Bristol Green Roofs

Everything you needed to know about building and maintaining a green roof.

– 40 minute

 

Introduction

Bin stores and burial mounds, sheds and workshops, extensions and new builds, wildlife habitats and rooftop vegetable gardens. Flat roofs are a waste of space, they leak, are seldom insulated, overheat and look awful. With so many altruistic reasons to install a green roof, it’s no wonder most motivations are self-serving. EPDM rubber is watertight and insulation can be added. Need more space, then make more land. Adding substrate to a roof buffers summer overheating, winter frosts and stops the rain pouring off. Planting gives back precious land to bugs, spiders and birds. Living roofs are recreation, look good and make us happy.

After ten years of designing and installing green roofs, we no longer provide and installation service. Consultancy is still available to help you design and detail your roof correctly. Designing and working successfully with EPDM rubber as well as opportunities for more cost-effective and better planting. Training and support are also available before and during installation.


On this page

Case Studies

  • Bin stores and burial mounds
  • Sheds and workshops
  • Extensions and new builds
  • Vegetable garden

Methodology

  • Membrane
    • EPDM
    • Upstands
    • Outlets
    • Inlets
    • Corners
    • Roof lights
    • Flashings
    • Damage
  • Deck-drain
    • Retention
    • Drainage
    • Storage
    • Irrigation
    • Flat
    • Pitched
    • Riverbed
    • Reservoir
  • Substrate
    • Moisture capture
    • Intensive
    • Extensive
    • Weight and structure
    • Economics of scale
  • Habitats
    • Sedum
    • Wildflower
    • Recreation
    • Ad-hoc

Suppliers

  • Hertalan
  • Shire substrate

Advice and support

 


Case Studies

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Bin stores and burial mounds – economics of scale.

Untitled

Sheds and workshops – self-build, managed or contracted.

Bristol Green Roofs

Extensions and new builds – responsibilities and liabilities.

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Vegetable garden – better gardening.

Read more


Methodology

EPDM Roof Light

Membrane

EPDM, up-stands, corners, outlets and gutters. Roof-lights, inlets and flashings. Accredited installation and the FLL guideline for green roofing.

Green roof deck-drain

Deck-drain

Water drainage and retention. Roof-pitch, no drain, reservoir and riverbed.

Green Roof Sub-strate

Substrate

Moisture retention and generation. Pozzolan, off the peg and grow your own.

Green roof habitats

Habitats

Successful and appropriate planting.


 

Membrane

Up-stands, corners, outlets and gutters. Roof-lights, inlets and flashings. Accredited installation and the FLL guideline for green roofing.

 

EPDM

EPDM Roof Light

Ethylene propylene diene monomer, synthetic rubber.  The most watertight cost-effective roofing system, impervious to water penetration and UV light degradation, whether covered with vegetation or left exposed.

 

Up-stands

Green roof up-stand

Rain-water management and ease of installation. When installed without planting a drop edge design hangs the rubber, like a table cloth over the sides, with just a curb edging detail to stop rainwater being blown off by the wind. When adding vegetation an upstaged is required, this ensures that water penetrates down through the substrate and deck drain rather than washing the substrate away. Moisture can be more easily captured and stored.

[Up-stands Photo hands to show successful folds and lost areas]

 

Outlets

Green roof outlet

No factory components required, just a scalpel, a ten pence piece and an of cut of the downpipe.

Purchasing a rubber outlet component is unnecessary. Rubber roofing components can be glued in place with the appropriate silicon however they are not suitable for green roofing. For the joint to be resistant to root penetration it requires welding in place using specialist equipment. It is, therefore, preferable to design out component dependent detailing. A simple design of four internal corners and a pipe outlet can be accomplished with nothing more than a membrane and knowhow.

 

Green Roof outlet

How to make your own

Using a hole saw cut through the roof-deck and secure a short off-cut of the downpipe. On a single-ply deck this simple plywood component will hold thing secure. Pilot holes ensure the mounting screws pull tight, whereas the four side screws pass through an undersized pilot hole to ensure the thread will tighten the tip of the screws against the pipe.

If the outlet pipe passes through multiple layers of ply and insulation it may be possible to glue the down-pipe in place using a foam applicator gun.

 

Green roof outlet

For a flat roof the membrane is glued down with contact adhesive applied to a minimum of a 150mm within any change of plain or component, i.e. 150mm around the perimeter and up and over the up-stands as well as 150mm of contact adhesive around the pipe outlet to ensure no movement. The pipe outlet should be a minimum of 150 from the edge of the roof.

With the membrane glued over the outlet, a hole needs to be cut one-third of the diameter of the outlet hole. For a 65mm down-pipe place a ten pence coin in the centre and score cleanly around with a scalpel, do not cut right through just yet as you’ll get halfway around and your money will disappear down the drain.

 

[PHOTO: scalpel and round rubber hole]

Remove the coin and re-follow the cut with the blade positioned vertically parting through the rubber. A clean unbroken circle is required any corners could start a tare when inserting the collet.

 

[PHOTO: collet cut from down-pipe]

The collet is made from a short off-cut of down-pipe with a section remove so as to fit within the internal diameter of the outlet allowing for the rubber. With 65mm diameter pipe about 20mm needs to be removed from the circumference for the collet to fit. A tight ‘click’ fit is desirable, a little trial and error may be required.

Holding and cutting out the section from the collet it semi-skilled and potentially hazardous when applying large pressures to a small component using a knife. Keep away from work, hold the collet in a vice or cut away the section from the collet before cutting the collet off the end of the section of down-pipe.

 

[PHOTO: stretching rubber with collet and silicon]

Silicon is applied both under and over the rubber, glueing everything together and lubricating the collet to stretch through the rubber.

 

Green roof side outlet

Side outlets

Although rubber will stretch and compress it is elastic and always wants to return to its original shape unless locked irreversibly in place as with the collet. It has to be formed and folded like origami or tucking the corners of a hospital bed. Forming side outlets without components is very nearly impossible. A pipe outlet can come through at the base of the up-stand, however, being within 150mm of where the deck meets the up-stand a factory-made component will have to be welded into place.

 

Green roof side outlet

Weir outlet

This bay window has no up-stand other than the kerb edging, the roofline has been raised as high as possible for maximum insulation. By adding in a gutter shape to the roof the rubber can then be inverted to drop into the main gutter. Getting water off the side is a tricky detail, can be done but not recommended.

Gutters

Don’t do it! Water retention, pitch, soil erosion and drop edges.


Inlets

EPDM pipe outlet

Factory welded components and FLL compliance

 

Corners

Green roof external

Internal and external. Internal corners such as those at the four corners of a simple square roof create an overlap, they require no components, just neatly folded ‘hospital’ corners. External corners ‘aretes’ part the rubber leaving a gap, a component is required and must be welded into place. Designing out un-necessary corners will save time, reduce costs, improve ease of installation and reduce risk of failure.

 

Roof-lights

Green roof roof-light

Daylight, aperture reparation, installation and welded components.

 

Flashings

Green roof flashing

Lead, rubber and off-cuts.

 

Damage

Untitled

EPDM is very resistant to damage, however, if used as a chopping board by the glazing contractors to cut ‘flash band’ to go around for the soil pipe with a ‘Stanley knife’ directly on the rubber? Deck-drain and substrate should be completed before access to the roof is permitted.

Easy to repair, if you know it’s there.

 

Accreditation

EPDM Welding

EPDM components must be heat welded for resistance to root penetration. 1.2mm rubber, all junctions and components welded for root resistance. Accredited installation and FLL guideline for green roofing.

 


Deck-drain

Drainage, retention, oof-pitch, reservoir, riverbed, irrigation and harvesting. Advantages and disadvantages of using a deck-drainage layer or not.

 

Deck-drain

Green roof deck-drain

Water drainage and retention.

With an intensive roof build-up of 50mm broken brick aggregate and sedum, the deck-drain layer adds lightweight intensive water buffering within limited space and weight.

With an extensive build-up of barren clay subsoil, 200mm, water retention is not necessary, sedimentation of the clay will form a natural filter layer and aquifers. The drainage layer only depletes the overall available depth available for substate, roof protection is lost however with mindful installation it should not be required.

A deck-drain creates an aquifer for the water to permeates through, it can then drain away sideways preventing the substrate from being washed away.

 

Roof-pitch
Visibility is good but retention is challenged. traditional flat roofing fillets create a very slight pitch e.g. 1:60 to prevent water puddling and assist runoff. This is not desirable for a green roof, you are trying to slow the rate at which water runs off. A pitch does, however, make the roof more visible, this can be achieved by varying the substrate depth, pitch the substrate, not the membrane.

 

Reservoir
A green roof’s water retention can be used to store a large volume of water. With an overflow in place and the roof out-let, ‘taped’ a 40m2 roof can store a cubic metre of water in a 25mm void

 

Riverbed
Drainage channel leading to a drain or overflow. The barren unplanted gravel base of the riverbed provides excellent hunting grounds for jumping zebra spiders.

 

Irrigation
An appropriate deck-drain layer can evenly distribute water across the whole roof. The vegetable garden irrigation system takes water under gravity to the fruit tree around the perimeter of the roof from here the water permeate down and fills the entire deck across the roof before overflowing through the deck-drain to the roof out-let and down to the storage tank. The water permeating sideways across the top of the deck-drain brings water to the tomatoes in the greenhouse without the need for individual dowsing pipes.

 

Harvesting rainwater
With water storage in place for irrigation why not use it to flush the loo, this saves money and eliminates limescale.

 

Green Roof Deck-drain

 

Engagement and cost
Bin store, garden shed or cycle store, a bit of old carpet will do, delivery cost and all v’s spending thousand pounds on sedum. Small roofs are often low, shaded, accessible and dispensable. Small structures can often accommodate more substrate, using old carpet and occasional having to engage with throwing on a bowl of washing-up water. Two square metres of deck-drain has a negligible material cost but comes with the same delivery cast as much larger roofs. On a large roof, the area adds up, exponentially.

 


Substrate

Green Roof Sub-strate

Moisture retention and collection
Pozzolan, off the peg and grow your own.

 

Green roof intensive, deck-drain, light weight substrate and sedum

Intensive or extensive

 

Green roof training

Structural limitation
A one size fits all, drought-resistant, systemised approach has led to the popularity of lightweight broken brick aggregate and sedum.

 

Economics of scale
Clay subsoil is freely available and can be dug up on-site, perhaps to create a pond.

 

Soil and compost contain lots of organic matter and require more depth. When saturated they gain additional weight.

Hygroscopic pozzolan collects moisture from the atmosphere.

 


Habitat

Green roof habitats

Successful appropriate planting

 

Sedum in flower

Sedum

 

Green Roof Habitats

Wildflower

 

Roof top vegetable garden

Wildlife habitats and vegetable gardens

 

 


Case Studies
Green roof projects

 

Suppliers

Hertalan

Hertalan
EPDM rubber roofing membranes

4A Isabella Court, Millennium Business Park, Mansfield, NG19 7JZ
01623 627285

info@hertalan.co.uk
http://www.hertalan.co.uk

 

Shire green roof substates

Shire Green Roof Substrates
Mineral Suppliers, Technical Consultants & Project Management

Charles Fentiman
31 Nutham Lane, Southwater, West Sussex RH13 9GG
01403 732186

info@greenroofsubstrates.co.uk
http://www.greenroofsubstrates.co.uk

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