Siding Installation Q: Is it acceptable to install vinyl siding over existing wood cladding?

If so, what is the proper installation method and what considerations need to be taken into account for best results?

A: The short answer to the first question is, yes, it is perfectly acceptable to install vinyl siding over existing wood cladding.

However, many factors need to be assessed to be sure that installation over the existing siding is the best course of action.

The primary factor to investigate is the condition of the existing siding

Water damage or rot must be addressed so as not to potentially compound the problem by covering it over with vinyl siding.

While fungi and mold become dormant when their moisture source is removed, or when the wood falls below 20 percent moisture content, the spores are still viable and decay will begin again if the wood is exposed to further favorable moisture and temperature conditions.

Topical fungicides will only temporarily kill active fungi and the effect of topical wood preservatives tends to be short-lived as well.

If you are certain that exterior moisture (rain, snow, sleet) is the only culprit for decay, then cladding the house with a foam board product and/or furring strips and vinyl siding can be a practical option. (If added insulation is important, there are manufacturers that offer siding with insulation attached.

For more information go to the PATH Technology Inventory page on "Insulative Vinyl Siding."

If the source of moisture for wood damage cannot be identified, isolated, and corrected, the safest route to follow with regard to occupant health and builder liability is to remove the existing siding and replace with the exterior cladding material of your choice.

This is a costly alternative considering the expense of removing and disposing of existing siding and potentially removing and reinstalling insulation. However, depending upon the extent of moisture damage, which in some cases can extend to loose-fill insulation, framing, and/or wood-based sheathing, this may be the most sensible action.

The Vinyl Siding Institute has created a comprehensive resource on siding installation entitled, Vinyl Siding Installation:

A How-To Guide. Published in February 1999, this manual contains the most recent techniques and practices and offers readers a step-by-step approach to installation. The Guide is available online at

You can also call the ToolBase Hotline for more information at (800) 898-2842. ToolBase is the home building industry's technical information resource.

It is a service of the NAHB Research Center, funded by private industry and HUD through the Partnership for Advancing Technology in Housing (PATH) program.


................exactly copied from the NAHB website from a few years ago.


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