Conventional Roofs: Measuring Impacts of Insulation Strategy and Membrane Colour in Canada

Transcription

1 Conventional Roofs: Measuring Impacts of Insulation Strategy and Membrane Colour in Canada LORNE RICKETTS, MASC RDH BUILDING ENGINEERING LTD. VANCOUVER, BC CO-AUTHORS: GRAHAM FINCH, MASC, P.ENG. & MARCUS DELL, MASC P.ENG.

2 Outline Introduction & Background Study of Conventional Roof Performance What prompted the study? Laboratory Testing Field Monitoring Energy Modelling Conclusions & Areas of Continuing Research

3 Conventional Roofing Recap Most common low-slope roof in North America Air barrier and vapour control layer below insulation on top of structure, then insulation, then membrane on top Insulation typically foam plastic (polyiso, EPS), mineral fibre also used Roof slope typically achieved by tapered insulation unless structure is sloped Roof membrane exposed to temperature, UV, traffic needs to be durable Attachment of membrane/insulation can be adhered, mechanically attached, loose laid ballasted, or combination

4 What Prompted the Study? Insulation Issues Long-term shrinkage Thermal expansion/contraction Polyiso Shrinkage Ridged Membrane EPS Shrinkage XPS Expansion

5 What Prompted the Study? Cover Board Issues Delamination & fungal growth Wood fiberboard cover-board wetting and delamination Wetting & resulting fungal growth on gypsum cover board

6 What Prompted the Study The Great Colo(u)r Debate Darker Colours (more absorptive, less reflective) Higher temperatures, more movement and membrane stress, higher cooling loads, lower heating loads Lighter Colours (less absorptive, more reflective) Lower temperatures, less movement and membrane stress, lower cooling loads, higher heating loads LEED points for use of highly reflective roofs regardless of energy implication and local climate Balance needed between membrane durability, assembly movement, heating and cooling loads New Confused owner? 5 Years Old

7 Study of Conventional Roof Performance

8 Guiding Purpose of the Study Why? Quantify performance of different colours of exposed roof membrane White, Grey, & Black Quantify performance of different insulation types Stone wool, Polyiso, & Hybrid Quantify combined impact of membrane colour and insulation Observe impact of the long-term soiling of white SBS cap sheets Monitor long-term shrinkage/movement of insulation and relative humidity/moisture levels within insulation Laboratory testing of material properties

9 Roof Membrane Colours 3 different 2-ply SBS roof membrane cap sheet colours (white reflective, grey, black) White Reflective Cap Sheet: SRI 70, Reflectance 0.58, Emittance 0.91 Grey Cap Sheet: SRI 9, Reflectance 0.14, Emittance 0.85 Black Cap Sheet: SRI -4, Reflectance 0.04, Emittance 0.85

10 3 Different Insulation Strategies Design target: Each Assembly the same ~R-21.5 nominal Stone wool - R-21.4 ( , adhered) Weight: 26.7 kg/m2 Heat Capacity: 22.7 kj/k/m2 Polyiso - R-21.5 ( , adhered) Weight: 4.6 kg/m2 Heat Capacity: 6.8 kj/k/m2 Hybrid - R-21.3 (2.5 Stone wool Polyiso, adhered) Weight 14.3 kg/m2, Heat Capacity 13.7 kj/k/m2

11 Insulation and Cap Sheet Layout 9 unique roof test areas, each 40 x 40 and each behaving independently Similar indoor conditions (room temperature) and building use (warehouse storage) Climate Zone Grey Polyiso Hybrid Stonewool White Black Polyiso Hybrid Stone wool Figure 1 Study Building and Layout of Roof Membrane Cap Sheet Color and Insulation Strategy

12 Sensor Selection and Installation Temperature Heat Flux Relative Humidity Moisture Detection Displacement Solar Radiation Heat Flux Temperature Relative Humidity & Moisture Detection Solar Radiation Displacement

13 Laboratory Testing of Insulation Performance

14 Laboratory Testing of Insulation R-values 3rd Party ASTM C518 thermal transmission material testing Polyiso and stone wool insulation removed from site & 4 year old polyiso samples from prior study

15 Laboratory Testing of Project Insulation Installed & Aged Insulation R- values - Based on Mean Temperature 7.0 R- value per inch Mean Temperature of Insulation [ C] Polyiso - Maximum Polyiso - Average Polyiso - Aged (4 years) Stone Wool - Average Polyiso - Minimum 50

16 Varying R-value of Field Roof Assemblies Effective Roof Insulation R- value - Based on Roof Membrane Temperature Effective Assembly R- value Stone Wool (Initial or Aged) Hybrid (Initial Average) 16 Hybrid (Aged) Polyiso (Initial Average) 15 Polyiso (Aged) Outdoor Membrane Surface Temperature (Indoor, 21oC) 60

17 Field Monitoring Findings

18 Study Findings: What is the Impact of Membrane Colour?

19 Colour Impact on Surface Temperatures May White Jun Jul Grey Aug * Black Sept * Temperature [ F] Temperature [ C] Monthly Average of Daily Maximum Membrane Temperatures and Maximum Membrane Temperature for Each Month by Membrane Colour 32 Oct Nov White - Maximum Dec Jan Feb Grey - Maximum Mar Apr Black - Maximum *W- ISO- SW had significant data loss in August and September and is removed from the average for those months. Increased temperatures affect: Membrane degradation/durability Heat/Energy Flow through assembly

20 Study Findings: What is the impact of insulation arrangement?

21 Metal Deck Roof Membrane Insulation Impact on Peak & Lagging Membrane & Metal Deck Temperatures

22 Heat Flow Variation with Insulation Strategy Heat Flux Sensors 10 Heat Flux [W/m²] G- ISO HF G- ISO- SW HF - 10 G- SW HF Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec SENSOR CODING: SW - stone wool, ISO polyiso, ISO-SW - hybrid

23 Net Annual Impact Insulation Monthly Average Daily of Energy Transfer by Insulation Strategy Arrangement May Jun Jul ISO 1 W/m2 = 0.32 Btu/hr ft2 Aug Sept ISO- SW Oct SW Nov Dec Jan Feb Mar Heating Degree Days (18 C) Apr Annual Degree Days [ C days] Daily Energy Transfer [W hr/m² per day] Inward Heat Flow Inward Heat Flow Outward Heat Heat Flow Outward Flow 100

24 Other Findings to Date Insulation Movement monitoring ongoing Observing daily insulation swings Seeing some long-term movement of insulation, but also movement of metal deck structure interfering with long-term data Relative Humidity and moisture movement ongoing Seeing harmless seasonal and daily movement of built-in water vapor Water vapor also moves energy latent heat Cut-tests confirm roofs all dry and no issues

25 Impact of Membrane Colour and Insulation Strategy on Energy Consumption

26 Energy Consumption and Membrane/ Insulation Design Energy modeling performed for a commercial retail building (ASHRAE building prototype template) to compare roof membrane colour & insulation strategy Included more realistic thermal performance of insulation into energy models Stone wool: Lower R-value/inch Higher heat capacity and mass Polyiso: Higher R-value/inch (varies with temperature a lot) Lower heat capacity Lower mass Hybrid: Moderates temperature extremes of polyiso makes polyiso perform better

27 Most Energy Efficient Roofing Combination? Lighter membrane, stone wool or hybrid is better for same design R-value Darker membrane, stone wool or hybrid is better for same design R-value

28 Conclusions & Continuing Research Aging and temperature have significant effects on the thermal performance of insulation all types affected to varying degrees Effective insulation R-values, thermal mass, latent heat transfer, membrane colo(u)r all impact membrane temperatures and heat flows Effects building energy consumption and membrane durability Rated R-values of insulation do not tell the whole story about actual heat flow through roofs. 2 years so far, but study is ongoing Soiling, long-term movements, aging etc. Confirm impacts of moisture movement within the assemblies

29 Questions LORNE RICKETTS, MASC, EIT rdh.com