# Why are Lichens Growing on My Roof? **URL:** \ **Category:** Factual Questions\ **Created:** [May 18, 2009, 2:54pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857 "2009-05-18T14:54:54Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [May 18, 2009, 2:54pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/1 "2009-05-18T14:54:54Z")
I don’t get it-lichens normally grow on rocks. Are asphalt roof shingles sufficiently nutritious? I once read that lichens are very susceptible to air pollution-but here they are, living off oil-derived asphalt. Maybe they are tougher than we think? Anyway, are they bad for the roof? ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [May 18, 2009, 3:15pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/2 "2009-05-18T15:15:07Z")
The asphalt holds the mineral surface (little rocks) in place. Without that UV would eat up the shingles even faster than it already does. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [May 18, 2009, 5:54pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/3 "2009-05-18T17:54:11Z")
[Lichens](http://en.wikipedia.org/wiki/Lichen) are a composite organism consisting of a fungus and (typically) algae living in a symbiotic relationship. They don’t feed off of the surface they grow on – the algae provides photosynthetic food and the fungus provides structure. ---
**Author:** ![smiling\_bandit](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@smiling\_bandit](https://boards.straightdope.com/u/smiling_bandit)\ **Post date:** [May 18, 2009, 8:56pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/4 "2009-05-18T20:56:06Z")
Yup. Luchen need very little other than a bit of water in the air and enough sunshine. The answer to your question is that Lichen can grow almost anywhere, on almost anything. ---
**Author:** ![Speaker\_for\_the\_Dead](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@Speaker\_for\_the\_Dead](https://boards.straightdope.com/u/Speaker_for_the_Dead)\ **Post date:** [May 18, 2009, 9:11pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/5 "2009-05-18T21:11:38Z")
Hmm, I’m lichen the sound of this. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [May 18, 2009, 10:03pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/6 "2009-05-18T22:03:04Z")
> [@Speaker\_for\_the\_Dead](#): > > Hmm, I’m lichen the sound of this. “Lichen keeps growin’ on my roof But that doesn’t mean that my shingles are uncouth” ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [May 18, 2009, 10:33pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/7 "2009-05-18T22:33:41Z")
They lichen themselves to reindeer. ---
**Author:** ![Satellite\_Guy](https://avatars.discourse-cdn.com/v4/letter/s/258eb7/32.png) [@Satellite\_Guy](https://boards.straightdope.com/u/Satellite_Guy)\ **Post date:** [May 18, 2009, 10:57pm UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/8 "2009-05-18T22:57:52Z")
I"m sure there’s a [lycan](http://www.123exp-beliefs.com/t/0080945577/) joke in there somewhere, but damned if I can find it… S^G ---
**Author:** ![fisha](https://avatars.discourse-cdn.com/v4/letter/f/da6949/32.png) [@fisha](https://boards.straightdope.com/u/fisha)\ **Post date:** [May 19, 2009, 1:11am UTC](https://boards.straightdope.com/t/why-are-lichens-growing-on-my-roof/496857/9 "2009-05-19T01:11:27Z")
Lichen is eventually bad for the roof. Not a huge concern, but the roots will deteriorate the shingles and loosen the granules.