What should be under this siding?

[fqp25]

This is a brick foundation with aluminum siding. I haven't seen this much of an overlap before.

What kind of protection is usually under the siding?

Any help is appreciated.

Frank

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[kurt]

I'm guessing you have 2 or 3 layers of other sidings under the aluminum. There's probably the original wood lap and at least one layer of that asphalt brick stuff.