This presentation Roofs, Cathedral Ceilings, Venting, Non ... · Roofs, Cathedral Ceilings,...
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University of Waterloo and Balanced Solutions Straube Presentation Building Canada June 2005 1 Roofs, Cathedral Ceilings, Venting, Non-Vented Dr John Straube June , 2005 www.BalancedSolutions.com www.civil.uwaterloo.ca\beg BEG Building Engineering Group John Straube 2 This presentation Scope: Pitched, Wood, Roofs Performance Problems Vented, cathedral, unvented etc What solutions John Straube 3 John Straube 4 Functions of the building enclosure Support – Structure: wind, gravity, earthquake Control – Heat – Air – Moisture (vapor, liquid) Finish Distribute (sometimes)
Transcript of This presentation Roofs, Cathedral Ceilings, Venting, Non ... · Roofs, Cathedral Ceilings,...
University of Waterloo and Balanced Solutions
Straube Presentation Building Canada June 2005 1
Roofs, Cathedral Ceilings, Venting, Non-Vented
Dr John StraubeJune , 2005
www.BalancedSolutions.comwww.civil.uwaterloo.ca\beg
BEGBuilding Engineering Group John Straube2
This presentation
Scope: Pitched, Wood, RoofsPerformance ProblemsVented, cathedral, unvented etcWhat solutions
John Straube3 John Straube4
Functions of the building enclosure
Support – Structure: wind, gravity, earthquake
Control– Heat– Air– Moisture (vapor, liquid)
FinishDistribute (sometimes)
University of Waterloo and Balanced Solutions
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Sloped Roofs vs Walls
Exposed to– Much more sun– Much more rain– Important aesthetics
Rain control– Drained / concealed barrier
Changes– Roofs are more complex
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Problems
Air leakage condensation– Mold– Decay– ridging
Rain leaks– At penetrations
Ice Dams icicles and leakageTruss uplift
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Review Roof Components
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Air leaks
Cold weather Hot air rises
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Air leakage
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Air leakage condensation
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Frost accumulation
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Ridging due to Excessive Wetting
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Problem: Air leakage at Ceiling
The Air+ The Air+ Thermal Thermal
BarrierBarrier
Cold Outside
Warm Moist Inside
Cold Surface,Vapor Barrier
Cold Cold WeatherWeather
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Soln#1: Bypass Roof Membrane
Cold Cold WeatherWeather
The Air+ The Air+ Thermal Thermal BarrierBarrier
Ventilate
Cold Surface,Vapor Barrier
Warm Moist Inside
Cold Outside
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Solution#2: Plug leaks
The Air+ The Air+ Thermal Thermal
BarrierBarrier
Seal tight
Cold Surface,Vapor Barrier
Warm Moist Inside
Cold Outside
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Cathedral Ceilings
No fundamental technical difference But .. Harder to get ventilation flowSo .. Ventilation not as effectiveSteeper slopes encourages ventilation by stack effect and windLarger vent spaces for larger spans?
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Air Leaks – cathedral ceilings
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Ventilated on top
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Unvented Cathedral Ceilings
Not absolutely necessary to vent if airtight and vapour tight material, – e.g. spray foam.– Or insulated sheathing
May be practical in retrofitIf no wetting, little drying required– Demands very high performance– >R40, no penetrations– spray foam is a practical solution– beware themal bridges
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Unvented Cathedral Ceilings
BUT this means ensure airtightness– beware partitions and lights– dense pack helps (slows air)– airtight exterior helps (stops through flow)– insulated foam sheathing very useful (control
temp)avoid absorbent roofing (inward vapor drives)
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Leaky Cathedral Ceiling
VapourVapourDiffusionDiffusion
Cold = Cold = CondensationCondensation
Air Air leakageleakage
Cold Cold WeatherWeather
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Roof with Insulated Sheathing
VapourVapourDiffusionDiffusion
Air Air leakageleakage
Cold Cold WeatherWeather
Warm = no condensation
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Unvented Solutions
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Unvented
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Convective loops
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Repair
Source: Building Science Corp John Straube34
Ice dams
Ridges of ice forming at eavesAlso typically icicles hanging from eavesice forms a “dam” that traps drained waterProblems
– inward leaking water– dangerous icicles
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FundamentalCause:Heat flow differences
Source: CMHCJohn Straube36
Cool Eaves
Warm Thermal Bridging
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Ice Dams1. Snow insulates
roof membrane
4. Cold air removesheat from underside
3. Snow melts andruns down roof
5. Ice dam andIcicles Form
All ice dams occur when upper part of roof is above freezing and eave part of
roof is below freezing.
= Leaks!
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Ice Dams: Causes & Solutions
Most common causes of ice dams are:– insufficient insulation or thermal bridging– air leaking into the space below the roof
membrane– a source of heat in roof such as a poorly
insulated duct, hotwater piping, etc.– a difference in snow thickness, especially
when combined with solar radiation.Solutions available for most causes
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Cause: Poor Insulation1. Snow insulates
roof membrane
2. Low thermal insulationlevels allows heat to flowto roof sheathing
4. Cold air removesheat from underside
3. Snow melts andruns down roof
5. Ice dam andIcicles Form
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Cause: Poor Insulation
University of Waterloo and Balanced Solutions
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Sol’n: Good Insulation
Energy Efficient Roofs = less Ice damsMinimal thermal bridging– use insulated sheathing
No Insulation compression at heelVentilation will help remove some heat
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Sol’n: Good Insulation/Ventilate Snow insulatesroof membrane
High and uniforminsulation prevents heatflow to underside ofsheathing
Ventilation of coldair removes the
little heat thatpasses through
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Cause: Air Leakage1. Snow insulates
roof membrane
2. Air leaks in ceilingallows warm air to flow
to roof sheathing
4. Cold air removesheat from underside
3. Snow melts andruns down roof
5. Ice dam andIcicles Form
Condensation
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Solution: Airtightness
Find the holes and plug themFind the holes and plug them
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Add sealed drywall or rigid foam, seal foamKnee walls/split levelDrill or punch block cores /framing cavities at ceiling line, then foam
Perimeter / Party walls
Add rigid air barrier and seal: drywall, rigid foamRecessed CeilingsBuild drywall box above or use special sealed unitsRecessed lights
Caulk boxes from below or add drywall box above and seal to ceiling air barrier system
Light fixturesSeal with expanding foam / caulkTop platesSeal with expanding foam / caulkElectrical penetrations
Seal with expanding foam / caulkPlumbing penetrationsUse drywall/sheet metal + high temperature caulkChimney StacksSeal with expanding foam / caulkPlumbing StacksAvoid, insulate R20, seal boot to ceilingSpace Cond DuctsWeatherstrip, caulk, positive action latch, insulateAttic HatchSealing MethodLeakage Path
Sealing Leaks
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Cause: Differential Solar Heating
3. Snow insulatesroof membrane
1. Sun warms shingleswere little or now snow
cover exists
4. Cold air removesheat from underside
2. Snow melts andruns down roof
5. Ice dam andIcicles Form
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Solar Melting
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Solutions
High and uniforminsulation prevents heatflow to underside ofsheathing
Ventilation of coldair removes thelittle heat thatpasses through
>6"
Self-sealingmembrane along
eaves
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A bit of peel and stick
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Sol’n to Heat Sources
Remove ducts, equipment, pipingHigh insulation (R20) / airtightness
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Sol’n: Bring into Building
Special trusses or rafter framingAirtightenSave money on duct insulation / tightening
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Sol’n: Bring into Building
Cathedral “attic”AirtightenSave money on duct insulation / tightening
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Roof Ventilation
Why?– Bypass vapour barrier roof membrane– direct vapor “leaks” to the outdoors
Solar exposure = Roofs hotter than outdoor air– Hot air hold more moisture than cold air– Small amount of ventilation can carry more water
vapourRoof ventilation aids dryingVentilation provides little cooling
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Ventilation Practise
Source: APA
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Providing Ventilation
Source: Building Science Corp John Straube60
Ventilation is not always THE answer
Some bad buildings have relatively air tight roofsroof membranes resist air leakage
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Ventilation is not always THE answer
Adding vents makes it easier for air to leak!
More leakage= more problems
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Ventilation is can be part of THE answer
Add air barrier means ventilation works!
Almost zero leakage + ventilation= no problems
Good air barrier
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Cause: Heat Sources
Ducts, equipment, piping
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Ventilation & Roof Temperature
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Some roofs do provide cooling
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Rain penetration
FlashingRoofing felt
Source: Building Science Corp
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Source: APA
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Roof Summary
Ventilation works to remove small moisture and heat leaksCannot overcome stupid thingsVentilation NOT needed– Spray foam unvented is most promising
Some ice damming cannot be solved– Consequences can be – eave protection
Rain penetration– No news, just common sense
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Truss uplift
Temperature-10 C 20 C5 C
50%RH
100%RH
