A key factor in successful guardrail application is the attachment of the posts to the substrate. Many pre-engineered post attachment methods are available to meet diverse needs of your projects, including mounting to concrete, structural steel, and engineered wood.
Additional post attachment options can accommodate fascia mounting with an offset, core mount and block-out, and parapet or pony wall applications. They all can be used in conjunction with various types of connecting hardware, including lag screws, thru bolts, expansion anchors (for concrete), or other specialty connection hardware.
Post attachment options
The most common post mounting option for guardrail applications includes surface, direct fascia, fascia bracket, and stanchion.
A surface mount solution is used to mount posts with an attached base plate directly on top of deck, patio, or stair tread surfaces. This type of mounting method can be used on both flat surfaces and angled runs and is a good choice for wide decks or walkways, and cases where there is no concern with posts consuming space on the structure.
In the majority of instances, concrete decks, wall top railings, interior pony walls, and exterior parapet walls will call for surface-mounted posts. Similarly, level wooden decks with at least 3 in. of structural backing at the post locations and rooftop decks with gutters or other obstructions that can prevent fascia mounting are well-suited for surface mounting.
Direct fascia mount
Surface-mounted posts can require up to 6 in.of space around the perimeter or the post due to the size and location of the mounting Flange, direct fascia-mounted railing posts do not take up space on top of the deck. Additionally, fascia-mounted posts can be less expensive, especially in cases where they are bolted directly through the post, typically utilizing two to three bolts instead of a mounting flange with four bolts.
Direct fascia mounting is usually recommended for smaller surfaces where space is an issue and the surface is uneven. It is important to be able to adjust the posts up or down, as needed. Fascia mounting also lends itself to situations where a standoff plate needs to be used to avoid a drip-edge flashing or where minimal backing makes it necessary to use a four-bolt mounting plate.
Many decks, especially those on rooftops, use a waterproof membrane to ensure the structure is protected from water. Direct fascia mounting helps ensure the railing posts do not puncture the waterproof membrane. Additionally, it provides a cleaner aesthetic as they hide the deck hardware along the side of the structure.
When using this method, post spacing may have to be reduced to account for the reduced cross-section where the hole is drilled.
Fascia bracket mount
Fascia mount brackets are designed for side mounting to fascia or rim joists when decking or nosing trim extends beyond the edge of the fascia board. These brackets are often used for installation of posts on flat roofs and concrete decks and accommodate both straight and corner runs.
Posts are attached using metal brackets that have a stand-off and are installed flush with the fascia board.
Stanchions are used to mount posts to stone or tile-covered concrete slabs, or on roof decks where the penetration of waterproof roofing membranes must be minimized. Short stanchions are attached to the structural members prior to pouring the slab or laying the roof membrane. Railing posts are then sleeved over the protruding stanchion ends and secured with screws. Stanchions are available in steel, aluminum, and stainless steel.
Post fastener method by substrate
A heavy timber beam either Douglas Fir or Western Red Cedar, EWP, glue-laminated timber know as glulam, laminated veneer lumber, and treated framing lumber are the most common substrate materials to which guardrails are attached. Other materials might include concrete, steel, and a pedestal system over substrate.
The fastener method chosen is often the most critical aspect of ensuring a railing frame can withstand the loads as prescribed by building code.
Guardrail attachment methods include base, direct fascia, and fascia bracket mount applications. All of these methods can use either lag screws or thru bolts, with specific considerations that depend on project variables and the type of wood being used.
The American Wood Council’s, National Design Standards dictate thread engagement requirements for lag screws into wood and respective tension strengths. This standard is referenced in the International Building Code (IBC).
Treated framing lumber
Guardrail attachment options include base, direct fascia, and fascia bracket mount applications. Lag screws or thru bolts can be used. When opting for the former, it is crucial to ensure adequate blocking to achieve necessary thread engagement. When using thru bolts, sufficient access must exist to install the washer and nut.
It is important to focus on the method of preservation, which may require particular fastener alloys or specially coated fasteners (hot-dipped, zinc-coated, galvanized steel, stainless steel, silicone bronze and/or copper.
All mounting methods can be used with concrete. The method chosen will depend on unique project specifications/variables. When using an attachment method requiring fasteners, options can include expansion and epoxy anchors and various embed hardware. It is important to pay attention to products designed and tested with both cracked and uncracked concrete.
In addition to concrete strength (f’c), effective embedment (depth of anchor), edge distance, and anchor spacing are all important engineering considerations when mounting to concrete. The slab must be an adequate depth to accept proper anchor mounting.
Mounting options are be limited with post-tensioned concrete slabs because the tendons may be too close to the slab edge, effectively eliminating the possibility of drilling/cutting the slab. Inadvertently damaging one of the tendons can release a tremendous amount of energy very quickly, potentially causing serious injury or death while irreversibly damaging the substrate.
Similarly, special care should be taken to not collide with or drill through rebar or interfere with rebar locations.
As with concrete, all mounting methods can be used when attaching posts to steel. Whether fastening to an H-beam, I-beam, C-channel, box beam, hollow structural section, architecturally exposed structural steel, or other structural steel members, project specifics need to be taken into consideration. Fastening methods can include drill and tap, welded studs, welded stanchions, and thru bolting.
When welding stanchions to a steel member, it is important to use similar metals and properly account for environmental conditions. For example, in coastal areas or in environments that regularly use de-icing chemicals such as magnesium chloride, potential galvanic reactions can occur when dissimilar metals make contact with one another.
Floating deck systems
Typical attachment methods include a stanchion or base mount. These systems add distance between the walking surface and mounting surface, which impacts the structural loading on the post and attachment connection. As a result, the moment load is increased due to the elongated lever length. Therefore, the mounting system that is used must be adequately designed and strong enough to accommodate a higher bending strength on the post and larger withdrawal (tension) capacity on the fasteners.
Mounting Guidance - InlineDesign
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