25 Apr 2017
Last month in France a law came into force requiring all new commercial buildings to be equipped with either rooftop vegetation (a green roof) or solar panels. France is the first country to enact such a requirement.
Whilst the benefits of solar panels are widely appreciated there is, in my experience, less understanding amongst architects and developers in the UK about the benefits of green roofs. The concept of a green roof goes back as far as the Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World, believed to have been a series of intensive green roofs built by Nebuchadnezzar II for his wife who was homesick for the plants of Persia. These days, green roofs are generally one of three different types: intensive – parks and gardens including urban agriculture; semi-intensive – garden green roofs; and extensive – natural low maintenance green roofs. The latter are the most common these days in the UK and can take the form of either sedum or biodiverse roofs.
In the past green roofs were seen primarily as a way of satisfying planning requirements to provide external amenity space in urban areas. However more recently it has become clear that they offer a wide range of other benefits which, if properly understood, could increase their attractiveness to the development industry.
Green roofs help to reduce urban heat islands which result from roads and buildings becoming impermeable and trapping excess heat. In warm climates, this can result in cities becoming nearly 3 degrees centigrade warmer during the day and up to 12 degrees at night. Green roofs are now known to decrease the heat transfer through the ceiling which improves the energy efficiency of buildings. Recent research by Universidad Politécnica de Madrid shows that, when vegetation density is high, the incoming heat into the building through the roof is 60% lower than the incoming heat without vegetation. Essentially a green roof with high density vegetation works as a passive cooling system, making it particularly suitable for use in warmer climates.
Green roofs impact the process of water cooling in chillers and improve the efficiency of heating, ventilation and air conditioning systems through reduction of temperature around them in the summer. Research into the effect of green roofs in different climates showed that green roofs are able to reduce the cooling energy demand in summertime up to six percent, whilst at the same time having a negligible impact on energy consumption in cold seasons. In cooler climates, green roofs also act as a wind shield which leads to reduction of heating energy demand.
Green roofs can also make a valuable contribution to surface water drainage, having the ability to limit storm water runoff by between 50% and 90%. They can also help reduce air pollution by providing a natural filter for pollution. Green roofs can increase the flora and fauna diversity in urban areas and they decrease the rate of carbon-dioxide emissions by converting carbon dioxide into oxygen via photosynthesis.
An important factor to consider when designing any green roof is the dead load capacity (or weight) that the roof exerts onto a building. Whilst retrofitting can be difficult, new buildings can easily be designed to ensure that they can withstand the weight of a green roof, making them a viable option on many sites.
Admittedly green roofs have higher capital costs than their traditional counterparts. This is particularly true in the UK, as they are relatively uncommon at present. Capital costs for extensive green roofs are generally between 150-200% more that traditional ‘black’ roofs. Since they are currently not common in the UK, there are few specialist contractors available and this is probably one of the primary causes of the increased capital costs. Maintenance of extensive roofs however is about the same as a traditional roof, only requiring visual inspections every six months. With the increased lifespan of a green roof (approximately double that of a tradition roof) the number of times the roof has to be repaired or replaced is halved - meaning that the introduction of a green roof can actually reduce maintenance requirements and costs.
In an ideal scenario, a green roof would be complemented by the addition of photovoltaics to generate electricity. Research shows that the two uses are complementary, since the cooling effect of the planting increases the efficiency of the photovoltaics. The original draft law put before the French Senate proposed solar and green roofs rather than a choice between the two. This would have removed the choice between technologies and promoted ‘biosolar’ roofs that deliver both biodiversity and renewable energy generation. Unfortunately the Senate concluded that such a requirement would result in “a negative impact on the economic vitality and employment”. Nevertheless, unlike the UK, the tariffs for renewables are still favourable in France and in some parts of the country, there are incentives for green roofs - so biosolar roofs may have a future in France after all.
Back in the UK Lichfields is working on a planning application for a residential development in the north east of England which incorporates an extensive sedum green roof across the entire 1,500 square metre roof area, along with 40 square metres of photovoltaic panels. The size of the photovoltaics in this project has been limited not by cost but by the potential generating capacity of the site. The installation of technologies which are capable of generating more than 12kWp of electrical energy cannot be assumed to be acceptable to the local electricity network operator. Even though one may not want to export the electricity generated, the operator still has a say. Anything above 12kWp needs the agreement of the network operator; below 12kWp, no agreement is necessary. In preparing the application, a review was undertaken of the local heat map for the area, which details the likelihood of larger scale electrical generating systems being approved. The heat map showed that the installation of a larger scale system in this location is unlikely to be accepted. To limit objections to the application, the client decided to keep the application to panels with a maximum generating capacity of 12kWp.
It is clear that there are many reasons why biosolar roofs are not being developed at a faster rate in the UK and there needs to be more encouragement to deliver such schemes. If such schemes are viable in north east England, then there is no doubt that they could be successfully delivered elsewhere in the UK as well.
 OLIVIERI, F.; DI PERNA, C.; D'ORAZIO, M.; OLIVIERI, L.; NEILA, J. “Experimental measurements and numerical model for the summer performance assessment of extensive green roofs in a Mediterranean coastal climate”. Energy and Buildings 63: 1-14. DOI: 10.1016/j.enbuild.2013.30.054. AUG 2013
 Ahmadi H, Arabi R, Fatahi L. Thermal Behavior of Green Roofs In Different Climates. Special Issue of Curr World Environ 2015;10(Special Issue May 2015)
In 2014, the European Parliament adopted further amendments to the 2011 Environmental Impact Assessment (‘EIA’) Directive, aiming to ‘simplify the rules for assessing the potential effects of projects on the environment’. Despite the United Kingdom’s pending exit from the European Union, the requirement to transpose the Directive into national legislation by May 2017 remains (my colleague Liz Evans has covered in detail in a previous post why).In the last few weeks, both Scotland and Wales (NLP’s summary can be found here) have started their respective consultations on transposing the Directive into their own Regulations, and environmental practitioners are awaiting consultation on how the Directive will be transposed into English legislation.Over the coming weeks, as consultation continues, NLP will look at various elements of the Directive, and what implications they are likely to have on EIA.One of the changes proposed by the Directive that has the potential to have a considerable impact on how EIA is undertaken throughout the UK is the requirement that, where a scoping opinion is issued by a determining authority, an EIA ‘report’ (the revised name for an Environmental Statement in the Directive) shall be “based on that opinion, and include the information that may reasonably be required for reaching a reasoned conclusion on the significant effects of the project on the environment”.Although voluntary, the current process of EIA scoping is a very valuable tool when undertaking assessments, as it allows developers to agree what topics should be assessed and how assessments should be undertaken. The scoping process is a non-binding tool, which allows for discussions between consultants and the determining authority to continue to engage on methodologies beyond issue of the opinion and as a scheme evolves in design.
Common practice sees a request for a scoping opinion detailing a scheme in a ‘worst case’ scenario. Should design changes prior to submission of an EIA report affect how a methodology has been agreed in the scoping opinion, the non-binding nature allows flexibility of approach, and the current process allows an EIA report to explain any changes.Whilst the Directive will allow revised Regulations to retain the voluntary nature of the EIA scoping process, does it allow retention of the flexibility for developers and consultants to amend their methodologies as a scheme evolves, if a scoping opinion has already been issued? On first view it would appear not, and it would suggest that a developer would have to seek a further scoping opinion (or multiple) to agree any changes. Given the statutory five-week process for issue of an opinion under the current Regulations, this could potentially lead to lengthy delays before submission.This amendment also potentially shifts the focus of the EIA scoping process from that of a helpful guide for methodologies within an EIA report, to a procedural set of handcuffs for a proposed development.If this is the case, does the Directive discourage the voluntary scoping process? Seemingly it does, however not seeking a scoping opinion could delay the determination of an application post-submission, presenting potentially bigger risks for a developer. The absence of a scoping opinion prior to submission gives no certainty to the content of an EIA report, and could delay the decision-taking process.This certainly appears to place increased importance on the timing of seeking a scoping opinion. Scope too early and the opinion might be out of date by the time of submission, but scope too late and the opinion might arrive too late to robustly include its requirements.Additionally, from a determining authority’s point of view, there is the potential that mandatory implementation of scoping opinions could result in authorities taking a more risk-averse approach and asking for more information at the scoping stage than would otherwise be needed to consider the significant effects of a development.By way of example, we have reviewed the Welsh consultation on its changes to the EIA Regulations which suggests amending (increasing) timescales for issuing scoping opinions to address this Catch-22 situation. Whilst this might allow a determining authority sufficient time to consider a development and provide a proportionate response, it doesn’t necessarily address the issue of how to amend a methodology as a scheme evolves, between the time of the scoping opinion being issued and the EIA report being submitted.It is hoped that the Regulations, when they do come into force, will clarify the implications of an EIA report being robust for submission but not meeting the requirements of an issued scoping opinion, in order to avoid delays to schemes post-submission. It is also certainly hoped that the Regulations allow the scoping process to retain its flexible and iterative nature rather than be bogged down in procedure which would restrict any assessment work.Are there any obvious solutions to this conundrum? Perhaps we could be heading down the route of scoping opinion addendums that could be issued quickly by determining authorities to update their scoping opinions? We do know the EIA process does like an addendum...