UNIT 6. BUILDING TECHNOLOGY IN CONSTRUCTION
P6- Describe the techniques used to construct and finish the component elements of a superstructure.
The two most common types of construction are:
Traditional block Cavity wall construction
Modern Timber Frame Construction
Traditional Block Cavity Wall
The fundamental principle of a cavity wall is to prevent moisture moving from outside to inside. A cavity wall consists of two separated walls or ‘leaves’ joined by rust proof wall ties. This allows the exclusion of dampness and the prevention of heat loss by incorporating insulation. Moisture will penetrate masonry walls where hairline cracks exist between masonry unit and mortar. Water which runs down the exterior wall surface will be drawn towards the inner cavity due to wind pressure exerted on the exterior of the wall and the negative pressure present within the cavity. Providing a clean air space will allow this moisture to flow unobstructed down the cavity face of the outer leaf. Flashing, installed at recommended locations will then divert this moisture back to the building's exterior through weepholes. Proper drainage of moisture will reduce the chance of efflorescence and freeze-thaw damage. The thickness of cavity wall can vary. This is mainly due to the thickness of insulation used. When constructing cavity wall leave minimum 50mm for the residual cavity. The steps of building a traditional block cavity wall domestic building: 1. Determine the overall cavity width by adding the thickness of insulation required to the residual cavity width (50 mm minimum). 2. All masonry walls will rest on a foundation or concrete slab. Prior to erecting a block or brick wall, the foundation must be clean so the mortar will adhere to it. It should also be relatively level. 3. Block work is built up to DPC level. This is usually located at 250mm above ground level. 4. Damp Proof Course laid on block work course and lapped with damp proof membrane. 5. Weep Holes are inserted at maximum centres of 800mm. They are small openings left in the outer wall of masonry construction as an outlet for water inside a building to move outside the wall and evaporate. 6. Continue building block work.
7. Wall Ties placed at intervals. Approximately 4 wall ties per metre square. Wall ties should include a retaining disc/clip (for insulation) and be of double drip type, installed drip downward. Additional wall ties at 225mm centres should be provided in areas around lintels. 8. Insulation boards should now be installed, ensuring each insulation board is retained tight against the inner leaf at three points. 9. Take care to remove excess mortar and protect the insulation board edges from mortar snots by using a cavity board. 10. Always ensure accurate trimming to achieve close butting joints and continuity of insulation. 11. A vertical damp proof course should be installed at window and door openings. 1. Install sills at window openings. Make sure sills are completely waterproofed using DPC and are positioned as to allow water to run off away from the building. 2. Incorporate lintels over window and door openings and heads of service boxes to support weight above. If you require a lintel longer than 3m, your architect will have to specify size and dimensions. DPC must be laid over the lintel and must extend 150mm beyond the ends of lintel. Two most common types of lintel are pressed metal lintels and precast composite lintels. When using concrete lintels, place a separate lintel under each wall leaf to avoid cold bridging which a single lintel would create. 3. Methods are available to prevent cold bridging at openings. Insulated cavity closers can be attached either flush to wall (flange fit) or to the return of block work (checked fit). 4. When insulating to ceiling height at a gable, wall boards should be continued 250 mm beyond the ceiling and a cavity tray installed above...
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