1. Walls
Ron Gatepain
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2. Basic Functions and Requirements
Enclose space
Provide support
Strength and stability
Resistance to the elements
Thermal insulation
Sound insulation
Fire resistance
Aesthetically pleasing
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3. Factors affecting the choice of materials
Structural type of building ‑ is the wall to be load bearing or non load bearing.
The requirements of the wall ‑ the wall of a recording studio will need special emphasis on sound insulation; a building in an exposed position will need emphasis on weather exclusion and durability.
Availability ‑ a shortage or long delivery date for certain materials may exclude their use if the building is required quickly.
Speed of erection ‑ wet trades normally take longer to construct a building than dry construction.
Cost ‑ this must not only consider the cost of the materials but also the cost of labour to construct the building.
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4. Types of Walls
Masonry ‑ this can be brick, block or stone. They can be:
Solid
Cavity
Frame
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5. Masonry Walls
Bricks, blocks etc. are laid one on top of the other with a binding material between each unit the purpose of which is to:
bind the units together.
evenly distribute pressure from unit to unit.
fill in the joints between units to prevent wind and rain penetration, and prevent loss of thermal and sound insulation.
allow a degree of adjustment between units.
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6. Solid Walls
Here the wall is solid from the outside to the inside, moisture is prevented from getting to the inside by one of two ways:
1) The sponge principle. Moisture is absorbed by the wall, which is of sufficient thickness to be able to prevent the moisture passing all the way through before evaporation from the external surface draws out the moisture from the material of the wall.
2) The impervious‑skin principle. The wall has an external finish which does not allow moisture to pass through it to the remainder of the wall.
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7. Cavity Walls
These consist of two leaves or walls with a narrow cavity ( usually 50mm ) between them. Each leaf is half a brick thick, and they are tied together to prevent over turning by the use of metal or plastic wall ties.
Wall ties provide a drip in the centre to prevent moisture being able to travel across the tie to the inner leaf. Problems can occur if this tie is bridged with mortar droppings. Ties should be placed at distances apart not exceeding 900mm horizontally and 450mm vertically. In addition they should be placed as near as possible to any opening at 300mm vertically.
Cavity walls will provide adequate resistance to moisture penetration and increases the thermal insulation properties of the wall.
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8. Wall ties These should be:
the type which permit differential movement between timber frame and cladding.
fixed to studs, not sheathing.
spaced at a minimum of 600mm horizontally, 450mm vertically.
spaced at jambs of openings of 300mm vertically within 300mm of the masonry reveal.
sloped away from the sheathing so that the slope is maintained following differential movement.
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9. Damp‑proof Courses
The purpose of a damp‑proof course ( DPC ) is to prevent moisture passing from the outside to the inside of a building, or into the fabric of the building.
Damp‑proof courses can be horizontal or vertical and are divided into three types:
1) Those below ground level to prevent moisture entering the structure from the soil.
2) Those placed just above ground level ( 150mm ) to prevent moisture creeping up the wall by capillary action ( Rising damp )
3) Those placed at openings or parapets to prevent rain‑water entering or soaking through.
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10. Timber Frame Construction
This consists of vertical timber members called studs and horizontal members called head and sole plates, these are connected by simple butt and nailed joints.
The frame is stiffened by plywood boards with a covering of building paper as protection.
Mineral wool or glass fibre insulation is fixed within the cavity formed by the studs, and a vapour barrier of polythene sheet is fixed on the warm side of the insulation and covered with plasterboard, alternatively, vapour check plasterboard can be used.
It is also important that the moisture content in the frame is below 20% before the vapour barrier is fixed, and that the timber is protected and kept dry during construction. All timber, not forgetting cut surfaces must be treated with preservative.
Once the frame is fabricated it can be clad and the outer leaf of brickwork constructed.
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11. Requirements
Cavity barriers - These are required in the following positions to prevent the passage of fire:
At the junction between compartment walls or floors and external walls.
At the junction between a compartment wall that separates buildings and an external wall.
At the top of an external wall cavity.
Fire stops should be provided at:
Junctions of compartment walls and compartment floors.
Junctions of separating walls with the roof.
The eaves and in boxed eaves at walls between buildings.
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