Common Weathertightness Issues
Common Issues When Installing a Weathertight Metal Roof
In this blog we will look at common weathertightness issues for metal roofs and how to avoid them. Taking time to ensure you have proper installation of all components is key to having a roof that will stand up to the elements.
* This blog is offered as general metal roofing guidance only. Steelscape does not offer weathertight warranties, these warranties are offered by the product manufacturers and installers that use Steelscape steel. Use the Where to Buy section to find reputable product manufacturers in your area.
Weathertightness is a key concern with any roofing surface. It refers to the resistance of the exterior surface to natural weather elements such as rain and snow and its ability to prevent moisture from penetrating to the structure below. Weathertightness issues can be a significant concern as penetrating moisture can cause permanent building damage and can be costly to repair. A key advantage of metal roofing is that if installed correctly, it provides long-lasting weathertight protection from the elements.
Weathertightness issues commonly present themselves in the form of water staining or water leakage within the interior of the building. By the time weathertightness issues are apparent in the interior of the building, water infiltration and subsequent damage can be extensive. This underlines the importance of correct installation in the first instance, and the need to remedy any weathertightness issues as soon they become apparent.
Identifying the source of weathertightness issues can sometimes be challenging due to the phenomenon known as capillary action. This action can mean that water can move upwards in narrow spaces, against the forces of gravity, due to the unique surface tension, attraction, and adhesion properties of water molecules. For roofing weathertightness issues, this means that indicators of moisture infiltration, such as interior damage, may be far removed from the original source of moisture penetration. Capillary action can often arise where improper design and installation results in the pooling of standing water at roof transition points.
Weathertightness issues are unique in nature and often represent a combination of contributing factors. However, common causes of weathertightness issues that stem from installation include:
- Incorrect installation of fasteners
- Improper usage of sealants
- Improper detailing for roofing equipment and penetrations
- Improper transitions or roof surfaces with insufficient pitch
Screws, rivets and other fasteners can often be a source of water infiltration as they reflect a penetration to the metal surface in order to attach the metal roofing or siding to the structure. Some metal fasteners have a flexible washer at the head of the fastener to create a gasket between the metal surface and the fastener. While this is an effective barrier, correct fastener placement that reduces the opportunity for water penetration is very important. The correct location of fasteners will be outlined by metal roofing product manufacturers. Common fastener related issues include the improper location of fasteners, improper pressure applied to fasteners (too little or too much pressure which compromises the effectiveness of the gasket), or the use of the wrong type of fastener.
For certain roof transitions, flashings, or some roof penetrations, sealants will be required to achieve weathertightness. Only metal roofing specific sealants should be applied and only in the locations outlined by the product manufacturer. Issues related to sealant include the use of the wrong sealant, incomplete use of sealants, or the overuse of sealant to rectify poor workmanship.
Often roofing areas feature penetrations such as skylights and vents. These must be sealed correctly and divert water appropriately to avoid weathertightness issues. Improperly sealed penetrations, such as the use of the wrong fasteners and sealants can result in leaks, and improper flashing designs, such as areas uphill of skylights and chimneys, can result in standing water and water infiltration. When detailing around penetrations, these will often have to account for the thermal movement of the metal panels in addition to providing weathertightness. Product manufacturers will detail the appropriate accessories and flashing methods for individual roof penetrations.
As highlighted earlier, roofing areas that do not shed water result in standing water and this can be a cause of weathertightness issues. Standing water is created where the roof area does not have sufficient pitch to swiftly shed water. For most metal products, a roof pitch of at least ¼:12 (rise over run) is required to adequately shed water. Improperly designed roofing areas, such as roof transition points between two roof planes, create this issue. In addition to standing water issues, panel transitions or material laps using the incorrect methods or flashing details can also be a source of weathertightness problems.
The weathertightness issues identified above are associated with installation and will result in weathertightness issues soon after project completion. Weathertightness issues can also occur over the long term as different element of the roofing system move and age. Common longer term weathertightness issues include:
- Screws backing out due to expansion and contraction
- Caulking and sealant break down
As metal roofs warm and cool due to the weather and sun exposure, they will expand and contract. Fasteners may move or back out due to these forces over extended periods of time. If these fasteners are not periodically checked and resecured, loose fasteners may be a source of water infiltration.
While metal is a durable material that is designed to last for decades, sealants are not as robust and degrade over time, especially when exposed to elements such as sunlight. Failure to maintain a roofing surface by addressing aging sealants can be a long-term source of weathertightness issues.
The two key strategies to avoid weathertightness and water infiltration issues are to ensure the roof is installed correctly and it is periodically inspected over time.
Skilled detailers will ensure the roof is designed correctly to shed water and account appropriately for roofing penetrations. Skilled installers that follow product manufacturer installation instructions will help ensure the system is installed correctly, including the correct use of fasteners, sealants, and penetration accessories.
Inspection of the roofing area during or upon project completion by an expert (such as a manufacturer’s representative) can help identify roof system issues before weathertightness arise. Most importantly. periodic inspection over the lifespan of the roof will help ensure weathertightness issues are caught early. These inspections will ensure that potential issues caused by roof aging (such as sealant degradation) are proactively addressed, and other maintenance issues (such as the buildup of leaves in roof transition areas) are addressed before they create weathertightness problems.
Warranties for roofing weathertightness can be offered by the roofing installer or metal roofing manufacturer. Manufacturer warranties cater to commercial projects that use high-performance commercial-grade roofing profiles. Of note, metal roofing manufacturer weathertight warranties are not implied, that is they do not come standard with the product. Weathertightness warranties are typically offered at an additional cost and require extensive review and inspection prior to issuance to ensure the roofing system is designed and installed correctly.
Weathertightness warranties can be offered at different lengths and offer different coverages. Some weathertight warranties will cover elements specific to product integrity, and this warrants that the interlocking metal roofing seam will remain free of water infiltration. Broader weathertight warranties may provide full roof system coverage. Weathertightness warranties will be subject to specific exclusions and routine roof maintenance protocols. Always ensure you read the terms of the warranty prior to acceptance.
In summary, taking time to ensure you have proper installation and usage in all of your roofing aspects is key. It is much easier to ensure something is done correctly than to need to replace and repair when a leak appears.
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