Okay with foam plastic under exterior roof? Insurance company/fire risk

[Finndjävel]

Why would a welding spatter land against cellplast inside a wall or ceiling?

 

[bossespecial]

If a house is fully engulfed in flames within 5-10 minutes, then the fire regulations probably haven't been followed properly, as houses should remain standing for at least 15 minutes

 

[Kallebo]

Isn't there any roofing felt over the rigid foam under the battens and tiles? That would prevent fire spreading somewhat.

I like KnW's solution and would definitely go for something similar if I were to build a house from scratch again.

 

[bossespecial]

The example with the welding splatter is taken from real life to show how explosively fire spreads with foam plastic. Often when building a house, parts are exposed before the house is finished, during different construction stages. For example, the foam plastic comes before the roofing felt in the mentioned example above, and thus the foam plastic is unprotected for a while.

 

[Finndjävel]

If a house is fully engulfed in 5-10 minutes, the fire regulations probably were not followed; a house should stay intact for at least 15 minutes

Interesting. Starting from the moment the curtains caught fire from a candle, it took seven minutes before the house was beyond saving. This was in a staged fire by the fire department. Having foam plastic inside a roof structure doesn't make a difference because once the fire reaches there, it's no longer possible to save it.

 

[bossespecial]

I would absolutely not use the aforementioned roofing solution.

 

[bossespecial]

Why build with materials that are known to be suboptimal? Just because the house can catch fire, should one use materials that are known to further fuel the fire?

 

[justusandersson]

The polystyrene on the roof is primarily a problem for fire spread between buildings. A large fire nearby can spread sparks over long distances. A single spark that finds its way under the concrete tiles is enough to ignite. Fire spread indoors is another problem. The Swedish fire regulations are designed so that the requirements are higher when many people are involved, the people have a poor understanding of the layout, their mobility is limited, the number of floors is greater, etc.

 

[KnockOnWood]

Is there no roofing felt over the cellular plastic under the battens and tiles? That would prevent the spread of fire somewhat.

No, no roofing felt over. However, there is a vapor-permeable roofing membrane underneath.
Besides, conventional asphalt-impregnated roofing felt probably burns quite well too

I like KnW's solution and would definitely go for something similar if I were to build a house from scratch again

Thanks, yes it's very nice to have a warm and dry storage attic, even though we actually only have a one-story house.

The cellular plastic on the roof is primarily a problem for the spread of fire between buildings

We are over 100 meters away from the nearest residential house, so we're not too worried about that