Causes of deterioration of underfelt

[mikric]

Have a look at the attached pics of deterioration of a tar building paper underfelt, is this typical of the age process of the product ? I believe it could be up to 50 years old ? Concrete interlocking Lindum tiles over, I suspect due to poor ventilation, condensation etc.
Could any of you knowledgeable fellows shed anymore light on the possible causes of the problem. Thanks

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• mikric
• 30 Jan 2011
• 1

Untitled

• mikric
• 30 Jan 2011
• 1

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[^woody^]

I don't think condensation will cause this

Generally the frayed edges are due to the felt detaching from the rafter and being blown about over time, or due to birds or rodents

The location of that felt looks like it is the end of the layer up against a chimney or wall, so would be prone to being ripped from the end rafter (normal expansion/contraction or wind forces) and being allowed to dangle in the loft

If any slight bit of light is getting through, that will degrade the felt too

 

[mikric]

Cheers for the reply Woody.
It has deteriorated elsewhere within the roof too, I know UV could cause this but normally only a problem at the gutter line. Tile covering is sand faced Lindums, could they become porous enough after 50 years to influence this ?

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• mikric
• 30 Jan 2011
• 1

 

[noseall]

I have only seen a few roofs with tarred building paper and all were 50+ years old and all were frayed or perished.

 

[datarebal]

As above
Your looking at simple building paper not a proper roof underlay.
On occasion it was used (cheap), and in virtually every case it ends up shredded as is this .