Green Roofing Jargon Busting and FAQ's

Green Roofing Jargon Busting and FAQ's

We get many questions on Green Roofing and Living Roofs and here is a list we believe should simplify things for you.

What is the Difference between Extensive and Intensive Substrates?

Extensive is the most popular substrate / media mix for green roofs and consists of 80-90% of inorganic materials (crushed brick/pumice/L.I.C.A.) and 10-20% of organic materials (compost).

Intensive is the choice for roof gardens (See below for details on green roofs vs roof gardens).

The term Extensive means "covering or effecting a large area"

The extensive mixture is designed for low maintenance hence its popularity as most roofs are difficult to get regular access to for watering and weeding. The extensive roofs shouldn't need any watering during the year, however this will depend slightly on your planting choice and how hot and dry the summer becomes. Use common sense as you would with your garden at ground level, if it looks like it needs watering, water it. In some commercial applications contractors install a miniature roof at ground level with the exact same elements as the higher level roof to give an indication of how it is performing.

The intensive substrate mixture (circa 20-30% inorganic and 70-80% organic) is designed more for roof gardens when access is easy and you can take care of watering and maintenance as you would a normal lawn area.

Do I need a Drainage Board / Layer?

This depends on your roof. Many experienced green roofers and designers love to argue about the need of a drainage layer on a green roof, we tend to use the popular German FLL standards in the UK however the Austrian standards that do not favour drainage/water retaining boards are very successful also. (In later posts we will serialise these two respective standards).

If you are doing an extensive roof and the roof has a slight pitch on it, circa 1 to 40 fall ratio, then you can get away without a drainage layer. This is because drought tolerant plant species such as sedums do not like too much water or sitting in water. If you are doing a roof with a fall of 1 to 5 ratio you would need to consider some kind of retention board that prevents slippage.

You can also use the drainage layer as a water storage board too. There are various types of drainage layers from gravel to specialised plastic systems.

This is unless you are creating a wetland roof in which case you are looking for more water storage and this design should be carefully approached and even consider an irrigation system to maintain moisture.

Normally commercial living roofs require a water retention/drainage layer as part of the design.

What maintenance is needed?

This depends on the type of living roof you go with.

Drought tolerant species such as Sedum's are the lowest maintenance as they can survive in drought conditions. All they need is a light hand weed once a year for wind blown seeds if you are concerned with these.

Wildflower green roofs will require weeding once or twice a year and its best to cut them back at the end of autumn and remove the cuttings to retain their appearance.

To create biodiversity in a living roof its best to leave them to do there own thing.

You can create living roofs that use grass and depending on the finish you are looking for it can require mowing. If you want the green roof to be neatly mown make sure there is easy access or alternatively look at installing a robotic mower for the roof.

What is the lowest maintenance green roof?

Extensive roofs are the lowest maintenance, they can survive with little water and a low amount of input.

What should I put on my green roof?

This is totally up to you. The most popular are Sedums or Wildflowers. Our Sedum and Wildflower mat gives the best of both systems. If you are totally unsure contact us and we can advise further.

Is Sedum the best for a living roof?

This depends on what you want from a living roof. There are advantages to all types of living roofs.

How do I know if the roof is strong enough to have a green roof on?

This is a job for a professional. Your local building control officer should be able to handle this enquiry or an experienced architect, building surveyor or structural engineer will be able to inspect your roof to see what loading it can withstand.

We can advise on the weights of different systems when completely saturated with water (the worst case scenario).

If it is a new build project you will be able to make sure that the joists and structure are strong enough for whatever living roof you want.

If its an existing building you may be limited by the structure and joists as to the loading that you can put on the roof. If the structure or joists aren't strong enough you will be able to talk to an architect, building surveyor or structural engineer to see how you can upgrade the roof to be able to take the weight of the system you want.

Do I need planning permission?

This depends on your location and its always best to check with your local planning office.

Some districts require certain criteria to be met when a green roof is installed which usually involves a border of pebbles or gravel around the edge of the living roof. 

What are the benefits of a green roof?

There are many benefits of a green or living roof.

• Attracts wildlife by creating habitats.
• Wildflowers attract and help bees.
• They also catch heavy metal particles from industry.
• Provides extra insulation on the roof which keeps the building cooler in summer and can reduce heating costs in winter.
• Provides sound proofing.
• Can add value to your property by prolonging the life of the waterproofing membrane.
• Provides storm water retention – it helps release water slower than a normal roof. Helping to reduce flash flooding which is part of the governments S.U.D.S. (Sustainable Urban Drainage Systems)
• Plus it looks great!

How can I attract the most wildlife?

The best living roof for wildlife is to create as many micro habitats as possible.

This can include some of the following ideas:

·       Bee hives.

·       Logs and stone/bricks for critters to live under and around.

·       Bird feeders.

·       Wildflowers for the bees.

·       Shaded areas.

You can also create other types of habitats such as wetlands. This along with meadow areas have been reduced in the wild so creating these types of habitats are vital.

Can I make a wetland living roof?

Yes, its a new way of creating a living roof. There is more strain put on the roof so you need to contact an experienced architect, building surveyor or structural engineer to make sure that you can put that amount of load onto the roof. You also need to make sure the waterproofing materials are happy to sit in water. The waterproofing options we recommend are perfect for it.

What is the best waterproofing for green roofs?

We recommend using EPDM for green roofs. Our systems carry independent certification that the membranes and essentially the joints are suitable.  Many people recommend using pond liners and cheaper alternatives but a green roof is something that is built to last so why put something substandard on.  The easiest systems to fit and install are the UK Flat Roofing EPDM, HERTALAN EPDM and PRO-EPDM. We always recommend using the PRO-EPDM system as this is the highest quality and thickest EPDM on the market.

How easy is it to install a green roof?

Green roofs are reasonable easy to install. It is just a series of layers and the hardest part is getting the right information to achieve the right depths and of course getting all the layers onto the roof.

Which is easiest to fit a modular green roof or a living roof kit?

For someone with no experience the modular system is the easiest to fit. It is quick and easy to install however many people also enjoy taking their time and building the living roof as you would enjoy building your own garden.

How long will a green roof last?

With 70mm of extensive soil substrate there are enough nutrients in there to last circa 30 years.

What is the difference between a green roof and a roof garden?

A Green Roof is a roof that is normally not easily accessible and you wouldn't be using the space as a garden/terrace. Usually uses extensive systems.

A Roof Garden is an area that typically has green roofing materials on but is used as a garden / terrace. You need a different build up on the roof with deeper intensive substrates and different drainage layers etc. Contact us for a roof garden build up.

The extra substrate needed for a roof garden will mean you need to allow for much more weight on the roof. Professional help should be sought from building control, an experienced architect, building surveyor or a structural engineer to work out the weight that the roof can take or can be designed to take.

How much Substrate do I need?

Sedum's can survive in drought conditions and need the smallest amount of substrate on a green roof. We recommend using 70mm of extensive substrate or more.

Wildflowers need more substrate 100mm as a minimum ideally. The more substrate you have the more variety of wildflower you will have on your living roof.

To create further biodiversity in a green roof you can mound up the soil in areas to encourage burrowing invertebrates.

Adding logs and reclaimed bricks can also add to the biodiversity of your living roof.

When checking with a professional ask them about point loads to see if your roof is ok for adding a biodiversity living roof.

View our online store for all our green roofing products

Which EPDM system is the most cost effective and best?

Which EPDM system is the most cost effective and best?

A client, who was looking to replace his old flat roof, asked me what system would I use on my own roof and why.

I immediately replied HERTALAN or PRO-EPDM

He responded by asking why would you choose these systems as their BBA length is less than other cheaper brands. Meaning Firestone and ClassicBond.

It got me thinking about the BBA certificates and what they actually mean for the systems, after-all the BBA certificates are on the full system not just the EPDM. So if you use adhesives and accessories that aren't listed on the BBA certificate you may as well tear it up.

The BBA certificates for all systems are very precise in how the products should be fitted to achieve the service life.

They give accurate details on the following key areas

• How to install the EPDM membrane.
• Which adhesives to use and how much.
• Which accessories are included in the system.
• Who should install the system.

All systems require training from the manufacturer. If you don't have training and want to know how to install the systems yourself then videos and instruction are easy to find on the internet. Also all manufactures offer training days.

After this the systems vary massively.
Some manufacturers will supply their systems with
• Cheaper adhesives.
• Accessories that are non BBA approved.
• HERTALAN and PRO-EPDM don't have any cheaper non BBA options.

Here are my costings based on the original 5m x 6m enquiry and if you want to read more on how I get these figures I explain all the BBA documents further on in this post.

This table shows the Non BBA certified options and the prices. (ex vat)

So remember non of the above systems comply with the BBA testing standards and therefore  wouldn't be guaranteed to last the length quoted by the manufacturer in their BBA and would highly likely start giving problems within 10 years. The Hertalan 1.0mm has the best chance as its the same EPDM as the Hertalan 1.2mm and has the same adhesive.  However the other 2 systems just aren't going to last that long due to being installed to an uncertified method.  If suppliers tell you that you need less than is suggested within the manufacturers BBA certificate, then the system will ultimately fail. If it would work with less adhesives it would have been put through the tests with less adhesive.

In the table below we have all the options that are covered by the BBA certificate.

Following on from my pricing I explain below how I reached these conclusions and how to interpret the BBA certificates and what quantities of adhesives are actually required by the manufacturers.

Firestone RubberCover EPDM
One of the cheapest systems on the market for EPDM is Firestone RubberCover. If fitted correctly the product comes with BBA certification for 30 years on roofs up to 150m2 for domestic applications. Anything over 150m2 there is no BBA certification. The perceived low cost of this system stems from stockists/retailers selling the incorrect amounts of adhesives to make these systems appear cheap. To give an example of this, take the 10 litres of water based bonding adhesive, most online retailers suggest it will cover 50 sq.m however to comply with the BBA you need to use 1.3 litres per m2 (0.8 litres on the deck and 0.5 litres on the EPDM) which is a massive difference to the advertised 0.2 litres. Similarly if you just put it onto the deck and push the EPDM into it you need between 1.47 litres to 2.45 litres, depending on the condition of the surface, so even more expensive. So the correct amount of adhesive required, based on the manufacturers figures and to comply with their BBA certificate, will cost you between £9.75 + vat (for the 1.3 litre option) or £18.40 + vat (for the 2.45 litre option). So maybe this system isn't as cheap as has been suggested.

ClassicBond EPDM
Then we have ClassicBond which is a very similar system to Firestone RubberCover.  On the face of things a 35 year BBA. But again everyone sells the ClassicBond with a water based adhesive that hasn't been through the rigorous BBA product testing.
So if you want to comply with their BBA then you need to use contact adhesive and you need to mechanically fix the sheet around all perimeters and around any openings (skylights access hatches etc) with their RUSS strip. (This is a reinforced piece of EPDM with a pre attached splice tape that is screwed down and then you splice the back of the main sheet to the tape) So by the time you have added on the Russ strip and the mechanical fixings plus the contact adhesive you end up a long way from the price quoted by some retailers with little or no flat roof experience. (ClassicBond is also sold under the name Carlisle Syntec)

Duoply EPDM
DuoPly is a Fleece backed version of ClassicBond and again on the internet is advertised with a water based adhesive (WBA) which isn't BBA certified. You have to use a polyurethane (PU) adhesive and the RUSS strip system at perimeters and skylights etc. (This is also sold under RubberBond)

HERTALAN and PRO-EPDM
HERTALAN and PRO-EPDM systems have a 25 year BBA and don't have any cheaper options for installation. So prices that are advertised on the internet are as they should be. This is where these systems start to prove how cost effective they are and look better than originally thought.

RESITRIX SKW & SR
RESITRIX SKW and SR both carry a 30 year BBA and the amount of primer that is advertised (250g per m2 when applied with a roller or 120g per m2 if applied with spray canister) is as per manufacturers guidelines and that which went through the BBA testing.

So now I have explained the most popular EPDM systems and what must be done to comply with their BBA certificates and the costings on my clients original enquiry which was his 5m x 6m double garage roof, you can clearly see to achieve a roof to a BBA certified standard its very different to what is advertised by many of the stockists and dealers and you can see why I immediately said HERTALAN or PRO-EPDM as my preferred systems.

When it comes to installation HERTALAN and PRO-EPDM are uncomplicated systems that make them fast and easy to install and therefore even more cost effective due to lower labour costs? So in terms of productivity and material costs to get a BBA certified roofing system HERTALAN EPDM and PRO-EPDM are certainly in my opinion the best option.

For anyone who is interested in seeing the BBA certificates I have included a link below.

All prices are from internet retailers and details are available on request.

References

BBA – HERTALAN and PRO-EPDM 
BBA – RESITRIX SKW
BBA – RESITRIX SR
BBA – ClassicBond 
BBA – DuoPly
BBA – Firestone