Managing Moisture in Taller WoodBuildings -...

Calgary Mid-rise Workshop 2016-02-04

Managing Moisture in Taller Wood Buildings

Building Enclosure Design Fundamentals

7 Separates indoors from outdoors, by controlling:

7 Water penetration

7 Condensation

7 Air flow

7 Vapor diffusion (wetting &drying)

7 Heat flow

7 Light and solarradiation

7 Noise, fire, and smoke

7 While at the same time:

7 Transferring structural loads

7 Being durable andmaintainable

7 Being economical & constructible

7 Looking good!

G.Finch - RDH - [email protected] 1

mailto:[email protected]


Building Enclosure Control Functions & Critical Barriers

Water Control – 5&6 Storey Wood-frame

7 Increased height = increased rain deposition at upper floors and cumulative run-down at lower levels

7 Water shedding features become more critical – continuity, drip edges, flashings etc.

7 Increased exposure to moisture during construction (severity & length of time)

7 Need for more robust water penetration control strategy–good practice: drained & ventilated rainscreen




Keep Wood Dry During Construction

7 Keep wood drying during construction

7 Have seen issues in west where wood assemblies have got too wet during construction and resulted in delays & significant costs to dry out

7 Hence guidance for protection during construction, temporary roofs, immediate roofing, windows, wall/roof water resistive barrier (WRB) pre-application, built-in assembly design & redundancy for drying

Protect Wood from Water – But Not tooLate

7 Ensure adequate rainwater protection for heavy mass timber elements such as CLT, nail-lam, LVL/LSL/PSL, glulams etc. and multi layer plywood assemblies – especially for horizontal surfaces

7 Either choose pre-application of waterproof elements or invest in good site protection




Construction Practices for Mid-rise Wood Frame

7 Many contractors in west will either intentionally (or unintentionally) invest in site protection so that roofing/waterproofing can be applied in inclement weather onto dry materials

7 Typically observe that walls are seldom covered with a WRB until top floor framing is complete

7 However window sills & rough openings generally covered right away – allow for immediate window install & site close-in as fast as possible

Site Protection & Sequencing




Site Protection & Sequencing – Far North

Managing Exposure - Wall Assemblies

7 Drained & ventilated rainscreen clad walls have been standard on essentially all mid-rise wood-frame buildings in Pacific Northwest for more than the past decade

7 A minimum code requirement for most western jurisdictions and good practice in all climates for this height & exposure of building

7 Details for drainage & ventilation equally as important!




Why Rainscreen for Mid-rise Wood?

7 Significantly improves wall assembly & cladding durability – reduces risk

7 Rainscreen cavity also allows for wood-frame construction tolerances to be concealed behind cladding

7 A 3/4” cavity created by vertical strapping/furring most common in mid-rise wood-frame – is above code minimum 3/8” (10 mm)

7 Strapping also helps keep WRB/AB membrane in place during construction

Rainscreen Claddings




Exterior Insulated Rainscreen Claddings

Water Resistive Barriers in Mid-rise Wood-frame

7 Water Resistive Barrier, WRB (aka sheathing membrane)

7 Secondary plane of moisture protection & innermost plane that can safely manage moisture and drain & dry it back out

7 Many different products available (mechanically fastened, self-adhered, & liquid applied)

7 Many products can also be taped/sealed/applied as air barrier – discussed later

7 Both vapour permeable & impermeable products available– choice depends on insulation placement & wall design




Care with Impermeable Materials and Wet Wood

7 Need to be careful with the use of vapor impermeable materials over wood that is wet or could get wet in service

7 Self adhered membranes

7 Metal flashings

7 Foam plastic insulations*

7 Vapor diffusion wetting & drying ability for assemblies & details should always be assessed – ensure balance

Vapor Retarders / Barriers

7 Vapor Retarders / Barriers control the diffusion of vapor through an assembly

7 Limit wetting (condensation)

7 At same time there is a desired to promote drying

7 Gets more complicated with exterior/split insulated assemblies & selection of AB/WRB materials and exterior insulation types




Vapour Control with Wood-frame Exterior Walls

7 Interior vapour barrier

7 Polyethylene, polyamide “Smart Vapour Retarder” or Vapour Retarder paint most common for standard wood-framed walls

› Canada – Poly most common

› US – Vapour Retarder paint or Smart Vapour Retarder more common

7 Vapour control strategies are reassessed in walls with exterior or split insulation

7 Interior vapour barriers do not need to be the primary airbarrier

Other Vapour Retarder / Barrier Materials

7 Concrete, glass, metal, plastics

7 Polyethylene sheet

7 Impermeable peel & stick

7 Vapour barrier paint, smart vapour retarder

7 Wallpaper

7 XPS, EPS & Polyiso

7 Closed-cell sprayfoam

7 Plywood/OSB (at low RH levels)




400

1200

1600

2000

Perm

eance

(ng/P

asm2

)

800

11.1 m m O S B

12.7 m m Plywo o d

~0.5 to 2 perms

Plywood~20 perms

OSB~6 perms

00 % 2 0 % 4 0 % 6 0 % 8 0 % 1 0 0 %

Relat ive Humidity

See ASHRAE Handbook of Fundamentals & Other Sources for Vapor Permeance with RH

Plywood and OSB - Impact of RH on Vapor Permeance

One Not So Great Practice Developed in BC

DO NOT DO THIS




Air Barrier Systems, Materials & New Trends

Air Barriers for Mid-rise Wood Buildings

7 Air Barrier Systems must:

7 Be Continuous

7 Be Durable

7 Resist Structural Loads –Sufficient Stiffness & Strength for Design Wind Load

7 Be Airtight

7 Not negatively affect durability or vapor diffusion drying ability

7 Air barrier materials and approaches suitable for low-rise buildings may not be appropriate for mid-rise(5&6 storey) wood-frame




Many Wood-frame Air Barrier System Options

7 Choice depends on a variety of factors including wall design & builder familiarity with system

7 Common Air Barrier Systems

7 Sealed Polyethylene (mastic & tapes)

7 Airtight Drywall (drywall/gaskets/sealant)

7 Sheathing Membrane (mechanically attached, taped &sealed)

7 Sheathing Membrane (self adhered or liquid applied)

7 Sealed Sheathing Board (sealants/tapes at joints)

7 Spray Polyurethane Foam & sealants

Air Barriers Are Systems

AccessoriesMaterials Components

Whole Building

Airtightness




Wood-frame Mid-rise Air Barrier Trends

7 Trend towards exterior air barrier approaches (at sheathing plane) utilizing rigidity & simplicity of exterior sheathing

7 Sealed sheathing membrane approach(vapour permeable AB/WRB)

7 Mechanically attached (taped & sealed), $

7 Self-adhered membrane, $$$

7 Liquid/fluid applied,$$$

7 Sealed sheathing approach(plywood/OSB/ext. gypsum AB) w/ loose WRB

7 Sealed sheathing joints (sealant or tapes), $$

7 Use of interior approaches not as common or as effective for mid-rise buildings

7 Sealed poly not appropriate for this height

7 Airtight drywall not widely used

Shift to the Exterior Air Barrier

7 Industry shift in midrise wood buildings from the use of interior airbarrier approaches (poly, drywall) to exterior sheathing approachesas the primary air barrier element

7 BUT! still need to maintain a reasonable degree of airtightness at interior side of cavity insulation (convection suppressor)

7 Vapor barrier/retarder at interior side depending on insulation ratio& type

With enough exterior insulation – risk for condensation at sheathing decreases as does need for interior air tightness

Primary Air Barrier System

Secondary Airtight element




Airtightness Does Not Happen By Accident

Building Enclosure Assembly Detailing

(WSS)(WRB)

(AB)(VR/VB)

(Insulating Materials)




Wood-frame Mid-rise Air Barrier System Trends

7 Trend towards exterior air barrier approaches (at sheathing plane) relying on rigidity of wood/gypsum sheathing

7 Sealed sheathing membrane approach

7 Mechanically Attached (Taped & Sealed), $

7 Self-adhered Membranes, $$$

7 Liquid/Fluid Applied, $$$

7 Sealed sheathing approach(plywood/OSB/gypsum)

7 Sealed joints (good sealant or tapes), $$

7 Use of interior approaches not as common for mid-rise

7 Sealed poly not appropriate for height

7 Airtight drywall not widely used

Mechanically Attached Air Barrier Membranes

7 Loose sheet mechanically attached to wall with cap staples/nails and sealed with tapes, self-adheredmembrane and sealants




Challenges with Mechanically Attached Air Barriers & Wind During Construction

Rigid Support for Mechanically Attached Air Barriers During Construction & In-Service




Exterior Insulation Sandwich Support for Mechanically Attached Air Barriers

Mechanical Attached Air Barriers & Masonry




Interfaces & Challenges - Penetrations

Interfaces & Challenges – Balconies & Roofs




Mechanically Attached Air Barrier Details

7 Pre-stripping AB membrane is often recommended at framing interfaces & roof-wall transitions – but usually forgotten!

Interfaces & Challenges – Parapet Solutions




Interfaces & Challenges – Parapet Solutions

Sealed Sheathing Approach Air Barrier

7 Joints in sheathing (Plywood, OSB, Gypsum) aresealed with good sealant (usually silicone), strips of self-adhered membrane, or high-quality tapes




Sealed Interior Sheathing (Pre-fab Wall)

Sealed Sheathing Approach – Water Protection

7 Mechanically attached Water Resistive Barrier (WRB) loosely installed over top of sheathing, but not taped and detailed as the air barrier




Case Study: Portland, Orchards Passive MURB

Orchards at Orenco, Walsh Construction

Self-Adhered Air Barrier Membranes

7 Self-adhered membranes (typically vapour permeable) applied to exterior wood sheathing along with tapes/self-adhered membranes at interfaces






Provides benefits of full sided wrapping for ease of detailing, addressing soffit/sloped details and shipping




Liquid/Fluid Applied Air Barrier Membranes

7 Liquid/Fluid applied membranes (roller, brush or spray)applied to sheathing with sealants/tapes or reinforcingat all joints, gaps, and fasteners

Applying Liquid Applied Air Barrier Membranes




Joints in Liquid Applied Air Barrier Membranes

“band-aid” joints and butt joints Reinforced tapes, meshes& membranes

Joints in Liquid Applied Membranes




Hybrid Approaches

7 Liquid applied membrane window rough openings becoming common approach with various air barrier approaches – cost effective & simpler than SAM origami

Air Barrier Challenges & Material Compatibilities

SBPOhouse wrap

“special silicone”

Below grade Granulated SBS membrane

Concrete Foundation wall

Foil faced SAM

Silicone membrane over plywood

Silicone sealant at joints and fastenerholes

Foil-faced SBS

Below grade SBS over Concrete Foundation

Cement board over XPS




New AB/WRB Materials in a Growing Market

7 Many new self-adhered and liquid applied vapour permeable sheathing membranes available on the market

7 Fills a niche of a combined vapour permeable air-barrier/ WRB on exterior ofwood sheathing in mid-rise wood-frame buildings

7 Current test standardsslowly adapting to thisclass of materials

Lessons Learned So Far with New Membranes

7 Not all products are created equal nor suitable for all substrates/applications

7 Key considerations & potential issues include:

7 Longevity, durability, exposure to UV & heat

7 Compatibility & adhesion with other materials

7 Flexibility and gap/crack bridging ability

7 Curing or adhering in cold weather – big issue in Canada

7 Important properties negatively changing with time




Wet Weather Challenges?

Compatibility Challenges?




Long-Term Durability Challenges?

Cold Weather Application Challenges?




Wood-frame Crack Bridging Challenges?

Vapor permeable self-adhered sheets

Liquids

Liquids

How Well is the Industry Doing – WA State?




How Well Is the Industry Doing – WAState?

0.10

0.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

1.00

4.50

4.00

3.50

3.00

2.50

2.00

1.50

1.00

0.50

0.00

5.00

Liquid Applied Sealed Sheathing (10 Buildings) (11 Buildings)

Sheet Applied (28 Buildings)

Curtain Wall/Window

Wall/Storefront (15 Buildings)

Airt

ight

ness

[cfm

/ft²

@75

Pa]

Airt

ight

ness

[L/(

s·m

²) @

75Pa

]

Leakiest tested

Tightest tested

Median & 1st/3rd

quartilerange

WA StateRequirement

54 Buildings, Oct 2015 RDH SEAData

Passive House Range equivalent ~ 0.6ACH50

Passive House Airtightness

<0.6 ACH @50 Pa~0.035 cfm/ft2 @75 Pa

Self-adhered sheet membrane primary AB, transition to poly at ceiling




Passive House Airtightness

0.13 ACH @50 Pa~0.014 cfm/ft2 @75 PaSealed sheathing primary AB transition to SA membrane at roof

Maintenance & Renewals Considerations




Maintenance and Renewals

7 Recognize how the in-service stage of a building’s life can impact maintenance and renewals

7 Architectural design of building is impacted

7 Accessibility and durability

7 Above 4 storeys – can no longer use a ladder!

7 Need to provide fall arrest anchors for Bosun chair, swingstages

7 Boom lifts – movement around the building and structural support provided by garage roof slab

Maintenance and Renewals

7 Dryer vent cleaning

7 Easily accessible from balconies or roof?

7 Additional lint clean-out

7 Condensing units?

7 Durable enclosure components

7 Minimal maintenance claddings & finishes

7 Durable Sealants

7 Corrosion resistant metals

7 Higher quality windows




Summary

7 Environmental Loads

7 Increase in height = higher wind and rain loads

› More robust air barrier systems

› Improved water penetration control strategy – appropriate assembly, materials and details - rainscreen

› Longer construction duration means more focus on drying and protection from moisture during construction

7 Claddings & Materials

7 Non-combustible claddings & in many cases non-combustible insulation

7 Thermal Performance & Energy Efficiency

7 More structure – less room for insulation, other services

Summary

7 Wood-frame Shrinkage

7 Higher shrinkage in 5&6 storey wood-frame – manage with:› Limit amount of cross grain wood, modified platform framing &

engineered floor joists/headers

› Use dry wood (and keep it dry)

› Horizontal compartmentalization and joints in cladding design

7 Details are critical, plan for appropriate slopes after shrinkage

7 Maintenance & Renewals

7 Access for maintenance is a significant issue – need to design for it & provide suspended access anchors

7 Consider reduction in extent and frequency of maintenance required through choice of components and materials




Additional Resources

7 Building Enclosure Design Guide –Wood-frame Multi-Unit ResidentialBuildings (HPO, 2011)

7 Currently being updated with latest information & new details, release late 2015

7 Guide for Designing Energy Efficient Building Enclosures (HPO, CWC, FP Innovations, 2013)

7 Illustrated Guide R-22 Effective Walls in Wood-frame Construction in BC (HPO, COV, 2015)

Discussion

GRAHAM FINCH – [email protected] - 604.873.1181

7 rdh.com




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