Difference between revisions of "Fasteners"
Difference between revisions of "Fasteners"
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| + | <big><big><big><big><big>Fasteners and Fastening Materials</big></big></big></big></big> | ||
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| + | | colspan="2" | '''NOTICE TO READER''': This is an <u>information page only</u>. To read the standards applicable to a particular Waterproofing or Water-shedding System, refer to the actual Standard located in [[Division B | '''Division B''']]. | ||
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=== General === | === General === | ||
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=== Mechanical Fasteners === | === Mechanical Fasteners === | ||
| − | Mechanical fastening to steel decks provides more effective wind uplift resistance and greater horizontal shear resistance than adhesives (thereby decreasing potential membrane splitting). Fastening patterns and rates that have proven to be successful are published in the '''''RoofStar Guarantee | + | Mechanical fastening to steel decks provides more effective wind uplift resistance and greater horizontal shear resistance than adhesives (thereby decreasing potential membrane splitting). Fastening patterns and rates that have proven to be successful are published in the '''''RoofStar Guarantee''''' Standards and should be enforced as a minimum. In addition to insufficient fasteners, the type of fastener can prove critical. For example, failure may occur from nails with inadequate head size to pull through the roofing felts. |
| − | The correct fastener should be specified by the design authority for each component of a roof system. | + | The correct fastener should be specified by the design authority for each component of a ''roof system''. |
The design authority should consult with the fastener manufacturer to determine the fastener's pullout strength in specific deck types to determine the number of fasteners required. | The design authority should consult with the fastener manufacturer to determine the fastener's pullout strength in specific deck types to determine the number of fasteners required. | ||
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=== Wind Uplift === | === Wind Uplift === | ||
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==== Design Wind Loads ==== | ==== Design Wind Loads ==== | ||
| − | + | For more information about the design of membrane roofs and wind-resistant design that conforms to the requirements of the Building Code, refer to Part 3 in any of the Standards in [[Division B | '''Division B''']]. | |
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==== Fastener Pull-out Strength ==== | ==== Fastener Pull-out Strength ==== | ||
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==== Deck Material ==== | ==== Deck Material ==== | ||
| − | Fastener requirements are not the same for all deck materials. As plywood thickness and steel gauge increases, fastener pull-out strength increases, hence fewer fasteners are required, as shown in the tables found in the '''''RoofStar Guarantee | + | Fastener requirements are not the same for all deck materials. As plywood thickness and steel gauge increases, fastener pull-out strength increases, hence fewer fasteners are required, as shown in the tables found in the '''''RoofStar Guarantee''''' Standards for roof waterproofing systems. |
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Latest revision as of 15:42, 9 September 2021
Division E - General Information
Fasteners and Fastening Materials
| NOTICE TO READER: This is an information page only. To read the standards applicable to a particular Waterproofing or Water-shedding System, refer to the actual Standard located in Division B. |
1 General
Securement of the roof system to the roof deck is necessary to prevent damage caused by wind uplift (possibly resulting in a blow-off) and lateral movement of the roofing materials due to thermal and moisture variations. Traditionally, the roof insulation and roofing are secured to the roof deck by means of mechanical fastening, adhesive, or a combination of both.
RoofStar Guarantee Standards requires mechanical fastening of the insulation wherever practical. Over concrete and other non-nailable decks, or where mechanical fastening is not feasible an adhesive may be used, usually bitumen.
2 Adhesives
In the past, roofing was installed over wood decks using mechanical fasteners. As construction technology progressed, many new types of decks developed bringing with them different securement requirements.
Concrete and other non-nailable decks dictated that an adhesive, usually bitumen, be used to apply the roof insulation and roofing. On sloped roofs where securement is required to prevent slippage, wood nailing strips must be cast into or fixed to the deck to permit mechanical attachment.
On steel decks, the initial use of bitumen as the adhesive has proven to be less successful than adhesion to concrete. Steel deck deflection can result in breaking the adhesive bond between the insulation and the deck. In addition, the use of bitumen may contribute to the fire hazards associated with steel decks.
Several adhesives successfully achieve adequate adhesion against wind uplift and lateral movement resistance. Many factors can influence the strength achieved, including substrate characteristics and preparation, bonding area, chemical compatibility of adhesive and insulation and moisture and temperature conditions at time of application. To properly evaluate an adhesive for use in a roof assembly, the design authority must
- Know if it is acceptable to the membrane manufacturer
- Understand the adhesion properties of the product, and
- Consult the list of tested assemblies compliant with the CSA A123.21-14 Standard test method for the dynamic wind uplift resistance of membrane roofing systems.
3 Mechanical Fasteners
Mechanical fastening to steel decks provides more effective wind uplift resistance and greater horizontal shear resistance than adhesives (thereby decreasing potential membrane splitting). Fastening patterns and rates that have proven to be successful are published in the RoofStar Guarantee Standards and should be enforced as a minimum. In addition to insufficient fasteners, the type of fastener can prove critical. For example, failure may occur from nails with inadequate head size to pull through the roofing felts.
The correct fastener should be specified by the design authority for each component of a roof system.
The design authority should consult with the fastener manufacturer to determine the fastener's pullout strength in specific deck types to determine the number of fasteners required.
Wind uplift has been shown to be greater at the perimeters and therefore fastener requirements vary between field and perimeter areas. In addition, mechanical fastening may be required at the perimeter detail to restrain lateral movement of the membrane.
4 Fastener Corrosion
Responsible fastener manufacturers have developed sophisticated fastener coatings and metal alloys to counteract or slow fastener corrosion. These fasteners are usually tested for corrosion resistance through a method called the Kesternich Chamber. This method stipulates that the fastener be exposed to sulphurous acid for a minimum of 15 cycles and show less than 15 percent rust after testing. Proof of successful testing at least gives an indication of corrosion prevention but the designer must still consider the other corrosion contributors discussed.
5 Roofing Nails
Manufacturers of roofing nails that conform to CSA Standard CSA B111, suitable for use in roofing systems include:
- National Nail Inc.
- Simplex Nails
These are available through selected RCABC Associate Members.
6 Wind Uplift
6.1 Design Wind Loads
For more information about the design of membrane roofs and wind-resistant design that conforms to the requirements of the Building Code, refer to Part 3 in any of the Standards in Division B.
6.2 Fastener Pull-out Strength
Fastener pull-out is the force required to remove the fastener from the substrate without unscrewing. Pull-out test results depend on the deck material, fastener material, shank size and length, and thread pitch and depth. A typical #14 screw designed for insulation attachment (as an example) in a 22 ga. steel deck has a pull-out resistance of 230 kg (507 lb).
The total fastener pull-out strength of all fasteners in a sheet must be greater than the total uplift for each sheet being attached. Distribution is also important.
6.3 Fastener Distribution
Fasteners must be distributed evenly throughout the sheet material being attached. The actual strength of the material between fasteners is the issue. If a roof requires 1.7 kPa (35 psf) uplift resistance, a 1.2 m x 2.4 m (4’ x 8’ or 32 ft²) sheet of insulation would require a total force of 508 kg (1120 lb) to resist uplift. A single fastener with 522 kg (1150 lb) pull-out strength would cover the uplift force but clearly would not be sufficiently distributed throughout the sheet. In most cases the distribution of fasteners takes precedence over pull-out strength.
6.4 Deck Material
Fastener requirements are not the same for all deck materials. As plywood thickness and steel gauge increases, fastener pull-out strength increases, hence fewer fasteners are required, as shown in the tables found in the RoofStar Guarantee Standards for roof waterproofing systems.
© RCABC 2024
RoofStarTM is a registered Trademark of the RCABC.
No reproduction of this material, in whole or in part, is lawful without the expressed permission of the RCABC Guarantee Corp.