Passive House Northwest - 2013 Annual Conference

Walls and Windows for Highly Insulated Buildings in the Pacific Northwest

Graham Finch, MASc, P.EngRDH Building Sciences Inc., Seattle, WA

Presentation Outline

Design Objectives, Durability Considerations, and the Pros & Cons for Alternate Highly Insulated Wall Assemblies in the Wet Pacific NorthwestBasics of North American, European and Passivhaus Window Rating Standards and Window Selection Guidelines

Passive design strategies require airtight & highly insulated walls with minimal thermal bridging

For energy efficiency, hygiene (mold/condensation) and thermal comfort

Effective R-values in range of R-30 to R-60 (depending on climate)No surface temperatures less than 3oC (5.4oF) below room temperature – for radiant symmetry, comfort, and prevention of condensation or mold Growing desire to apply passive house wall assemblies & windows for houses to taller and more exposed buildings including MURBs – what are the considerations & risks?

Design Objectives – Passive House Wall Assemblies

Thermal insulation continuity – energy & passive design strategyAirflow control/airtightness – energy & passive design strategy, building code/durabilityVapor diffusion control – building code/durability Exterior moisture/rainwater control layers & details –building code/durabilityMore insulation = less heat flow to dry out moisture

Amount, type and placement of insulation mattersPotentially greater sensitivity to vapor diffusion, air leakage, rain water leaks, & built-in moistureGreater need for more robust assembly designs & details (rainscreen) and more durable materials

Fundamental Requirements

What about the Pacific Northwest

Climate Zones – Energy Code Classifications

Guides Minimum Insulation levels

Climate Zones – Rainfall Exposure

Guides Assembly Choices & Detailing

Continue to repair moisture damaged buildings in the Pacific Northwest

Not Passive Houses.. Lower Risk But Still Failed

Not Passive Houses.. Lower Risk But Still Failed

Definitely Not Passive Houses.. But Still Failed

Passive House Performance Level Glazing .. Failed

Systemic Failure of proprietary triple glazing units

Rainwater penetration causes most problems –poor details (e.g. lack of, poorly implemented, bad materials)Air leakage condensation also causes many problems Vapor diffusion alone contributes but doesn’t cause most problems – unless within a sensitive assemblyMany windows leak and sub-sill drainage and flashings are critical, other details and interfaces also importantInsulation inboard of structural elements decreases temperatures which increases risk for moisture damageDurability of building materials is very importantWatch over-use of impermeable materials in wet locationsDrained & ventilated rainscreen walls & details work wellUnproven materials/systems can be risky

What Have We Learned from Past Building Failures?

Insulation Placement & Wall Design Considerations

Interior Insulation

Exterior Insulation

Split Insulation

Getting to Higher R-values – Insulation Placement

Baseline2x6 w/ R-22 batts = R-16effective

Exterior Insulation – R-20 to R-40+ effective• Constraints: cladding attachment, wall thickness• Good for wood/steel/concrete

Deep/Double Stud–R-20 to R-40+ effective• Constraints wall

thickness• Good for wood,

wasted for steel

Split Insulation–R-20 to R-40+ effective• Constraints: cladding

attachment• Good for wood, palatable for

steel

New vs Retrofit Considerations

Insulation outboard of structure and control layers (air/vapor/water)Thermal mass at interior where usefulExcellent performance in all climate zonesCladding Attachment biggest source of thermal loss/bridgingNot the panacea, can still mess it up

Exterior Insulated Walls

Steel Stud Concrete Heavy Timber (CLT)

Key Considerations:Cladding AttachmentWall Thickness

Heat Control: Exterior Insulation

Air Control: Membrane on exterior of structure

Vapor Control: Membrane on exterior of structure

Water Control: Membrane on exterior of structure (possibly surface of insulation)

Exterior Insulation Assemblies

Many Possible Strategies – Wide Range of Performance

Cladding Attachment through Exterior Insulation

Minimizing Thermal Bridging through Exterior Insulation

Longer cladding Fasteners directly through rigid insulation (up to 2” for light claddings)

Long screws through vertical strapping and rigid insulation creates truss (8”+) – short cladding fasteners into vertical strapping Rigid shear block type connection

through insulation, cladding to vertical strapping

Key Considerations - Split Insulation Assemblies

Key Considerations:Exterior insulation typeCladding attachmentSequencing & detailing

Heat Control: Exterior and stud space Insulation

Air Control: House-wrap adhered/sheet/liquid membrane on sheathing, sealants/tapes etc. Often vapor permeable

Vapor Control: Poly or VB paint at interior, plywood/OSB sheathing

Water Control: Rainscreen cladding, WRB membrane, surface of insulation

Split Insulation Assemblies – Exterior Insulation

Foam insulations (XPS, EPS, Polyiso, ccSPF) are vapor impermeable

Is the vapor barrier on the wrong side?Does your wall have two vapor barriers?How much insulation should be put outside of the sheathing? – More the better, but room?

Rigid Mineral or Glass Fiber Insulation are vapor permeable and can address these concerns Vapor permeance properties of WRB and air-barrier also importantInsulation selection suitable for wet exposure – moisture tolerant, non absorptive, hydrophobic, draining

Several other alternate strategies to build highly insulated walls including Larsen Trusses and other exterior trussed assemblies filled with low-density fibrous fill or sprayfoam insulation

Split Insulation – Larsen Truss

Whole building energy model set a effective R-value design target for ofU-0.055 (R-18.2) for walls, with initial design discussions up to R-25Expectation to be cost effective, buildable and minimize wall thickness 6” steel stud frame wall structure (supported outboard of slab edge, and perimeter beams)Were tasked with the evaluation of a number of potential optionsLack of performance from standard practice and available products in 2010 helped develop a new product

Bullitt Center – Exterior Wall Assembly

Bullitt Center – Exterior Wall Assembly Evaluation

Baseline: R-19 batts within 2x6 steel stud with exposed slab edges = R-6.4 effective

Considered 2x8 and 2x10 studs - still less than R-8

Target >R18.2 effectivew/ potential up to R-25

Vertical Z-Girts (16” oc)5” (R-20) exterior insulation plus R-19 batts within 2x6 steel stud

= R-11.0 effective

Horiz. Z-Girts (24” oc)5” (R-20) exterior insulation plus R-19 batts within 2x6 steel stud

= R-14.1 effective

Crossing Z-girts also evaluated <R-16 effective

Intermittent Metal Clips5” (R-20) exterior insulation plus R-19 batts within 2x6 steel stud

= R-17.1 effective

up to R-21 with some modifications

The Need to Go Higher – Reduce the Thermal Bridging

The Need to Go Higher – Reduce the Thermal Bridging

Intermittent Fiberglass Spacers, 3½” to 6” (R-14 to R-24) exterior insulation

= R-19.1 to R-26.3 + effective

Metal panel1” horizontal metal hat tracks3 ½” semi-rigid mineral fiber (R-14.7) between 3 ½” fiberglass clipsFluid applied vapor permeable WRB/Air barrier on gypsum sheathing6” mineral fiber batts (R-19) between 6” steel studsGypsum drywall

Supported outboard slab edge (reduce thermal bridging)

Effective R-value R-26.6

Bullitt Center – Exterior Wall Assembly

Double 2x4/2x6 stud, Single Deep 2x10, 2x10, I-Joist etc…Common wood-frame wall assembly in many passive housesLends itself well to pre-fabricated wall/roof assembliesInterior service wall – greater control over interior airtightnessHigher risk for damage if sheathing gets wet (rainwater, air leakage, vapor diffusion)

Double/Deep Stud Insulated

Key Considerations – Double Stud/Deep Stud

Key Considerations:Air-sealingRainwater management/detailing

Heat Control: Double stud cavity fill insulation(s)

Air Control: House-wrap/membrane on sheathing, poly, airtight drywall on interior, OSB/plywood at interior, tapes, sealants, sprayfoam. Airtightness on both sides of cavity recommended

Vapor Control: Poly, VB paint or OSB/plywood at interior

Water Control: Rainscreen cladding, WRB at house-wrap/membrane, flashings etc.

Air Barrier Strategies – Double Stud/Deep Stud Wall

Influenced by Wall Assembly & Structural SupportType of Window, Rebate vs FlangeFramePlacement within Opening: In vs Out vs Middle

Big difference to ψ install

Thermal Performance/Condensation/Thermal Comfort

Window Placement within Highly Insulated Walls

Highly Insulated Wood-Frame Design Guide for Marine and Cold Climates (tall building/multi-family building focus)WUFI later

Further Guidance on Highly Insulated Walls & Details

Windows for Passive Design

Window Selection Guidelines for Passive DesignNorth American NFRC , European EN/ISO Window Rating StandardsClimate Specific Window Selection Guidelines

Recently completed a large industry research project to look at the validity of the Canadian ER Rating and to evaluate/rank windows in terms of U-values SHGC while also assessing thermal comfortDifferences between North American & European ( and Passive House) window rating systems being studied as part of a follow-up task – Today: What we have uncovered so far…

Understanding Window Rating Systems

High performance windows form integral part of strategy to achieve whole building energy target (ie 4.75 kBtu/sf/y)

Provide necessary solar heat gainsReduce heat loss to a point where window becomes a gain

High performance windows provide high interior surface temperatures for thermal comfort & prevent condensation or surface mold growthSelection of window properties is climate & building dependant – though general guidelines existWindows from Europe are rated differently than in North America – Passive house guidance from Germany uses European standards and climate recommendations

Window Selection for Passive Houses

North America – NFRC 100 (U-value) and NFRC 200 (SHGC/VT)

Computer simulation (THERM) using laboratory validated test for calibration/confirmation of modelNFRC 100& 200 are ISO 15099 compliant methods

Europe – ISO 10077-1 (Whole Window U-value), ISO 10077-2 (Frame U-value), EN-673 (Glazing U-value), EN-410 (Glazing g-value/SHGC)Passive House Institute Darmstadt (PHI-D) –references ISO 10077, EN 673, EN 410

Plus minimum surface temperature criteria

Window Rating Standards

Boundary conditions (temperatures & air film resistances)Standard size of window IGU airspace – NFRC vs CEN calculation methodologyEdge of glass vs spacer bar linear transmittanceSHGC (g-factor) for window or just glassFrame size, thin profile vs thick – ratio of glass to frameModeling vs physical laboratory testing

European U-value is not the same as North American U-value – careful in comparisons & in energy modelingPHI-D guidelines based on European methods not NFRC

Key Differences

European vs North American Passive House Window - Typical Differences

European (EU) Style Window North American (NA) Style Window

Operable Hardware Preference – EU (Inswing) vs NA (Outswing)

EU Frames tend to be deeper (avg. ~4.75”) than NA frames (avg. 2.75”)

EU glazing spacer buried within frame vs inline with NA frame sightline

SAME Argon & SAME low-e emissivity coatings

IGU gap, 1/2” optimum under NA NFRC vs 5/8” optimum under EU CEN/ISO

Why Different?

More standard EU 4mm vs NA 3mm glass panes

NFRC vs ISO Window Rating Procedures – U-valuesISO 10077 – European Style Window NFRC 100 – North American Style Window

Uframe x Aframe

Standard Window Size 1.23m wide x 1.48m high (48” x 58 ¼”)

Standard Window Size 1.2m wide x 1.5m high (47 ¼” x 59”)

Uglazing x Aglazing

ψspacer x L glazed perimeter

ψinstall x L window perimeter

Uframe x Aframe

Uglazing x Aglazing

Uedge glz x Aedge glz 2.5”

Uedge glz (NFRC) can be converted into a ψedge glz

EN/ISO relatively easily (but not vice versa)

NFRC vs ISO Window Rating Procedures – Solar Heat GainISO 10077 – European Style Window NFRC 100 – North American Style Window

g-value in Europe, SHGC in North America, essentially the same thing, but used differently

g-value provided for center of glass only (neglects frames) (eg. sometimes buried in wall)Convert to whole window by multiplying by glass/window ratio (becomes lower by 20-40%+)

SHGC provided for whole window (includes frame effect) Convert to just glazing by dividing by glass/window ratio (becomes higher by 15-25%+)

Many European glazing manufacturers also use low-iron glass to get the SHGC a few percent higher

Passive House SHGC/g-value guidelines are for center of glass, not including the frames, which reduces the overall SHGCAs NFRC includes this frame impact – a direct comparison in the SHGC of a Passive House to NFRC window cannot be made, however perception is that the glass has a higher SHGC . In PHPP software g-value only applied to glazed area, so calculation works out.Following demonstrates the approximate impact

Impact of Frame on Overall SHGC Recommendations

50%

60%

70%

80%

90%

100%

36" x 48" 48" x 60" 60" x 96"

Gla

ss t

o W

ind

ow

Are

a R

atio

Window Size

Glass to Total Window Area Ratio - Based on Frame Size

2.75" Frames(North AmericanAverage)

4.75" Frames(Passive HouseAverage)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

60% 65% 70% 75% 80% 85%

Wh

ole

Win

do

w S

HG

C

Glass to Window Area Ratio

Approximate Whole Window SHGC Correction of Glass SHGC Based on Glass to Window Ratio

0.4

0.5

0.6

0.7

0.8

Window Rating Standard

Exterior Temperature –

oC (oF)

Interior Temperature –

oC (oF)

Exterior Boundary

Condition –W/m2∙K

Interior Boundary

Condition –W/m2∙K

NFRC 100 & 200

-18 oC (0oF) 21 oC (70oF) 26.0 2.44 * convection

ISO 10077-1 and 10077-2 and EN 673

0 oC (32oF) 20 oC (68oF) 25.0 7.7combined

ISO 15099 0 oC (32oF) 20 oC (68oF) 20.0 3.6 *convection

Passive House Cert. Criteria

-10 oC (14oF) 20 oC (68oF) 25.0 7.7combined

NFRC vs ISO Window Rating Procedures – Boundary Conditions

For U-value Calculations (Insulated Frames)

This matters because temperature affects air thermal resistance (NFRC/CEN account differently) and interior/exterior air films add thermal resistance directly

0.5

0.6

0.7

0.8

0.9

1.0

7 8 9 10 11 12 13 14 15 16 17 18 19 20

Ce

nte

r o

f G

lazi

ng

U-V

alu

e (

W/m

2 K)

IGU Argon Space Gap Width (mm)

U-value of Triple Glazed IGU, Cardinal 366 #2, 180 #5 Argon

NFRC 100, -18C

NFRC 100, 0C

CEN 673, -18C

CEN 673, -10C

CEN 673, 0C

Differences in NFRC & CEN on Glass U-values

13 mm (½”) gap:NFRC (-18oC): U-0.72 (U-0.13)CEN (0oC): U-0.70 (U-0.12)

16 mm (5/8”) gap:NFRC (-18oC): U-0.72 (U-0.13)CEN (0oC): U-0.59 (U-0.10)

Big implications in our climate where 0oC/32oF is winter low average

So How Do Some Windows Compare under Each Standard

North American Fiberglass Frame (Double Glazed Reference)Fixed NFRC Size, 1200 x 1500 mm (47¼” x 59”)

NFRC U-value = 0.266 (0.27 rounded), SHGC 0.534 productCEN/ISO U-value = 0.233 (0.23 rounded), SHGC 0.667 glass

European Reinforced Vinyl Frame (Triple Glazed)Tilt & Turn PHI-D Size, 1230 x 1480 mm (48” x 58¼”)

NFRC U-value = 0.149 (0.15 rounded), SHGC 0.371 productCEN/ISO U-value = 0.140 (0.14 rounded), SHGC 0.538 glass

Two European window certification programsPassive House Institute Darmstadt (PHI-D)ift Rosenheim WA-15/2

Common evaluation criteria:Overall product U-value: 0.8 W/m2∙KInstalled product U-value: 0.85 W/m2∙K

Different evaluation methods:PHI-D: simulation only, based on “standard” glass with U-value = 0.7 W/m2∙K , computed ψspacer valueRosenheim WA-15/2: same as PHI-D, OR by physical testing using actual glass and spacer

Passive House Window Certification Programs

Use of real glazing with lower U-value than standard panel provides more accurate evaluation of product performance

Simulations based on glass with U-value = U-0.70 W/m2∙K and computed ψspacer value require frames with very low U-values to meet whole product evaluation criteriaTesting with actual glass having U-values of 0.5 – 0.6 W/m2∙K and real spacer bar shows frames with higher U-values can meet the same whole product evaluation criteria

Lab test results suggest that ISO simulation methods are less accurate for product design purposes, resulting in “overdesign” of window framing membersNFRC simulation methods are more accurate as the results correspond more closely to tested product performance

Interesting Findings about Rosenheim Lab Testing

Example – PHI-Darmstadt vs Rosenheim Certified Windows

Same Window Extrusion, Same Manufacturer, Two Product Lines

PHI certified version: Uframe = 0.79 W/m2∙K by computer simulation. The lack of steel reinforcing limits the application of this product in terms of size and resistance to heat distortion (white frame only)

Rosenheim certified version: Uframe = 0.87 W/m2∙K by laboratory testing (guarded hot-box) vs 0.93 W/m2∙K by computer simulation.Adding steel reinforcing makes this a more versatile and more practical product line (any color, larger frame sizes)

Myth: Windows must be PHI-D Certified to be used in certified Passive Houses -FALSEWindow certification and guidance is provided to demonstrate or pre-qualify that certain criteria is met in European Climate Zone:

U-value (Frame)Edge of Glass/IGU Spacer and Window Installation Linear Transmittance (ψ, psi)Product will meet other passive house criteria including comfort (surface temperature, condensation, hygiene), max 3oC (5.4oF) differential

Passive House Window Myths

U-0.8 W/m2∙K (U-0.14 Btu/hr∙ft2∙oF) window criteria, calculated by EN/ISO methods used by PHI-D

Frame U-value as low as possibleGlazing U-value <0.75 W/m2∙K (U-0.13 Btu/hr∙ft2∙oF), under CEN/ISO rating (-10oC)Triple glazing, 2 low-e coatings (#2/#5), Argon fillSolar Heat Gain as high as possible (>0.50)Is as much a comfort requirement (minimum surface temperature) as much as energy

This is based on recommendations for cool-temperate climates (Germany)BUT – there is actually an underlying climate specific formula which is used: Ug – (Climate Solar Factor) ∙ g < 0

European Climate Specific Guidelines for Windows

Reference: Passivhaus Institut. 2012. Certification Criteria for Certified Passive House Glazings and Transparent Components. Darmstadt, Germany.

Passive House Institute (PHI-D) Climate Zones

Passive House Institute (PHI-D) Window Guidelines

Reference: Passivhaus Institut. 2012. Certification Criteria for Certified Passive House Glazings and Transparent Components. Darmstadt, Germany.

Following DOE/ASHRAE Climate Zones (different than above #s), Germany = Zone 5 (referred to as cool-temperate above)Vancouver*, Seattle & Portland Zone 4 (on warmer side of cool-temperate, but not quite warm-temperature)

Passive House Institute (PHI-D) Window Guidelines

Cool U-0.8 (U-0.14, R-7.14)Warm U-1.25 (U-0.22, R-4.54)

Half Way? U-0.97 (U-0.17 R-5.8) range – interestingly this is the best most high-end N.A. products are

PHI-D and Rosenheim certifications for cool-temperate climate (Germany) are not necessarily fixed guidelines for other climate zonesPHIUS has recently developed North American climate specific passive house window U-values and SHGC targets based on ASHRAE/DOE Zones 1-8

North American Passive Window Guidelines

PHIUS – Climate Specific Window Selection Guidelines

ASHRAE/DOE North American Climate Zone

Overall Installed

Window U-value - Uw

Btu/hr∙ft2∙oF

Center of Glass U-value

- UgBtu/hr∙ft2∙oF

SHGC –South

SHGC –

North, East, West

8 ≤0.11 ≤0.10 ≥0.50 ≤0.40

7 ≤0.12 ≤0.11 ≥0.50 ≤0.40

6 ≤0.13 ≤0.12 ≥0.50 ≤0.40

5 ≤0.14 ≤0.13 ≥0.50 ≤0.40

4 ≤0.15 ≤0.14 ≥0.50 ≤0.40

Marine North ≤0.16 ≤0.15 ≥0.50 ≤0.40

Marine South ≤0.22 ≤0.20 ≤0.50 ≤0.30

3 (west) ≤0.18 ≤0.16 ≤0.50 ≤0.30

2 (west) ≤0.18 ≤0.16 ≤0.30 ≤0.30

2 (east) ≤0.20 ≤0.18 ≤0.30 ≤0.30

Reference: Table Values PHIUS, Climate Map DOE/ASHRAE/NECB Zones by RDH

NFRC and EN/ISO calculate and report window U-values differently and under different conditions (apples vs oranges)

Neither is necessarily better, both have limitationsProcedures exist (LBNL, PHIUS) to calculate NFRC and ISO values from THERM files and vice versaCareful what values you advertise/brag-about or input into energy models (PHPP is EN/ISO calibrated, most other NA software uses NFRC) – “NFRC values appear conservative, EN/ISO values appear optimistic”Design for your climate/site/building – guidelines existU-value specification to meet energy target & comfort/surface temperature criteriaSHGC to meet energy target & thermal comfort (but watch overheating without shading)

Conclusions about Passive House Window Selection

Discussion

Graham Finch – gfinch@rdhbe.com