Insulating Old Walls Without Sheathing

Introduction

• Problem: Old walls often lack sheathing; siding is fastened directly to studs.
  • Occasionally separated by tar paper.
• Challenges: Insulating without removing siding due to historical purposes.
  • High water and air leakage.
  • Insulation reduces drying potential of walls, keeping them wet longer.

Importance of Controlling Water and Air Leakage

• Don’t insulate until water and air leakage is controlled.
• Insulating without control increases the risk of wall damage due to prolonged moisture.

Strategy for Insulating Without Removing Siding

• Drainage Plane and Air Gap: Ensure behind the siding.
  • Labor-intensive and requires high workmanship.
• Installation Steps:
  1. Dimple Mat: Behind existing siding or tar paper.
     • Acts as drainage plane, waterproofing layer, and air gap (rain screen function).
     • Prevents water from rotting the wall cavity if insulated.
  2. Air Barrier Membrane: Over the dimple mat.
     • Stapled to studs and sealed with high-quality tape to prevent exterior air leakage.
  3. Insulating with Mineral Wool:
     • Allows moisture to dry out of the wall cavity.
     • Vapor permeable and moisture resistant without encapsulating studs.
  4. Smart Vapor Retarder Membrane:
     • Interior air barrier and vapor control layer.
     • Prevents interior vapor from condensing in the wall cavity.
  5. 2x3 Strapping: Installed to provide airtight service cavity for the vapor retarder.
  6. Fiberglass Matte Face Gypsum:
     • Provides resistance to moisture and mold growth.

Protecting Sill Plates

• Issue: Water must drain away from sill plates.
• Solution:
  • Remove bottom course of siding to access sill plate.
  • New stainless steel Z flashing with end dams and flashing membrane underneath.
  • Flashing extends past the floor assembly to the foundation with a drip edge.
  • Entangled mesh provides drainage gap; water can dry and drain out.
  • Optionally, use drainable WRB (Weather-Resistive Barrier) like HydroGap SA.

Additional Tips

• Smart vapor retarder should be air sealed and integrated into floor sheathing.
• Summary:
  • Dimple mat: Drainage plane and water control layer.
  • Air barrier membrane: Prevents air leakage.
  • Smart vapor retarder: Control interior vapor.
  • Ensure proper flashing and drainage to protect framing.

Further Reading

• Book: "A Guide to Moisture Management for Residential Remodels".
  • Solutions for various building conditions (old walls, basements, crawl spaces, roofs, etc.).
  • Ebook link available in the description.