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7. EXTERIOR FINISHES TO WOOD
LIGHT FRAME BUILDING
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Chapter 6Exterior Finishes for Wood Light Frame Construction
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7.1 EXTERIOR FINISHES TO WOOD LIGHT FRAME
BUILDING - OVERVIEW
Operations:to make buildings tight (Exterior finishing) to the weather
Eaves and rakesof the roof to be finished (window and doors installed - notcovered)
Siding applied:Wooden siding, plywood siding, wood shingles, metal/plasticsidings,brick/stone facing veneer, stucco
Paints and coats:Function and requirements, Ingredients, Types of
coatings/paints, Material for surfacepreparation, Requirement for field painting
Roof decks, Thermal insulation, Vapor retarder, Membrane,Drainage components
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Normal Shell Sequence
Structural Framing & Sheathing
Eaves & Rakes
Roofing (Edge, Felt, Shingles)
Exterior Openings & Siding
then
Interior Finishes
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Roof TerminologyEaves & Rakes
Rake - Sloping roof edge
Eave - Horizontal roof edge
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Rake Details- without Overhang
Siding
Rack Board
Metal Drip Edge
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7.2 EAVES AND RAKES
Before the roof can be shingled, the eaves (horizontal roof edges) and rakes
(sloping roof edges) must be completed
Rakes: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 anygutter, 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
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Rack Details- with Overhang
Lookout
Rafter
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Eaves DetailsEave Details
Metal Drip Edge
Soffit
WoodMetal
Plastic
Gutter
Facia
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Materials - Typically
Metal - alum., copper
Plastic
Gutter
Downspout
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7.2 EAVES AND RAKES (Contd)
Ice dams and roof ventilation:Formed at the bottom of the slopingroof 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 ventscreate 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 ridgeboard
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To Ridge or
Gable Vent
Soffit Vent Strip or
Perforated Soffit
Roof Ventilation
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Eave Venting
Ridge Vent
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Gable Vent
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7.3 SIDING
Exterior claddingmaterial applied to the walls of a wood light framebuilding is called siding
Before 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 paperacts as air barrier and backup water-proofing paper; stapled as large sheets and
seams sealed with tape
Boards sidings: Solid wood sidings or composite panels - Appliedhorizontally and nailed to studs - Siding nails (hot dip galvanized) provide
holding power - Siding should not absorb too much water - Siding can be hadwith wood spacers (European style) - Boards made with heartwood of
redwood, cypress or cedar need not be painted
Plywood sidings:Popular due to cheaper costs - Labor costs are alsocheaper - Sheathing can be eliminated, if plywood is used and should be
painted or stained - Plywood joints sealed with Z flashing of aluminum
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Wood Siding
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Shingle sidings: Require a sheathing of OSB (oriented strand board) orplywood 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 (2x8)could be used
Metal 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
impact
Stucco:A type of Portland cement plaster which is strong, durable,
economical, and fire-resistant for siding use
Masonry veneer: Light frame building can be faced with a single wythe ofbrick 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
7.3 SIDING(Contd)
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Wood Siding
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Wood Shingle Siding w/ Stone
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Vinyl Shingle Siding
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VinylSiding
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Brick Siding
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Stone Siding
(stone facing)
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Stone Siding
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7.4 PAINTS AND COATINGS
Paints and coatings (stains, varnishes, lacquers, and sealers)protect andbeautify the surfaces of buildings
Good coating jobbegins with thorough surface preparation to make the surfaceready 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 coating
Paints and Coating materials:Consist of four types of ingredients -Vehicle(or film-former), solvents, pigments, and additives
Vehicles:Provide adhesion of paint to the substrate and forms a film over it -Film-forming substances can be either macromolecular products or low molecularmass 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
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Solvent:Volatile liquids used to improve the working properties of the paint orcoating - Most common solvents are water, and hydrocarbons; but turpentine,
alcohols, ketones, esters, and ethers are also used
Pigments:They are finely-divided solids that add color, opacity, and gloss tothe coating materials - They also impart hardness, abrasion resistance, andweatherability 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
pigmentsare made from titanium oxide, zinc sulfide, a mixture of ZnS + BaSO4,
Zinc oxide/Zinc white, and white lead [basic carbonate, 2PbCO3. Pb (OH)2] - Ironoxide 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 Cr2O3color is green -
Other pigments are Cadmium pigments, Bismuth pigments, Ultramarine pigments
etc.
7.4 PAINTS AND COATINGS(Contd)
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Extendersare used to increase the volume of paint and obtain certain technicalproperties and improve the optical properties of paint
Additives:Modify various properties of the coating materials - Dryers hastenthe 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 agents
Two major groups of coatings:Solvent-based coatings and water-basedcoatings - 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
7.4 PAINTS AND COATINGS(Contd)
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7.5 TYPES OF COATING MATERIALS
Paints:Contain relatively high amounts of pigments and a low proportion ofvehicles - Solvent is water - Flat paints contain the highest amount of pigments
Enamels:Produce glossy surface - High-gloss enamel contains largeamounts 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-glossenamel has a lower proportion of vehicle
Stains:Range from transparent, semi transparent to solid stains -Transparent stainscontain 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 wipedoff 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
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Clear coatings:High in vehicle and solvent content, and contain littleor 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 ofcabinet 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
7.5 TYPES OF COATING MATERIALS(Contd)
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7.6 ACCESSORY MATERIALS FOR PAINTS
A number of additional materials are designated specifically to prepare thesurface to receive paints or clear coatings - Paste fillersare used to fill smallpores 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 primeris 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 sothat it can be sanded smooth after priming - Other primers are designed as first
coats for various metals or masonry materials - A sealeris 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 finisheris 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 tosight, smell and touch - Beeswax and carnauba could be rubbed over sealed
surfaces of wood and masonry to give a pleasing lustrous finish - Other
coatingsadd fire resistance to steel - Impermeable coatingsbased on asphalt
prevent decay in wood.
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Field application of architectural coatings:Substrate must beclean and dry - Coatings must be applied to only dry surfaces
(temperature to be between 10o to 32oC) 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.
7.6 ACCESSORY MATERIALS FOR PAINTS(Contd)
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7.7 DETERIORATION OF PAINTS AND FINISHES
Coatings: Exposed to heavy wear and weathering deteriorate withtime and require re-coating. The ultraviolet rays damage the coatings
Water: Gets behind sidings and penetrates the wood and makes itdamp - Then it gets behind the paint and lift it off the surface
Other deteriorating agents: Oxygen, Air pollutants, Fungi, Dirt,Degradation of substrate through rust or decay, and Mechanical wear
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Roofing (Chapter 16)
First line of defense against the weather
Precipitation (Rain, snow)
Sun
Thermal Transmission
Subjected to extreme heat and cold
Surface can have wide temperature swings
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7.8 ROOFING MATERIALS(contd)
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 roofs
Low slope roof deckscovered 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 insufficientlysloped, 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.
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Roof Groups
Steep Roofs
Low-Slope Roofs
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Steep Roofs
Drain quickly
Less opportunity for gravity or wind to push/pull water
through the roofing material
Facilitate the use of shingles small, overlapping roofing units
Advantages:
Can be inexpensive, easy to handle & install,
Accommodate thermal expansion/contraction & structuralmovement
Vents water vapor easily
Visible - Aesthetics
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Low-Slope Roof Components
Structural Support - Deck
Thermal Insulation
Vapor Retarder
Roof Membrane
Roof Ballast
Drainage Flashing
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Thermal insulation and the vapor retarder:Thermal insulation maybe 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 insulationis a material that is added to any building assembly forthe 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
7.9 THERMAL INSULATION AND VAPOR
RETARDER
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Roof Deck
Materials (Plywood, OSB, Steel, Concrete)
Performance requirements
Support Roof Loading
Resist Uplift
Sloped for Drainage
Expansion & Contraction - Roof & Structure
Smooth, Clean Surface
Dry Prior to Membrane Placement
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Thermal Insulation
Resist Heat Transfer
Location / Placement
Below the Deck
Between the Deck & Membrane Above the Membrane
Rigid Insulation Attachment (adhered or mechanicallyattached)
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Rigid roof insulation being placed over metal decking
(mechanically fastened to decking)
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Vapor Retarder
Purpose - Prevent transmission of Water Vapor
Location / Placement
Generally Below the Insulation
Material - hot mopped felts most common
Insulation Ventilation
Roof Vent
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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 insidethe 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
7.9 THERMAL INSULATION & VAPOR RETARDER(Contd)
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Low-slope roof membrane:Membranes, used for low-slope roof, fall intothree 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 chloridesheet, 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
7.9 THERMAL INSULATION AND VAPOR RETARDER(Contd)
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Roof Membranes
Three Categories
Built-up Roof (BUR) Membrane
Single-Ply Roof MembraneFluid Applied Roof Membrane
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Built-up Roof Membrane
Multiple plies of asphalt-impregnated felt
bedded in bitumen
Application:
Felts laid in Hot Asphalt (or coal tar)
Overlapping Layers
Forms a laminated membrane
typically 2-4 plies thick
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Single-Ply Roof Membrane
Sheet materials that are applied to the roof in
a single layer
Attached to the Roof:
Adhesives
Ballast Weight
Concealed fasteners
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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
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7. 10 ROOFING
Edge and drainage details:For low-slope roofs
Structural panel metal roofing:for low-slope roofs
Steep roofs -Shingles:Wood, asphalt, slate, clay tiles - Sheet metalroofing:lead-coated copper sheet, terne-coated stainless steel
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Edge Flashing
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Building/Roof Expansion Joint
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Roof Drain
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Steep Roofs
Roofs with a pitch of 3:12 (25%) or greater
Three General Categories
Thatch
Shingles
Architectural sheet metal
Insulation & vapor retarder
Typically installed below the roof decking
Deckingtypically plywood or OSB
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Shingles
applied to the roof in small units and inoverlapping layers with staggered vertical
joints
MaterialsWood (shingles & shakes)
Asphalt
Slates
Clay Tiles
Concrete Tiles
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Cedar Shakes (split rather than sawn)
Natural decay resistant wood
Moderately expensive
Fire Resistance low unless treated
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Asphalt Shingles
Die-cut from sheets of asphalt-impregnatedfelt faced with mineral granules
Typical size12x36
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Slate Roofing & Copper Flashing
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Clay Tiles
Architectural Sheet Metal Roofing
Materials typically thin sheets of aluminum or galvanized steel
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Materialstypically thin sheets of aluminum or galvanized steel
Coatingstypically a polymeric available in various colors
Seamsraised interlocking edge seams
Fastenersconcealed or exposed fasteners with rubber washers
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