How to ensure high performance in large well insulated roofs

Jyri NieminenKey Account ManagerVTT Technical Research Centre of Finland

218.10.2011

Climate change

Possible long-term changes in climate in the North

Average temperature increasesPrecipitation in winter increasesCloudiness in winter increasesSnowfall decreases

ConsequencesRain load on buildings increaseConditions for mould growth increasePossibility of rain leaks increase

Hygrothermal quality requirements!Climate change increases the moisture risk level in all buildings

Yearly average rainfall in Finland according to different scenarios

Cha

nge

(%)

Source: The Finnish Meteorological Institute (FMI)

318.10.2011

Amount of moisture

Rain, with 1% of rain leaking in.

Normal and worst case gives big variation

Reason for moisture g/m2hRain 0,65 – 2,40

Diffusion 0,002Air leakage 0,036 – 5,20Built-in moisture 0 – 0,300TOTAL 0,688 – 7,902

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Moisture in building structures

Moisture damages are one of the main cause bad indoor air qualities and they affect the occupants´ health and comfort.

Moisture is the main cause of deterioration of building materials and structures

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Ventilated roof: Scope of application

“To ensure the drying of built-in moisture, and ensure a proper performance of the roof by minimizing the moisture risks during the life-circle of the roof”.

No mechanical ventilation is neededPre-requisitions for performance:

Design and construction made according to guidelinesMaterials, construction methods and work supervision are carried out according to good workmanship.

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Ventilated roof

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Openings

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Performance of the grooves

Micro climate around the building is the main driving force for the groove ventilation. Air speed 0,01 – 0,10 m/s.The air flow direction in the grooves is not constant but changes according to changes in the pressure field.

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Vapour barrierHousing, offices and commercial buildings: Low indoor humidity in winter

< 50 %Water vapour resistance 500-1000 m2 s Pa/kg

Schools, sports halls, process industry: Medium indoor humidity in winter > 50 %

Water vapour resistance 1000-2000 m2 s Pa/kg

Swimming halls, pulp industry: Extreme conditions in winter especially below roof > 80 %

Water vapour resistance 2000-10000 m2 s Pa/kg

Vapour barrier can be , e.g., a bitumen membrane or rubberized bitumen membrane, or product with vapour resistance 500 x109 m2 s Pa/kg, minimum

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Roof ventilation and heat losses

t > 200 mm: + 2%

= 0,001 W/m K

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Drying potential, cold continental climate

Katto 10 m, tuuletettu 0.1 m3/m2h

-0,05

0,00

0,05

0,10

0,15

0 90 180 270 360 450 540 630 720

Kuivuminen, kg/h

168 per. Mov. Avg.(Kuivuminen, kg/h)

0 720

Dagar från Jan. 1

Utto

rkni

ngsh

astig

het,

kg/h

10 x 1 m2 Tak, ventilering 0,1 m3/m2 h

Flytande medelvärde

Days from January 1

Floating average

10 x 1 m2 roof, ventilation 0,1 m3/m2 hD

ryin

g ra

te k

g/h

1218.10.2011

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400 500 600 700 800

Tid [d]

Drying through ventilation

Tota

l moi

stur

e, k

g

Time, days

Example:

40 m2 of wet roof due to rain during installation

Average moisture 10 % of weight corresponding to 2 kg/m2

Drying through ventilation, start January 1

Outcome in practise

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Ventilation design step by step

Identify type of use for the building

Identify outdoor conditions

Identify the roof ventilation conditions

Identify roof type and required U-value Choose of roof combination slabs, thicknesses of:- Top layer - Grooved layer - Middle layer- Bottom layer

Step 1

Step2

Step 3

Step 4

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Design step by step, continued

Define moisture conditions and required ventilated rate

Define Ventilated area

Define Dimensions for a ventilated area

Step 5

Step 6

Step 7

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Indoor air humidity in winter

Example of buildings Indoor climate type, humidity in winter

Warehouse Dry; < 30 %Shopping centre Low; < 40 %Housing Average; < 50 %Office Average; < 50 %Process industry, sport halls High; > 50 %Swimming hall, pulp industry Extreme; > 80%

Step 1

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Types of outdoor conditions

Climate type LocationsCold continental Kiruna, Jyväskylä, Rovaniemi,

MoscowMild continental Kiev, Minsk, Warsaw, RigaCold maritime Helsinki, St Petersburg,

Stockholm, TallinnMild maritime Copenhagen, Gothenburg

OsloRainy maritime Bergen

Step2

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Total maximum moisture load

Calculated moisture load for dimensioning:

Climate Total moisture load;kg/m2

Average moisture load; g/m2/h

Cold Continental 7,5 0,86Mild Continental 6,5 0,74Cold maritime 6,5 0,74Mild maritime 5,7 0,65Rainy maritime 8,2 0,94

Step 2

Source: RESEARCH REPORT No VTT-R-03394-06

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Roof ventilation conditions

Groove ventilation conditions

Open or low density area

Dense-developed area

Windscreen by topography or forest

Excellent 1 level roof, some obstructing structures

1 level roof, without obstructing structures

Forest high building, 1 level roof without obstr. struct.

Good 1 level roof with obstr. struct.

1 level roof, some obstr. struct.

1 level roof without obstr. struct.

Fair Roof in 2 or more levels

1 level roof with obstr. struct.

1 level roof, some obstr struct.

Poor Roof in >2 some obstr. struct.

Roof in > 2 levels 1 level roof with obstr. struct.

Step 3

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U-values and thicknesses

Rmembrane = 0.04 m2K /W; Rsi + Rse = 0.14 m2K /Wboard = 0.039 W/m K; slab = 0.037 W/m K with grooves

U-value Total thickness

Bottom layer

Middle layer

Grooved layer

Top layer

0,10 360 60 140 140 200,11 330 50 120 140 200,12 300 60 120 100 200,13 280 60 100 100 200,14 260 60 80 100 200,15 240 60 80 80 20

Step 4

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Build up of the roof

Alternative 1 Vapour/air barrier

Bottom layer

Middle layer Grooved layer

Top layer Roofing

Bitumen membrane

30 -160 mm 30 - 160 mm 100 -160 mm 20 - 30 mm According to design

Alternative 2 Bottom layer

Vapour/Air barrier

Middle layer Grooved Top layer Roofing

20 - 50 mm Bitumen membrane

30-160 mm 100 -160 mm 20 - 30 mm According to design

Recommended thicknesses of insulation layers from bottom to top

Step 4

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Define moisture and required ventilation rate

Cold continental climate

Step 5

0,05

0,1

0,15

0,2

0,25

0,3

0,35

150 200 250 300 350 400

Req

uire

d ve

ntila

tion

rate

, l/m

2 s

Insulation thickness, mm

Cold continental climate

Extreme conditions: pulp industry, swimming hall

Dry conditions: warehouse, dry spaces

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Define ventilated area

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0,350

60 80 100 120 150 200

Ventilated area, m2

Req

uire

d ve

ntila

tion

dm3 /s

m2

Maximum for a sunny roof

Good ventilation conditions

Step 6

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Other Ventilation conditions

Step 6

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0,350

60 80 100 120 150 200

Ventilated area, m2

Req

uire

d ve

ntila

tion

dm3 /s

m2

Maximum for a sunny roof

Very good ventilation conditions

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0,350

60 80 100 120 150 200

Ventilated area, m2

Req

uire

d ve

ntila

tion

dm3 /s

m2

Maximum for a sunny roof

Fair ventilation conditions

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0,350

60 80 100 120 150 200

Ventilated area, m2

Req

uire

d ve

ntila

tion

dm3 /s

m2

Maximum for a sunny roof

Poor ventilation conditions

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0,350

60 80 100 120 150 200

Ventilated area, m2

Req

uire

d ve

ntila

tion

dm3 /s

m2

Maximum for a sunny roof

Low ventilation conditions

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Define ventilated area

Ventilated area = a x b;a =distance between

hoodsb = distance between

connecting grooves

Step 7

Roof vent

Connection groove Ventilatedarea

Ventilatedarea

Slope

ab

Slope

Drainage

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Suggested length of ventilated areaIndoor climate type

Roof characteristics

Open areaNo solar,

m

Open area Solar,

m

Shady area

No solar, m

Shady area

Solar, m

Dry,Ware house

1 levelLarge roof

20 20 20 20

Average humidity Offices, schools

Moderate area several levels

15 - 20 20 10 - 15 15 - 20

Extreme humidity Swim hall

Large roof, High building

< 10 10 - 15 < 10 10 - 15

Step 7

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Conclusions/Suggestions

Moisture can be calculated Air leakage is the main problemAverage ventilation guarantee dryingDesign based on required air flow rateMaximum length is set depending on available wind conditions

2718.10.2011

Thank You!