[odie91]

1977 house, 2 story colonial. I opened up some drywall on an external wall and pulled back the insulation. I noticed the board nailed into the studs from outside was not plywood or OSB; in fact it was a flimsy fiber board like the backing of the cheap furniture you buy at Ikea. I'm pretty sure there was not an additional layer of sheathing... just the aluminum siding next. Isn't the plywood/OSB what gives the house a lot of its structural strength from swaying and tipping over? If relevant, basement is a full basement, and attic is trusses.

 

[SeniorSitizen]

In that construction plywood is normally at the corners.

 

[ron45]

Ah.... If it ain't broke don't fix it...

 

[joecaption]

Likely it was Celotex.
http://www.blueridgefiberboard.com/premium-insulating-sheathing-energy-saving-r-values/

 

[joecaption]

They did some funky stuff back then to try and cut cost.
1/2" sub flooring with particle board over that, Quest tubing, stapled vinyl siding and shingles come to mind.

 

[roobinsteen]

My house has the same stuff on the 2nd floor-celotex fiber sheathing. The 2nd floor was an addition put on in the early 90s, they used plywood at the corners. It's not "the best", but there's plenty of homes that are sheathed with it.

 

[danpik]

My 1959 built ranch has the same material. Walls are still straight and plumb. Plywood at the corners and at two locations down the length of a 44' long wall.