Q. Is it a good idea to install vinyl siding over OSB sheathing without putting up any housewrap or felt? I see this more and more often, and wonder whether the OSB should be protected since vinyl is fairly leaky. Apparently there is nothing in the codes against this practice.

A.Corresponding editor Paul Fisette responds: I agree with you that this is a bad practice. OSB is not manufactured to withstand repeated wettings, and over time it will deteriorate, as rainwater is driven behind the vinyl siding. Once OSB swells, it will not return to its original thickness, and this permanent deformation can telegraph through to affect the surface appearance.

As you note, most building codes unfortunately (and incorrectly I think) don’t require protection over OSB and plywood. Omitting the paper not only leaves the OSB or plywood unprotected, it also gives you no way to protect the top edge of window and door flashings with an overlapping layer. Water running down the sheathing can run behind the window flanges and into the framing cavity.