From R3114 Feb 2019, Q2.

a)      Describe the characteristics of green roofs under EACH of the following headings:

i)                 site selection and preparation;                                         2 marks

ii)                growing media:                                                                     2 marks

iii)              characteristics of suitable plants.                                     4 marks

b)     Name TWO plants suitable for use on green roofs.           2 marks

This question relates to the following part of the syllabus:

Outcome 1. Understand the practices of establishing and maintaining planting in a range of specialist areas. 

1.1 Describe the characteristics of a range of specialist areas.

Garden and urban situations to include the following:

 - woodland; - prairie; - wildlife; - wildflower meadows; - sensory; - potager; - courtyards; - container gardens; - roof gardens; - living walls; - green roofs; - street plantings; - community gardens; - amenity bedding (to include: traditional,  carpet, three-dimensional and sub-tropical).

 Please note for assessment 1.1 (describe the characteristics of a range of specialist areas), plant examples are needed where appropriate.

For this question it is particularly useful to look at the mark allocation for each part. For a) the first two parts are worth 2 marks, whereas part iii) is 4 marks so needs more detail.

For part a)i) the examiners’ comments suggest the following as correct answers:

... checking the weight bearing capacity of the roof, carrying out a structural survey using a structural engineer, using a waterproof membrane to protect the roof beneath, installation of grids to contain growing media, using materials to suit pitch of roof.

For part ii) correct answers are suggested as:

... the use of lightweight growing media and a free draining open structure which also had to be moisture retentive, depth of growing media needed for type of green roof stated.

The examiners’ comments also point out incorrect answers which is useful to see. These included the use of materials that would be too heavy for the roof, such as stones.

The suggested plant characteristics were:

...evergreen, non-invasive root system, low growing, carpeting, spreading or mat forming, robust/hardy, drought tolerant, small and/or fleshy leaves.

When you are revising make sure you check through all parts of the syllabus. Part b) includes the plant examples which are included at the very end of this section.

Suggested suitable plants were Sedum lydium, Sedum acre, Sempervivum spp., Thymus spp. The question doesn’t ask for distinct examples, which makes it easier. Always check whether ‘distinct’ is in the question, and if it is you must include plants from different genera. It is probably a better approach to always use ‘distinct’ examples all the time.