Some renovation projects install new siding over old. Here's when this is acceptable and what risks to consider.
Siding Installation and Repair
Installing new siding over existing siding — rather than stripping to the sheathing — saves demolition labour and disposal cost. Under the right conditions, it's an acceptable approach; under others, it creates problems.
The existing siding must be in adequate condition. Rotted siding, siding with active moisture problems, or siding with significant gaps or voids shouldn't be covered. These conditions worsen beneath the new installation.
Material Selection Guide
Structural implications must be considered. Existing windows, doors, electrical boxes, and trim details all need adjustment when adding a new siding layer. Window and door trim depths change, and the new exterior plane affects how these elements are weathered.
Weight loading increases. Two siding layers are heavier than one. This is generally not a structural concern for standard residential framing, but it's worth confirming there are no specific concerns for the structure in question.
What the Installation Process Looks Like
Moisture management is the critical consideration. Adding a layer over existing siding without creating a drainage plane can trap moisture between layers. Using a housewrap or drainage mat over the existing surface before new siding creates a drainage plane that reduces moisture risk.
Vinyl-over-vinyl is generally not recommended. The combined thermal movement of two vinyl layers can cause buckling and buckling-related failure in the outer layer.
The building permit application should accurately describe the installation method. Some municipalities require specific approvals for over-cladding work, particularly when it affects window and door rough opening dimensions.
Key Takeaways
- Installing new siding over existing siding — rather than stripping to the sheathing — saves demolition labour and dispos...
- Structural implications must be considered.
- Moisture management is the critical consideration.
- D&D Exterior Finishing serves Kitchener, Waterloo, Cambridge, Guelph and surrounding areas
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Sources & References
- Ontario Building Code — Relevant Standards & Guidelines
- D&D Exterior Finishing field experience across Waterloo Region
