TRIVIA: the logic of icicles

[John L]

What's the logic behind this? --

I'm in a semi-detached. I have about a foot of insulation in our loft by now. I'm willing to bet that my neighbour has 3" or 4" at best.

On the front of the houses (SOUTH facing) I have loads of icicles: neighbour has none. On the back of the houses (north facing) (yes I know you could have worked that out but I wanted to emphasise that the houses are *directly* on an east-west axis), he has LOADS of icicles, and I have virtually none.

I can't work out what's going on, icicle-forming-wise. The roofs, by the way, are respectively heavily covered (mine) and more lightly covered (his).

Cheers John

[TMC]

This may seem obvious but

You have no icicles at the back because there has been no thawing on that face

You have icicles at the front because you have some thawing on that face

Neighbour has icicles at the back as some thawing on that face (heat loss from inside)

Neighbour has no icicles at the front as lots of thawing due to heat loss and external warming) so no re-freezing on that face

Tony

[Jules]

Agreed. Not necessarily heat loss, either; I've seen recommendations to reduce the amount of insulation at the edges in the roof-space, because too much can keep that portion of the roof above too warm and promote thawing (and then freezing). A lot of ice weight can do quite a bit of damage...

[...]

Your gutter leaks at the front and your neighbours leaks at the back. Simples