Design For Durability

The Green Roundtable

Design for DurabilityPaul Marquis – 4-24-08

paul@greenroundtable.org

Green Roundtable

Consulting, education, trainingand strategic planning

to create healthy environments byintegrating principles of

sustainability into mainstreamplanning, design and construction.

Objectives

- What are the key design principles in creatingdurable structures

- What are some specific strategies we can employ?

- What are the economics of creating durablestructures?

- How does durable design integrate with other designstrategies

Answer the following questions:

- Why are durable structures greener?

Why build green?

• Reduces the ecological footprint of the building

• Creates a safer and healthier indoor environment

• May improve property resale value

• Saves on utility expenses

• May increase affordability

• Typically results in a more durable,maintenance-free structure

• Reduces our dependence on foreign oil

Building green:

• Provides security/ passive survivability

• Economics- Reducing energy cost/ protecting thebottom line

• Health- Maintaining a safe and healthy environmentfor one’s family & oneself

• Personal impact- Addressing the greater good-minimizing environmental footprint

The three prime movers (in order):

Defining green building:

The effective and responsible integrationof the built environment into the naturalworld to protect natural resources andensure healthy and comfortable indoor

environments

What makes it green?

• Low embodied energy (entire lifecycle)

• Minimizes impact on wildlife habitat, green space,waterways, etc

• Minimizes depletion of natural resources

• Poses minimal harm to humans during itsmanufacture, transport, installation, end-use ordisposal

Underlying all:

ScaleScaleScale

The average size of a U.S. single-familyhouse has increased by 33% since 1975. At

the same time average family size hasdecreased.

Consider this:

The quantity of energy required to manufacture, andsupply to the point of use including:

• Extraction• Transportation• Manufacturing

• Assembly• Installation• Some definitions also include:

Disassembly & Removal

What is embodied energy?

Water Efficiency

Sustainable Sites

Energy & Atmosphere

Materials & Resources

Indoor Environmental Quality

Innovation & Design Process

The LEED Credit Categories

Cornerstones of green building (structure itself)

Site Site

How green is it?

• The “no-build” option is always the greenest way

• Smaller is greener

• More efficient material resources use is better

• The more durable (in use) & maintenance free thebetter

• Incorporate energy efficient design details

• Create a high-performance building envelope

• Employ water conservation strategies

• Employ natural daylighting techniques

• Use energy-efficient lighting, equipment & appliances

General strategies:

• Create comfortable & healthy indoor environments

• Minimize impact on building sites/ area

Keys to success

• Careful design

• Using a team approach between owners,design professionals and code officials, andbringing everybody together early in theprocess

• Early planning

• Using a systems approach- viewing thestructure and all elements as integrated system

Economic realities

Up front costs or first-costs of green buildingare often greater than conventional building

That doesn’t need to be the case!

Justifying increased up-front costs

Making the case for reduced Life-Cycle Cost or TotalCost of Ownership (TCO):

• Green buildings usually use less energy to operatethan their conventional counterparts

• Green buildings are typically more durable &maintenance-free due to the application of soundprinciples of building science

• There are typically additional benefits that help towarrant the increased cost

Take advantage of marginal cost of installing higherquality materials- e.g. adding more durable

materials/ systems

Managing costs- Labor vs. materials

Consequences of ignoring durability

• Reduced indoor environmental quality

• Reduced resale value

• Aesthetic issues

• Early failure of systems

• Increased cost of ownership

• More intensive maintenance routines

Why is durable design greener?

• Fewer replacement cycles

• Simplified maintenance routines

• Healthier indoor environments

Design for Durability- Key principles

• Create a weather-resistant shell

• Choose durable materials

• Simplify maintenance

• Respect site & local climate

• Manage interior moisture

• Direct water away from the structure

Design for Durability- strategies

• Employ double-shell or rain-screen designs

• Avoid complicated designs w/ many intersecting planes

• Reduce envelope penetrations, esp. in roof

• Use good flashing details

• Use adequate roof overhangs

• Avoid siting structures at bottom of hills, in low-lying orflood-prone areas, or generally, areas w/ poor drainagecharacteristics

• Design for local wind & seismic conditions

Design for Durability- strategies, cont.

• Reduce air movement through envelope

• Direct water away from foundation/ structure

• Familiarize occupants w/ proper maintenance routines

• Effectively design/ manage site vegetation

• Provide adequate ventilation

Climate/ topo maps

• http://www.nrel.gov/gis/maps.html- Solar, Windresources

•Topographical maps:http://store.usgs.gov/scripts/wgate/ZWW20/!?~language=en&~theme=GP&OSTORE=USGSGP&~OKCODE=START

• Asst maps: http://maps.massgis.state.ma.us/massgis_viewer/index.htm

Durability: Low-hanging fruit

• Minimize roof penetrations

• Maintain proper grading & ground clearances

• Incorporate overhanging roofs

• Keep vegetation away from structure

• Use well-designed wall sections

What kills “stuff”

• Moisture and associated problems (e.g. mold, rot)

• Sunlight (UV)

• Temperature extremes

• Friction

• Mechanical damage

• Exceeding something’s mechanical capacity

• Critters

The prime suspect:

Ways that water moves into a building

• Capillary (wicking) action & surface tension

• Gravity

• Air movement (wind driven moisture)

• Condensing water vapor

• Hydrostatic pressure

Preventing water from entering a building

• Appropriately lap building materials; start at bottom!

• Adequately direct water away from structure(s) infirst place

• Provide capillary breaks like drip channels & air gaps

• “Be the drop of water”

• Adequately seal gaps & penetrations

Roof/ site drainage

• Reduces water infiltration

• Reduces conditions favorable to structural pests

• Reduces frost heaves against foundation

Good drainage

Roof/ site drainage

• Install gutter screens/ hoods

• Provide adequate clearance (6-8” min) betweensiding and grade

• Make sure your downspouts discharge a minimum of4 feet from the foundation (5 – 6 ft ideally)

• Don’t run downspouts (& basement window wells)into foundation drain system!

• Discharge foundation drain pipes ‘to daylight’ wherepossible

Creating a weather-resistant shell

• Minimize roof penetrations

• Minimize intersecting planes

• Provide adequate overhangs

• Choose ‘effective’ roof style

• Understand that outermost roof & wall finishes aretypically only first line of defense

• Provide good drainage planes/ ventilation cavities

• Use good flashing details

An important note about process:

Make shell weather tightASAP!

Design for Durability- Roof structures

• Hip roofs generally better than simple gable roofs

Design for durability – Roof plane integrity

• Minimal roof penetrations- use side venting, runalong sides of house, etc.

• Use AAVs (air admittance valves) instead of stackvents (where permitted by code)

• Use TDDs instead of skylights

• Use direct-venting high-efficiency heating/ hot water

Skylights also more likely to contribute to summeroverheating and winter heat loss.

Sky tube (TDD)

Design for durability – Overhangs

Effective overhangs:

• Protect the walls from precipitation

• Protect wall finishes from UV

• Help to direct water away from the structure

• May facilitate attic ventilation

• May help to minimize ice dams

• Provide summer shade to reduce unwanted solar gains

Design for durability – Effective flashing details

• Provide flashing wherever two or more buildingplanes meet, at margins of roof and around openingsin shell

• Common flashing materials: Aluminum, zinc, copper,galvanized steel, bituminous tape

• Install water/ ice shields at roof margins (better touse on entire roof??)

• Install ‘crickets’ or saddles behind chimneys & otherlarge roof structures

• Use step-flashing where appropriate

• Caulking should not be used as flashing substitute!

Rain-screen wall

Design for durability - Materials

• Use materials and products appropriate to task- e.g.pressure-treated lumber, corrosion-resistant fasteners,UV-resistant finishes, etc.

• Always use products in manner intended- e.g. propertemperature range, humidity; don’t overload, etc.

Characteristics of durable exterior finishes

• Moisture resistant

• UV resistant

• Fire resistant

• Decay resistant

• Wind & impact resistant

• Minimal maintenance requirements

• Easy to replace

Some durable siding options

• Fiber cement-HardiPlank-Certainteed WeatherBoard

• Masonry

• Vertical-grain bevel siding

• Eastern white cedar not bad if back-primed

• Stucco

Some durable roofing options

• Clay tile

• Metal

• Faux slate, shakes, etc made from recycled plasticsor rubber

• Slate

• Fiber-cement

• Also, cedar shakes if from sustainable wood source& installed properly

Some roofing examples

• Ecostar- www.ecostarinc.com

• Interlock- www.interlockroofing.com

• Authentic Roof- www.authentic-roof.com

• Naturals- www.naturalsroofing.com

• Note: Some of these given high marks based ondurability more so than recycled content

• Natural slate a fairly sustainable option

Some decking options

• Composite

• Vertical-grain lumber; douglas fir, hemlock, etc.; lookfor FSC ceretified

• Ipe, if from sustainable source

• Pressure treated if maintained properly

• Cedar & redwood not typically sustainable (usuallyfrom old-growth forests)

• Torrefied lumber (see www.purewood.net)

• Always seal or back prime backside of wood siding,trim, etc. (DON’T back prime fiber-cement siding)

• Seal end grain of all exterior wood, even if pressuretreated (w/ boiled linseed oil or paint)

Design for durability – Exterior finishing details

• Use water-shedding design details, such as slopes,bevels, overlaps, etc.

• Maintain adequate ventilation in and aroundexterior trim where appropriate

• Use drip-channels, drip edges & capillary breaks whereappropriate

• Glue shingle tabs at roof edges

Painting/ caulking tips

• Proper prep is critical- clean, sand, remove loosematerial as necessary

• Clean surfaces thoroughly; remove mildew; canpressure wash, but be judicious!

• Never paint if temperature is below 45 deg orabove 85 deg, or there is excess humidity

• Follow manufacturers recommendations forcoverage; latex paints are often applied too thinly

• Use proper brush- generally synthetics for latex,natural bristle for oil paint

• Prime all raw wood before painting or caulking

• Use ‘backer-rod’ where appropriate

Design for durability - Vegetation

• Keep plantings immediately adjacent to the foundationto a minimum; maintain adequate clearance (18 – 24” &allow for additional growth)

• Keep overhanging vegetation to a minimum

• Vegetation like vines attached to trellis-work ratherthan being allowed to grow on structure

Design for durability- Foundations/ Basements

• Favor monolithic construction

• Avoid basements altogether! Favor pier foundations,FPSFs, etc.

• Insulate & waterproof

• Provide adequate foundation drainage

• Ventilating basements & crawl spaces in summermay be a bad idea!

• Never install carpeting or wood floor finishes directlyon top of concrete floors

This usually better…

…than this.

Detail basement insulation correctly

Frost-protected Shallow Foundations

• Improves thermal performance

• Reduce excavating expense

• Reduce site impact

• Reduce material expense

• Implied approval in code: MA CMR 5403.1.4.1

Note: Local code officials may be resistant to approving

• Use engineered joists to minimize deflection

• Use drywall clips to minimize corner cracking

Design for durability- Structural elements

• Engineered I-beam joists have pre-perforatedpunch-outs for plumbing/ mechanicals

• Use construction adhesive:- Increases strength- Minimizes squeaks- Provides additional air sealing

• Use hurricane ties & anchor straps

Laminated-veneer lumber (LVL) – stiffer & stronger

Rafter (“hurricane”) ties

Good Wall Sections/Building Envelope

Building envelope, definition

All of the elements of a building that separate andisolate the unconditioned outdoor environment from

the conditioned indoor environment. This may includewalls and wall finishes, roofs and roof finishes, doors,

windows, skylights and basement floors and walls.

Key Principle- Saving home energy

As a general rule, for the average home/homeowner, the greatest energy savings will beachieved through managing the demand side of

the equation, rather than the supply side.

In other words, you’ll get better bang for your buckthrough energy conservation measures, like insulating

& minimizing air infiltration, than incorporatingexpensive renewable energy systems such as wind

and solar.

Building envelope, functions

• Protect structural elements and interior of structurefrom weather, esp. moisture

• Help to maintain proper thermal regime withinstructure

• Help to maintain proper humidity regime withinstructure

• Prevent infiltration of outside air and contaminants

• Acoustically isolate interior of structure from outsidenoise

• In essence, act as ‘membrane’ for the structure

Building envelope failure

• External water leaks leading to:-Damaged structural elements-Damaged interior finishes-Insulation failure-Damaged interior furnishings and appliances-Mold problems

• Air leaks leading to:-Infiltration of unconditioned air/ Drafts-Direct escape of conditioned air to outside-Infiltration of outdoor contaminants

• Excessive accumulation of interior moisture in wallcavities causing structural/ insulation failure & mold

• Excessive heat transfer from inside to outside

Effective wall section design

Good wall sections:

• Reduce air infiltration

• Are breathable

• Provide drying to the outside, inside, or both

• Reduce passage of potentially moisture-ladeninterior air into wall cavities

• Reduce possibility of cavity temperature to dropbelow dew point temperature

• Provide good thermal (& acoustic) insulation

Building envelope components

• Exterior finish- wood siding, vinyl siding, brick, etc.

• Weather membrane/ air barrier/ drainage plane-building paper, Tyvek, Typar, etc.

• Exterior sheathing- usually plywood or OSB

• Wall/ ceiling cavities (inc. structural members &insulation)

• Vapor retarders/ barriers

• Interior wall finish

• Doors & windows

Codes and standards

• Sixth edition of MA building code was officiallysuperseded by 7th edition as of January 1st, 2008

• New MA energy code based on 2006 InternationalEnergy Conservation Code; more stringent

• Better to follow Energy Star Homes or HERSguidelines for maximum energy efficiency and codecompliance (see resources slide)

Housewrap tominimize airinfiltration &protect frommoisture

Minimizing air infiltration(sealing building envelope)

• Min .35 Air changes per hour (ACH) for goodventilation; max .50 for energy efficiency (EnergyStar)

• Openings to attic spaces are some of worst offenders

• Seal obvious openings- pipe penetrations, atticscuttles, electrical receptacles, recessed lights, etc.

• Any place where two building planes meet is goodcandidate for air sealing

• For additions/ new construction, use exterior airbarrier to minimize infiltration

Some important points about insulation

• Effectively used, can reduce condensation in wallcavities (e.g thick foamboard sheathing)

• Open-cell foam types (e.g. Icynene) are not aseffective at reducing infiltration, and are not asmoisture-resistant as closed-cell types

• Even open-cell types can help to reduce cavitycondensation by minimizing air leakage throughinterior wall finishes

• Moisture in wall cavities can permanently destroysome insulation’s effectiveness (e.g. fiberglass batts)

• Some insulating materials can provide air sealing

• Some closed-cell foams can marginally increasestructural integrity

Blower doortest tomeasure airleakage

Air leakage pathways

Air leakage proportion through various pathways

Attic hatches/ scuttles are a major leakage pathway

A commercial solution for attic openings

Design For Durability

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