I’m sure we’ve all been there: the client wants to refurbish their flat roof areas, and “Oh, while you’re at it, could you install a timber deck area where our staff could have barbecues and maybe a wee area of green roof? We need to improve our environmental credentials.”
You turn up to do the condition survey, step on to the roof and are confronted with the following:
Figure 1: Congested city centre roof top
OK, so maybe that’s a bit extreme, but the designing and specification of refurbishment works may need to include some management of your client’s expectations.
However, regardless of what needs to be done, NBS Chorus has a wide range of options and solutions for even the most demanding of clients.
Surveys
Undertaking a detailed survey of the existing roof is of vital importance to the success of a refurbishment project. In addition to the usual condition survey, it may be necessary to undertake a thermal imaging (infrared) survey of the roof surfaces to determine moisture ingress/ thermal bridging or a full structural assessment. This is particularly relevant where additional loading is to be applied, e.g. a green roof, attenuated water (blue roof) or timber decking (and footfall).
Relevant CAWS sections
- B ‘Complete buildings/ structures/ units’.
- C13 ‘Building surveys/ audits/ appraisals’:
- 120 ‘Building fabric surveys’.
- 140 ‘Defects surveys’.
- 150 ‘Deleterious materials surveys’.
- 160 ‘Energy assessment surveys’.
- 170 ‘Pre-refurbishment audits’.
- 190 ‘Structural appraisals’.
- 225 ‘Infrared thermographic surveys’.
- 285 ‘Survey and testing for asbestos-containing materials’.
- 295 ‘Survey and testing for moisture’.
- C14 ‘Building services surveys’:
- 110 ‘Building services surveys generally’.
Relevant Uniclass sections
Ac_15 ‘Survey activities’:
- Ac_15_50_10/110 ‘Building fabric surveying’.
- Ac_15_50_12/115 ‘Building measurement surveying’.
Insulation and isolation options
One of the key objectives of the aforementioned surveys is to establish the existence, position and condition of any thermal insulation in the existing flat roof build-up. Historically, it was commonplace for the insulation (and a ventilated cavity) to be placed below the structural deck (cold deck roof construction). Refurbishment provides an ideal opportunity to improve the thermal performance of the roof by introducing additional (or new) insulation above the existing waterproofing layer (warm or inverted roof constructions).
Where existing warm deck insulation has indicated higher than normal moisture contents, there may be a need for full or partial removal of the affected areas prior to application of the new waterproofing system.
Isolation products may also be required where existing or new plant or services equipment is to be positioned/ repositioned on the roof. This may be particularly pertinent where equipment is to be placed on newly installed thermal insulation that is now positioned above the existing waterproofing. Connections to internal services may also need to be fire-protected as they penetrate the roof deck.
The positioning and specification of thermal insulation is typically dealt with within the various general clauses/ system outlines in both CAWS and Uniclass. These systems are highlighted under the heading ‘Waterproofing options’. However, some associated isolation and fire protection systems and products may be dealt with in the following:
Relevant Uniclass sections
P ‘Building fabric sundries’:
- P10 ‘Sundry insulation/ proofing work’:
- 432 ‘Cavity barriers’.
- 440 ‘Fire protection’.
- 500 ‘Anti-vibration mats or pads’.
- P12 ‘Fire-stopping systems’:
- 130 ‘Fire-stopping systems to individual services penetrations’.
- 140 ‘Fire-stopping systems to multiple services penetrations’.
Relevant Uniclass sections
- Pr_80_77 ‘Services support and containment products’:
- Pr_80_77_94_50 ‘Mat mountings’.
- Pr_80_77_94_60 ‘Pad mountings’.
- Ss_25_60_30 ‘Fire-stopping systems’:
- Ss_25_60_30_40 ‘Individual services penetrations fire-stopping systems’.
- Ss_25_60_30_55 ‘Multiple services penetrations fire-stopping systems’.
Waterproofing options
Within both CAWS and Uniclass, the roof-waterproofing systems are classified along product lines, e.g. mastic asphalt, liquid-applied, reinforced bitumen membrane and single-layer (polymer) sheet. These systems are further divided depending upon the position of the thermal insulation, e.g. warm, inverted and cold roof construction. The cold roof construction option has been omitted from the listing below.
For specific guidance on product selection, see the ‘Sources of information’ below.
When overlaying with a different waterproofing material, guidance on any compatibility issues should be sought from manufacturers.
J ‘Waterproofing’:
- J21 ‘Mastic asphalt roofing/ insulation/ finishes’:
- 110 ‘Warm deck roof coating’.
- 120 ‘Inverted roof coating’.
- J31 ‘Liquid-applied waterproof roof coatings’:
- 120 ‘Warm deck roof coating’.
- 130 ‘Inverted roof coating’.
- J41 ‘Reinforced bitumen membrane roof coverings’:
- 110 ‘Built-up reinforced bitumen membrane warm deck roof covering’.
- 115 ‘Single-layer reinforced bitumen membrane warm deck roof covering’.
- 120 ‘Built-up reinforced bitumen membrane inverted roof covering’.
- 125 ‘Single-layer reinforced bitumen membrane inverted roof covering’.
- J42 ‘Single-layer polymeric sheet roof coverings’:
- 110 ‘Warm deck roof covering’.
- 120 ‘Inverted roof covering’.
Relevant Uniclass sections
- Ss_30_40_30 ‘Flat roof covering systems’:
- Ss_30_40_30_43 ‘Liquid-applied warm roof covering systems’.
- Ss_30_40_30_42 ‘Liquid-applied inverted roof covering systems’.
- Ss_30_40_30_55 ‘Mastic asphalt warm roof covering systems’.
- Ss_30_40_30_52 ‘Mastic asphalt inverted roof covering systems’.
- Ss_30_40_30_72 ‘Reinforced bitumen membrane warm roof covering systems’.
- Ss_30_40_30_71 ‘Reinforced bitumen membrane inverted roof covering systems’.
- Ss_30_40_30_80 ‘Single-layer sheet warm roof covering systems’.
- Ss_30_40_30_79 ‘Single-layer sheet inverted roof covering systems’.
Green (living) roof options
A green or living roof is partially or completely covered with vegetation on a growing medium, laid over the roof’s waterproofing membrane. This area of vegetation may also incorporate ponded areas, which may be used to store rainfall (see blue roof options) or to treat grey water.
Green roofs have several advantages. They can be used to: absorb rainwater; provide additional thermal and acoustic insulation; create natural habitats for wildlife; and provide a more aesthetically pleasing backdrop where the roofscape is accessible or overlooked.
Green roofs are suitable for the refurbishment of small or larger industrial, commercial, municipal and some larger residential buildings. When considering design options, check the suitability of products with waterproofing manufacturers.
Relevant CAWS sections
Q ‘Paving/ planting/ fencing/ site furniture’
- Q37 ‘Green/ blue/ biosolar roofs’:
- 110 ‘Intensive green roofs’.
- 120 ‘Semi-intensive green roofs’.
- 130 ‘Extensive green roofs and biodiverse roofs’.
Relevant Uniclass sections
- Ss_45_40_47 ‘Living roof systems’:
- Ss_45_40_47_09 ‘Brown roof systems’.
- Ss_45_40_47_28 ‘Extensive green roof systems’.
- Ss_45_40_47_40 ‘Intensive green roof systems’.
- Ss_45_40_47_75 ‘Semi-intensive green roof systems’.
Figure 3: Green (living) roof
Blue roof options
Blue roof systems are flat or low-slope roofs that are designed to allow short-term storage. They also allow the controlled release or attenuation of rainwater during heavy and storm events. Designed as part of a sustainable drainage system (SuDS), they reduce the risk of inundating conventional drainage systems. A blue roof releases water at a managed and controlled rate directly into the sewers, waterways or river systems.
Blue roof systems may incorporate a green or living roof that aids the attenuation of water and may provide some filtering prior to release into the natural environment. Specific performance and details should be confirmed with manufacturers/ suppliers of systems.
For specific design guidance relating to blue roofs, refer to the ‘Sources of information’ below.
Relevant CAWS sections
Q ‘Paving/ planting/ fencing/ site furniture’
- Q37 ‘Green/ blue/ biosolar roofs’:
- 150 ‘Blue roofs’.
Relevant Uniclass sections
- Ss_30_40_30 ‘Flat roof covering systems’.
- Ss_30_40_30_07 ‘Blue roof systems’.
Sources of information
National Federation of Roofing Contractors (NFRC).
Single Ply Roofing Association (SPRA).
Liquid Roofing and Waterproofing Association (LRWA).
Green Roof Organisation (GRO).
Green Roof Organisation (GRO) publication ‘GRO green roof code of best practice incorporating blue roofs and biosolar application’.
National Federation of Roofing Contractors (NFRC) publication ‘NFRC Technical Guidance Note for the construction and design of Blue Roofs’.
Conclusions
The refurbishment of flat roof areas can be complicated, and is made more difficult by: different roof levels; hazardous materials; access; the large range of waterproofing choices; the need to incorporate environmentally acceptable and sustainable choices; and even managing the client’s expectations!
However, Chorus offers extensive guidance and detailed specification clauses to assist in the delivery of a successful outcome. You might even be able to fit that timber deck in (Q55 ‘External decks, boardwalks and bridges’ or Ss_30_20_30_25 ‘Decking systems’)!
