DESIGN CONSIDERATIONS FOR THE BUILDING ENVELOPE
COURSE DESCRIPTION
The presentation focuses on how the modern building envelope should perform and understand some of the different control layers that go into it. Additionally, the performance considertations when designing and choosing products for your building on looks and designs.
LEARNING OBJECTIVES
1. The Evolution of the Building Envelope
2. Building Envelope Control Layers
3. Design Considerations
4. Compatibility
THE EVOLUTION OF THE MODERN BUILDING ENVELOPE
EXPECTATIONS OF THE BUILDING ENVELOPE
- Keep the water out
- Maintain a comfortable interior environment
- Be energy efficient
- Maintain a low maintenance / operating cost
- Use durable materials that last forever
- Have minimal impact on the environment
Studies have shown that failure to observe basic design functions of the Building Envelope leads to high energy costs and premature deterioration of building materials.
Low capital costs translates to high operating costs
BUILDING ENVELOPE CONTROL LAYERS
Water control layer (water penetration)
- Water is governed by momentum, gravity and capillary forces
- Impervious to water, continuous, flexible and sealed
- Provisions for drainage to the exterior
Air control layer (infiltration/exfiltration)
- Air movement is caused by wind loads, fan pressure and stack effect
- Must be continuous, flexible, strong and sealed
Vapor control layer
- Vapor diffusion is caused by vapor pressure differences i/s to o/s
- Must not trap moisture
Thermal control layer (heat flow)
- Continuous insulation layer in conjunction with ACL and VCL reduces energy consumption
DESIGN CONSIDERATIONS- WALLS
Moisture or water vapor moves into building cavities in two ways:
- Diffusion
- Channel
- The type of barrier and location on the wall assembly depends on the climate (cold, hot-humid, mix) and building use (residential, office, educational, hospitals, museums).
- In relatively mild or balanced climates a barrier may not be necessary or a vapor retarder could be enough.
Any material that resists diffusion. Materials have a moisture vapor transmission rate that is established by a standard method (ASTM E96) and is usually reported in US perm ≈ 57 SI perm = 57 ng/s.m2.Pa.
J. Lstiburek, Building Science Corp. “Moisture Control Handbook”, 1993
Air Barriers: Why are they so important
The volume of moisture by diffusion is considerably lower than the movement of moisture that infiltrates the building enclosure through gaps, cracks and joints.
Air Barriers:
- Air barriers are systems of materials designed and constructed to control airflow between a conditioned space and an unconditioned space.
- Air Barrier Material: Designed and constructed to provide an air permeance rate no greater than 0.004 cfm/ft2 @ 1.57 lb/ft2 in accordance with ASTM E 2178.
- Air Barrier System: Designed and constructed to provide an air permeance rate no greater than 0.04 cfm/ft2 @ 1.57 lb/ft2 in accordance with ASTM E 2357.
DESIGN CONSIDERATIONS- WINDOWS & JOINTS
KEY FUNCTIONS- SEALANTS
- Stop Water Intrusion
- Stop Air Movement
- Join dissimilar materials
- Sealant joints accommodate differential movement caused by thermal gain or structural design
KEY FEATURES- SEALANTS
Select sealants designed for the application:
- Anticipated movement
- Substrate
- UV resistance
- Paintable
- Color Retention
A disproportionate number of Building Renovations are due to premature failure of the weatherproofing sealant. Here are ways that sealants fail and how to prevent:
- The wrong sealant may be the weakest link in the façade system.
- Failures include splitting / cracking (cohesive failure), UV degradation, adhesion failure at the bond line.
- Specifying the correct sealant increases the bldgs’ life cycle costs, and reduces maintenance costs.
- The joint design
- The application
- The properties of joint sealant selected
DESIGN CONSIDERATIONS- BALCONIES, PLAZA DECKS & PARKING GARAGES
WHY PROVIDE CONTROL LAYER PROTECTION
- Stop Water Intrusion
- Prevent chloride/salts ingress
- Eliminate carbonation intrusion
- Absorb Thermal Shock
- Extend life of the structure
- Address cracks in the concrete
- Aesthetics
WHY CONCRETE FAILS
- Poor Drainage & Cracks
- Water Intrusion
- Marine Environments
- Chlorides
- Permanent exposure to weather
- Rainfall
- Thermal Shock
- Surface defects, cracks & bugholes are ‘weak links’ in painted coatings that provide access for water, carbon dioxide chloride ions.
2-Component Epoxy Based
- Tough Durable Flexible Membrane
- Fast turn around time
- Superior resistance to abrasion & wear
- Prevents moisture & chloride intrusion
2-Component Cement Based
- Polymer-modified Base Coat
- Embedding Mesh; utilized for crack & joint treatment
- Acrylic Top Coat
- Superior resistance to abrasion & wear
- Prevents moisture & chloride intrusion
1-Component Polyurethane Elastomeric Waterproofing
- Dynamic crack bridging properties
- Excellent resistance to abrasion & wear
- Impervious to water & deicing salts
2-Component Polyurethane Elastomeric Waterproofing
- Fast cure, low odor, solvent free
- Fast turn around
- Dynamic crack bridging properties
- Excellent resistance to abrasion & wear
- Impervious to water & deicing salts
- Renewable and Sustainable
2-Component Low Mod Epoxy Broadcast Waterproofing
- Fast curing Solvent free
- Excellent resistance to abrasion & wear
- Crack bridging properties
- Impervious to water & deicing saltsIdeal for ramps and high traffic areas
DESIGN CONSIDERATIONS- BELOW GRADE WATERPROOFING
TYPICAL WATERPROOFING APPLICATIONS
- Pedestrian and Vehicular Tunnels
- Environmental below grade structures
- Below grade parking structures
- Basements
- Mechanical equipment
- Buildings on marginal sites
- Storage Tanks
- Any below grade archival space, i.e. museums, libraries, etc.
- Waterproofing can be continuously wet
- Potential hydraulic head pressure
- Systems are generally inaccessible (bad place to cut cost)
- Warranties should be scrutinized for value they provide
- Various materials are available requiring varying expertise
- Details and sequences can differ
- Drainage is handled differently
- Consequences of improper installation are much greater
- Soil and ground water contamination need to be considered
According to the Sealant, Waterproofing and Restoration Institute (SWRI) these are the main waterproofing categories:
- Hot Applied Liquid
- Cold Applied Liquid
- Sheet Applied
- Bentonite
- Bituminous Membrane
- Cementitious
- Integral
- Asphalt
COMPATIBILITY
WHY IS IT IMPORTANT?
- Ask consultants what their biggest challenge is and often they will say compatibility
- Facilitates design consultants job
- One company stands behind the products and the transition points
- Details and specifications are based upon the compatibility results
- Avoid incompatibilities
COMPATIBILITY TESTING- WHAT SHOULD BE DONE?
Rigorous program to test compatibility of products
Test transitions points:
- Roof to wall air barrier
- Air barrier to window flashing
- Air barrier to sealant
- Air barrier to through-wall flashing
- Air barrier to balcony waterproofing
Testing at room temperature for 21 days:
- Test at 100F
- Test at freezing
- Water soak