When first exploring a siding installation project many homeowners assume the best way to install vinyl siding is right on top of their existing wood shingles or clapboard.

So let’s answer the questions: “Is it a good idea to install vinyl siding over existing wood shingles or clapboards?”

There have been a few select cases in which we as a company were willing to do this, but it’s rare–probably less than 1% of our siding installations.  So our answer is typically “NO, it’s rarely a good idea to install vinyl siding over wood.” Why?

  1. Hidden Rot, Mold, and Deterioration
  2. Lack of Weather Protection
  3. Adds Thickness to Walls

1. Hidden Rot, Mold, and DeteriorationRotted-wall-under-vinyl-sid

1. Most likely there is more rot, damage, or mold under your existing siding than you ever expected.  Installing another layer of siding would not solve the problem and in fact make it worse. We’ve completed thousands of siding projects over the years and in most cases we find some amount of rot, mold, or deterioration that was undetectable from the surface. It’s not usually widespread (Although is some cases it is), but it’s enough that homeowners are usually shocked at what is found. The second reaction from homeowners is that they’re glad they didn’t just go over the old siding with another layer.

2. Lack of Weather Protection

2. When installing a layer of siding over another layer, you forgo the option to wrap the wall with a moisture protection barrier, also known as a vapor barrier. The most common product is Tyvek®, but there are other products like Typar®, and Everwrap®. Although thin, these products perform a significant duty in protecting your home.  A moisture barrier provides protection from outside moisture, but is breathable in order to let built-up moisture escape from your home.  In conjunction with wall insulation, moisture barriers also reduce draftiness.

3. Adds Undesirable Thickness to Walls

bad-windows-with-vinyl-sidiThe most common practice when installing vinyl siding over existing wood shingles or clapboard is to first put up rigid foam or fan fold.  These products are designed primarily to pad imperfections on the walls so the new layer of siding will lay flatter.  However,this means adding 1/2″ padding, and another 3/4″ or 1″ of siding to your existing wall.  It total you’ve added about 2″ of thickness to the walls which means your windows and doors will be set in more than usual.  Most people consider this a rather unattractive look.

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