William B. Rose University of Illinois at Urbana-Champaign

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2 William B. Rose University of Illinois at Urbana-Champaign 2

3 Ralph Britton. Crawl spaces From Ralph Britton, "Crawl Spaces: their effect on dwellings - an analysis of causes and results - suggested good practice requirements", HHFA Technical Bulletin No. 2.

4 What happens in attics is very indeterminate It s really hard to make indeterminate conditions more determinate especially by adding airflow! Forest, Tom W., and Iain S. Walker. Field Study on Attic Ventilation and Moisture In CANCAM '91,. Proceedings CANCAM '91,. University of Manitoba, Winnipeg, Canada.,

5 212 Reducing air leakage Reducing air leakage has always been one of weatherization s most important functions. Objectives of air leakage reduction are to: Save energy by cutting air leakage Maximize insulation s thermal resistance by reducing air movement through it, Avoid moisture migration into building cavities, and Increase comfort. 2137: Installing attic ventilation or increasing attic ventilation is an optional measure and is left to the discretion of the Weatherization Agency. 5

6 Lessons from weatherization, for existing buildings Measure opening areas in the ceiling and roof Provide air-sealing at the ceiling level Important, strong effect, critical Pretty much all upside, pretty much no downside. Highly recommended Attic ventilation? Diminishing importance with airtightening Has moderate effect, but not a critical effect Has upside dilutes moisture Has downside resilience and energy. Contingent. 6

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9 White roof, Tucson, cold underside of the sheathing Temperature, outdoor and under sheathing, dry bulb and dewpoint Degrees Fahrenheit Temperature under sheathing Dewpoint under sheathing Temperature outdoor 35 cloudy days clear days 30 1/25/2005 1/26/2005 1/27/2005 1/28/2005 1/29/2005 1/30/2005 1/31/2005 Date 9

10 101 Intro 09:03 min 102 backg. 13:31 min 103 airflow 15:17 min 104 icedams 16:16 min 105 shingles 12:29 min 201 heatttrans 11:28 min 202 psychro. 08:03 min 301 model 44:05 min 302 wrapup 23:50 min Spaces are underscores Slow. Use 1.5x or 2x speed. High resolution, slow download. 10

11 Attic ventilation. Rowley. First attic research regarding moisture, University of Minnesota. Small test huts within a conditioned chamber. Preliminary Condensation indicated by frost on a retrievable aluminum panel. 11

12 Test No. Outside Air Temp., ºF Inside Air Conditions Natural Ventilation ºF % Rel. Hum. Opening 1, in 2 Attic Temp., ºF Condensation Opening in square inches per square foot ceiling area in each gable. 2. Condensation in grams per square foot ceiling area per 24 hours. = 1/288 = 1/576 12

13 Critique of Rowley s conclusions Assume 1 sq ft. of 3/4 pine sheathing. Weighs about 1000g. Safe range of moisture content 10% to 23%, or accumulation range of 130g. Assume -10 F, constant, unchanging. Indoor 40%RH To go from the dry end to the wet end of the safe range requires: For unvented attic: 43 days For undervented attic (1/576): 2 years+. Rowley never studied attics with vapor barriers in place. 13

14 Attic ventilation. FHA First appearance of 1/300 attic vent ratio January Incidentally, first vapor barrier specification and crawl space ventilation requirement Author? Probably Ralph R. Britton. 14

15 15 From Ralph Britton, "Crawl Spaces: their effect on dwellings - an analysis of causes and results - suggested good practice requirements", HHFA Technical Bulletin No. 2.

16 Ralph Britton, Report

17 HHFA 1948 Ralph Britton was the principal author of Condensation Control, a booklet with guidance for the post-wwii housing boom. Recommended attic ventilation and vapor barriers. 17

18 HHFA

19 National Paint and Varnish Association 1952 Oh, it s a battle, all right a constant struggle between mankind and moisture. The price of victory is eternal vigilance. It s up to you, of course, as it is to every home owner. First do everything possible to keep the moisture pressure within your home below the danger point by providing adequate ventilation at all times. As an added safeguard for the walls of your home, retard the invasion of excess moisture from the room side. As allies you have vapor barriers and water-repellent paint. 19

20 National Paint and Varnish Association

21 Condensation Conference Frank Rowley 1952 Another point brought up by Mr. Teesdale is this question of attic ventilation. I think most people have had some experience with attic ventilation in trying to get good distribution of air around the attic.... Too much ventilation may even cause damage by cooling off the top of the insulation. We have taken cases where excess ventilation will cool the top surface of the insulating material So too much ventilation may be dangerous just as well as too little. 21

22 Ventilation and shingle warranties With information provided so far, first warranties requiring code-level ventilation appeared in early 1980s version of 1974 Principles of Attic Ventilation (AirVent, Inc.): Also, the remodeling industry is increasingly aware of the importance of proper ventilation to assure roof shingle durability and performance. ARMA Asphalt Roofing Manual 1988: Proper ventilation of the attic areas is a little understood but very helpful method of not only controlling heating and cooling costs, but also getting maximum service life out of the building materials used in the roof assembly. 22

23 Background summary Teesdale: Frost on nail points in Madison WI. Rowley: one data point in one study Britton: 1/300. Maybe. Nat l Paint and Varnish Assn.: Be afraid, be very afraid Nat l Roofing Contractors Ass n.: Vent attics. Forest and Walker 1991: Venting results not determinate. Not a great pedigree. 23

24 Measuring opening area William B. Rose 24

25 ARTA Airflow Resistance Test Apparatus 25

26 Figure 2: Section Through Test Apparatus Flow Straightener Screen Pressure Tap Variable Orifice Screen Vent Sample Screen Pressure Taps Pressure Tap AIR FLOW Fan 1' 10" 7' 1" 1' 7" 7' 1" 6" 3' 2" 7' 4" 2" 1" 7' 5" 2' 26

27 Equivalent net free area test results 27

28 Test results If it looks like air can go through easily, it can, but not at 100% of rated net free area. If it looks like air would have trouble getting through, it does have trouble. Snow enters through open vents, does not enter through tight vents. The industry generally takes credit for the rated NFA, not the actual NFA. 28

29 Zone pressure testing Let s assume blower door tests reach 50 Pa. It gets complicated otherwise. A zone pressure test (as part of a blower door test) measures the pressure in a cavity that is partially inside and partially outside. 29

30 Zone pressures If the attic zone pressure is close to 0, then zone is more OUTSIDE and the ceiling is relatively airtight. If zone pressure is close to house pressure, then the attic is more INSIDE the house, and the ceiling is relatively air-loose

31 Blower door test 1 Input: Blower door test 1, reference to outdoors HP1 House pressure 50 Pa HF1 Air flow 3350 cfm50 ZP1 Zone pressure 2.5 Pa, RF1 A roof ZP1 A ceiling HP1 HF1 31

32 Blower door test 2 Blower door test 2, reference to outdoors Opening: zone to inside HP2 House pressure 50 Pa HF2 Air flow 5200 cfm50 ZP2 Zone pressure 37 Pa RF2 A roof ZP2 A ceiling HP2 HF2 32

33 Calculation Assuming: One square inch adds 10 cfm at 50 Pa HP2 = HP1 = 50 Pa n = 0.65 RF2 A roof ZP2 A ceiling HP2 Blower door test 1, reference to outdoors HP1 House pressure 50 Pa HF1 Air flow 3350 cfm50 ZP1 Zone pressure 2.5 Pa, Blower door test 2, reference to outdoors Opening: zone to inside HP2 House pressure 50 Pa HF2 Air flow 5200 cfm50 ZP2 Zone pressure 37 Pa HF2 Output: opening area House to zone Zone to outdoor 45 in2 272 in2 33

34 Derivation A roof A ceiling F total1 A roof F roof1 ZP 1 HP 1 : 50 Pa F house1 F roof2 ZP 2 A house Empirically: 10 cfm50 for each in 2. Therefore: Flow / Area = 10 (cfm50/in 2 ) Flow at 50 Pa requires a constant C, and Flow = C Area 50 n, n = 0.65 The only value for C which satisfies both equations: C = 10 / 50 n Since HP 1 = HP 2, and A house is constant: F total2 F total1 = F roof2 F roof1 Since F roof = C A roof ZP n for both tests: F roof2 F roof1 = C A roof (ZP 2 n ZP 1n ) Therefore: A roof = (F roof2 F roof1 ) / (C (ZP 2 n ZP 1n )) And: A roof = (F total2 F total1 ) 50 n / ((ZP 2 n ZP 1n ) 10) F total2 F house2 HP 2 : 50 Pa A house In test 1, flow through A roof equals flow through A ceiling : F roof1 = C A roof ZP 1 n = C A ceiling (50 ZP 1 ) n And: A ceiling = A roof ZP 1 n / (50 ZP 1 ) n 34

35 104. Ice damming William B. Rose 35

36 Canada Mortgage and Housing Corporation, Don Fugler 36

37 Look for: Ice damming Outdoor temperature degf following a big snow. Valleys Vagrant heat from the attic Volume of ice + water formed T.S. Rogers, Design of Insulated Buildings for Various Climates,

38 Spreadsheet Assume No venting, no 3-D effects (gables, etc.) No vagrant heat loss from chimneys, ducts, equipment, bypasses All heat transfer is one-dimensional conduction Then Melting occurs at the 2-phase interface How much melting? How does that compare with what we see? If we see more than can be calculated, the assumptions must be wrong. Most ice dams are associated with vagrant heat loss. Then...assume Vent. All heat goes out the vent leaving none for melting How much heat is that, and how much air? Can we really vent away an ice dam? Don t the roof vents get covered with snow? 38

39 Attics 105. Shingles William B. Rose 39

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41 Attic performance project 41

42 Attic Performance Project Bay framing Vented Color Shingle type 0 Hip Yes White A 1 Truss Yes White A, B and C 2 Truss Yes Dark A and B 3 Truss , no 1991-pres, yes Dark A, B and C 4 Truss , yes 19910pres, no Dark A, B and C 5 Truss No Dark A and B 6 Cathedral Yes Dark A 7 Cathedral No Dark A 8 Cath + 1 rigid No Dark A and B 9 Hip no Dark B 42

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44 Attic Performance project Organic felt 1989 fiberglass 1991 fiberglass 44

45 Table 2. Shingle temperatures compared to base case (shown in bold) Summer data, two years Bay 1 Shingles white white white white white white Vented yes yes yes yes yes yes Orientation north north south south north south roof location eave ridge ridge eave ridge ridge Layers exposed/buried exposed buried buried exposed exposed exposed cooler (-) hotter (+) -32.0% -34.3% -23.4% -22.7% -38.0% -27.2% crossing (ºC) St. Error of estimate (K) Bay 3 Shingles dark dark dark dark dark dark Vented yes yes yes yes yes yes Orientation north north south south north south roof location eave ridge ridge eave ridge ridge Layers exposed/buried exposed buried buried exposed exposed exposed cooler (-) hotter (+) -14.9% -14.5% -4.3% Base case -11.1% 3.0% crossing (ºC) St. Error of estimate (K) Bay 4 shingles dark dark dark dark dark dark vented no no no no no no orientation north north south south north south roof location eave ridge ridge eave ridge ridge layers exposed/buried exposed buried buried exposed exposed exposed cooler (-) hotter (+) -12.5% -14.3% 0.0% 2.7% -9.0% 4.7% crossing (ºC) St. Error of estimate (K) Attic Performance Project How much warmer is an unvented shingle compared to a vented shingle? If vented shingle is 100 degf, a neighboring unvented shingle is 103 degf. How much cooler is a white shingle compared to a dark shingle? If dark shingle is 100 degf, a neighboring white shingle is 78 degf. Rose, W Measured values of sheathing and shingle temperatures for residential attic and cathedral ceilings. Thermal Envelopes of Buildings VIII, December

46 From Manual J ACCA 46

47 Attics 201. Radiation, etc. William B. Rose 47

48 Radiation measurements from SURFRAD (NOAA network) 48

49 Solar and infrared net fluxes, Bondville IL 49

50 Solar and infrared net fluxes, Desert Rock NV Solar absorptance 100% 80% 15% 50

51 Notes Bondville IL net infrared flux: -50 W/m 2. Desert Rock NV net infrared flux: -150 W/m 2. Average outdoor humidity is a good predictor of infrared flux. The sky temperature varies by angle from zenith. Sky temperature at the horizon approaches ambient outdoor air temperature. White roof with parapets sees the coldest part of the sky. Can you read effective sky temperature using a pyrometer set to ε = 1.0? Apparently so. For roofs with low solar absorption, heat loss to the sky may be much greater than heat gain from the sun. 51

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55 Construction BUR with very white coating OSB sheathing, 3/8 per foot slope Top chord of 30 deep truss Temp/RH sensor. Above insulation R-38 fiberglass insulation attached to truss members with foil facing (facing downward). No intentional gap or ventilation beneath sheathing. Temp/RH sensor. Below insulation Bottom chord of truss Gypsum wallboard 55

56 Wintertime measured conditions, cloudy and clear Temperature, outdoor and under sheathing, dry bulb and dewpoint Degrees Fahrenheit Temperature under sheathing Dewpoint under sheathing Temperature outdoor 35 cloudy days clear days 30 1/25/2005 1/26/2005 1/27/2005 1/28/2005 1/29/2005 1/30/2005 1/31/2005 Date 56

57 Cloud cover effect 57

58 Attics Summary William B. Rose 58

59 Attics acknowledgements US Department of Energy, Weatherization Action Program. Illinois Department of Commerce and Economic Opportunity (DCEO), Illinois Home Weatherization Assistance Program. 59

60 Attics 101 Provide air-sealing at the ceiling level Important, strong effect, critical shown Pretty much all upside, shown pretty much no downside. not shown in this series Highly recommended Attic ventilation? Diminishing importance with airtightening shown Has moderate effect, but not a critical effect shown Has upside dilutes moisture shown Has downside resilience not shown in this series and energy. shown for winter, may not be the case for summer Contingent. shown 60

61 Illinois Home Weatherization Assistance Program. Field Standards Manual 212 Reducing air leakage Reducing air leakage has always been one of weatherization s most important functions. Objectives of air leakage reduction are to: Save energy by cutting air leakage Maximize insulation s thermal resistance by reducing air movement through it, Avoid moisture migration into building cavities, and Increase comfort. 2137: Installing attic ventilation or increasing attic ventilation is an optional measure and is left to the discretion of the Weatherization Agency. 61

62 Illinois Weatherization Standards Corresponds to a 10% opening ratio: Ceiling opening to roof opening Good for Illinois Colder climates may need smaller ratio Warmer climates may allow higher ratio Can be achieved either through air-tightening or attic ventilation Air-tightening improves overall performance and energy performance 62

63 Measuring opening areas Easy with a blower door, using add-a-hole methods in zone pressure testing. Use the opening area ratio to achieve good overall performance and energy performance. 63

64 Ice dams Find the sources of vagrant heat Leaky ducts, equipment in the attic, chimneys, flues, holes in the ceiling (cabinet bulkheads), bypasses Fix them Provide good valley protection and eave protection Vent? May be helpful if large flows can be established. Not very helpful with limited flow. 64

65 Shingle service life Depends heavily on shingle composition Shingles in the 1980s seemed troublesome Shingles today seem very good Venting provides a slight cooling effect Like driving 100 miles to the north Color has a very strong cooling effect (8x greater than venting) Does venting have a noticeable effect on shingle service life? Not in the shingles in my study. Building was un-conditioned for the last 8 years. 65

66 What does the model tell us? Depends on the model, and on the inputs to the model. With a monthly-average steady-state model we were able to show the benefits of the opening ratio approach. That approach stresses the importance of airtightening of the ceiling, allowing a greater range of ventilation. How wet is too wet? What criteria to use? ASHRAE Standard 160: Avoid 80% monthly average RH at warm temperatures With cold temperatures, high RH may be unavoidable Run sequential monthly-average models Find an assembly that works in your area, run the model on that assembly, use it as criteria for other assemblies 66

67 What should I do as a roofer? Relax. Lighten up. Recognize that most roofs are sorta vented Some parts are vented and others aren t Even sealed roofs are usually not well sealed Vented roofs are not well vented Any vent police out there don t know what they re talking about Follow the path of least resistance. Whatever. Provide air-tightening at the ceiling. Yes, YOU 67

68 Venting attics? New construction Comply with building codes. Low-slope roofs cannot, should not, be vented. Concrete? Use of rigid foam permits moisture-safe construction without venting ( air-impermeable insulation, Class II vapor retarder ) Comply with venting requirements, or Use strong, numbers-based arguments for variance. But don t repeat stupid arguments for venting. Run the numbers. Existing construction Measure opening areas Achieve good balance between ceiling opening and roof openings. Favor air-tightening over added ventilation. 68

69 Common questions Kneewalls and slants in 1 ½ story construction Open-cell v. closed-cell spray-applied foam Cellulose-filled cavities Diffusion vents High-venting and low-venting Shingle warranties Hips and valleys, dormers, flats, complicated geometry Vents with foam Model, using your own assumptions. Make the ceiling airtight. Allow yourself latitude on venting. 69