Walls - DPCs & Cavity Walls

Walls - DPCs & Cavity Walls

1. Act as a barrier to the passage of moisture or water between the parts separated by the DPCs

2. Requirements

   • should be continuos for the whole length and thickness of the wall
   • at least 150mm above finished ground level

3. Types

   • Flexible
   • Semi-rigid
   • Rigid

4. Modern DPCs

   • separate DPC for each leaf
   • most made from polythene
   • co-polymer thermophastic is now used
   • all laps and joints sealed by >100mm using double sided jointing tape

5. Bitumen Felt DPCs

   • traditional material is used for DPCs
   • extrude under pressue when loaded
   • can become brittle when exposed to UV light
   • minimum moisture capillarily in walls

6. Polyethylene DPCs

   • inexpensive DPC material that does not extrude under load or suffer from UV embrittlement

7. Cavity Walls

   • first proposed in early 19thC. developed through 20th
   • Resistance to weather & ground mositure
   • Thermal insulations
   • Strength & Stability
   • Regulations
     • min width of 50mm
     • kept clear of mortar snots
     • can be full or partially insulated
     • for full insulation, a clear cavity of 50mm should be provided
   • Internal walls
     • fully filled
     • provide a better u - value
     • Insultion fitted snug into the cavity the internal wall is kept dry/warm; less susceptible to degradation and moisture
   • External walls
     • requires careful attention to spec & finishing
     • fully filled- any ingress of moisture will dampen wall and insulation
   • Cavity wall ties
     • Functions
       • provide a connection
       • transfer lateral load
       • permit in-plane movement to accomodate differential movements
       • connect 2 leafs together to provide better restraint against transverse and lateral loads
       • provide strength and stability
       • Act in TENSION as TIES
       • Act in COMPRESSION as STRUTS
     • Spacing
       • 450 x 900mm
     • Positioning
       • bedded 50mm into mortar joints in each leaf
       • slight fall to outer leaf