ASSIGNMENT 2 /SUMMATIVE ASSESSMENT CONSTRUCTION DESIGN PRINCIPLES
Kei Little
Summative assessment D/ On poor soils you need to choose a foundation that can spread the load evenly so choose a spread foundation but not a strip foundation. Because of the uneven bearing capacity the foundation needs reinforcement to hold everything together and spread the load evenly. I have chosen a raft foundation that has a thickened edge to give support under the walls, and the pad supports the floors and internal walls. Raft foundations are often used on poor soils for lightly loaded buildings. They are designed to be capable of taking small settlements of the sub soil. The raft foundation covers the whole of the floor and wall area of the structure. The reinforced slab is generally thickened out substantially under all the walls and the loads from the walls are transferred over the whole slab. The raft is capable of taking small settlement issues. The rigidity of the reinforcement is minimising the effect of differential settlement.
Hard areas in the trench should be excavated to a suitable depth and backfilled so the bearing capacity equals that of the remainder of the site. Generally is considered to thicken the edge of the slab to prevent weathering away of the soil under the perimeter of the raft. When excavating a trench for a raft foundation, the trench required for the thickened edge must be supported with metal or timber formwork fixed temporarily around the sides of the foundation. The formwork can be supported by strutting to prevent the formwork from moving.. When the concrete is poured the supported edge prevents earth spilling into trench and slab. The concrete will need to be levelled but first the steel fabric reinforced mesh must be laid out in a crisscross pattern. The mesh will need a 250 thick covering of concrete. The mesh comes in flat sheets of steel welded together, and where all 4 corners of sheet meet reduce the build up of the mesh. Steel spacers will help find the correct position for the steel mesh. For steel mesh first lay a thin layer of concrete spread over the ground to provide a level platform to construct and lay the reinforced cage. Lay the cage and pour half the concrete, leave to dry, wait, and then lay the other mesh, then cover again with concrete. No polished steel here, only textured steel gives a good grip. Cover and protect concrete from frost. Concrete needs time to cure - an irreversible process- so not to disturb. Concrete needs vibrating to get the air out. To cure the concrete so it gains maximum strength and durability you must prevent it from losing too much water too quickly essential cover with polythene sheeting or spray with proprietary curing compounds to seal the surface.
The concrete slab is the base for the finished floor and needs rigid insulation (rigid polyurethane foam boards) that you can walk on and that takes the loads of the floor positioned under the floor screed. The insulation layer must be sufficiently strong and rigid to support all the weight of the screed and floor loads without compression or deformation. Very little brick work is needed BGL. DPC is 150 above ground. To prevent Cold bridging (A gap in insulation) through the foundation wall and through the screed floor, Insulation is fitted around the edges of the floor combining with a layer of insulation down inside the cavity wall. Care must be taken when tipping, spreading and compacting the wet screed. With the DPM laid below the insulation it is necessary to lay a separating layer of 500 gauge polythene sheet over the insulation. This will prevent wet screed running into the joints between the insulation boards.. DPM runs continuous with DPC. Wall ties hold cavity wall together.
E/A cold roof was a traditional conventional method used ever since we started insulating our roofs. Cold roof means what it says- the space in the roof is left cold. The roof is insulated with, Rockwool in two layers 150mm layer and a 120mmlayer. The roof only insulates between the joists and across the top of the ceiling joists. It is easy and simple to lay out the rolls. They are easily spread out right across the ceiling in both directions, and extend over the insulation in the walls, overlapping preventing a cold bridge with two continuous layers. A 10mm soffit vent is on the underside of the fascia boards, soffit vents at both ends of the roof dissipate condensation. A ventilation spacer allows room for air to circulate (An open gap) in the roof passing above the layer of insulation in the eaves creates a cross flow of air from both sides of the roof. The insulation covering the ceiling area is the most convenient and economic place for insulation. Loft hatches will be insulated and draught sealed. To prevent damage from water freezing, pipes and water tanks must be insulated. The roof insulation could easily get compressed and lose efficiency as an insulator if walked on, so walkways for access should be raised on battens above the level of insulation. The roof space above the insulation is cold. Warm air that rises as vapour can permeate through the insulation in the roof, and meets the cold air of the loft, and condenses into moisture. The cold roof must be adequately ventilated to outside air to reduce the likelihood of condensation. With ventilation you get a cross flow of air from the eaves that disperses any rogue condensation and damp. Tiles and slates can come with special fittings to provide ventilation in the eaves, ridge, and in the slopes. Gable walls can have air bricks built in to help ventilate small pitched roofs. Ventilation openings promote cross-ventilation. The moisture in a cold roof could rot the timbers, corrode the metal fixings, degrade the insulation and could short-circuit the wiring.
Air carries water vapour, the amount increases with the air temperature. The increase in water and pressure migrates from warm areas to cold areas. The condensation that manifests as a result of the air temperature cooling and reducing, along with its ability to hold water, makes cold roofs not suitable for loft accommodation. The warm air rests on cold surfaces where condensation will occur. Pg 422 Building Construction Handbook. A cold roof means a lot of heat loss so a warm roof is needed. A warm roof offers improved energy efficiency and reduced condensation and is not costly in the long term with reduced heating bills. Building regulations emphasize the need for energy efficiency. The NHBC 2003 standards state that all roof voids should be ventilated to prevent condensation.
Warm roofs were introduced in the 1980s.The two opposing temperatures that cause condensation in a cold roof, are eliminated in a warm roof, as there is insulation surrounding the outside of the roof inside the structure. The insulation is moved up into the rafters laid on the outside of the roof structure so the whole house including the loft space, is covered and kept warm and interstitial condensation is prevented. This is what is known as a warm roof ideal for occupying the roof space and saving energy and reducing heat loss. Suitable rigid insulants include: low density polyisocyanurate (PIR) foam, reinforced with long strand glass fibres, both faces bonded to aluminium foil with joints aluminium foil taped on the upper surface; high density mineral wool slabs over rafters, with less dense mineral wool between rafters. Pg 405 Building Construction Handbook.
Heat loss is reduced by increasing air tightness. As the roof is now a temperature similar to the rest of the rooms in the house, little or no ventilation is needed. With no condensation there is no need for ventilation, but where there are voids left with no insulation, some degree of ventilation is still required in a loft trussed roof. Because there is still the chance that moist air will condense on the cold side of the insulation, high performance roofing felts (Sarking) have been developed which allow water vapour through to escape, but prevents condensed water from getting back in. These felts are much tougher than traditional type 1f under- slating felts and don’t tear so easily. Instead you could use a breather membrane or vapour control layer on the cold side of the insulation allowing water vapour through, but won’t let liquid water through. Also Place a vapour barrier on the warm side of insulation. Insulation provides a support for underlay. Pg 405 Building Construction Handbook. Counter battening in the roof that supports the roof tiles provides a continuous air circulation gap as ventilation to help drain cavity moisture away. The underlay should sag between rafters to allow rain to flow under tile battens and drain to the eaves, where counter battens are used.pg 401 Building Construction Handbook. Vapour check plaster boards line the loft space and make up the ceiling. A cavity closer (a thin board e.g. calcium silicate) is also required to function as a cavity barrier to prevent fire spread. Pg 404 The Building Construction Handbook. The emphasis of an airtight building is to seal the building and only allow air to escape into and out by a ventilation duct. It would be wrong to over ventilate a building and this also applies to the roof space. What is needed is a controlled ventilation approach, ventilation controlled by design. When planning a newbie (new build) design you should build a warm roof from the start to easily convert the roof space as a loft room or extension. Specifications for using a roof space for accommodation states that the tops of the walls should rise at least 1.5m above floor level before meeting the sloped ceiling.
F/ There are three types of floor. A hollow plank floor is a floor type 1. A concrete base with a ceiling and soft floor covering. This is the description for the floor type in this description for hollow plank is floor type 1.2b. The floor is described a ceiling treatment in combinations. The b in 1.2b describes ceiling treatment B. Others are A and C all refer to the correct ceiling treatment they rank A as the best sound insulation Ranking from A-C. Treatment B is plaster board (or Maxiboard 1 hours fire protection) on proprietary resilient bars ( Hush bar plus resilient bar system))with an absorbent material, mineral wool (or Earthwool acoustic roll). The resilient layer a layer of mineral wool can be 25mm paper faced on the upper side to prevent screed entering. The single layer of plasterboards should have a minimum mass per area of 10kg/m2 they are fixed using the proprietary resilient metal bars. Theses resilient bars need to be fixed to a timbre batten. Within the floor the resistance to airborne sounds depends mostly upon the mass per unit area of the ceiling. A soft floor covering (Instalay 30) reduces impact sound. Any service pipes shall be adequately insulated. Recommendations are given for construction that is necessary to control flanking transmissions through structures for airborne noise and impact noise. Air borne sounds propagate through the air, air borne insulation reduce the sounds between buildings. To block flanking through joist/plank spaces install them parallel to party walls. Direct impact causes impact sound such as footsteps. Floor type1 is most suited to new builds for residential purpose. Correctly built should achieve performance standards. Fill all joints (fully grouted) in the floor and avoid air paths to get air tightness. For The junction between floor and cavity wall the outer leaf can be any construction. Fully fill the cavity wall with mineral wool or use a flexible closer. Cavity sock will reduce flanking noise and restrict the spread of smoke and flames (Rockwool sleeved in polythene). Build the floor
base, Carry the floor through to the cavity face of the inner leaf excluding screed so cavity isn’t bridged. The planks should be a min of 300mm from cavity face. The separating concrete floor is built entirely into the walls where the walls are masonry and block. The junction between the separating walls has a wall type 1.1 separating wall, brick blocks that extend the full width of the wall .A dense aggregate concrete block with a lightweight plaster (13mm) on both faces. The 215mm blocks are laid flat to the full thickness of the wall with 110mm coursing. The blocks density is 1840kg/m3. Junctions are made to resist flanking transmissions. The plank should not be continuous under the separating wall they must be a joint between the planks between the walls. Seal the gaps that form between the block wall and the underside of the hollow plank with mortar. Each unit gets hoisted into position with a crane and joints are grouted up. Immediately the floor becomes a working platform. Concrete topping laid out increases the strength for floor loadings. Forms a monolith floor. Water may accumulate in construction so weep holes can be drilled to release trapped water. Great spans can be achieved and increased loadings. It is the simplest form and widely used because of the speed of assembly. Beams lay out side by side. The hollow floor reduces the dead weight. Rectangular sections with reinforcement in the lower angles are usually 300mm wide 600mm long and 130-205 deep. The end s of the hollows is filled with concrete solidly so they are strong enough to bear the weight of the heavy brick work. G/A portal frame is a two dimensional rigid frame of steel that has rigid joints between the column and the frame. All joints and connections are rigid and give low bending moments. Portal s can have small, medium16-35m and large spans up to 60m. The frame acts as a structural unit. The objective is to reduce the bending moment on the beam to achieve a single span roof. Gives more room for storing large item and assembling large items or storing stock with high stacks or shelves. Suitable as agricultural sheds are large shops like furniture or DIY shops. My portal is used as a workshop with a 15 width 20 length 7 high with a pitch of 14 degrees, a medium span portal. Because they have considerably large spans means there is no advantage in using multi-bay steel portals here where the long span would be sufficient. Portals have as low a pitch as practical to minimise the spread of the knee of the frame (spread increases with the pitch of the rafters). The knee is the rigid connection of the rafters to the post. Short and medium spans the frame can be made on site where the apex or ridge where the rafters join, are bolted together. This is convenient because you can transport the two halves onto site. Medium spans must be manufactured from one mild steel I section for the rafter and the column. The connection of the rafter to the post is haunched at the knee to make a connection that’s deeper hence stiffer. The haunch connection is fabricated by welding a cut I-section to the underside of the rafter. The rigid knee joint will carry the loads from horizontal wind pressure on the roof and wall claddings also the column and their fixed bases that support the roof frame act as a cantilever to carry the same loads of the wind pressure. The junction of the rafters and the ridge is stiffened b welding cut I-sections to the underside of the rafters under the bolted connections. In the setting out of the portal additional bracing is used to stabilise the roof frame and adds additional resistance to the wind. To stabilise the frame from uplift due to wind pressure longitudinal ties between the frames are used. Standard Z section Purlin or sheeting rails are made from thin sections of steel make up the secondary structure. Purlins are fixed across rafters and sheeting rails across the columns to provide support and fixing for roof and wall cladding.
Purlins and rails help facilitate direct fixing of the profile sheeting by using self-tapping screws. Purlins and rails are fixed to the structural supports (bolted to cleats then to structural frame). To stop purlins moving during the fixing of the roof sheeting anti-sag bars can be fixed in between. The purlins get a great degree of stiffness from the sheeting. To support the wall cladding they are across or between the steel columns. The steel cladding is impermeable to water and the side and end laps keep water out. Preferably screwed at the ridge of the trough where they will be less visible, neoprene washers help against water penetration. Steel sheeting is practical and economic thin sheets with adequate strength and stiffness. Protected by zinc coating it won’t corrode (Galvanising process). A wide range of profiles are available. I choose a golden yellow colour finish to a two coated steel profiles bonded to core insulation as weather proofing envelope of the building. The wall cladding is normally the same profile as the roof. Fasteners have coloured heads to match the colours of the sheeting. Thermal rigid insulation is fixed under the cladding sheets, provides thermal insulation. Fixing insulation is economic and straight forward process when a rigid insulation is laid across purlins and sheeting rails (With an inner lining). Steel sheeting can be used with a lower wall of masonry. Pad foundations transfer the point load of the column. A base plate is welded to the post and bolted to the pad foundation using anchor bolts. A reinforced concrete ground-beam carries the cavity wall and ties the pad foundation together .A solid floor slab is used to cover the area of portal on the ground. Insulate only the perimeter of the concrete floor and forget the floor screed, it will make a dusty floor. Using the latest rolling and laser technology manufacturers are able to design with precision. Cold rolled profiles can reduce weight by 40%. Reduced weight reduces erection time and takes away the need for heavy plant machinery. The design should include a roller door and personal access door. Bibliography: Mitchell's Structure and fabric part1 7th edition / Jack stroud Foster and Roger Greeno Mitchell's structure and fabric part2 7th Edition / Jack Stroud Foster Raymond Harington and Roger Greeno Building construction handbook / Roy Chudley & Roger Greeno Building technology 5th edition / Ivor H. Seeley Barry's Introduction to Construction of Buildings Second edition / Stephen Emmit / Christopher A. Gorse Approved Document E Approved Document F
Websites: http://www.millbank.co.uk/hollow core-floor-planks.php http://www.sound reduction .co.uk/products/soundproofing-for-ceilings/installation guide http://www.hush.uk.com/sound-control-products/hush-bar-plus.php http://www.tarmacbuildingproducts.co.uk/products.co.yk/products_and_services/blocks_and_mortar/blocks http://www.knaufinsulation.co.uk Ridge seals- http://shedblog.co.au www.masteel.co.uk http://www.interarchbuildings.com www. Encon.co.uk/products/view/81/arc-cavity-stop-socks-60na
Portal Frame workshop industrial building
Steel zed section purlins fixed across frame and supports the roof covering 200-250 deep 1.6-3.5mm thick
Concealed Insulated trough gutter
Thick ridge capping bolted to composite roof panelling Ridge of portal frame
Profile steel sheeting fixed over insulation to roof purlins
Galvanised steel flashing Filler
Sealant Insulation boards laid on galvanised profile steel lining sheets
Tracdek HiRib crimp curve eaves Knee Flashing
Zed section sheeting rails
self drilling, self tapping screws, fasteners for profile steel sheeting
Haunch or gusset plate welded to rafter
Rafter of steel bolted and welded to post.
Web stiffener
Ridge plate welded to rafters and bolted together on site
Stanchion/post of steel 10mm thick cleat
Bracing I beams with anti- sag bars in between Steel sill
Insulated cavity wall
Reinforced concrete ground- beam carries weight of cavity wall and ties the pad foundation together
Perimeter insulation
Base plate welded to post and bolted to pad foundation Pad foundation transfers the point load of the column
150mm thick RC slab
Single bay only portal frame
Raft foundation with deepening edge beam and screed finish floor
External wall Plasterboard Skirting 25mm*200mm
Floor screed 50mm Cavity insulation
Separating layer 500 gauge
Damp proof course 150mm abgl
Rigid insulation 60mm polyurethane boards DPM 2000 gauge
Ground zone
Fabric reinforcement 25mm steel rods Hard core 100mm Deepening of edge beam Blinding 50 mm
Slip membrane
Hollow plank separating floor and concrete block separating wall. The first Floor section
The junction between the first floor and the external wall
soft floor covering Instalay 30 Hollow concrete plank
Concrete topping
Timbre batten Resilient bars or hush bar plus system
Mineral wool fibre or Earthwool acoustic roll sound insulation 12.5mm plasterboard or maxiboard
The junction between the first floor and an internal wall backing onto another flat
Separating wall /Party Wall
Grouted joints
External cavity wall
Cavity sock Rockwool sleeved in polythene
COLD ROOF
WARM ROOF The area above the insulation will be cold Breather vapour control under counter battens
Cross ventilation Ventilation spacer Tile Battens Counter batten
Underlay Single lap inter-locking tiles
Breathable sarking will help to avoid Condensation forming within the roof space.
100*50mm Wall plate with holding down straps min 1m long. Soffit
Clear 10mm vent through soffit then through ventilation spacer into the roof space to circulate
Rigid insulation in two layers between battens 120mm &150mm layers.
170mm Insulation rolled across the joints Ceiling joist Counter batten 100mm Insulation between trusses and ceiling joists Vapour check Plaster board ceiling
Fascia
Tile batten
Rafter
Cavity wall and cavity insulation
Ventilator Fascia
soffit
Vapour control layer backed plaster board
100*50mm Wall plate with holding down straps min 1mlong. Calcium silicate cavity closer Cavity wall and cavity insulation
CONSTRUCTION TECHNOLOGY PRINCIPLES PART A, B ,AND C
KEI LITTLE
A. Trench fill mass concrete filled trench used on clay soils Deep strip must reach down to strong load bearing strata I am placing at 1100mm deep. Surrounding clay soil can help support loads by stabilising foundation, frictional resistance around sides. Depth avoids seasonal soil movements. Adds Extra stiffness. A deeper foundation where stronger moisture content doesn’t vary and seasonal change are unlikely to cause cracks. Clay soil means firm soil doesn't need temporary supports until a depth of 1.5 meters in dry weather in wet weather sides may collapse. The soil around the external faces of the foundation will still expand and contract. To prevent the pressure on the external faces a 50mm sheet compressible clay board can be placed on inside face. Also favoured because it avoids below ground level walls in trenches that can be deep. Word count 139 Notes: A1/2 2E2athe foundations should be centrally under the wall.
A1 The building shall be constructed so that the combined dead, imposed or wind loads are sustained and transmitted by it to the ground.
B. I have chosen to use short bored piles in these areas of high volume change here’s why. Where in clay
soils if tree growth is stopped for building on, having shallow foundations will only be affected by differential movement. Where trees have been cleared on sight in preparation for a new building built on firm clay under the building for years after the clearance you will have Ground recovery as the clay gradually recovers water previously sucked up by the trees. The depth and design of the pile foundations will allow for the gradual expansions and limit the damage caused by differential settlement. Volume changes occur up to depths of 4 meters where the trees routes extend to, piles will be able to go below that depth. Below the area where seasonal variations will increase and decrease. The expansion and contraction will cause damage (cracks).piles are economic and satisfactory. The pile will transmit loads to lower levels of the ground by a combination friction along the sides, shaft resistance and end bearing at the pile point or base. Piles provide vertical load transfer. Reinforcement goes in after pile has been dug and filled. Ground beam will anchor pile into position piles don’t always go in dead centre. Compressible material stops beam lifting or moving when the clay soil expands keeping pile into position and on the sides for side swell. Ground beam supports the wall line. We build and design for the movement to allow heave to happen, an upward movement, and expansion and shrinkage. On ground susceptible to heave you build a suspended floor (concrete suspended or block and beam) above the soil as a precaution. The void should be left for the ground swell at least 150mm probably more to allow for building settlement. Settlement is due to foundation loading. Foundations are designed so settlement is even. Put a Slip liner, a polythene sleeve around pile. word count 319 Notes: C1.5Where mature trees are present (Particularly on sites with shrinkable clays) The potential damage arising from ground heave to services and floor slabs and oversight concrete should be assessed.
Approved document A ; Ground movement caused by swelling, shrinkage or freezing of the sub soil, landslip or subsidence will not affect stability of any part of the building. C.
Bricks are pourus suck up moisture from the ground Capillary action up to 1 meter up the wall. The outer leaf keeps weather out but driving rain can penetrate so a 100mm gap in cavity wall keeps moisture from tracking across to the inner leaf that supports the internal finish. Movement of moisture is upwards in foundation walls or floors. A damp proof course and damp proof membrane provide an impermeable barrier to the passage of water. DPC must be at least 150mm above ground level. The DPC a water proof membrane is laid on the bottom of a wall to prevent dampness from rising. A DPC can be made flexible from lead, copper and bitumen traditionally but more likely a 0.25mm thick 1200 gage polythene sheet (comes in 3m rolls) or polymer based sheet. Or could be rigid from slate or semi rigid from mastic asphalt. DPC must be continuous with any DPM in the floors. DPM must go up wall to meet DPC. DPM is used under the floor to form a continuous barrier. 50 mm Blinding will protect the DPM from puncture from
the hard core. DPM must be covered up quickly to prevent damage from sunlight. . DPC must have sealed joints and corners. Joints must fully overlap by 300mm, tape and seal joint (a heat seal using mastic asphalt). DPC is protected by floor screed. Mortar both sides of DPC. DPM protects concrete from sulphate attack.Concrete is permeable to water. Concrete slab stops growing vegetation under floors. word count 251 Notes: BS EN 13967:2004 "Flexible sheets for waterproofing" Have similar or better performance compared to traditional DPM. C1.6 Joints should be made so that roots will not penetrate them. C4.5 all floors should be designed so they do not promote surface condensation or mould growth. C4.2 Floors next to the ground should: Resist the passage of ground moisture to the upper surface of the wall. Not be damaged by the moisture from the ground. Not be damaged by ground water Resist the passage of gas. C4.4 Floor next to the ground and floors exposed from below Should be designed and constructed so that their thermal performance are not adversely affected by interstitial condensation. Bibliography;Barry’s Introduction to construction of buildings. Emmit, Stephen. Building construction handbook. Chudley, Roy. Construction technology 4th edition. Chudley, Roy. The practice of construction management 4th edition. Fryer, Barry. Building regulations in brief. Ray Tricker/ Samantha Alford.