I strongly advocate removing all the old siding, installing a wind/moisture membrane like Tyvek over the wall sheathing, and then applying the new siding. Current building technology experts advocate and promote this critically important practice of removing old siding.
Consider this … As moisture moves from inside the wall cavity and from the interior of the house, the moisture condenses back into water form on the “first cold surface,” which is usually the exterior sheathing or sometimes the exterior siding. If the old siding remains on the house exterior with new siding applied over the old, then the moisture will become trapped as condensed water INSIDE the wall cavity. This wet wall cavity leads to rot, mold, mildew and can cause some very serious health and structural consequences. Not all moisture remains trapped inside walls because some wall systems allow drying to the interior of the house and wall system. But are YOU willing to take this risk and gamble that the structural integrity of your home around a decision to remove the old siding? It is so simple to just remove the old siding and do it right that there is no real risk.
Compounding this matter is that the current Metro St. Louis industry practice is to apply new siding right over the old existing siding of homes. Seldom do re-siding installers offer, advocate or remove the old siding for cost reasons. I have debated this issue with local siding installers who defend their practice of residing over existing siding by citing how few houses actually sustain this moisture damage. But how do we really know what is happening or not inside a wall cavity without opening up the wall?
Rot, mold and structural problems routinely devastate homes, equity, and families when the moisture problem occurs. This problem is more prevalent in the colder climates typically north of St. Louis. I follow the best, brightest and most experienced building technologists in the country …. who tend to make a good living testifying against unknowing contractors and their insurance companies.
One exception to this removal of siding is when the existing siding – typically plywood or OSB sheet material – is applied directly to the wall stud framing as wall sheathing. This wall framing system which was more common in the 1970’s will have only siding and no wall sheathing on the studs. This siding, which provides the structural rack bracing, must stay on the wall system as part of the structure. This is commonly found on garages, roof gables in attics and other areas where insulation and interior heating is absent.
Generally speaking, removing the old siding prior to re-siding your house is good practice, good business and a wise consumer service, even though this removal practice is unpopular with both the siding contractors and customers paying the additional costs.
Please remove the old siding before applying new siding or phone my company to have siding done correctly.