Presentation on theme: "7. EXTERIOR FINISHES TO WOOD LIGHT FRAME BUILDING"— Presentation transcript:
1 7. EXTERIOR FINISHES TO WOOD LIGHT FRAME BUILDING
2 Exterior Finishes for Wood Light Frame Construction Chapter 6Exterior Finishes for Wood Light Frame Construction
3 7.1 EXTERIOR FINISHES TO WOOD LIGHT FRAME BUILDING - OVERVIEW Operations: to make buildings tight (Exterior finishing) to the weatherEaves and rakes of the roof to be finished (window and doors installed - not covered)Siding applied: Wooden siding, plywood siding, wood shingles, metal/plastic sidings,brick/stone facing veneer, stuccoPaints and coats: Function and requirements, Ingredients, Types of coatings/paints, Material for surface preparation, Requirement for field paintingRoof decks, Thermal insulation, Vapor retarder, Membrane, Drainage components
6 Rake Details - without Overhang Metal Drip EdgeRack BoardSiding
7 7.2 EAVES AND RAKESBefore the roof can be shingled, the eaves (horizontal roof edges) and rakes (sloping roof edges) must be completedRakes: Specially two types, one without a lookout and other with a lookout - Metal drip edges, rake board, spacer strip, siding - Lookouts, Fly rafter, Trim board, etc.Eaves: Three possible types - one with wooden gutter, the other without any gutter, and the third one with aluminum/plastic gutter - Plywood/aluminum soffit, screen ventilation strip, roof rafter, vent spacer, metal drip edge, gutter and downspouts - Water coming down the spouts must be taken away from the basement walls to prevent erosion and basement flooding - Drip line at the ground line must be protected with a bed of crushed stones
11 7.2 EAVES AND RAKES (Cont’d) Ice dams and roof ventilation: Formed at the bottom of the sloping roof due to inadequate insulation combined with a lack of ventilation - Attic ventilation and vent spacers prevent ice from melting on the roof in buildings with an attic, if the attic itself is ventilated and kept as cold as possible - Where there is no attic and the insulation is installed in between the rafters, the spaces between the rafters should be ventilated by means of air passages - Soffit vents create required ventilation openings at the eave - Ventilation openings at the ridge can be achieved either through gable vents, just below the roof peak, or through the continuous ridge vent, a screened cap that covers the ridge of the roof and draws air through gaps in the roof sheathing on either side of the ridge board
12 Roof Ventilation To Ridge or Gable Vent Soffit Vent Strip or Perforated Soffit
15 7.3 SIDINGExterior cladding material applied to the walls of a wood light frame building is called sidingBefore siding is applied, the exterior is covered with plywood sheathing or gypsum board - Then it is covered with a layer of felt (asphalt-saturated) or fiber paper (vapor permeable) applied for better heating efficiency - The paper acts as air barrier and backup water-proofing paper; stapled as large sheets and seams sealed with tapeBoards sidings: Solid wood sidings or composite panels - Applied horizontally and nailed to studs - Siding nails (hot dip galvanized) provide holding power - Siding should not absorb too much water - Siding can be had with wood spacers (European style) - Boards made with heartwood of redwood, cypress or cedar need not be paintedPlywood sidings: Popular due to cheaper costs - Labor costs are also cheaper - Sheathing can be eliminated, if plywood is used and should be painted or stained - Plywood joints sealed with Z flashing of aluminum
17 7.3 SIDING (Cont’d)Shingle sidings: Require a sheathing of OSB (oriented strand board) or plywood or wafer board - Corrosion resistant box nails or staples to be used - Most shingles are made from cedar/redwood heartwood - Application is labor intensive - Shingle panels (2’x8’)could be usedMetal or plastic sidings: Wooden sidings decay prevented by painting every 3-6 years - Pre-finished aluminum sheet or vinyl plastic siding more durable - Last for 20 years without decay - Also has resistance to denting or impactStucco: A type of Portland cement plaster which is strong, durable, economical, and fire-resistant for siding useMasonry veneer: Light frame building can be faced with a single wythe of brick or stone - Corrugated metal ties support the masonry against falling away from the building, but allow for differential movement between the masonry facing and wood frame
25 7.4 PAINTS AND COATINGSPaints and coatings (stains, varnishes, lacquers, and sealers) protect and beautify the surfaces of buildingsGood coating job begins with thorough surface preparation to make the surface ready to receive the coating - Coating materials should be carefully chosen and skillfully applied using proper tools and techniques to finish the job properly - Environmental conditions must be right for drying or curing of coatingPaints and Coating materials: Consist of four types of ingredients - Vehicle (or film-former), solvents, pigments, and additivesVehicles: Provide adhesion of paint to the substrate and forms a film over it - Film-forming substances can be either macromolecular products or low molecular mass compounds that react to form macromolecules on curing - Film formers of the first group are cellulose nitrate or vinyl chloride copolymers - Second group includes poly-urethanes or epoxy resins - Most of the resins are soluble in either organic solvents or water, but not both
26 7.4 PAINTS AND COATINGS (Cont’d) Solvent: Volatile liquids used to improve the working properties of the paint or coating - Most common solvents are water, and hydrocarbons; but turpentine, alcohols, ketones, esters, and ethers are also usedPigments: They are finely-divided solids that add color, opacity, and gloss to the coating materials - They also impart hardness, abrasion resistance, and weatherability of the coating materials - Metals, inorganic, organic and organo-metalic compounds are used as pigments - Hiding power and tinting strength of a paint depend on the particle size of the pigment (0.1 to 2.0 micro-metre) - White pigments are made from titanium oxide, zinc sulfide, a mixture of ZnS + BaSO4, Zinc oxide/Zinc white, and white lead [basic carbonate, 2PbCO3. Pb (OH)2] - Iron oxide paints - Color ranges from red (a- Fe2O3, hematite), black (Fe2O4, magnetite), yellow ( -FeOOH, goethite), and orange ( -FeOOH, lepidocrite) or mixtures as brown - Chromium oxide paints: composed of Cr2O3 color is green - Other pigments are Cadmium pigments, Bismuth pigments, Ultramarine pigments etc.
27 7.4 PAINTS AND COATINGS (Cont’d) Extenders are used to increase the volume of paint and obtain certain technical properties and improve the optical properties of paintAdditives: Modify various properties of the coating materials - Dryers hasten the process of curing the paint (metallic soaps) - Plasticizers are organic liquids of oily consistency and low volatility (esters of ploy acids) which lower the softening temperature range of the binders and improve the flow and flexible properties - Anti-skinning agents - Curing agents - Leveling agents - Wetting, anti-floating , and anti-flooding agents - Dispersion agents - Flattening agentsTwo major groups of coatings: Solvent-based coatings and water-based coatings - Solvent based coatings: Vehicles are usually alkyd resins or some natural oils or polyurethane resins - Cure by solvent evaporation, oxidation of the vehicle, or moisture curing from reaction of the vehicle with the moisture in air - Cleanup after painting done by mineral spirits or turpentine - Water-based coatings: Use water as solvent - Most vehicles are vinyl or latex resins - Cleanup after painting is done by soap and water
28 7.5 TYPES OF COATING MATERIALS Paints: Contain relatively high amounts of pigments and a low proportion of vehicles - Solvent is water - Flat paints contain the highest amount of pigmentsEnamels: Produce glossy surface - High-gloss enamel contains large amounts of vehicles and a relatively low amount of pigments - Vehicles cure to form a hard, shiny film in which the pigment is submerged - A semi-gloss enamel has a lower proportion of vehicleStains: Range from transparent, semi transparent to solid stains - Transparent stains contain little or no vehicle and pigment, but contain a large amount of solvent and dye additive - Transparent stains only change the color of substrate, which is usually wood or concrete - Excess of stain is wiped off with a rag, a few minutes after the application - Semi-transparent stains: These have more pigment and vehicle than transparent ones - Intended for exterior applications - Solid stains: Water-based and contain more pigment and vehicle than the other types of stains - Exterior use
29 7.5 TYPES OF COATING MATERIALS (Cont’d) Clear coatings: High in vehicle and solvent content, and contain little or no pigment - Protects the substrate, makes it easy to keep clean, and brings out the inherent beauty - Lacquers: Clear coatings that dry extremely rapidly by solvent evaporation; based on nitrocellulose or acrylics and are employed chiefly in factories for rapid finishing of cabinet and millwork - A slower-drying clear coating is known as a varnish which hardens by oxidation of the oil vehicle or by moisture-curing - Available in gloss, semi-gloss or flat formulations - Shellac: Clear interior coating made from the secretions of an Asian insect; dries rapidly and gives a fine finish
30 7.6 ACCESSORY MATERIALS FOR PAINTS A number of additional materials are designated specifically to prepare the surface to receive paints or clear coatings - Paste fillers are used to fill small pores in open-grained woods such as oak, walnut and mahagony prior to finishing. Various patching and caulking compounds serve to fill larger holes in the substrate - A primer is a pigmented coating, especially formulated to make a surface more paintable. A wood primer, for example, improves the adhesion of paint to wood. It also hardens the surface fibers of the wood so that it can be sanded smooth after priming - Other primers are designed as first coats for various metals or masonry materials - A sealer is a thin, unpigmented liquid that can be thought of as a primer for clear coating. It seals the pores in the substrate so that the clear coating will not be absorbed - A finisher is used for furniture and indoor work - Boiled linseed oil plus turpentine, when rubbed into wood in many coats, gives a soft water-resistant finish that is attractive to sight, smell and touch - Beeswax and carnauba could be rubbed over sealed surfaces of wood and masonry to give a pleasing lustrous finish - Other coatings add fire resistance to steel - Impermeable coatings based on asphalt prevent decay in wood.
31 7.6 ACCESSORY MATERIALS FOR PAINTS (Cont’d) Field application of architectural coatings: Substrate must be clean and dry - Coatings must be applied to only dry surfaces (temperature to be between 10o to 32o C) and wind speeds not to exceed 15 miles per hour - Painting to be applied by brush, roller, pad, or spray - Usually one coat of primer plus two coats of finish material - Two coats of varnish are required over raw wood.
32 7.7 DETERIORATION OF PAINTS AND FINISHES Coatings: Exposed to heavy wear and weathering deteriorate with time and require re-coating. The ultraviolet rays damage the coatingsWater: Gets behind sidings and penetrates the wood and makes it damp - Then it gets behind the paint and lift it off the surfaceOther deteriorating agents: Oxygen, Air pollutants, Fungi, Dirt, Degradation of substrate through rust or decay, and Mechanical wear
33 Roofing (Chapter 16) First line of defense against the weather Precipitation (Rain, snow)SunThermal TransmissionSubjected to extreme heat and coldSurface can have wide temperature swings
34 7.8 ROOFING MATERIALS (cont’d) Roof protects the interior of the building from rain, snow, and sun - It helps to insulate the building from extremes of heat and cold, and to control the accompanying problems of condensation of water vapor - Low slope roofs and steep roofsLow slope roof decks covered either with plywood/OSB panels, or solid wood decking over heavy timber framing, or corrugated steel decking ( with wood panels or insulating panels), or panels of wood fiber bonded together with Portland cement, or pored gypsum over insulated form-board, or site-cast concrete slab, or precast concrete slab - Decks must slope towards drainage points at an angle sufficient to drain reliably, despite the effects of structural deflections (1/4” per foot of run is recommended). If a roof is insufficiently sloped, puddles of water will stand for extended periods of time leading to premature deterioration of roofing materials - Roof should be provided with enough movement joints to control the effects of expansion and contraction on the roof membrane - A roof membrane must be laid over a smooth surface of the wood deck and no large gaps or knotholes should exist below membrane.
36 Steep Roofs Drain quickly Facilitate the use of shingles Less opportunity for gravity or wind to push/pull water through the roofing materialFacilitate the use of shinglessmall, overlapping roofing unitsAdvantages:Can be inexpensive, easy to handle & install,Accommodate thermal expansion/contraction & structural movementVents water vapor easilyVisible - Aesthetics
38 7.9 THERMAL INSULATION AND VAPOR RETARDER Thermal insulation and the vapor retarder: Thermal insulation may be installed below the structural deck (fiber batt insulation above a vapor retarder), between the deck and the membrane (rigid insulation above vapor retarder) or above the membrane (rigid insulation and the membrane also act as the vapor retarder)Thermal insulation is a material that is added to any building assembly for the purpose of slowing down the conduction of heat through that assembly. Effectiveness of a building assembly in resisting the conduction of heat is specified in term of its thermal resistance (R value), and expressed in foot-hour-degree-Fahrenheit-per-BTU or in square meter-degree-Celsius-per-watt. The higher the R-value, the higher the insulating value - In wintertime, it is warm inside and cold outside
40 Thermal Insulation Resist Heat Transfer Location / Placement Below the DeckBetween the Deck & MembraneAbove the MembraneRigid Insulation Attachment (adhered or mechanically attached)
41 ‘Rigid’ roof insulation being placed over metal decking (mechanically fastened to decking)
42 Vapor Retarder Purpose - Prevent transmission of Water Vapor Location / PlacementGenerally Below the InsulationMaterial - hot mopped felts most commonInsulation VentilationRoof Vent
43 7.9 THERMAL INSULATION & VAPOR RETARDER (Cont’d) Water vapor and condensation: Air always contains water vapor - The amount of water vapor the air actually contains, divided by the maximum amount of water vapor that it could contain, is relative humidity of the air - If a mass of air is cooled, its relative humidity rises - When a mass of air is cooled below its dew point, it can no longer retain all its water vapor - Some of the vapor is converted to liquid water by condensation; condensation takes place in many different ways inside the building - To prevent condensation inside the building assemblies, a vapor retarder (or a vapor barrier) is installed on the warmer side of the insulation layer - Some examples of vapor retarders are: Plastic sheeting, aluminum foil, Kraft paper laminated with asphalt, roofing felt laminated with asphalt, trowelled mastic, etc.Rigid insulation: Has high thermal resistance - Some examples of rigid insulations are: Cellulose fiber board, Glass fiber board, Polystyrene foam board, Polyurethane foam board, Polyisocyanurate foam board, Perlitic board, and Composite insulating board
44 7.9 THERMAL INSULATION AND VAPOR RETARDER (Cont’d) Low-slope roof membrane: Membranes, used for low-slope roof, fall into three categories - Built-up roof membrane (BUR), Single-ply roof membrane, and Fluid-applied roof membrane - BUR is assembled in place from multiple layers of asphalt-impregnated felt embedded in bitumen. Single-ply membranes fall into two general groups : thermoplastic (softened by application of heat) and thermosetting (cannot be softened by heat) - Thermoplastic: Polyvinyl chloride sheet, Polymer-modified bitumens, PVC alloys, Chlorinated polyethylene, EPDM, etc. - Thermosetting: Hybrid membrane - Fluid-applied membrane: Applied in liquid form with a roller or spray gun - e.g., Neoprene, Silicone, Polyurethane, Butyl rubber, Asphalt emulsion
46 Built-up Roof Membrane “Multiple plies of asphalt-impregnated felt bedded in bitumen”Application:Felts laid in Hot Asphalt (or coal tar)Overlapping LayersForms a “laminated” membrane typically 2-4 plies thick
47 Single-Ply Roof Membrane “Sheet materials that are applied to the roof in a single layer”Attached to the Roof:AdhesivesBallast WeightConcealed fasteners
48 Fluid-Applied Membranes “Membranes applied with a roller or spray gun and cure to form a rubbery membrane”Uses“Complex shapes that are difficult to roof by conventional means”Examples: Domes and shells
49 7. 10 ROOFING Edge and drainage details: For low-slope roofs Structural panel metal roofing: for low-slope roofsSteep roofs -Shingles: Wood, asphalt, slate, clay tiles - Sheet metal roofing: lead-coated copper sheet, terne-coated stainless steel
53 Steep Roofs Roofs with a pitch of 3:12 (25%) or greater Three General CategoriesThatchShinglesArchitectural sheet metalInsulation & vapor retarderTypically installed below the roof deckingDecking – typically plywood or OSB
54 Shingles“applied to the roof in small units and in overlapping layers with staggered vertical joints”MaterialsWood (shingles & shakes)AsphaltSlatesClay TilesConcrete Tiles
55 Cedar Shakes (split rather than sawn) Natural decay resistant woodModerately expensiveFire Resistance low unless treated
56 Asphalt Shingles Die-cut from sheets of asphalt-impregnated felt faced with mineral granulesTypical size – 12”x36”
59 Architectural Sheet Metal Roofing Materials – typically thin sheets of aluminum or galvanized steelCoatings – typically a polymeric available in various colorsSeams – raised interlocking edge seamsFasteners – concealed or exposed fasteners with rubber washers
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