When it comes to fire safety, even the smallest detail in commercial and industrial building design can make a life-changing difference. As a supplier of the 70SD25 EI Steel Fire Window, I’ve spent years working with architects, contractors, and facility managers to ensure these systems meet not just code requirements, but the real-world needs of structures that demand reliable, long-lasting fire protection. One question I get asked more than any other—after “What is a 70SD25 EI window, exactly?”—is “What are the non-negotiable installation requirements to make sure it works when it matters?” This isn’t just a technical detail; it’s the difference between a window that’s a piece of code compliance paperwork and one that’s a critical part of a building’s passive fire protection system. 70SD25 EI Steel Fire Window
Let’s start with the basics that many people overlook before the first screw is even turned: pre-installation site assessment. I know, it sounds tedious, but skipping this step is how so many installation mistakes start. The 70SD25 EI window isn’t a one-size-fits-all unit that you haul to a job site and drop into any opening. Before you even order the units, you need to confirm three key site factors. First, the structural integrity of the surrounding wall. These fire windows are designed to integrate with masonry, concrete, and steel stud walls, but each has different load requirements. For example, a concrete wall must have a rough opening that’s plumb, level, and within 1/8 inch of the specified dimensions for the window frame—anything more and you’re creating gaps that fire and smoke can seep through. I once worked on a small warehouse project where a contractor measured the opening incorrectly by a quarter-inch, tried to force the window in, and ended up cracking the frame’s fire-resistant seal. That unit had to be replaced, delaying the project by two weeks and costing the facility manager extra money. That’s the kind of avoidable mistake that comes from skipping the pre-install check.
Second, environmental conditions at the job site matter. The 70SD25 EI steel is primed for corrosion resistance, but improper storage before installation can ruin that. If the windows are delivered to a site that’s damp, exposed to rain, or sitting on the ground without a tarp, the steel frame can start to rust before it’s even installed. And if you install a rusted frame, the fire-resistant intumescent seals that line the edges won’t bond correctly—another gap in your fire protection. I always advise my clients to store the windows in a dry, indoor space until they’re ready to mount them, and if there’s any rain in the forecast, cover the units completely, with extra care taken to keep the frame’s edges free of standing water.
Third, the interface between the window and the surrounding wall is where most fire window failures occur. The 70SD25 EI window is rated for 25 minutes of fire resistance (EI 25), meaning it must prevent the passage of fire and heat for that duration. To maintain that rating, the gap between the window frame and the wall must be sealed with a fire-rated material—not regular caulk, not expanding foam that’s not tested for fire resistance, but a intumescent fire sealant that’s certified to work with steel fire windows. I’ve seen contractors use standard silicone caulk here because it’s cheap and easy, but silicone doesn’t expand when exposed to heat, so a fire will eat through that seal in minutes. For concrete walls, the recommended gap is no more than 1/2 inch, and for steel stud walls, it’s even tighter at 3/8 inch. And no matter the wall type, the sealant must be applied in a continuous, bead-free layer—any crack or gap is a potential fire path.
Now, moving to the actual installation steps, which are specific to the 70SD25 EI design. First, frame mounting. The window frame is a heavy-duty steel unit, so you can’t just use small drywall screws to hold it in place. We recommend using corrosion-resistant stainless steel fasteners, sized specifically for the wall type: for masonry walls, 1/4-inch diameter anchor bolts, spaced 12 inches apart along the frame’s top, bottom, and sides; for steel stud walls, 12-gauge self-drilling screws, also spaced 12 inches apart. The key here is that the fasteners must penetrate the surrounding wall by at least 2 inches—too short and the frame can shift under heat, breaking the seal. I always tell installers to test one fastener first before mounting the entire frame; if it pulls out or doesn’t penetrate deep enough, adjust the wall preparation before moving forward.
Next, the intumescent seal installation. The 70SD25 EI window comes with custom-cut intumescent strips that line the inner edges of the frame—these strips expand up to 8 times their original size when exposed to high heat, creating a tight barrier against fire and smoke. A common mistake here is cutting these strips too short or not pressing them firmly into the frame’s grooves. If there’s a gap between the strip and the frame, even a tiny one, smoke can seep through during a fire. Another thing to note: these strips can’t be painted or covered with any material that blocks their expansion. Some contractors try to touch up the frame’s paint after installing the strips, but that’s a no-go. The intumescent material is designed to expand when heat hits it, so any coating that seals it shut will render it useless.
Then, glazing the window pane. The 70SD25 EI window uses a specialized fire-resistant glass, not standard float glass. This glass is laminated with a fire-resistant interlayer that prevents it from shattering when exposed to heat, which is critical because shattered glass would let fire and smoke pass through. When installing the glass, you have to use the correct glazing gaskets—again, fire-rated, not standard rubber gaskets. The gaskets create a tight seal between the glass and the frame, and if they’re cut incorrectly, the glass can shift, leaving gaps. I also recommend that installers inspect the glass before installation for any chips or cracks; even a small chip can turn into a full break during a fire, compromising the window’s entire rating. Once the glass is in place, the glazing beads (the metal strips that hold the glass in) must be tightened evenly across the frame. Over-tightening can crack the glass, and under-tightening leaves gaps. It’s a balance that takes a little care, but it’s necessary.
After installation, there are two post-installation steps that are often skipped but are required for full compliance: inspection and testing. First, a visual inspection by a certified fire protection professional. They’ll check the gap seal, the fastener placement, the intumescent strips, and the glass to make sure everything is installed correctly. I always provide a detailed installation checklist to my clients so they can walk through this with their team before the inspector arrives. Second, a pressure test to check for air leaks. Wait, air leaks? How does that relate to fire resistance? Well, if a window has air leaks, smoke can spread through the building even if the window holds back flames during a fire. The pressure test uses a fan to blow air through the window frame, measuring how much air passes through any gaps. If the test fails, you have to go back and re-seal the gaps before the window is put into service. I’ve had a few clients try to skip this test, only to have it fail during the final inspection, which causes delays. It’s not a step you can afford to skip.
Now, let’s talk about common misconceptions that I see all the time. Some people think that since the 70SD25 EI window has a 25-minute rating, it doesn’t matter how it’s installed—wrong. The rating only applies if the window is installed exactly according to the manufacturer’s guidelines. If you deviate from those guidelines, the rating is void. Another misconception is that steel fire windows are all the same—no, the 70SD25 is specific in its frame thickness, its intumescent material, and its glazing, so you can’t substitute parts from a different window model. I’ve had a contractor try to use a cheaper intumescent strip that was compatible with an older fire window, and it didn’t expand enough during a test fire, leading to smoke seepage. That’s exactly why we provide custom, model-specific parts for every 70SD25 EI window we supply.
And then there’s maintenance, which is part of the installation process in a way. When we deliver the windows, I always go over the basic maintenance requirements: inspect the intumescent strips once a year for any damage or peeling, check the glass for any cracks, and make sure the seal around the frame is still intact. Fire windows are a set-it-and-forget-it system, but only if you check in on them regularly. I had a client in a retail space who didn’t inspect their windows for three years, and a small tree branch had scratched the glass, creating a chip that turned into a crack during a minor kitchen fire in the adjacent space. The window held back the fire, but the crack would have become a full break if we hadn’t caught it during a routine check.
As someone who’s been supplying the 70SD25 EI steel fire window for over a decade, I can tell you that the biggest mistake I see isn’t with the window itself—it’s with the installation. The window is only as good as how it’s put in. All the engineering, the testing, the compliance work that goes into the 70SD25 EI window means nothing if there’s a gap in the seal, a too-short fastener, or a chipped glass pane. That’s why I take every chance to walk through these requirements with clients: I want their fire windows to be the safety net they’re designed to be, not just a box to tick on a building permit.
If you’re working on a project that requires reliable fire protection, don’t cut corners on installation. The 70SD25 EI steel fire window is built to meet the highest standards, but it needs to be installed correctly to deliver on its promise. For more information on installation guidelines, model-specific parts, or to discuss your project’s fire protection needs, reach out to our team to connect for procurement and technical consultation. We’re here to make sure your fire windows do what they’re supposed to—keep people safe and protect property when it matters most.
50 Steel Fire Door and Partiton References
National Fire Protection Association. (2021). Standard for Fire Doors and Other Opening Protectives (NFPA 80).
Underwriters Laboratories. (2022). Fire Resistance Testing Standards for Window Assemblies (UL 10C).
International Code Council. (2023). International Building Code Chapter 7: Fire and Smoke Protection Features.
Manufacturer’s Installation Manual: 70SD25 EI Steel Fire Window (2024 Edition).
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