The problem with installing siding, particularly vinyl siding, over wood shingles or other wood siding is that it does not breathe, while the wood underneath does. That causes the wood underneath to absorb moisture and ultimately decay.
Installing vinyl siding over wood shingles or siding results in problems including hidden rot and deterioration beneath the vinyl siding, having less protection against weather elements, and inconsistent thickness to the walls. These concerns need to be addressed and dealt with before you consider installing vinyl over wood, or else you might need to consider not doing it.
By installing siding over wood, it covers up the development and discovery of rot, mold and holes in the siding that you aren’t going to be aware of because of the vinyl siding until bugs or rodents start making their way into the home, or until you catch that unmistakable scent of mold. Also, installing another layer of siding means often not laying foam, making it harder to protect against the weather elements and affecting the interior temperature controls and climate defenses. Then, there’s the thickness of the walls. Because the vinyl siding was probably laid over unlevel wood shingles, there’s a good chance the walls are not going to be uniform through the side of the house, which could cause additional problems down the road.
In most cases, you would be better off to strip the wood shingle siding and repair any damage, or add additional bracing, before putting up the new siding. Consider speaking to a professional about this process before you put up vinyl siding over wood shingles to avoid future hassles and repairs down the road.