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Treating Knee-Walls and Attic Hatches

Adrian Scott, WECC, Madison, WINate Byrnes, UMDWTC, North Dartmouth, MA

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O iOverview

• What is a Knee-Wall Anyway?• Gaining Access• Working in the Kneewall • Insulation Choices• Effectiveness of Insulation• Attic Hatches and Stairways• Attic Hatches and Stairways• Chimney Chases and Attic Dams

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Wh t i K W ll? What is a Knee-Wall?

• A short bearing wall intended to support roof rafters in balloon framed homes. I l tf t ti it b b i ll d t • In platform construction it can be a bearing wall or used to eliminate unusable space in a room

• This creates a space that can be used for storage that can be heated or unheated.

• If it is unheated this space becomes a outer joist beam attic and a buffer zone even if used for storage

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K W ll DiKnee-Wall Diagram

Diagram excerpted from the Wisconsin Weatherization Field Guide

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C N th t “C ” St l HCommon Northeastern “Cape” Style House

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U h t d O t J i t B Atti K W ll Unheated Outer Joist Beam Attic Knee Wall

• Defines the pressure and thermal boundary • The knee-wall itself must be air sealed and insulated • Any access through the wall must be insulated and sealed

and mechanically fastened

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G i i O t J i t B Atti A Gaining Outer Joist Beam Attic Access

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Atti A S ttl d D S ttl H t h Attic Access - Scuttles and Doors Scuttles or Hatch (Horizontal Access )• Need to be insulated to the same r-value as surrounding

insulation or maximum structurally allowabley• Must have a insulation dam surrounding scuttle

• Made of material that allows repeated access (plywood lumber)

• Must have air seal and be mechanical fastened • Must have air seal and be mechanical fastened

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Atti S ttl H t h (V ti l A )Attic Scuttles or Hatch (Vertical Access )

• Need to be insulated to the same R-value as surrounding insulation or maximum structurally allowable

• Must have air seal and be mechanical fastened

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V ti l Atti A Vertical Attic Access

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V ti l Atti A Vertical Attic Access

Using R-11 unfaced fiberglass batt Using R-11 duct wrap and house wrap

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Access DoorsAccess Doors• Insulated to the R-value of

the surrounding insulation • Must be weather stripped pp

and mechanically fastened • May use a plug if access

does not allow you to attaché insulation to door attaché insulation to door

Using R10 Polystyrene foam board

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Alt ti M th d f Atti A Alternative Methods of Attic Access

• Using gable and roof vents • Removing siding • Creating access thru knee wall

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Th h G bl V t R f V t Through a Gable Vent or Roof Vent

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C tti Th h K W ll Cutting Through Knee-Wall

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R Sidi d R l Remove Siding and Replace

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D li ith K ll Dealing with Knee walls

• Need to be air sealed first • Fiberglass needs to be covered on all six sides• Dense pack insulation works the best • Don’t forget get the critical junctures

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Eff ti f I l ti i R d d b• Gaps• Voids• Compressions

Effectiveness of Insulation is Reduced by:

Compressions• Air flow within the insulation• Misalignment

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• Insulation installed with approximately 5% voids and gaps will result in approximately a 17% reduction in ff

Effectiveness of Insulation

effectiveness.• R19 insulation compressed into a 3 1/2 inch cavity will

have an R-value of approximately R16.

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Eff ti f I l ti ( t )Effectiveness of Insulation (cont.)

• Continuous exterior (foam) insulation is more beneficial than cavity insulation (approximately 25% of wall area is framing about R 4 7) framing about R 4 – 7).

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A Bl k Sl t A Blank Slate

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Insulating and Sealing Knee Walls Using Polyisocyanurate Board

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Insulating and Sealing Knee Wallsg g

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I l ti ith T P t FInsulating with Two-Part Foam

Photo courtesy of the US Department of Energy

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D ill d Bl Drill and Blow

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I Eff ti bIncrease Effectiveness by:

• Prevent wind washing of attic insulation by installing blocking and baffles at perimeter.

• Cover batts on all six sides to prevent air movement.

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Seal Before Batt InsulationSeal Before Batt Insulation• If installing fiberglass, seal

seams and around outlets at the pressure boundary

• In this case, seal from the attic side where no one will see

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U i I l b d Bl C ll l Using Insulweb and Blown Cellulose

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T d D P k C ll l Tyvec and Dense Pack Cellulose

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B ilt i B k Sh l Built-in Book Shelves

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Unheated Finished AtticUnheated Finished Attic

Open Unfloored Floored

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Knee Wall Attics

MAIN ATTICOpen Wall CavitiesOpen Wall Cavities

KNEEWALL ATTIC

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B k dBackground

From small straw cans to truck-mounted rigs and everything in between

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Ad t Advantages

• High R-value per inch• Compatible with existing fiber insulation• Closed cell structure• Disposable kits in a variety of sizes• Expands

R d l (i l t d i l )• Reduces energy loss (insulates and air seals)

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Di d tDisadvantages

• High cost • Ultraviolet light destroys exposed foam• Storage temperature and application restrictions• Local building code regulations (manufacturer

specifications)• Health hazards (more on this later)Health hazards (more on this later)

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Closed Cell vs Open CellClosed Cell vs. Open CellClosed

• Higher R-value per inch• Lower moisture permeabilityLower moisture permeability• Higher strength and rigidity• More dense• Higher resistance to air flow• Higher cost per R

Open• Lower R-value per inch• Higher moisture permeability• Lower strength and rigidity• Less dense• Lower resistance to air flow• Lower cost per R• Higher cost per R

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G l G id li

GAPS ≤ 1/4”Caulk

General Guidelines OTHERFoam board,

GAPS 1/4” – 3” fiberglass in Spray foam plastic bags, etc.

Energy Blast ServicesThe Daily Green

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Di d tDisadvantages

• High cost • Ultraviolet light destroys exposed foam• Storage temperature and application restrictions• Local building code regulations (manufacturer

specifications)• Health hazards (more on this later)Health hazards (more on this later)

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C O t• Lineal foot

• Number of feet in a straight line

• One part foam yield is described in lineal feet

Coverage: One-part

• One-part foam yield is described in lineal feet• Example: a 24 ounce can of one-part foam may yield 2200

lineal feet at a ¼ inch bead

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High Temperature IssuesRecessed Light Fixtures

High Temperature IssuesFlues

High-temp caulkHigh-temp caulk

IC Rated Fixture

Maintain appropriate clearancesMaintain appropriate clearances

Non-IC Rated Fixture

Photos courtesy of the US Department of Energy

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Ab t S FAbout Spray FoamSpray foam insulation is modified polyurethane foam plastic. •It is used primarily to seal air leaks in building cavities.•It may be used to insulate vertical or horizontal surfaces•It may be used to insulate vertical or horizontal surfaces.

- Knee walls- Under floors- Attic hatches

•Due to fire rating it may not be left exposed in living areas•Due to fire rating, it may not be left exposed in living areas.

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P d t O tiProduct OptionsAvailable in a variety of shapes, sizes and uses

Froth-Pak, Dow Chemicalshttp://building.dow.com/na/en/products/sealants/index.htm

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Product OptionsAvailable in one-part and two-part formulas

Product Options

One-part: Two-part:

• Spray cans • Portable 2-tank kits –(e.g., Great Stuff) small, medium, and large

• Spray guns with • Truck-mounted rigsscrew-on cans

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O

SPRAY FOAM INSULATION

P y F OptiOne- art SpraP t S F O tionsoam

Non-adjustable Adjustablecanisters Gun-type applicators

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One-Part Foam: Advantages and DisadvantagesOne Part Foam: Advantages and Disadvantages

ADVANTAGES

• Quick and easy for small holes and gaps 2 hoursholes and gaps.

• Creates an effective seal for small holes.

• Lightweight and portable.

2 hours

DISADVANTAGES

• Set up time can exceed .

• Not cost effective for large jobs.

• Freshly gunned product will not adhere on will not adhere on overhead surfaces.

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Two Part Foam KitsTwo-Part Foam Kits

Photo courtesy of Dow Chemicals

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Two Part Foam: Advantages and Disadvantages

SPRAY FOAM INSULATION

Two-Part Foam: Advantages and DisadvantagesADVANTAGES

• More thorough sealing.

Significantly reduced labor

DISADVANTAGES

• Expensive; hazardous materials shipping fees.• Significantly reduced labor

costs.

• Motivates workers.

• Good adhesion.

pp g

• Easy to waste material.

• Restrictive dispensing temperatures. (around 75˚ )

• Quick cure time.( F recommendedaround 75 F recommended)

• Specialized and expensive personal protection equipment required.

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Safe Use of Spray Foam InsulationMaterial Safety Data Sheet (MSDS)• Must have at job site whenever spray foam is used.• Follow precautions for safe handling and use.

Safe Use of Spray Foam Insulation

• Lists emergency and first aid procedures.

Use in well-ventilated area• Provide ventilation fans to exhaust fumes and ensure

cross-flow of fresh air.

W l t ti i tWear personal protection equipment• Coveralls, rubber/latex gloves, eye protection.

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Atti A S ttl H t h (H i t l A )Attic Access Scuttles or Hatch (Horizontal Access)

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Atti A S ttl H t h (H i t l A )Attic Access Scuttles or Hatch (Horizontal Access)

• Must have insulation damming • Sturdy enough to allow repeated entry

M t b t th fi i h d R l f th di tti• Must be to the finished R-value of the surrounding attic• Must be weather-stripped • Must be mechanical fastened• Same level as pressure boundary Same level as pressure boundary

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I l ti D Insulation Dam Material strong enough to handle repeat entry

Seal Seal

Mechanical Fawners

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Diff t W t W th St i Different Way to Weather Strip

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I l ti H i t l A Insulating Horizontal Access

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F B d Foam Board

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O C t W ith Fib l d H W One Correct Way with Fiberglass and House Wrap • Insulation to correct R-value. • Is not compressed and is covered on all six sides.• Fits into insulation dam touching sides – allowing minimal air movement.

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Thi D N t W k This Does Not Work

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Diff t St l f H i t l A Different Styles of Horizontal Access

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Atti St i Attic Stairs

• Are large and heavy • May need to be adapted to home owner • Must be to same R-value as surrounding insulation • Hole may be reduced to attic access if no storage is

provided

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Atti St i (C ffi D )Attic Stairs (Coffin Dam)

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A th O ti Another Option

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I l ti A D d D 'tInsulating Access Dos and Don'ts• Do

• Should be as close to the attic pressure boundary as possible

• Should be the same R-value as surrounding attic insulation• Fills insulation damming as much as possible still allowing

for easy removal • Fiberglass should touch sides of insulation damming • Foam board should be within ¼ inch of the sides

• Insulation should be covered on six sides • Insure insulation is anchored for repeated removal

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I l ti A D d D 'tInsulating Access Dos and Don'ts

• Don’ts• Do not compress fiberglass

D t ll i t d th h i l ti• Do not allow air movement around or through insulation• Don’t make it so tight that it can’t be removed

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Chi D Chimney Dams

• Must be non-combustible • 3 inch clearance • Need to air seal first • Higher than surrounding insulation

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Treating the Chimney ChaseTreating the Chimney Chase

Photos courtesy of The US Department of Energy

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Chi Ch

HOUSE AS A SYSTEM

Chimney Chases

Photo courtesy of The US Department of Energy

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S l d Chi B

Sealed chimney bypass…

Sealed chimney bypass…

with insulation barrier.

with insulation barrier.

Sealed Chimney Bypass

Photos courtesy of The US Department of Energy

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A Alt ti M th dAn Alternative MethodDetail for Sealing Thermal Bypass Around Chimney

Photos courtesy of The US Department of Energy

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M t l D i Metal Damming

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D i R d Fl Damming Round Flue

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PRESSURE & THERMAL BOUNDARIES

Photo courtesy of NRCERT

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P V t k E Ch t Proper Vents a.k.a. Eve Chutes

• Needs to be in to eave• Needs insulation stop • Ned s to be mechanical fasten

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E Sh t Eave Shute

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N W C St t I l tiNow We Can Start Insulating

• Blower-door/IR scan guided to find condition of key junctures, interstitial spaces, hidden interior holesholes

• Devise a plan; some drilling may be visible and done from the interior

• Identify thermal boundaries

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D li ith C iti l J t Dealing with Critical Junctures

• It is important to seal the critical junketers before insulation the knee-wall or the outer joist beam attic

• Must identify what the pressure and thermal boundaries are

• Insulating only slows down heat loss air sealing stops heat loss

• The golden rule is seal first than insulate

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Th M i C iti l J t A e Main Critical Junctures Are

• The floor line • The ends of slants • The knee wall to floor connection• The ends of knee wall to exterior wall • The outside wall to outer joist beam attic floor

Th

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S li th C iti l J t d P t ti M th d Sealing the Critical Junctures and Penetrations Methods • One Part Foam • Two Part Foam • Bag Method• Bag Method• Foam Board • Dense pack cellulose

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Th C iti l Fl LiThe Critical Floor Line

Open floor joist cavitiesOpen floor joist cavities

A good candidate for the BAG method

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D li ith th fl li Dealing with the floor line

• Bag Method• Onion bags

I l B • Insulwepp Bags

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Fi C i l J t f th St d H lfFive Crucial Junctures of the Story and a Half

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AIR LEAKAGE OCCURS AT

ROOF

WOOD FRAMED

THE OPEN JOIST AREA

FLOOR JOISTS EXTENDPAST WALL TO FORM

WALL WITH CAVITY

INSULATION

PORCH CEILING

Dense PackCelluloseAir-Seal While Insulating

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S l P t ti Seal Penetrations

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T f E t i W ll Tops of Exterior Walls

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T f E t i W ll Tops of Exterior Walls

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Wh t i t d What are you going to do

Built in Built in Dresser

Floor pockets empty

Access