How long before this type of metal roof will melt in a house fire?

[Awwtumn]

Given a gauge 25 (0.02" or 0.5mm) metal roof roll formed made from hot-dip galvanized cold rolled mild steel. How long can these thin metal roof melt in a typical house or office fire with typical fire load?

I read conflicting information. Some roof contractor said these thin gauge 25 metal sheet were so fireproof that during a fire, the firemen have to use saw to cut them to vent them. While other engineers say it has zero fire rating and can't last 2 minutes.

But if the metal sheet melting point is 1370°C (2500°F) and the fire tip is only 2500 degree Fahrenheit. Maybe it's that context where the fireman has to open it with saw to vent the fire?

In a typical fire with house or office items fire load. What temperature does it reach at the metal roof line?

If you can also show pictures of burned or melted metal roof, the better as I can't find a single one of them hence ignorance of it is rampant anywhere.

 

[berkeman]

Welcome to PF.

We cannot support accident investigations for car accidents, and similarly, we cannot support your efforts to augment the Fire Department's investigation into a house fire.

What incident is this from? Why don't you trust your local Fire Department investigators to supply the correct final report? Or is this a general question for your interest in trying to understand how best to fireproof structures?

 

[Awwtumn]

What accident? What report? The roofing hasn't even been built. It's just a general question what kind of temperature before such a thin metal roof can melt. And there are thousands of houses like this everywhere. I understand Class A means the exterior is protected from say burnt ambers from forest fires like in Florida. But how about internal fires from within the building. How long fore the metal roof melts or burns away? Is it 3 minutes? or 3 hours?

Please show me pictures to get an idea. Ty.

 

[russ_watters]

You can read the descriptions of the tests performed and results received, but if you want to speculate about conditions other than what is tested for, it's pretty much going to be guesswork.

[Edit] Also, it seems you have conflicting information from different sources? Please cite the actual information/sources. There's not much we can do with vague second-hand anecdotes.

And I too would like to know exactly what the point of this line of questioning is. Architects/engineers have specific code and license requirements for specificifying construction, and there is generally not a ton of wiggle room.

 

[berkeman]

What accident? What report? The roofing hasn't even been built. It's just a general question what kind of temperature before such a thin metal roof can melt. And there are thousands of houses like this everywhere. I understand Class A means the exterior is protected from say burnt ambers from forest fires like in Florida. But how about internal fires from within the building. How long fore the metal roof melts or burns away? Is it 3 minutes? or 3 hours?

Please show me pictures to get an idea. Ty.

Okie dokie. I'm still not convinced. What is your motivation for asking this question? I'm finding it increasingly hard to believe that you are asking it out of general daydreaming interest...

Are you a firefighter or part of EMS? Have you recently experienced a fire on your property?

 

[Baluncore]

Given a gauge 25 (0.02" or 0.5mm) metal roof roll formed made from hot-dip galvanized cold rolled mild steel. How long can these thin metal roof melt in a typical house or office fire with typical fire load?

The material is too thin and flexible to be relied upon to slow the spread of a fire. The material may need to be cut away by firefighters to gain access. Those are not contradictions.

It does not need to melt. The galvanising will burn off quickly to white zinc oxide, which is blown away. Then the iron sheet will glow red-hot and distort. The hot iron surface will be burned if it contacts oxygen remaining in the air, so material will be lost and the sheet will become thinner. Once burned, it cannot be reused.

 

[Awwtumn]

I'm reading the following regarding

SR409 Fire spread from lower roofs project: Final report (2019)​

https://www.branz.co.nz/pubs/research-reports/sr409/

Nowhere does it mention how fast thin metal roof burns. There are thousands if not millions of houses all over the world that uses metal roof. Some be have adjacent buildings.

So why can't I find single pictures of burnt metal roof? A roof contractor told me it takes 2 hours for the thin metal roof to burn that's why no pictures of it. But I'm not convinced because other engineers said it takes only a minute for the metal roof to burn.

So does it take a minute? 30 mins? 60 mins? What usually is the temperature at the roof level of a typical house? My house roof is also thin metal roof.

 

[berkeman]

Who cares? Corregated metal sheets like that are not used as fire insulation layers between floors of a multi-story building. And I'm not going to climb onto a flimsy corregated metal roof like that to ventilate it for any reason that I can see.

What is the point of your post? You are hiding your cards, IMO...

 

[DaveC426913]

So why can't I find single pictures of burnt metal roof?

Perhaps because there are only two long-lived states of metal rooves in fires:
1. Did not get burned, therefore any pictures are of intact metal rooves.
2. Did get burned, roof collapsed, any pictures are of houses without rooves.
Transitional state is too short-lived to be captured by insufficiently frequent photo sampling.

 

[Baluncore]

To see various stages of roof destruction, Google images; 'burnt metal roof'
Walk around after a bushfire has destroyed houses and look at the evidence.
The first thing that goes to scrap when clearing the site is the remains of the metal roof.

 

[russ_watters]

But I'm not convinced because other engineers said it takes only a minute for the metal roof to burn.

Where, exactly, did you hear that? Please cite the actual source.

So why can't I find single pictures of burnt metal roof?

What is the value of pictures here? Unless they are photos from tests under specific conditions they aren't going to tell you much that is useful.

 

[Awwtumn]

Who cares? Corregated metal sheets like that are not used as fire insulation layers between floors of a multi-story building. And I'm not going to climb onto a flimsy corregated metal roof like that to ventilate it for any reason that I can see.

What is the point of your post? You are hiding your cards, IMO...

Ok. Here is my situation. My house is adjacent to a tall building with their columns part of their firewall. I also have a firewall. The city official just told me to put 39 inches parapet in the roofline.

But is it enough? If there was a fire below and it would breach the thin metal roof, then it can reach the adjacent building wall, is that right?

If it takes only minutes for the 0.02" thin metal roof to burn through. Then I will remove the roof and make it open it would become just aircon bay so no possibility of that occurring. Because if the fire occurred and there were damages. I may lose the entire house/building to them. This is the reason I need to know exactly how long thin metal roof can burn. The roof contractor who made it said it takes 2 hours, and thin metal roof are fireproof. But I don't believe him as he only wanted to sell roof. The architect and structural engineer said they didn't know too the behavior of thin metal roof in fire.

Don't worry. No one would sue you guys. It's just asking general question.

 

[Baluncore]

The time it takes for the roof to fail during a fire will also be dependent on the quantity of fuel below, and the rate of the airflow. Those are highly variable parameters.

 

[DaveC426913]

This is the reason I need to know exactly how long thin metal roof can burn.

No. What you really want to know is how long a thin metal roof can withstand fire before any part of it burns through.

It might take 2 hours for the whole roof to burn, and it might also take 2 minutes for a six-inch burn-through that allows the fire to spread. A chain is only as strong as its weakest link.

But I don't believe him as he only wanted to sell roof. The architect and structural engineer said they didn't know too the behavior of thin metal roof in fire.

Which is why it behooves you to assume the worst case.

To-wit: you can't assume the roof will retard a fire for any useful duration.

 

[Awwtumn]

If it takes an hour for the metal roof to burn through, there is enough time for the firetrucks to get to the building and street. But if it takes only 10 minutes for the metal roof to burn through, then better to remove the entire roof and make it as open deck. It's all concrete floor and wall below it. The thin metal roof is roof of the 3rd storey.

Let's assume the residential below the metal roof is full of stuff like bed, sofa, clothes, books, etc. that is part of a house. Based on the the following, what is heat flux of a typical residential with full things in the floor? What heat flux can burn a 0.02" thin metal roof in 10 minutes? If the heat flux matches that of typical residential. Then I have to make the decision to remove at least 13 feet of the metal roof from the boundary and make it open and use as aircon bay. I need to make the decision based on the computations because the architect, engineer don't know how compute for it (so they just ignore stuff like this and just believe the roof contractor that metal roof is fireproof).

from https://www.branz.co.nz/pubs/research-reports/sr409/

 

[DaveC426913]

I need to make the decision based on the computations because the architect, engineer don't know how compute for it

So, yes, you do want us to help you make a decision whose the result is that your house may or may not burn down.

Don't worry. No one would sue you guys.

Not to belabour the point but postings on the internet remain in perpetuity, and an uncountable number of future readers will be drawn to - and possibly rely on - information in this thread.

That may not be of conern to you, but it's certainly a concern to PF.

 

[Awwtumn]

The concern is not whether my house would burn or not. It is a concrete house so in the event of fire. There is bound to be fire damage to the things inside and even the stucture The concern is whether any possible fire in my house could breach the metal roof and affect the adjacent building. Because it takes only 30 minutes for a concrete column to soften by fire and become unusable. So I don't want the adjacent building columns got damaged, and sue me.

To make things simple. Don't deal with my building then so it won't be a concern to PF. My simple question now is just. What kind of flame or heat flux (right term?) can make a hole in a 0.02" thin metal roof? Just to estimate. This is also for correct information, because in the entire internet, they always write a metal roof is fire proof so people don't think much how it can be affected by internal fire, not external.

 

[anorlunda]

The city official just told me to put 39 inches parapet in the roofline.

I think this is your real purpose. You are looking for an excuse to not comply with that order. The end result will likely be litigation between you and the city. PF does not advise in such situations.

 

[berkeman]

Thread closed for Moderation...

 

[berkeman]

You have not been honest with us from the start of your thread:

The roofing hasn't even been built. It's just a general question what kind of temperature before such a thin metal roof can melt.

What is your motivation for asking this question? I'm finding it increasingly hard to believe that you are asking it out of general daydreaming interest...

And finally you start to come clean:

Ok. Here is my situation. My house is adjacent to a tall building with their columns part of their firewall. I also have a firewall. The city official just told me to put 39 inches parapet in the roofline.

As has been said already multiple times in this thread, we cannot help you with legal or building code issues. This thread will remain closed.