[ponch37300]

Are you 100% sure there isn't sheathing under the Styrofoam? It's pretty common to add Styrofoam over the top of the sheathing when upgrading the siding to get some more R value for cheap and easy. I would find a spot and take a wire coat hanger or similar metal "poker" and stick it threw the Styrofoam and if it hits something hard just after the Styrofoam you have sheathing behind it, unless you hit a stud. I believe there are insulation sheathing that is also structural but not Styrofoam, the stuff I have seen is blackish in color and is more of a fiber board.

 

[ponch37300]

There is absolutely nothing between the siding and the styrofoam. What I'm calling foam is yellow hard stuff. I'm certain there isn't anything there, I actually cut a hole in the garage wall (attached garage, shares outside wall with two bedrooms) and dug through the insulation and then the foam and I was moving around a joint piece on the lap siding.

It was built in the early 90's so Framer you may be right. I remember my dad telling me about that kind of construction now that you mention it...

Jagans - I did not check near an outside corner. I thought they would probably have felt papered it back then but again, I saw not evidence of it although I would sure think they would have under the J-channel they used for the siding (this j-channel with lap siding was apparently an approved method of install with Canexel siding).

Ponch - I'm 100% sure. I did almost exactly what you said only I cut a hole so I could visually see what was under there. I dug out some foam with a screw driver and then it was the lap siding...

So you have old lap siding and then the foam/insulation and then the newer siding, correct? If so this is "normal" when updating siding. They go over the lap siding with foam to add R value and also give a "flat" surface for the new siding. then use long nails to attach the new siding.