Roof to Wall Transition." Roof to Sheet Metal Roof Edging Transition Expansion-Joint Cover: Fabricate from the following material 1.
  • New Zealand Steel Installers Guide, NZ Steel Co. "New Zealand Steel Installers Guide, COLORSTEEL®, ZINCALUME® steel and GALVSTEEL™ Installer's Guide", [PDF], (2005), New Zealand Steel Limited, Private Bag 92 121, Auckland, New Zealand. Tel: 0800 100 523, or 0-9-375 8999 Fax 0-9-375 8213, Website: http://www.nzsteel.co.nz/, Email: info@colorsteel.co.nz - retrieved 2015/12/07, original source [check for and remove any blanks in the following URL] : http://www.nzsteel.co.nz/content/media/ 77012/New%20Zealand%20Steel%20Installers%20Guide%20-%20November%202005.pdf

    Excerpt: [Metal roof panel] Fixing systems used must allow for expansion and accommodate the longitudinal movement which results. If this is not done, ‘canning’ of the profile may occur and ponding of low pitch roofs, or noise may become a problem.
  • Warseck, K. A. R. E. N. "Roof failure: effect and cause." Building Operating Management', Available from http://www. findarticles. com/p/articles/mi_qa3922/is_200304/ai_n9220745, accessed 8th December (2006).

The Role of Metal Roof Profile Type in Roof Noise Levels

The metal roof profile type may also affect the level of noise transmitted by the roof to the building interior. Raised profile metal roofs may be noisier than a flatter profile roof on the same building. Metal roofing that is supported directly by the roof deck below will deflect less and should be more noise and sound resistant than metal roofing that has a raised profile. For example, some metal roof shingles employ a raised profile that includes an empty air space below the metal shingle surface.

The Role of Metal Roof Fasteners in Roof Noise Levels

Because improper choice of fastener, improper fastener location, or improper number of fasteners may permit metal roof components to move in ways that increase the roof noise level during temperature changes, review the manufacturer's specifications for your particular roof product to be sure that the roof was installed as recommended.

Check panel lengths, panel side-interconnections, fastener type, size, interval, location, and any other fastener and panel specifications in the roofing manufacturer's product installation guide. Pay particular attention to panel end abutments against immovable surfaces. A roof panel, even a fairly short one, that tightly abuts a vertical surface such as a chimney, wall or parapet, may be noisy when heated by normal temperature changes.

Suggestions for Reducing Noise Transmission Through Metal-Covered Roofs

These metal roof installation options can reduce roof noise transmission from metal roofs, such as the sound from falling rain or hail:

Adding faced metal building insulation alone to the metal building construction can reduce noise levels in a metal building by 5-6 dB. However, construction techniques do impact the way sound travels. To maximize a metal building’s acoustical performance, the wall and/or roof panels should include at least one layer of faced metal building insulation, and one layer of unfaced metal building insulation. Additionally, the construction should be tight, with attention to detail such as filling gaps with flexible sealants to assure that sound does not transit via air leaks from one space to another. - NAIMA [4]

See METAL ROOFING and METAL ROOF EXPOSED FASTENER FLASHING for details.

Metal roofing references and other detailed articles about metal roof selection, installation, diagnosis & repair begin at METAL ROOFING

Sound Transmission Class - STC & OITC: Sound Transmission Loss Properties for Building Walls & Roofs

STC or sound transmission class is defined as the level of reduction of sound transmission from outside noise sources to the building interior. Higher STC numbers mean higher resistance to sound transmission to the building interior, or as acousticians would describe it, higher STC means greater sound transmission loss between outdoors and the building interior. Typical STC values for metal buildings are STC=20 to STC=55.

OITC or Outdoor-Indoor Transmission Class describes the sound transmission loss properties of building exterior components like windows and walls against noise from traffic, trains, or low flying aircraft. - General Steel Corporation [3]

Details about sound transmission are at SOUND TRANSMISSION CLASS RATINGS

TPO Roof Noise

Reader Question:

5/9/2014 LarryDri@aol.com said:

Interested in rain impact sound transmission on TPO Roofs

Reply:

Larry,

Thermoplastic polyolefin (TPO) single-ply roofing membranes are rather recent roof products for which I have not seen much research on noise transmission. Here are a few citations of interest but you'll see the focus has been for the most part elsewhere. Nebesnak (patent disclosure) discusses the need for sound-isolating underlayment. Baskaran et al have done a bit of research and may have some data for you as may Beer who've researched a decade of TPO roof performance. Thanks for the query. I'll continue to look at this question.

Reader Question: What causes roof noise in our flat roof during cold nighttime weather? How can we fix it?

Roof noise - during the winter our torched-on membrane (180g. polyester base sheet & 280g. polyester SBS Cap Sheet) covered flat roof (installed 2002 on the apartment building) makes noises typically at night which disturbs the tenants and has caused some to move out. There are no leaks and the roof looks properly installed. What causes the noise and what can be done about it? Regards, Steve Rickard

Reply: suggestions for diagnosing cold weather flat roof noise - the diagnosis will define the steps to cure roof noise

Steve: re: how to diagnose & cure annoying night time noise from a flat roof.

Tar and gravel roof with ponding (C) D Friedman

With no information and no building inspection, we can't say with confidence exactly what is causing the annoying roof noise you report. An onsite expert should be able to help however. Here are some of the roof noise diagnosis observations that we would expect a roof noise consultant to consider:

Other more general observations that can help track down roof noise sources

Comments, suggestions, or questions from readers are welcome in helping to diagnose this roof noise issue.

...


Continue reading at SOUND ABSORPTION vs. SOUND ISOLATION or select a topic from the More Reading links or topic ARTICLE INDEX shown below.

Or see NOISE / SOUND DIAGNOSIS & CURE - home, where we describe how to locate the source of, identify and correct various building sounds and noises indoors or on occasion, noises from outside that penetrate indoors at annoying levels.

Or see SOUND CONTROL in BUILDINGS - home , we provide a series of detailed articles on reducing unwanted building noise levels through building design, insulation, sound isolation, and noise barriers.

Or see SOUND CONTROL for FLOORS - methods that may help with roof noise control

Or see SOUND ISOLATION STRATEGIES

Or see SOUNDPROOFING MATERIAL PROPERTIES


Suggested citation for this web page

ROOF NOISE TRANSMISSION at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ROOFING

OR use the Search Box found below at Ask a Question or Search InspectApedia

...

Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman