Many openings for windows and doors require special design consideration to ensure that the weight of the wall above the opening is suitably catered for and to ensure that any pressure (wind force) applied to the opening will not compromise the structural integrity of the opening (see Figure 1).
The most common method of strengthening an opening is to install a substantial lintel. Most engineers would simply state that a structural lintel is required for the opening but a standard heavy-duty lintel poses a considerable problem when used in steel stud walls... “How do I connect the lintel to the jamb studs?”
The answer is simple: by ignoring structural steel options and looking at some lightweight systems that have been engineered and tested for compliance (see Figure 2). But more on this later.
“Right now, I need to know when should I use a lintel?”
You can apply a couple of basic rules to check whether you need to ‘beef up’ your opening...
Is the opening on an external wall?
Is the opening inside but subject to considerable wind forces from outside?
Is the opening wider than 1.6 metres?
Is the wall height above the opening greater than the opening itself?
Is the lining material heavy or multi-layered?
Is the opening in a chase wall or a wall lined on one side only?
If you have answered yes to any of these questions, then you can be sure that your opening needs a lintel system of some sort.
The question that is commonly asked next is: why? “Why do I need to have some heavy beam at the top of an opening? Why can’t I get away with just running a piece of standard track across the top?”
Lintels serve multiple purposes in any given installation and some of those purposes are as follows…
Horizontal load - to withstand a load being applied against the opening, such as wind pressure or the opening being accidentally hit with an object passing through the opening. A hospital with trolleys being rushed in and out of rooms is a good example.
Vertical load - to carry the weight of the wall system located above the opening. A recent installation that we saw had a small doorway in a 8.0 metre high wall that had feature lining weighing nearly 100kg/m2. Imagine the downward force above the doorway!
Spread the load - to evenly distribute both the horizontal load and the vertical load to the jamb studs. The load can’t go down to the floor, like normal, so it has to go somewhere.
Openings in walls tend to get a lot more abuse than the rest of the wall: objects knock them, people collide with them, doors slam against them. All this extra wear and tear points up the need for a more robust wall design around openings. Hence, the use of an engineered lintel system.
Lintels are commonly used in conjunction with a sill (like a lintel at the base of the opening, such as a window opening) and jamb studs (the studs on either side of the opening). The design of the sill and of the jamb studs also needs to be taken into consideration (see Figure 3).
Most contractors don’t realize the importance of a lintel system and how the whole wall’s integrity may rely on the inclusion of the correct lintel. Indeed, most openings are only thought about five minutes before you start framing it. This poses a question about how contractors can incorporate the correct lintel system into the wall without having to have it specifically engineered, without having to order in special sections and without throwing the project timeline into disarray.
The two most practical ways that openings can be framed into lightweight steel walls are (a) to use a combination of standard steel studs and tracks in such a way that it creates a structurally sound section, or (b) to use a lightweight structural member that is specifically designed for the application.
Firstly, let’s look at how we can use standard stud and track products to create an opening. In most instances, single sections of stud and track cannot be used as lintels, sills or jambs. For example, a single piece of standard track is relatively flexible and light, and with a constant applied pressure, it may catastrophically fail in some way, thus making it unsuitable for use as a lintel or sill in high load applications (see Figure 4). Many unsuspecting contractors get caught using standard metal sections for openings, assuming that normal building practises can be used when framing openings into lightweight steel walls.
So to create a suitable lintel, sill or jamb that has structural integrity, you need to use a combination of several standard stud and track sections (see Figure 5)
For example, a suitable lintel may be constructed using two steel studs, two deflection tracks and two standard tracks: six sections in total, fixed together with screws at 300mm spacings (see Figure 6a). This section offers considerable strength and rigidity and in some instances, can span up to more than 5 metres. For jamb studs, a common combination to use is two steel studs and two deflection tracks: four sections in total, fixed together with screws at 300mm spacings (see Figure 6b). Sills are generally lighter sections and may consist of two deflection tracks fixed back to back (see Figure 6c).
Another consideration is the way the lintel, sill and jambs are fixed to each other and how they are connected to the top and bottom tracks of the wall. In many instances, simply screwing the intersections together is insufficient at likely to fail. There are connection brackets available that are specifically designed to connect steel studs to track sections and that have been tested to take high loads. These brackets are readily available and easy to install.
Using this construction method, it’s possible to fabricate extremely strong lintels and jambs from materials that are possibly already on site, allowing the framing contractor to simply address each opening quickly and easily as they get to it. Many framing contractors in Australia already use this method and it has proven to be a simple yet adequately strong solution to creating openings in walls.
Using this technique is an approved way of making your wall opening code compliant with the latest BCA, NCC and Australian Standards guidelines.
The alternative method for framing wall openings is to use a steel section that is designed for efficient framing of openings, such as the Studco HEDA System. Such systems use a heavy C-section profile that is larger than a standard wall stud and can span much greater distances when used as either a jamb or a lintel (see Figure 7). These sections are designed to fit into a standard 92mm track section, allowing them to fully integrate into a steel stud wall structure without any major modifications. Large internal openings, such as long windows, may adopt the use of such a system and external openings of all shapes and sizes can be framed quickly using these sections (see Figure 8). Connection brackets are used for making a rigid connection at the various intersections.
To ascertain the correct combination of studs and tracks for lintels, sills and jambs, or to determine which heavy duty section to use, it is essential to always engage a structural engineer in advance. An engineering service that was recently introduced by Studco to assist the wall and ceiling industry uses a simple, interactive form where you can fill out with the details of your opening requirements and fax or email it off. The necessary engineering documents will then be sent back to you, ready for implementation and installation on site.
To sum up, wall openings are a vital part to the whole building’s structural integrity and it is of utmost importance that they are framed correctly. This article serves to highlight the fact, to give contractors a basic understanding the technical background of wall openings and to provide some practical solutions.