Cavity walls

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Cavity walls

  1. 1. WallsEnclosure and structure
  2. 2. Nearly all buildings have walls
  3. 3. What to walls do?• Provide enclosure – Separation of interior from exterior – Control of access – Control of daylight and ventilation – Temperature control• Structure – Walls may support floors and roofs as well as themselves – Walls can brace other walls
  4. 4. Types of walls• Almost endless variations: timber, glass, fabric, stone, mud…• In domestic English construction two types dominate – Masonry • Brick, stone or concrete blocks, bedded and cemented with a mortar in a cellular structure – Timber framed • Softwood framework braced by sheet coverings such as plywood or wafer board and protected form the weather by an external barrier
  5. 5. Masonry walls• Not just stone• Principles of all masonry construction is the same, small units build up large walls which brace each other at the corners• Vertical joints staggered for strength.
  6. 6. Bricks and blocks• The difference is in the size – A brick is small enough to hold in one hand whilst the mortar is laid with the other – A block is so big that two hands are needed to place it, after the mortar is laid – Laying blocks is slower individually, but a block is 6 times bigger than a brick, so the wall goes up faster
  7. 7. Bricks and blocks• Bricks are usually clay and used for facing work• Blocks are usually concrete and used for hidden work• The mortar is a mixture of sand, cement and lime, to make it soft and sticky
  8. 8. It’s all to do with size65 x 102.5 x 215mmMortar joint 10mm 2 brick widths plus one joint = 215 3 brick heights plus 2 joints = 215
  9. 9. Blocks are bigger, but exact size is important 215 x 102.5 x 440mm Mortar joint 10mm
  10. 10. Blocks are bigger, but exact size is important 215 x 102.5 x 440mm Mortar joint 10mm 1 block equivalent in size to 6 bricks laid in mortar. Fast building
  11. 11. Bonding of brickwork• Vertical joints are staggered for strength• Straight horizontal joints are not a problem, friction keeps them lockedStretcher bond Header bond English bond Flemish bond
  12. 12. Wall thickness can tell you a lot about construction“9 inch” wall. Actually215mm. Indicates solid, onebrick length construction.Unusual in modern externalwalls “4 inch” wall. Actually 102.5mm. Indicates solid, one brick width construction. Used in internal walls
  13. 13. The cavity wall Brick outer leaf Block inner leafOutside Inside 50mm cavity
  14. 14. Cavity wall: the basic function is to keep rain out We build cavity walls to keep the rain out, not to keep the house warm
  15. 15. Cavity wall: the basic function is to keep rain out We build cavity walls to keep the rain out, not to keep the house warm
  16. 16. Cavity wall: the basic function is to keep rain out Some rain gets through the outer leaf, but it trickles down inside the cavity, on the wet, outer side We build cavity walls to keep the rain out, not to keep the house warm
  17. 17. Cavity walls: structural tiesA 250 cavity wall isnot as strong as a215 solid wall. Weput cavity ties intoalternate courses tostrengthen it. Drip to stop rain Stainless steel cavity ties crossing
  18. 18. Keeping rising damp out Floor FillGround
  19. 19. Keeping rising damp outDamp proof courseDPCSheet plastic, lead,modifiedbituminous felt Floor Min 150mm Fill Ground
  20. 20. Keeping rising damp outDamp proof courseDPCSheet plastic, lead,modifiedbituminous felt Floor Min 150mm Fill Ground Damp proof membrane The structure below DPC/DPM DPM is always wet Sheet plastic, asphalt
  21. 21. Cavity walls in reality DPC DPCVentilation ducts
  22. 22. Wall stability: masonry wall fall over easily
  23. 23. Wall stability: masonry wall fall over easily
  24. 24. Wall stability: masonry wall fall over easilyThe DPC is a particular weak line
  25. 25. Cross wall constructionPrinciple of thebuttress on gothicchurches
  26. 26. Cross wall constructionPrinciple of thebuttress on gothicchurches
  27. 27. Cross wall constructionPrinciple of thebuttress on gothicchurches
  28. 28. Cellular construction: the structural basis of masonry constructionA cellular structure resists forces from all directions
  29. 29. Insulating a cavity wallThick, insulatingblock inner leaf
  30. 30. Insulating a cavity wallThick, insulating Fill the cavity withblock inner leaf insulation, risky
  31. 31. Insulating a cavity wallThick, insulating Fill the cavity withblock inner leaf insulation, risky
  32. 32. Insulating a cavity wallThick, insulating Fill the cavity with Internal insulatingblock inner leaf insulation, risky lining
  33. 33. Masonry walls take all shapes and sizes

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