EXTERIOR FINISHES TO WOOD

8/12/2019 EXTERIOR FINISHES TO WOOD

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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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EXTERIOR FINISHES TO WOOD