Summary - lecture 4-6 - BLDG1211 PDF

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Summary

Summary of floor and wall framing - Summary of wall framing and wall construction - Summary of roof design merged files: BLDG1211 Lec 4 - Floor + wall framing.docx - BLDG1211 Lec 5 - Wall framing & const..docx - BLDG1211 Lec 6 - Roof designs.docx...

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Domestic construction – lecture 4

FLOOR FRAMING Span- unsupported distance a member bridges between two supports Spacing – centre to centre distance between parallel members

Bearers - Main members laid directly on brick piers, posts or timber stumps - Generally made of 100mm x 75mm hardwood spaced at approx. 1800mm centres - Supported on piers, stumps, and posts that are spaced at 1800mm centres - Span (unsupported distance) approx. 1500mm – 1600mm - Joined at point of support > not over span (unsupported distance) - Joins can be scarf, halved and lapped, butt, overlap - Skew nailing > nail inserted into timber at an angle - Excessive packing to obtain even levels should be avoided > packing timber between the joist and the bearer to create an even level from slanting brick work - Transfers loads from roofs and walls into the footings - Should be laid spring up - If load bearing wall is perpendicular to the bearer then a pier is required under the bearer

Floor joists - Most numerous floor members and sit directly on top of bearers - Generally 100mm x 50mm hardwood laid spring up - Both joists and bearers may be crippled (cut half way through on top half) to reduce the effects of spring - Laid perpendicular to bearers Flooring - Suspended flooring or slab on ground flooring - Two main types of flooring: 1. Platform “sheet” flooring 2. Cut-in “strip” flooring -

Platform sheeting: o Floor sheets laid on joists before the walls are erected o Advantage is safety (no falling through joists and bearers) o Savings in bearer and joists costs (due to even spacings of members being achievable) o Materials are usually particleboard, plywood sheets (uncommon) o Particleboard  Sheets laid perpendicular to joists  Joints are staggered  Sheets required to be flood coated with a water repellent sealant if left in the weather for an extended period of time  Holes drilled in sheets to assist with drainage

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Cut in (fitted strip) flooring: o Usually uses tongue and groove (t&g) strip footing o Cut in t&g floors are laid after the walls are erected and usually after the building has been made weatherproof as the timber strips swell and become damaged upon exposure to excessive moisture and sunlight o If laid over concrete slabs, must wait for slab to fully dry to avoid swelling o Can be adhesive fixed to concrete

Floating floors - Floor covering that usually has the appearance and feel of timber strip flooring - Laid on concrete slab or over a platform floor without the need to provide framing or battening to support real timber strip floorboards - Timber or laminate veneer strips glued to plywood backing sheets - Sheets locked together with t&g edges - Sheets laid over a thin rubber sheet underlay to provide cushioning - Entire system locked down at the edges by the skirting boards or timber beading

Piers - Isolated piers of brick or posts of steel or timber are used to support the bearings in the central floor areas of the building - Attached piers commonly used in brick veneer construction and uses brick ties to connect the attached pier bricks to the external wall. The bricks are laid parallel to the wall. Used to support bearers and joists below ground level. - Engaged brick piers used in cavity brick construction (building with two ‘skins’ or two layers of brick wall). Because the position of the pier is visible from the outside skin but in cavity brickwork the extra external skin covers the brick skin that has the pier engaged within it Every second course (row) in the brick pier is laid perpendicular to the wall and these bricks extend across both the pier and the wall and engage both brick skins Deep floor joists/beams - Joists considered deep if their height is equal to or greater than 4 times their width - Due to the joists being higher than they are wider, they are prone to ‘rack’ or fall over sideways - To prevent racking, blocking between the joists is needed which is piece of timber attached to adjacent joists - Joist hangers (steel brackets) can also be used to connect deep floor joists to other members Fire cut joists - In cavity brick construction the use of timber deep floor joists requires a special cut (fire cut) at the end of the joists where they are laid in the brickwork - Designed to counteract a floor collapse in the event of a fire by allowing the joist to rotate out of the opening in the brick wall without dislodging the upper part of the brick wall and causing it to collapse Reinforced suspended concrete floors - Far more expensive to build than suspended timber floors - Greater heat and noise insulation than timber - Quite cost effective in the long run - Reinforcement placed in lower section of the slab to resist tension in lower areas - False work used as framing that supports the formwork Ultra floor - Can be economically viable for sloping sites - Formwork is achieved by using precast concrete beams and fibre cement slabs over which reinforcement is laid and concrete poured in the usual manner

WALL FRAMING

Top plate – Purpose is to distribute load from roof frame to studs. Acts as a lintel over short distances Studs – Transfer load from top plate to bottom plate. Commonly installed in a staggered arrangement to make installation by nailing easier Noggings – Stop studs bending under compressive load Bracing – Stops wall frame racking i.e. collapsing along its own length like dominos Bottom plate – Distributes load from studs to floor joists, slab or other supporting structure Head and sill plate – Provide support for the window unit between studs Lintel – Carries a load over an opening and distributes it to the evenly throughout supporting structure

Jamb stud – Supports the lintel and transfers the load to the adjoining structure for lintels of short spans Secondary and additional secondary jamb studs – Used where the span of the lintel is large and a concentrated load will travel through the supporting studs. These two studs provide additional thickness to the jamb studs and stop the combined jamb stud from bending under the additional load

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Bracing Comes in two forms 1. Temporary bracing 2. Permanent bracing

Temporary bracing - Used to support the incomplete wall and roof frame structure during construction - Essential during construction it is placed at right angles to the wall frame and connects the top plate to the floor frame or slab Permanent bracing - Is provided by a number of different methods which all supply the same resistance to racking o Sheet bracing – Plywood, hardboard (Masonite) or particleboard sheets are nailed to the wall frame on the plates and studs. The shear strength of the sheet stops the wall from racking. The sheets must extend to the full height of the wall frame. Relies on shear strength of the material to resist deformation o Steel tension straps – Used in opposing pairs, these straps act only in tension. They are flat straps of steel that will fold up when under compression but will resist tensile loads. Stop the wall from collapsing along its own length (racking) o Steel angle brace – Resists both compressive and tensile forces in racking. Requires a cut into the framing members. Can cause bumps in plasterboard if not cut and nailed deeply enough in to the frame o Let in timber brace – Not often used nowadays due to intensive labour. Timber brace is housed into the studs and plates

WALL FRAMING

Top plate – Purpose is to distribute load from roof frame to studs. Acts as a lintel over short distances Studs – Transfer load from top plate to bottom plate Noggings – Stop studs bending under compressive load. Commonly installed in a staggered arrangement to make installation by nailing easier Bracing – Stops wall frame racking i.e. collapsing along its own length like dominos Bottom plate – Distributes load from studs to floor joists, slab or other supporting structure Head and sill plate – Provide support for the window unit between studs Lintel – Carries a load over an opening and distributes it to the adjoining and supporting structure Jamb stud – Supports the lintel and transfers the load to the adjoining structure for lintels of short spans Secondary and additional secondary jamb studs – Used where the span of the lintel is large and a concentrated load will travel through the supporting studs.

These two studs provide additional thickness to the jamb studs and stop the combined jamb stud from bending under the additional load

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Bracing Comes in two forms 1. Temporary bracing 2. Permanent bracing

Temporary bracing - Used to support the incomplete wall and roof frame structure during construction - Essential during construction it is placed at right angles to the wall frame and connects the top plate to the floor frame or slab Permanent bracing - Is provided by a number of different methods which all supply the same resistance to racking o Sheet bracing – Plywood, hardboard (Masonite) or particleboard sheets are nailed to the wall frame on the plates and studs. The shear strength of the sheet stops the wall from racking. The sheets must extend to the full height of the wall frame. Relies on shear strength of the material to resist deformation o Steel tension straps – Used in opposing pairs, these straps act only in tension. They are flat straps of steel that will fold up when under compression but will resist tensile loads. Stop the wall from collapsing along its own length (racking) o Steel angle brace – Resists both compressive and tensile forces in racking. Requires a cut into the framing members. Can cause bumps in plasterboard if not cut and nailed deeply enough in to the frame o Let in timber brace – Not often used nowadays due to intensive labour. Timber brace is housed into the studs and plates

BRICK VENEER AND CAVITY BRICK WALL CONSRUCTION Skins (or leaf) - Brick walls are regarded as separate brick skins - In brick veneer construction, all external walls are constructed of face brick (for aesthetic purposes) unless the walls are to be cement rendered or bagged - Bagging is where excess mortar is rubbed by hand over the bricks to achieve a surface with lumps and bumps still visible after painting - Cement rendering provides an even and smooth surface - In cavity brick construction the external walls are constructed of an external skin of face brick (again rendered or bagged) - Internal brick skin is constructed of common brick - Generally unnecessary for face brick to be used internally as they cannot be seen

Brick joints - A brick course is a row of bricks having common reduced level laid on a bed of mortar - Horizontal joints are called bed joints (normally 10mm) - Vertical joints are called perpend joints or perps - Perpend joints are perpendicular to the bed joints (normally 10mm) - Most courses of brickwork contain cut bricks (i.e. cut down in length to ensure they fit allowing the perps to be reasonably consistent) - One of the signs of good brickwork is vertically aligned perps Control joints/articulation - Not mortar filled joints - Joints are vertical breaks in the brickwork to form distinct and separate panels - They are broken into two groups: o Expansion joints – in place to combat thermal expansion of walls. Foam rod placed inbetween brick perps (to block silicon from spilling out the other side), silicon then injected in front of foam. Brick tie placed behind foam/silicon to connect the adjacent brick skins together. o Articulation joints – in place to combat movement in the footing systems on reactive sites. Ground movement will cause building panels (i.e. brick walls separated between windows and doors) to rise at hence rotate around the joint slightly. Joint of similar composition to expansion joint. - Ties must be built into both sides of the joint Brick bonds - The pattern in which bricks are laid - Stretcher bond is most common (course of full bricks where every course is offset half a brick from the course below) Gauge - Height for brick courses - Bed joints are required to be a maximum of 10mm thick - Joints can be adjusted to suit the gauge required to achieve a desired number of courses within a specific height - Adjustment means that cut bricks can be avoided Construction - Bricks are laid on a wall by racking up a number of courses at each end and in the centre of the wall - Toothing is used where a wall T intersection is required or a separate panel of brickwork is to be continued - One wall is laid to its full height before the other is started - This method is commonly used in cavity brick construction (even though it is not allowed by the AS masonry code) because the joints are usually not fully pointed and thus are weak

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An advantage of toothing is that the internal walls do not congest the work area

Mortar - Standard composition (compo) is mortar mixture of 1 part cement, 1 part lime and 6 parts sand - Bycol used by brickies to improve plasticity (workability) but this reduces the mortar strength and causes additional shrinkage - DPC mortar – 1 part cement to 3 parts clean sand - Lime mortar – lime and sand mixed at a ratio of 1:3 to 4. Easily cleaned from brickwork but is soft and joints in existing brickwork can be easily damaged. Has longer setting/working time Ties -

The external skin of brickwork in both brick veneer and cavity brick construction is tied to the internal frame or brick skin by ties The external skin is generally non load bearing and supported by the internal load bearing frame or brick skin In cavity brick construction the ties also ensure wind loads are resisted by both skins of brickwork Spaced 600mm centres both vertically and horizontally In coastal areas stainless steel or nylon ties are required to resist corrosion Ties required to be bent upwards when connected to wall framing so water cannot flow across to the timber and cause rot.

Fixing straps and tie down systems - In cavity brickwork the top plate (pitching plate) must be tied to the brickwork to resist uplift forces from the roof on windy days Lintels - Beams used in brickwork to support brickwork over openings - Given lateral support from the brickwork to the sides of the lintel, they generally only support the triangle of bricks directly above the lintel - Pre stressed concrete and terracotta lintels – either a cast concrete beam with steel bars placed under tension or a terracotta (ceramic) shell with reinforced concrete placed within its walls Brick veneer - A veneer is a non structural skin applied over a substance or supporting material - Brick veneer construction uses brickwork as a veneer over a structural frame - This frame may be either timber or steel and it supports the brick veneer skin through veneer ties - Brick veneer provides a durable aesthetic cladding to the building that is also weatherproof

Cavity brick - External walls consist of two separate skins (or leafs) of brickwork separated by a cavity and tied together with brick ties - The internal walls are typically single skins of brickwork, however they may occasionally be timber framed - The function of the cavity is to provide a barrier to water penetration (i.e. it keeps the internal wall dry) - Bricks are porous like sponges and will absorb moisture. Once saturated, water may run freely down the internal surface of the external skin. If this moisture can reach the internal wall, problems of mould, timber rot, peeling paint etc. may occur - By providing a gap between the two walls, water will not be able to transfer horizontally from the external skin to the internal brick skin or timber frame - It is therefore important that brick and veneer ties are regularly cleaned during construction and all mortar dags (excess) be removed so the only contact between external and internal walls is the ties - A by-product of the cavity is low level ventilation of the wall and roof voids, though this is not the primary function - The bottom area of the cavity (below finished ground level) should be filled with mortar and the top surface graded to fall to the outside skin - The brick veneer cavity is 40mm which allows for plumbing pipes and some imperfections, such as mortar dags Flashings - Are required above and below all windows and doors and around the wall perimeter at the base of the wall when building on concrete slabs - Not required around the base of the wall when building on bearers and joists as any water will merely travel down to the soil level - The flashing is required to extend vertically within the cavity, a minimum of 2 standard brick courses Weepholes - Water is allowed to exit the cavity via weepholes - Empty perpend joint - These are merely empty brick perpend joints - Any water in the cavity is caught and directed by the flashing to and out of the weephole - Max spacing of weepholes is 1200mm Pitching plate (top plate) - Same as a top plate in a timber framed wall but is used on cavity brick walls - Held down onto the top coarse of bricks by a galvanised steel strap Brick cleaning - Types of stains

1. Efflorescence – a white powdery deposit on the surface of concrete, mortar and bricks. This results from moisture and dissolved ground salts being absorbed by the masonry, rising up the masonry where it evaporates approx. 1m above ground level, leaving the salts on the surface. Remove with a stiff brush and hosing 2. Vanadium salt (Clay bricks) – non-permanent yellow/green/red brown stains. Hydrochloric acid turns stains black and are difficult to remove. Remove with oxalic acid and water 3. Manganese stains (clay brick) – remove with acetic acid or phosphoric acid 4. Calcium carbonate – major problem on concrete. Remove with Noskum or Wallkleen 150. Heavy deposits may need sand or grit blasting 5. Mortar smears – When white Portland cement has been used, clean with grit paper or a piece of the brick. Grey Portland cement mortar can be removed with hydrochloric acid (puts Portland cement into a solution). Thoroughly wet the wall to reduce the absorption of acid into bricks – minimize decay of brick. Use high pressure water blaster to remove acid solution and mortar stains a work proceeds. Take care not to damage bricks with pressure cleaner. Alternative cladding - Weatherboards and fibre cement are forms of external cladding, which are good alternatives to brickwork and were common in the 1960’s and 70’s - Problems with cladding is they require maintenance (painting) - Can have thermal and speed of construction advantages - Common cladding materials range from real timber cut into various profiles to aluminium and vinyl siding and fibre cement sheets - Lightweight concrete panels can also be used that are screwed to timber or steel all frames, rendered and painted

BLDG1211 – Lecture 6 ROOF DESIGNS Hip roofs - A hip roof has two adjacent sides of the roof sloped inwards at the same pitch, forming a hip - Neat design - As they age, can cause leaks as the mortar used in bedding and sealing causes tiles to crack and fall away. New flexible bedding and pointing compounds are reducing this issue however Hip and valley roofs & broken hip and valley roofs - Valleys are produced on hip roofed structures when there is a wing component or 90o bend in the structure - Broken hips are the product of L shaped buildings where one wing is wider than the other causing the height of one of the hip roofs to be lower than the other Gable roof - A gable roof is generally comprised of two flat panels of roof meeting at a central ridgeline - The ends of the roof meet at the gable, the vertical triangular panel of the wall - Advantage is that trusses can be used from one end to the other whereas in the case of hip roofs the trusses must be truncated to allow for the slope - A flush gable is a gable roof with no eaves or verge overhangs Gambrel roof - Symmetrical gable-style roof with two slopes on each side, rather than one Skillion roof - Low pitch roof covered in sheet metal cladding - Simple design - Usually additions to side or rear of houses covering rear porches/verandahs Flat roof - May have slight slopes of under 3o to prevent water ponding (but still regarde...