Adding new siding can trap moisture

Insulation · The Basics · printed page 235 (PDF page 236)

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Book index entries

Moisture – Trapped behind Siding Siding – can Trap Moisture Insulation – the Basics

Text in the illustration

moisture
adding new siding (especially a face-sealed system such as stucco) over existing siding reduces the wall's ability to breathe and can lead to moisture being trapped in the wall (rot, mold, mildew, discoloration etc.)
old siding (asphalt shingles)
Stucco added later
trapped in wall
floor framing
foundation
insulation and air/vapor barrier not shown

Generated explanation

The illustration shows a cutaway exterior wall with existing asphalt-shingle siding partially covered by stucco added later. Wood wall framing and floor framing are shown above a foundation. Black arrows contrast moisture passing outward through the original siding with moisture becoming trapped behind the added stucco. The annotation warns that adding a face-sealed siding system over existing siding reduces the wall's ability to dry and can lead to rot, mold, mildew, and discoloration. Insulation and the air/vapor barrier are explicitly noted as not shown.