Non - Residential New Build 4.2.5 Green Roofs · Green roofs Solution optimiser and pathfinder 344 Sales 0844 800 0135 Technical Advisory Centre 01744 766666 4.2.5 Non-residential

Non - Residential New Build4.2.5 Green Roofs

August 2008: Issue 1

4.0Non-residential new build

Non-residential New Build

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

Introduction find online pageSolution optimiser and pathfinder 344Design considerations 346

Design Details 558

Green Roof - Contents

find online pageWarm deck green roof withsingle ply membrane Gr01 558

Protected membrane green roof Gr02 560

Green roofsSolution optimiser and pathfinder

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk344

4.2.5 Non-residential new build: Roofs

A green roof is a roof that is partially orcompletely covered with vegetation and soil,or growing medium, planted over awaterproofing membrane.

Green roofs may also include additionallayers such as a root barrier and drainageand irrigation systems.

Green roofs not only provide amenity spacefor building users, but critically, reduceheating (by adding mass and thermalresistance value) and cooling (byevaporative cooling) loads on a building.Additionally, the inclusion of the growingmedium and vegetation will help control stormwater run off.

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 345

4.2.5Non-residential new build: Roofs

Protected membrane green roofProduct*: Polyfoam Slimline SystemDescription: Protected membrane green roof with ultra strong XPS insulation andwater-shedding system

Page No: 560

Warm deck green roof with singleply membraneProduct*: Polyfoam Roofboard ExtraDescription: Warm deck green roof withultra strong XPS insulation below singleply membrane

Page No: 558Gr01

Gr02

KeyU-values achievable by constructions within this document.

* Recommended Knauf Insulation product(s). Other products may be applicable.

Find online. Visit www.knaufinsulation.co.uk and key in construction code to find the most up to date information on your chosen solution.

Pb01

Elemental U-value requirement

Green roofsConstruction compatibility with Part L2A

Knauf Insulation solution

Area weighted average max

U-value England and Wales

and Northern Ireland

U-values 0.26 0.25 0.24 0.23 0.22 0.21 0.20 0.19 0.18 0.170.29 0.28 0.270.32 0.30 0.140.31 0.15

Typical U-value for compliance England

and Wales and Northern Ireland

0.16

Green roofsGreen roof design


4.2.5 Non-residential new build: Roofs

Types of green roofsThere are three types of green roof:

1. ExtensiveThese have shallow (typically 70mm) soils andsupport sedums, moss, herbs and grasses. Theyare used where roof access is not required. It isthe lightest type of green roof. Extensive greenroofs provide attractive protection to thewaterproof membrane and significantly reducedwater run-off. When the green roof is completed,the building owner must water and weed on aregular basis for the first year until the plants areestablished to ensure proper growth and success.

2. Semi-intensive

A deeper soil layer (typically 150mm) thanextensive roofs enables a wider variety of plantsto be grown, including shrubs and woody plants.They are ideal where the roof is overlooked andyear-round colour is required with only periodicmaintenance. Where access is required, areas ofpaving can be included in the design.

3. IntensiveWith a deep soil layer (150mm upwards) a wide

variety of plant types can be grow, from lawns tosemi-mature trees. The type of planting willdetermine the depth of soil required, the need foran irrigation system and the level ofmaintenance. Regular roof access is normallyprovided on this type of green roof, so pavedareas, walls and even water features areincorporated in the design.

The benefitsImproves environment

• Creates a beneficial microclimate by cooling and humidifying the

surrounding air

• Absorbs greenhouse gases

• Absorbs air pollution and dust

• Provides a habitat for animals and plants

• High water retention

• Run-off attenuation reduces stress on surface water drainage systems

Building fabric

• Protects the roof from mechanical damage and ultra violet radiation,

frost and weathering – thus extending the life of the waterproof

membrane

• Reduces noise levels

Can use recycled materials

• Many of the materials used in green roof construction are

manufactured from recycled building materials and plastics, reducing

landfill disposal

The green roof can vary from simple plantsto mature trees and shrubs which will imposehigher loads on the structure and thus theinsulation layer. Besides the enhancedthermal resistance, another major benefit of green roofs is their ability to slow the rate of rainwater runoff. It has been found that they can retain up to 75% of rainwater, graduallyreleasing it back into the atmosphere via condensation and transpiration,while retaining pollutants in their soil. Green roofs can be categorised as"intensive", "semi-intensive" or "extensive", depending on the depth ofplanting medium and the amount of maintenance they need.

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 347

4.2.5Non-residential new build: Roofs

InsulationThe thermal insulation should be capable ofresisting both the dead load of the green roofand any additional live loads if regular access tothe roof is planned.

In a protected insulation roof, the insulationshould also be impervious to water. Extrudedpolystyrene is the preferred choice.

The soil in a green roof does offer someinsulation value but is normally ignored in U-value calculations. This is because the insulationvalue of the soil varies with the water content.

Waterproof membraneThe green roof makes it difficult and expensive torenew and repair the waterproof membrane. Thewaterproof membrane, therefore, should beselected for its high performance and longevity.

The waterproofing system beneath any greenroof should preferably be root resistant in thelong term to the German FLL standards. If thewaterproofing is not root resistant then the greenroof system must include a separate root barrier,usually immediately above the waterproofmembrane. The waterproofing system must beleak tested and certified as such immediately before the installation of thegreen roof.

The design of the waterproofing and its detailingto perimeters, outlets, protrusions through the roofetc., should take into account the depth of thegreen roof build up. The waterproofing shouldalways be 150mm above soil level at upstandsand protrusions, and at least 50mm at externalperimeters. A 300 to 500mm wide layer ofgravel or paving is recommended at all junctionswith upstands, rooflights etc.

DrainageGreen roofs should be designed with a fall of atleast 1:60. This prevents the risk of ponding indeflections in the roof deck, which can be harmfulto the plants.

Each roof area should contain at least two roofoutlets, or a roof outlet and an overflow. Aninspection chamber should be constructed overeach outlet to allow regular inspection andcleaning of vegetation from the outlet grating.Consult the supplier of the green roof componentsfor their recommendations on the number ofdrainage outlets.

A green roof can absorb and store a highproportion of the rainwater that falls on it,helping to prevent local flood risk.

Wind upliftWind uplift is greatest at the edges of roofs. Atthese points, paving slabs or coarse gravel areusually used to prevent wind suction displacingthe soil layer in a green roof. The soil layer ismost vulnerable in its early stages, before the rootsystem of the planting material helps to provide adegree of reinforcement.

Generally, the higher the building above theground, the greater the risk of wind uplift.

Fire performanceThe soil layer generally provides the fireprotection in a green roof. For extensive roofs,the soil layer should be at least 30mm deep andcontain less than 20% organic matter. Gravelstrips or paving slabs are required to act as firebreaks around all rooflights and below windowsto walls. They must be kept free of flammablevegetation.

Table 4: Design loads on a green roof

Type of green roof Weight (kg/m2)

Extensive design 60-150

Gravel surface 90-150

Paved surface 160-220

Intensive design 200-550

Regulatory complianceThere are no regulations or British Standardsspecifically relating to green roofs in the UK.Most suppliers of green roof components complywith the German Green Roof Standards, knownas the FLA. However, a building with a green roofis of course subject to the same buildingregulation requirements as a building with aconventional flat or pitched roof.

Roof loadingsTable 4 indicates typical loadings ona green roof. Advice on particular schemesshould be sought from the green roof supplier.

A reputable manufacturer/supplier of green roofsystems will be able to supply product data sheetson each of the components comprising anyparticular green roof build-up.

Warm or inverted build-upIt is possible to design a green roof system aboveboth warm and inverted roof constructions. Thegreen roof elements are the same in both cases,only the demands on the insulation and theposition of waterproof membrane change.

Green roofsWarm deck green roof with single ply membrane


6.1.4 Design details: Green roofs

Advantages� Highly cost effective solution with

compressive strength that willsupport a green or garden roof

� Suitable for use in any green or garden roof system

� Protects the waterproofingmembrane from UV degradation

� Green roofs reduce peak hour run-off, improving watermanagement and reducing the risk of flooding

Where a fully bonded membrane system isused, each layer of insulation must be bondedas well as the waterproof membrane itself. Apolyurethane based adhesive is recommended.

The specified green roof system is then installed,each layer is laid on an advancing front inorder to protect the waterproofing membranefrom mechanical damage as the materials aretransported across the roof.

Green or garden roof systems may differ bysupplier. In all cases, the insulation layer needsto have high compressive strength in order tooffer the right level of long term structuralsupport to the growing layer.

InstallationThe vapour control layer should be laid over the structural deck and all joints lapped andbonded.

The insulation boards are then laid in astaggered pattern from one corner of the roof.If a PVC membrane is being used themembrane should be separated from thePolyfoam to prevent plasticiser migration.Alternatively, Polyfoam Roofboard Extra (FoilFaced) board can be used.

Where a mechanically fixed membrane isbeing used, Polyfoam Roofboard Extra shouldbe mechanically fixed to the deck with twocentrally placed fixings in each board to secure the boards in place before themembrane is fixed.

ProductsPolyfoam Roofboard Extra is a 100% ozonefriendly, extruded polystyrene, rigid boardinsulation. It is lightweight, yet has excellentcompressive strength. It is supplied withinterlocking rebated edges.

Typical constructionAny type of roof deck designed as a new build,or intended for refurbishment, can bedesigned as a green or garden roof, providedthe roof structure is capable of carrying theassociated loads.

The waterproofing is installed above theinsulation to create a warm deckconstruction. The waterproofing layer is thencovered with moisture reservoirs (and in somecases, root barriers). These are then overlaidwith a filtration membrane, and planting tocreate a green or garden roof.

A green roof (or extensive roof) constituteslightweight growing matter, e.g. sedum. A garden roof (or intensive roof) can vary fromsimple plants to mature trees and shrubs whichwill impose higher loads on the structure andthus the insulation layer.

Gr01Polyfoam Roofboard

Vapour control layer

Growing mediumand planting

Filter membrane

Waterproofing membrane

Screed laid to falls

Polyfoam Roofboard Extra

Concrete roof deck

Drainage element/reservoir and root barrier

559

6.1.4Design details: Green roofs


Typical specificationThe vapour control layer andPolyfoam Roofboard Extra*, thickness......mm to be mechanically fixed*/adhered* to the roof deck. (*delete as required)

The single ply membrane should be appliedover the insulation in accordance with theappropriate manufacturer’s recommendedspecification.

The single ply membrane to be overlaid with a root barrier/ moisture reservoir asspecified ensuring there are no gaps andedges are overlapped. This to be coveredwith a filtration layer, and growing matter as specified to client requirements.

Alternatively, consult the NationalBuilding Specifications (NBS)based on Standard Version J42.It contains a set of proprietaryclauses, which are editedversions written by KnaufInsulation.


Growing medium and planting

Filter membrane


Vapour control layer


Concrete roof deck

Waterproofing membrane

Typical section

Performance

Compression resistancePolyfoam Roofboard Extra has a minimumcompressive strength of 350 kPa.

A factor of safety of 5 should be applied to the compressive strength of the products forlong term static loads.

Thermal performancePolyfoam Roofboard Extra up to 120mm thickhas a thermal conductivity of 0.029 W/mK,and 0.031 W/mK above this.

The actual performance in use is outlined in Table 30.

Fire performanceWhen Polyfoam Roofboard Extra is installed in a green roof it will not contribute to thedevelopment stages of a fire.

Table 30: Typical U-values of warm deck green roof

Product U-values (W/m2K)

150mm concrete Thickness 40mm screed

(mm) 13mm plasterPolyfoam Roofboard Extra

170 (120 + 50) 0.16160 (110 + 50) 0.17

150 (2 x 75) 0.18140 0.19130 0.21120 0.22110 0.24

Note: The U-values have been calculated to BS EN ISO 6946: 1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

Green roofsProtected membrane green roof


6.1.4 Design details: Green roofs

Advantages� Highly cost effective solution with

compressive strength that willsupport a green or garden roof, aswell as a paved or terraced area

� High thermal performance due toPolyfoam Slimline System

� Suitable for use in any green or garden roof system

� Protects the waterproofingmembrane from UV degradationand temperature extremes,increasing the membrane’s inservice life

� Thermal performance and stabilityof the insulation is unaffected bymoisture

Installation

The waterproof membrane must be free of loosegravel and grit before the insulation board islaid. On existing roofs, any existing chippingsshould be covered with a polyethylenecushioning layer, such as Floorfoam 5.

For mastic asphalt finishes, a separating, non-woven polyester fleece should be laidimmediately below the insulation and turned upat all upstands.

The boards should be laid in a staggered patternfrom the point of access across the roof. It isimportant that all joints between boards are tightfitting and there are no gaps at junctions withrooflights, upstands etc.

The specified green roof system is then installed,each layer is laid on an advancing front in orderto protect the waterproofing membrane frommechanical damage as the materials aretransported across the roof and to protect theboards from wind uplift.

Typical constructionAny type of roof deck designed as a new build,or intended for refurbishment, can be designedas a green or garden roof, provided the roofstructure is capable of carrying the associatedloads.

The waterproofing is installed below theinsulation to create a protected membraneconstruction. The waterproof layer is overlaidwith Polyfoam Roofboard and the PolyfoamSlimline membrane. This is then covered withmoisture reservoirs (and in some cases, rootbarriers). These are then overlaid with afiltration membrane and planting to create agreen or garden roof.

A green roof (or extensive roof) constituteslightweight growing matter, e.g. sedum. A garden roof (or intensive roof) can vary fromsimple plants to mature trees and shrubs whichwill impose higher loads on the structure andthus the insulation layer.

Green or garden roof systems may differ bysupplier. In all cases, the insulation layer needsto be both highly resistant to the effect ofexposure to water and have high compressivestrength in order to offer the anticipated level ofthermal performance and structural support tothe growing layer in the long term.

ProductsPolyfoam Roofboard Extra/Super are 100%ozone friendly, extruded polystyrene, rigidinsulation boards that are lightweight, yet haveexcellent structural strength and moistureresistance.

Polyfoam Slimline membrane is a highperformance, non woven polypropylenegeotextile membrane that prevents the passageof water and is water vapour permeable.

Gr02

Waterproofinglayer

Growing mediumand planting

Filter membrane

Polyfoam Slimline membrane



Concrete roof deck


Polyfoam Slimline System

561

6.1.4Design details: Green roofs



Growing medium and planting

Filter membrane

Polyfoam Roofboard Extra/Super

Waterproofing layer


Concrete roof deck

Polyfoam Slimline membrane

Typical specificationThe whole of the roof area, lined with a waterproof membrane to be insulated withPolyfoam Roofboard Extra*/Super*,......mmthick, covered with Polyfoam Slimlinemembrane. The Slimline membrane to beoverlaid with a root barrier/ moisturereservoir as specified ensuring there are nogaps and edges are overlapped. This to becovered with a filtration layer, and growingmatter as specified to client requirements.

Alternatively, consult the NationalBuilding Specifications (NBS)based on Standard Version J21,J41 or J42. It contains a set ofproprietary clauses, which areedited versions written by KnaufInsulation.

Table 31: Typical U-values for green or garden roofs insulated with Polyfoam Slimline System in protected membrane roof

Product U-values (W/m2K)

150mm concrete,Thickness 40mm screed

(mm) 13mm plasterPolyfoam Roofboard Extra 200 (2x100) 0.15

190 (130+60) 0.14180 (120+60) 0.15170 (120+50) 0.16160 (110+50) 0.17

150 (2x75) 0.18140 0.19130 0.21120 0.22110 0.24

Polyfoam Roofboard Super 225 (3 x 75) 0.15200 (2 x 100) 0.16

175 (100 + 75) 0.19150 (2 x 75) 0.21

125 (75 + 50) 0.25100 0.32

Note: The U-values have been calculated to BS EN ISO 6946: 1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

Performance

Compression resistancePolyfoam Roofboard is highly resistant tocompression and withstands both occasionaland long term static loads.

Knauf Insulation recommends a factor of safetyof 3 for occasional loading (5 for long termstatic loads) is applied to the compressivestrength of the product.

Moisture resistancePolyfoam Roofboard is highly resistant tomoisture and can be laid in standing water orup against wet concrete with negligible impacton the performance of the product.

Thermal performanceThe thermal conductivity of Polyfoam RoofboardExtra up to 120mm is 0.029 W/mK and 0.031W/mK above this.

The thermal conductivity of Polyfoam RoofboardSuper varies between 0.034 and 0.036 W/mKdepending on thickness.

The actual performance in use is outlined inTable 31.

Fire performanceWhen Polyfoam Roofboard is installed in agreen roof it will not contribute to thedevelopment stages of a fire.

Typical section

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August 2008: Issue 1

Ref: KB57608

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Non - Residential New Build 4.2.5 Green Roofs · Green roofs Solution optimiser and pathfinder 344 Sales 0844 800 0135 Technical Advisory Centre 01744 766666 4.2.5 Non-residential