Duluth SIP Fire Case Study: What 18 Core Samples Revealed About Fire-Damaged SIPs
A room-by-room look at a real SIP house fire in Duluth, Minnesota: what burned, what didn’t, and how 18 core samples decided which panels could stay and which had to go.
Written and Analyzed By Joe Pasma, PE | PGS Consulting LLC, Licensed Professional Engineer | 40+ Years in SIP Engineering, Manufacturing, and Forensic Analysis | Published October 9, 2026
House Fire Involving SIP Roof and Wall Panels
When a house built with structural insulated panels (SIPs) catches fire, everyone asks the same question: does the whole thing have to come down? In this case, the answer was no. Some panels had to be replaced. Many others came through the fire structurally sound, sometimes just a few feet from areas that burned badly.
In August 2026, PGS Consulting LLC investigated a residential SIP fire in Duluth, Minnesota. The home was nearing completion but was still under construction. The fire started in the garage and spread into parts of the home and garage's SIP walls and roof. We cut 18 core samples, reviewed 87 videos, and went room by room to sort out what was damaged, what wasn't, and why.
If you read our SIP Fire Myths article, this is the house behind it. Below is the full room-by-room breakdown, so you can see exactly what fire does to a SIP and what it doesn’t.
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| Detail | Summary |
|---|---|
| Location | Duluth, Minnesota |
| Investigation date | August 2026 |
| Project type | Residential home under construction, SIP exterior walls and roof |
| Fire origin | Attached garage |
| Evidence reviewed | 18 core samples, 87 videos, photo documentation |
| Areas studied | 8 zones, from untouched to total loss |
| Outcome | Panels protected by drywall, siding, plywood, or wood ceilings stayed sound. Some panels hit by direct, sustained flame lost their structural bond and were replaced. |
Key Takeaways
The fire did not damage the house evenly: some SIPs were a total loss, while others a few feet away had no structural damage at all.
Coverings made the biggest difference: drywall, siding, plywood, and wood ceilings shielded the panels behind them, even when those coverings were badly charred.
Burnt wood on the surface is not the red flag: the real warning sign is foam that has melted away from the wood skin, called EPS melt-back.
Core samples settle the question: of 18 samples, 8 showed a solid bond and 10 showed a failed bond. Every failed sample came from an area the fire hit hard and directly.
Structural framing held up differently: the garage door headers came through undamaged, even though SIP material right around them had to be replaced.
Repair vs. replace is a panel-by-panel call: this home needed targeted replacement, not a teardown.
SIPs 101: The 30-Second Version
A SIP is a sandwich, like an Oreo cookie with vanilla wafers. In the middle is a thick layer of rigid foam called EPS (expanded polystyrene). On each side is a wood panel called OSB (oriented strand board), which we'll call the "skin." The foam and the skins are glued together.
That glue bond is the secret to a SIP's strength. On their own, foam and OSB aren't very strong. Bonded together, they work as one stiff, strong panel, the same way an I-beam is stronger than its separate parts. Engineers call this "composite action."
So when we investigate a fire, we're not just asking "did it burn?" We're asking one specific question: is the glue bond between the foam and the skin still holding? If yes, the panel is usually still doing its job. If no, that part of the panel has lost its strength.
New to SIPs? Start with What Are SIPs? or our guide to SIP core types and materials.
EPS foam starts to soften once it gets hot, and it begins losing its structural integrity at roughly 180°F. That's well below the temperature it takes to burn wood. OSB reacts differently: when heated, its surface chars first, and that char layer acts like a heat shield that slows heat from reaching the foam underneath. That's why a panel can look scorched on the outside and still have a perfectly good bond inside. You can't tell which is which by looking. You have to cut a sample.
What Happened in Duluth
The fire started in the attached garage and spread into parts of the home. The house was still under construction, with SIPs used for the exterior walls and roof. That detail matters, because it meant the home was a mix of finished and unfinished areas:
Some SIPs were already covered with drywall, siding, plywood, or a tongue-and-groove wood ceiling.
Other SIPs had no covering at all, with the bare OSB skin exposed to the room.
Firefighters cut openings in some walls and roof sections to check for hidden fire.
The mechanical room between the house and the garage was a total loss.
That mix of covered and uncovered panels turned the house into a natural side-by-side test. We could compare protected and unprotected SIPs that went through the same fire.
How We Investigated: What a Core Sample Is (and Why It Matters)
A core sample is a round plug cut through the panel skin with a hole saw. It shows you all three layers (skin, adhesive, foam) exactly as they are inside the wall or roof. panel Think of it like cutting a slice out of a layered cake to see whether the frosting is still holding the layers together.
Here's what we look for:
A good bond: when you pull the skin away, chunks of foam stay stuck to the wood. This is called "foam tear-out," and it means the glue is stronger than the foam itself. That's a healthy panel.
A failed bond: the foam has melted back and pulled away from the skin, leaving a clean gap where the glue line used to be. That section has lost its strength.
Looking at the surface can't tell you this. A badly charred skin can sit on top of a perfectly healthy panel, and that's exactly what we found in several rooms.
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| What You See | Bond Held | Bond Failed |
|---|---|---|
| Foam on the skin | Foam chunks stuck to the OSB (tear-out) | Clean separation, no foam attached |
| Foam core | Full thickness, no melting | Melted back away from the skin |
| OSB skin | Clean, or charred on the surface only | Often charred deep into the wood |
| Panel strength | Still working as one panel | Lost in that area |
| Typical next step | Keep, clean, or repair | Engineer decides repair or replacement |
Room-by-Room: What the Fire Did
1. Stairway to the Second Floor
The drywall here was removed after the fire so we could see behind it. The SIP skins underneath had no fire damage. Above the stairs, the wood ceiling was charred, but the SIP roof panels behind it were fine. Core samples 1, 2, and 3 from the roof panels showed no foam melt-back.
Verdict: Panels were protected and structurally sound.
2. Second Floor, South Wall
Core samples 4 and 5 showed no fire damage. The skins were still firmly bonded, with foam tear-out visible.
Verdict: Panels remained structurally sound.
3. Second Floor, North Wall
Firefighters cut rectangular openings here to check for hidden fire inside the wall. There wasn't any. The heat never made it into the panel.
Verdict: No fire damage inside the panels.
4. Garage Door Wall
This was some of the worst SIP damage in the house. The OSB skins were heavily charred, and core samples 6 through 10 all showed foam melt-back with a clean split at the glue line. The melting reached well behind the skins, which tells us the heat here was intense enough to destroy the bond.
Verdict: Panels lost their strength and were repaired because structural elements in the panels were undamaged and carried the structural loads.
5. Garage Door Headers
This area holds the most useful lesson in the whole investigation. A header is the beam over the garage door that carries weight down around the opening. The SIP material below the headers was badly damaged. But the OSB skin directly over the engineered headers had no fire damage, because a drywall ceiling attached to the floor trusses shielded that zone.
Verdict: The headers held. The damaged SIP material around them was replaced.
The point: the parts of a SIP wall that carry load through framing don't fail in the same way as foam-only areas. That's why repair decisions have to be made by someone who knows where the load actually travels. (We saw the same thing in Myth 6 of our SIP Fire Myths article.)
The garage door headers are the part of this job I'd want every adjuster to see. The SIP material right next to them was gone, and someone eyeballing it could easily call the whole wall a loss. But the headers were carrying the load, and the drywall ceiling kept them out of the worst of the heat. If you don't know where the load is going, you'll replace things that don't need replacing.
-- Joe Pasma, PE6. Mechanical Room
This room had the most severe damage. The OSB skins on the inside, south wall, had no covering yet, so they faced the fire directly. The roof panels above had heavy charring and foam melt-back, and the wall panels showed different levels of charring. Core samples 12 and 13 showed melt-back and failed bonds.
There was one important exception. The west wall, the common wall between the garage and the mechanical room, had a plywood covering. The plywood charred, but core sample 11, taken behind it, showed the SIP skin and foam were completely intact.
Verdict: The roof panels were replaced. Wall sections that had a covering held up, the south SIP wall was replaced.
7. One-Story Area, North Roof Slope
Above the front entrance, the roof panels had severe charring and foam melt-back, plus firefighter cuts. Core samples 14, 15, and 16 all showed failed bonds.
Verdict: Panels were replaced.
8. One-Story Area, South Roof Slope
The other side of the same roof only had soot on it, with minimal charring. Core samples 17 and 18 showed no melt-back.
Verdict: Panels remained sound. Soot is a cleaning job, not a structural problem.
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| Area | What Protected It (or Didn't) | Core Samples | Result |
|---|---|---|---|
| Stairway | Drywall and wood ceiling | 1-3: bond held | Sound |
| 2nd floor, south wall | Distance from fire | 4-5: bond held | Sound |
| 2nd floor, north wall | Heat never reached panel | Firefighter cuts showed no damage | Sound |
| Garage door wall | Direct, sustained flame | 6-10: bond failed | Repaired, other structural elements carried the load |
| Garage door headers | Drywall ceiling shielded header zone | Visual: no damage over headers | Headers held, surrounding SIP replaced |
| Mechanical room south wall & roof | Uncovered, direct flame | 12-13: bond failed | Replaced |
| Mechanical room west wall | Plywood covering | 11: bond held | Sound |
| North roof slope | Direct flame | 14-16: bond failed | Replaced |
| South roof slope | Soot only | 17-18: bond held | Sound, cleaned |
Repair or Replace? How the Decision Was Made
The investigation didn't end with "the house had a fire." It ended with a clear, panel-by-panel list.
Areas that stayed or could be repaired:
Stairway walls and roof panels
Second floor south wall
Second floor north wall
Garage door wall panels, since other members were carrying structural load
Covered sections of the mechanical room west wall
One-story south roof slope (cleaning only)
Areas that needed replacement:
SIP material below the garage door headers
Mechanical room south wall and roof panels
One-story north roof slope
The deciding factor was never "how bad does it look?" It was "did the bond fail, and is that section carrying load?" If the bond held, the panel stayed. Small, localized damage in a sound panel can often be fixed by patching the OSB skin or injecting expanding foam. Where the bond failed in a section the house depends on for strength, we replaced that section. This is an engineering call made one panel at a time, which is why a general fire damage estimate often gets SIPs wrong in one direction or the other.
Dealing with fire or smoke damage on a SIP home and not sure which panels can stay? Talk to Joe Pasma, PE: he'll tell you what core sampling would show before anyone signs off on a repair scope.
Same Lessons, Different House
This isn't the first SIP fire we've documented. Our earlier SIP fire case study found the same patterns:
Foam melted back where the panel edges had no protective trim.
Charred OSB on its own did not mean the panel had failed.
Smoke spread soot far from the fire without causing structural damage.
Two different fires, different houses, panels from different manufacturers, and the same result. SIPs don't fail randomly. They fail in predictable, diagnosable ways, which is good news for anyone who has to decide on a repair.
Heard That SIPs Burn Like Crazy?
This case study shows the evidence. Our SIP Fire Myths article takes the seven most common fire fears about SIPs and checks each one against what we found in this house.
Read SIP Fire MythsWhat This Means for You
If You Own or Are Buying a SIP Home
Your drywall is doing real fire-safety work. Code requires it over interior SIP surfaces for exactly this reason, and this fire showed why. Keep it continuous, and don't leave panels exposed in finished spaces.
If You're a Builder
A SIP home is most vulnerable during construction, before the drywall, siding, and trim go on. The same is true of a stick-framed house. In Duluth, the worst damage happened where panels had no covering yet. Getting coverings on promptly and protecting exposed panel edges with trim reduces that risk. See our SIP Installation Guide for detailing basics.
If You're an Insurance Adjuster
Don't price a SIP fire claim from the surface. Char, soot, and smoke smell don't tell you whether a panel lost its strength. Core samples do. A SIP-specific forensic evaluation keeps you from paying to replace panels that only needed cleaning, and from missing panels that really did fail.
Frequently Asked Questions
What is EPS melt-back in a SIP fire?
EPS melt-back is when heat causes the foam core of a SIP to shrink and pull away from the wood skin. It starts once the foam gets hotter than about 180°F. When the foam pulls away, the glue bond that gives the panel its strength is lost in that area. It's the most important warning sign in a SIP fire investigation.
Does charred OSB mean a SIP panel has failed?
No. When OSB heats up, its surface chars, and that char layer actually slows heat from reaching the foam inside. In Duluth, several panels had charred coverings or surfaces but a perfectly good bond underneath. A panel has only failed when the char comes with foam melt-back and a broken bond.
Why were some SIPs undamaged when materials right next to them burned?
Because they were covered. Drywall, siding, plywood, and wood ceilings absorbed the heat and kept the panels behind them below the temperature where foam starts to melt. In the mechanical room, a plywood-covered wall survived intact while the uncovered roof above it had to be replaced.
How did the garage door headers survive when the SIPs around them didn't?
A drywall ceiling attached to the floor trusses shielded the header zone from the worst heat. Headers are structural framing that carries load, so they behave differently than foam-only parts of a panel. The SIP material below them was replaced, but the headers themselves held. Read more in our SIP Fire Myths article.
Why do you need core samples after a SIP fire? Can't you just look?
You can't see the glue bond from the outside. A core sample cuts a round plug through the panel skin so you can see whether the foam is still stuck to the skin. It's the only reliable way to know if a panel is still structurally sound. Learn more about SIP forensic analysis.
Can fire-damaged SIPs be repaired instead of replaced?
Often, yes. If the bond between the foam and the skin is still holding and the damage is limited to the surface or a small area, repairs like patching the OSB skin or injecting expanding foam can be realistic. A licensed engineer should make that call for each panel.
When do fire-damaged SIPs need to be replaced?
When the bond between the foam and the skin has failed in a section the building depends on for strength. In Duluth, that was the mechanical room roof, and the north roof slope above the front entrance. Those areas had melt-back and failed core samples.
Are SIP homes more vulnerable to fire during construction?
Yes, and so is every other type of house. Before drywall, siding, and trim go on, the panels don't have the protective layers a finished home has. In Duluth, the most severe damage happened where the SIP skins had no covering yet, or the fire was so intense that it consumed the drywall and the SIP panel. Code-required drywall in a finished home is there for exactly this reason.
Is smoke damage on a SIP a structural problem?
No. Smoke and soot are a cleaning problem. On the south roof slope in Duluth, the panels were covered in soot, but core samples showed no melt-back and a solid bond. Only sustained heat damages the bond.
What should insurance adjusters look for in a SIP fire claim?
Look for foam melt-back, check the bond with core samples, note which areas had protective coverings, check the condition of headers and other structural framing, and separate smoke-only areas from areas with direct flame. For background on how SIPs handle fire and code requirements, see Are SIPs Combustible?
Go Deeper
SIP Fire Myths: What's True and What's Not: the seven most common SIP fire fears, checked against this investigation.
SIP Fire Performance Case Study: how SIPs respond to full flame, high heat, and smoke-only exposure.
Are SIPs Combustible?: materials, drywall thermal barriers, and what the building code requires.
How SIPs Perform in Wildfire Zones: what solid-panel construction means for ember resistance.
SIP Forensic Analysis: What It Is, When You Need It, and How It Works: what a real SIP investigation looks like.
SIP Problems and Failure Modes: the most common ways SIP assemblies fail and how to spot them.
Fire Damage on a SIP Home?
PGS Consulting LLC provides independent, SIP-specific fire investigations, including core sampling and panel-by-panel repair vs. replacement recommendations, backed by 40+ years of engineering, manufacturing, and forensic experience.
Talk to Joe Pasma, PE
SIP Fire Performance Case Study: How SIPs Behave in a Real Residential Fire Event
A residential SIP fire produced three very different outcomes depending on exposure: total loss, partial damage, and no structural loss at all. Here's what determined the difference — and what builders, insurers, and adjusters should take from it.
Written and Analyzed By Joe Pasma, PE | PGS Consulting LLC, Licensed Professional Engineer | 40+ Years in SIP Engineering, Manufacturing, and Forensic Analysis | Published July 30, 2026 | Updated October 9, 2026
If you have ever wondered what actually happens to a Structural Insulated Panel in a house fire, the honest answer is: it depends entirely on how close the panel was to the flames. This case study walks through an actual residential fire in Cottonwood MN, and breaks the outcome into three zones so you can see exactly how distance and heat exposure change the result.
A garage fire spread and became fully involved before it could be safely fought from the inside. That fire compromised the SIP wall panels and the truss framed roof in the garage itself, affected some SIP panels where the garage met the home, and sent smoke into a vaulted SIP roof space in the home that never got hot at all. Three zones, three very different outcomes, all from the same event.
That spread of results is the whole point of this case study. It gives builders, designers, insurers, and anyone doing forensic work a clear, real-world picture of how SIPs actually behave in fire, instead of a vague yes-or-no answer to "are SIPs safe."
Note: This scenario is a specific example of a SIP home occupied by homeowners for many years after the SIP installations were completed. The material behavior, damage thresholds, and construction details described are representative of what we documented in the field and are recurring patterns across multiple SIP fire investigations.
| Detail | Summary |
|---|---|
| Project Type | Residential SIP home with an attached SIP garage |
| Construction | SIP home built in the mid-1990s, plus a SIP garage addition from a different manufacturer, joined by a stick-framed common wall |
| Fire Origin | Garage fire, fully involved before firefighters could safely enter |
| Exposure Zones Studied | Full flame involvement, localized high heat, and smoke-only |
| Outcome | Garage SIPs: total loss. Interface SIPs: partial loss, replaced. Attic SIPs: no structural loss, cleaned only |
Key Takeaways
SIPs did not fail uniformly in this fire. The outcome depended entirely on exposure: full flame contact caused total loss, localized high heat caused partial loss, and smoke alone caused no structural loss at all.
No building system, not SIPs, not stick framing, not ICF, not mass timber, is designed to survive a fully involved structure fire. The garage's total loss reflects normal fire behavior, not a defect in SIP construction.
Smoke and soot do not damage the structural integrity of a SIP. Panels that were only exposed to smoke needed cleaning, not replacement.
Small construction details made a real difference. Missing fascia that left foam edges exposed, and a roof design that trapped heat against the panels, both made the damage worse than it needed to be.
An open attic ladder gave smoke a direct path into the home's vaulted space, which is why smoke reached an area far from the actual fire.
Telling heat damage apart from smoke damage is critical for an accurate insurance claim. Confusing the two leads to either unnecessary panel replacement or missed structural damage.
Builders and designers can reduce fire risk to SIPs with a few specific choices: protect exposed foam edges, avoid roof details that trap heat against panels, and control how smoke can travel through open spaces like attic ladders.
Background: How SIPs Actually Respond to Heat
A Structural Insulated Panel is a sandwich: two rigid facers, almost always OSB (oriented strand board) in the US, glued to a foam core, almost always EPS (expanded polystyrene) in the US. The strength of the panel comes from all three layers working together. That matters here because it explains why SIP fire performance is not one simple story. It is a story about what happens to each layer at different temperatures.
Under sustained direct flame, the EPS core melts. The OSB facers char on the surface first, similar to how heavy timber chars while staying solid underneath, but under prolonged heat that char layer is eventually consumed. Once the foam has melted and the OSB is compromised, the panel loses what is called composite action, meaning the layers no longer work together structurally. For a broader explanation of how SIPs handle fire and what the building code requires, see our full breakdown: Are SIPs Combustible? Performance, Codes, and What Actually Keeps You Safe.
EPS foam begins to lose structural integrity above roughly 180°F and fully melts under sustained flame. OSB behaves differently: under moderate, contained heat it forms a protective char layer, but that protection is eventually consumed once flame exposure continues long enough. Those two thresholds, not one single "ignition point," are what actually determine how much of a panel survives a given fire.
The Fire Scenario: What Happened
The home in this case had a fairly common layout for SIP construction: a SIP-built house (walls and roof) from the mid-1990s, and a garage, added later, with SIP wall panels by a different manufacturer and a truss framed roof. The two structures were connected by a stick-framed common wall, and the roof where the garage met the home was "over-framed," meaning a small framed cavity was built over the SIP roof connection. The home also had a vaulted SIP roof space above the living area, reachable through an attic ladder.
When the garage fire started, it grew quickly and became fully involved, meaning the entire structure was burning and firefighters could not safely enter to fight it from the inside. That fire directly hit the garage's SIP wall panels along with the truss framed roof, and also reached the SIP roof panels of the home right where the two structures connected. At the same time, heavy smoke worked its way into the home's vaulted roof space, helped along by that open attic ladder acting as a direct pathway.
A few construction details shaped how the damage played out. Fascia trim was missing at the roof edge in one area, which left the EPS foam exposed instead of protected. The over-framed roof connection created a small cavity that trapped heat right where the two SIP systems met.
| Zone | Exposure | EPS Response | OSB Response | Outcome |
|---|---|---|---|---|
| Zone 1 | Full flame involvement | Complete melt-out | Char consumed, material lost | Total loss, panel failure |
| Zone 2 | Localized high heat | Melt-back at the facer | Surface char formed | Partial loss, panels replaced |
| Zone 3 | Smoke only | No degradation | No discoloration | No structural loss, cleaned only |
Zone 1: Full Flame Involvement (Total Loss)
The garage roof and wall panels took the worst of it. Once the structure was fully involved, those panels were exposed to sustained flame and temperatures well beyond what EPS or OSB can handle.
What happens to a SIP under that kind of exposure:
The EPS core fully melts. Above its structural limit, the foam loses shape and melts out under sustained flame.
The OSB burns past its char layer. Moderate heat produces a protective char, but prolonged flame consumes the wood material underneath it.
Composite action is lost. Once the foam is gone and the OSB is compromised, the panel no longer behaves as a structural sandwich.
The panel fails. SIPs, like every other building material, are not engineered to remain structurally intact under full involvement.
In 40+ years of SIP forensic work, full involvement fires are the one scenario I never expect a panel to survive intact, and I would say the same thing about stick framing, ICF, or mass timber. That is not a knock on any of these systems. It is just what fire does once suppression is not possible.
-- Joe Pasma, PEZone 2: Localized High Heat (Partial Loss)
The panels right at the home-garage connection tell a different story. These panels were close enough to feel serious heat, but they were not sitting inside a fully involved structure. The result was damage, but not total failure.
What was found in this zone:
EPS melt-back. The foam retreated from the facer in the areas closest to the heat source, rather than melting out completely.
OSB char formation. The wood facers charred on the surface, the expected first response to heat.
Surface charring on an adjacent LVL header. The engineered wood beam supporting that section also showed heat exposure.
Loss of composite action where the foam retreated. Wherever the EPS pulled away from the OSB, the panel's structural sandwich behavior broke down in that specific area.
These panels, along with the LVL header, needed to be fully replaced. Two construction details made this zone worse than it should have been: missing fascia left foam edges exposed to direct heat, and the over-framed roof connection trapped heat right against the SIP facers instead of letting it dissipate. Both are addressable at the design and installation stage, and both are covered in more detail in our SIP Installation Guide.
Zone 3: Smoke-Only Exposure (No Structural Loss)
This is the zone that often surprises people. The vaulted SIP roof space behind the garage was never touched by flame or direct heat. It only saw smoke, carried in through the open attic ladder.
What was found in this zone:
Heavy soot deposits on the floor framing and blackened flooring from smoke migration
Soot buildup where the wall panels met the roof panels
No discoloration of the OSB facers
No degradation of the EPS core
No delamination and no loss of adhesion between the foam and the facers
Despite how much smoke moved through this space, the SIPs here stayed fully structurally sound. The fix was cleaning, not replacement.
What Made the Damage Worse Than It Needed to Be
| Factor | Why It Mattered |
|---|---|
| Missing fascia | Left EPS foam edges directly exposed instead of shielded, accelerating heat damage in Zone 2 |
| Over-framed roof connection | Created a cavity that trapped heat against the SIP facers at the home-garage interface |
| Open attic ladder | Provided a direct, unobstructed pathway for smoke to migrate into the home's roof space |
| Mixed construction types | SIPs, stick framing, and LVL headers all responded differently to the same fire event, complicating the damage pattern |
None of these factors are unique to SIP construction. They are the kind of detailing issues that affect fire outcomes in any building system. The difference is that SIPs respond to them in specific, predictable ways once you understand how the material behaves.
Recognizing the Difference: Heat Damage vs. Smoke Damage
This distinction is the single most important thing an insurer, adjuster, or forensic investigator needs to get right after a SIP fire event. Getting it wrong means either replacing panels that only need cleaning, or missing panels that actually lost structural integrity.
Heat-damaged SIPs show physical material change. Look for EPS melt-back or melt-out, OSB char or consumption, and any separation between the foam core and the facer. These indicate real structural compromise.
Smoke-damaged SIPs show surface residue only. Soot deposits, blackened surfaces, and smoke odor with no change to the EPS or OSB material itself mean the panel is still structurally sound.
Location relative to the fire source is a strong early indicator. Panels with direct or near-direct flame exposure are candidates for heat damage. Panels several rooms or floors away, reached only through smoke pathways like an open attic access, are far more likely to be smoke-only.
When in doubt, a SIP-specific forensic evaluation settles it. General fire damage assessments are not built to evaluate composite panel behavior. For more on how that process works, see SIP Forensic Analysis: What It Is, When You Need It, and How It Works.
Not sure if that damage is structural or just cosmetic? Guessing wrong costs money either way — replacing panels that only needed cleaning, or missing a structural compromise that shows up later as a bigger repair. Schedule a consultation with Joe Pasma, PE, and get a straight answer before you write the repair scope.
Not sure if you're looking at a total loss or a cleaning job? That's exactly the call a SIP-specific forensic evaluation is built to make — I've seen adjusters miss it in both directions. Talk to Joe Pasma, PE before you sign off on a repair scope.
What This Means for Builders, Designers, and Insurers
Protect Exposed Foam Edges
Fascia, trim, and other coverings exist for more than looks. They keep EPS foam edges shielded from direct heat exposure. Skipping them, or letting them go missing, creates a weak point in an otherwise well-performing wall or roof assembly.
Avoid Heat-Trapping Roof Details
Over-framed roof connections, like the one at this garage-to-home interface, can create small cavities that trap heat directly against SIP facers. Where two different SIP systems or two different construction types meet at a roofline, that connection deserves extra attention during design.
Control Smoke Pathways
Open attic access points, unsealed chases, and similar gaps do not just affect air leakage and energy performance. They also give smoke a direct route into spaces far from the actual fire. Sealing and detailing these pathways properly limits how far smoke damage spreads.
Use SIP-Specific Forensic Evaluation
A general contractor or a standard fire damage assessment is not equipped to tell EPS melt-back from cosmetic soot staining. That distinction requires someone who understands how the composite panel behaves under heat.
Replace Only What's Actually Compromised
Once heat damage and smoke damage are correctly separated, the repair scope becomes much clearer. Heat-compromised panels need replacement. Smoke-only panels need cleaning. Treating every affected panel the same way leads to either wasted cost or overlooked risk.
Lessons From This Case
SIPs fail predictably under extreme heat, not randomly. EPS melts, OSB chars and eventually burns, and composite action breaks down once the foam separates from the facer. Understanding this sequence makes fire damage far easier to evaluate accurately.
Full structural involvement is not a fair test of any building material. The garage's total loss says nothing negative about SIP technology. It reflects what happens to virtually any building system under sustained, uncontrolled flame.
Smoke exposure alone is not a structural threat to SIPs. This is worth repeating because it is so often assumed otherwise. Soot on a panel does not mean the panel is compromised.
Small detailing choices carry real fire-performance consequences. Fascia coverage and roof cavity design are not just aesthetic or energy-efficiency decisions. They directly affect how a SIP assembly responds to heat.
Forensic evaluation needs to be SIP-specific. Insurers and adjusters who understand how to read EPS and OSB behavior after a fire will make more accurate, more defensible damage assessments.
For a broader look at how SIP assemblies fail and how to recognize the warning signs, see SIP Problems and Failure Modes in the Resource Hub.
Frequently Asked Questions
Do SIPs fail differently in a fire compared to stick framing?
Yes. SIPs behave as a composite panel, meaning the OSB facers and the EPS foam core work together structurally. Under high heat, the EPS melts and the OSB chars, and the panel loses that composite behavior once the two layers separate. Stick framing fails differently because the studs, sheathing, and insulation are separate systems that respond independently to heat.
Why did the SIP garage suffer a total loss while the home's SIPs mostly survived?
The garage became fully involved, which exposed those panels to sustained flame and extreme temperatures beyond what EPS or OSB can withstand. No building system, SIPs, stick framing, ICF, or mass timber, is designed to survive full structural involvement. The home's SIPs experienced either localized heat or smoke-only exposure, both of which are survivable conditions for the material.
Does smoke damage compromise the structural integrity of a SIP?
No. Smoke and soot deposits alone do not degrade EPS foam or OSB facers. SIPs exposed only to smoke typically need cleaning, not replacement. Structural damage only occurs when temperatures actually exceed the thermal limits of the panel materials.
What construction details affect how SIPs perform in a fire?
Detailing matters more than people expect. Exposed foam edges from missing fascia, poorly sealed joints, and roof configurations that trap heat against the panel can all accelerate damage. Proper detailing protects the EPS core and limits how much heat actually reaches the panel. See the SIP Installation Guide for more.
How should insurers evaluate SIP damage after a fire?
Insurers should distinguish between heat-compromised SIPs, showing EPS melt-back, OSB char, or loss of composite action, and smoke-only SIPs, showing soot deposits with no material degradation. SIP-specific forensic evaluation is essential here to avoid replacing panels that only need cleaning, or missing panels that are actually structurally compromised. Learn more in SIP Forensic Analysis: What It Is, When You Need It, and How It Works.
Are SIPs safe to use in residential construction given how they perform in fire?
Yes. SIPs are not fireproof, and nothing is, but they behave predictably and consistently under fire conditions once you understand how EPS and OSB respond to heat. When properly detailed, protected, and finished per code (typically with a fire-rated interior membrane such as gypsum board), SIP assemblies are built to meet the same fire-resistance requirements as conventional framing under the applicable building code. For a full breakdown of SIP fire performance and code requirements, see Are SIPs Combustible? Fire Performance, Codes, and What Actually Keeps You Safe.
Related Resources:
Are SIPs Combustible? Fire Performance, Codes, and What Actually Keeps You Safe -- A full breakdown of how EPS and OSB respond to heat and what the building code requires
SIP Forensic Analysis: What It Is, When You Need It, and How It Works -- What a real SIP forensic investigation looks like, from a licensed PE
SIP Problems and Failure Modes -- An overview of the most common ways SIP assemblies fail and how to recognize them
SIP Installation Guide -- How SIP assemblies should be detailed, sealed, and protected during construction
SIP Building Codes and Compliance -- Code requirements relevant to SIP fire performance
Forensic Case Study: Exterior OSB Deterioration at the SIP Ridge Joint -- Another real-world SIP forensic case study, this one on moisture rather than fire
Have Questions About Fire or Smoke Damage on a SIP Structure?
PGS Consulting LLC provides independent, SIP-specific forensic evaluation, distinguishing heat-compromised panels from smoke-only exposure, backed by 40+ years of engineering, manufacturing, and forensic experience.
Talk to Joe Pasma, PE