What are these things on this roof?

[mojo]

I've noticed that many roofs in Japan have these things, or similar, on them. What are they?

 

I thought maybe something to do with snow, but I don't think there is much around Tokyo.

 

[lighthouse]

Looks like a simple snow protection... 🤔 Maybe it is mandatory in the Tokyo area from a certain roof pitch?

Edited December 21, 2022 by lighthouse

[railsquid]

Correct, to help prevent snow sliding off the roof.

 

It doesn't snow as often in Tokyo as it does say in Niigata, but does enough that I own a snow shovel:

 

 

as it doesn't snow enough for the authorities to have enough snow ploughs to able to clear snow away from the main roads, so when it does the whole place grinds to a halt and everyone goes out with their snow shovels.

Edited December 21, 2022 by railsquid

[brill27mcb]

I don't know about Japanese practice, but here similar projections have been used to hold snow on the roof back. Notice that they are located just above the bottom section of roof that overhangs the walls. Often there is less escaping building heat in this bottom area. In a partial melt under sunlight, some sitting snow can melt but then re-freeze in this lower area, forming an "ice dam" along the bottom edge. Then when the sun remelts some of the snow again, the still-frozen "ice dam" holds the water back and it can creep up underneath the shingles. This causes leakage and damage to the roof under the shingles. I have had this happen on my roof, which has large overhangs out from the walls.

 

Rich K.