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There are many reasons why it may be necessary to refurbish a roof including;

  • The waterproofing membrane may have reached the end of its serviceable life.

  • The thermal insulation is not good enough. This can often be brought up to current standards by installing additional insulation during refurbishment.

  • A change of use may be intended. Occupiers of buildings with flat roofs are often able to enjoy the advantage of increasing their living space by using the roof as a terrace or roof garden. Many existing flat roofs may be modified to take pedestrian traffic or soil for a roof garden.

The main refurbishment choices include, repair [applying patching to original waterproof membrane], and over-roofing [i.e. applying a completely new skin, which may or may not have a separate supporting structure]. Over-roofing generally includes adding thermal insulation on top of the existing roofing materials.




Add thermal insulation


Add more floors above

Create amenities for residents


Create a green roof

Install photovoltaics

Install wind turbines

Roof insulation


The preferred method of insulating a flat roof is to locate the insulation on the out side of the roof slab i.e., warm deck or inverted warm deck.

  • Warm deck flat roof: Insulation is installed on the concrete slab and covered by a waterproof membrane.

  • Inverted flat roof: Insulation is placed above the waterproof membrane and retained in place by heavy ballast or paving slabs.

Warm deck should be considered where the waterproof membrane is being replaced. Warm deck construction (including a new waterproof membrane) can also be applied over the existing waterproof membrane of an un-insulated roof, which may be preferable to creating an inverted roof.


If external roof insulation is not feasible then internal insulation [ceiling] must be considered. Whilst considering internal insulation, the reduction in thermal mass [which helps in stabilising temperature] and risk of interstitial condensation needs to be taken into account.


Insulation beyond a thickness of 200mm is not advised unless convective heat gains are controlled [e.g., heat recovery ventilation].


Other considerations



Warm deck and inverted flat roof constructions can be used in most cases where increased thickness is not a problem, but it should be ensured that the roof structure is able to take the extra weight of any ballast materials. Upstands also need to be checked and raised where necessary.

Environmental impact of insulation

Although insulation helps to conserve energy, they in general cause environmental impact during their production. Thus the selection of low impact materials for the insulation is likely to have significant environmental benefits.


Mineral wool insulation is a good mainstream insulation. However, use of natural and local materials such as sheep's wool should also be considered.


Insulation materials such as extruded polystyrene must be avoided.



For a tower block, the roof insulation will provide marginal cost savings, as the heat loss though the roof surface only contributes about 3-5% of the total heat loss thtough the fabric.

However it has substantial impact on the flats on the top floor. Approximately 30 to 40% saving can be achieved for the upper most flats.

Roof insulation can also reduce cold surfaces, condensation, and mould growth.

Embodied energy: Insulation materials

Typical Cost

□   Warm deck roof £40-80/m2

assuming existing roof slab waterproofing is in good condition to receive new insulation and waterproofing. No allowance for any pathway for maintenance purposes

□   Inverted deck roof £65-110/m2

assuming existing roof slab waterproofing needs to be replaced with new waterproofing, place new insulation and with heavy ballast or paving on top. Will be good if there is a lot of foot traffic on the roof

Funding opportunities:
  Energy Savings Trust

Also see:

□  Facade insulation

More information:

□  Energy Efficient Best Practice


  Knauf Insulation

□  Kingspan Insulation

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Add floors above


High-density inner-city housing is likely to become a priority for urban centres of UK over the next ten years. Given the increasing demand for inner city housing and the likely formation of many new households, many of them single parents or couples; high-rises have an important role to play in the regeneration of our cities.


The Urban White Paper, which aims to ease the pressure on our countryside by bringing people back into town and city centers, explains that we may need to provide for up to 3.8 million new households over the next twenty years.


As a high density form of housing they allow housing need to be met while keeping land use to a minimum, freeing up green space which would otherwise be required for low density housing development.

Adding more floors over existing buildings could provide much needed affordable homes.

Other considerations

Structurally the 1960's tower blocks are typically designed to take 1.4 times the dead load and 1.6 times the live load. Therefore, as a rule of thumb, 10% of the mass of the building can be added as additional floors.



  • Additional houses can create adequate density for provision of services such as concierge or combined heating and power plants.

  • The new flats could be sold and profits could be used to cross subsidies the cost of refurbishment of the whole building.

  • New homes are created on existing footprint therefore area which would have otherwise used up valuable virgin land is saved.

Typical Cost

□  £68,000/flat

Cost based on the following assumptions- flat areas 35m2; steel structure frame & upper floor @ 65kg/m2; existing structure can take the additional load;

Cost includes extension on existing staircore and structure to the new floor;
- excludes cost for balcony enclosure
- excludes extension of lift core and replacement of new lift to serve the new floor on top; assuming this will form part of the lift budget
- excludes extending the existing refuse chutes to this floor assuming this cost will form part of the overall refuse chute cost

Funding opportunities:
□  n/a

Also see:

□  Change layout to increase solar gains

More information:

□  n/a



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Create amenities 

The space on the top of a tower block is an asset that is often neglected. In many cases it may provide some income for the residents association if it is sued as the site for mobile phone masts. Concern over electro-magnetic radiation from such masts may limit further use, but if not then there are many ways such a space can be used.


What need to be done

The basic improvements needed are firstly to ensure that the surface of the roof can take heavy use: a suitable flooring may need to be provided. The second consideration must be safety. Adequate fencing must be provided; there are also likely to be insurance issues to be resolved in the roof is to be used by residents.


The third key point is access. The stairs from the top floor the lift reaches will need to be improved to permit access. There will also be a need to ensure that the  door to the roof is strong and secure and can be locked e.g. at night time.


Basic actions

The first steps would be to discuss possible use with the residents and carry out basic works as above. Someone in the block, either a care-taker, concierge or resident will need to be responsible for opening the roof and closing it and checking it at the end of the day.


Leisure amenities

If the roof can be improved to basic standards in this way then there are many possible uses, although it is likely that informal leisure, especially sun-bathing, will be most popular. A roof garden of some suitable nature can be developed to make the areas more attractive. Areas not in use could become ‘green roofs’.


Social areas

If a roof area is suitable for heavy use then more extensive facilities could be developed. These might include a roofed social area (if this is to be used in winter it should be directly linked to the stairwell) that could include a café space for use in summer.


Such developments can be very popular. A block at Cowley in Oxford became so used in summer that people would arrive early to get the best spaces.


Other uses will depend on local needs. In St. Petersburg, Russia, residents have used the large roof space on a long tower as the base for a business growing and selling turf for lawns.


Other considerations


Maintenance and security will need to be central issues at all times, as will limiting unauthorised use by those outside the block.



  • A well-planned roof space can be a popular focus for social inter-action in a block

Typical Cost

□  n/a

Funding opportunities:

Also see:

□  Increase lobby area

□  Entrance

More information:

□  n/a


□  n/a

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Green Roof

Green roofs have been fundamentally divided into two categories, intensive and extensive.

Intensive green roofs are roof gardens and like any garden provide space for people. They require the intensive management of a ground level garden, are usually based upon a thick soil or substrate layer and require artificial irrigation. Preferred plants are selected and the roof conditions created to support them. They are heavy systems and thus can have major structural implications for the building.

Extensive green roofs are not usually recreational (although extensive planting can be integrated with intensive systems). They have low management requirements and do not usually require artificial irrigation. Plants are selected that will succeed with only minimal modification of the normal roof conditions. Planting styles are usually naturalistic with the objective of establishing a self-sustaining plant community on the roof. Based on a thin layer of soils or substrates, they are lightweight systems with minimal structural implications for the building. The main reasons for installing an extensive green roof are visual appeal, reducing the environmental impact of the building, creating habitat for native flora and fauna, and enhancing building performance.

Other considerations


Based on a thin layer of soils or substrates, they are lightweight systems with minimal structural implications for the building. The main reasons for installing an extensive green roof are visual appeal, reducing the environmental impact of the building, creating habitat for native flora and fauna, and enhancing building performance.

If the thickness of the roof cannot be increased by adding insulation on top of the deck, then internal insulation can be applied internally to the ceiling - this may be preferable to cold deck construction because of the condensation risks associated with the latter.



Source: NRC, Canada


  • They can reduce the expansion and contraction of roof membranes that historically have helped cause roof failure.

  • They can help insulate buildings against extremes of heat and cold

  • Improve rainwater management by retention of the rainwater in substrate and drainage layers and thus reduce the pressure on drainage systems.

  • They can help reduce dust and carbon dioxide in built up areas.

  • They can help retain a higher humidity level in city areas and reduce heat island effect.

  • Provides wind breaks for the upper level open areas.

  • They can provide a habitat and ‘stopping off place’ for birds and insects.

Typical Cost

□  Landscape roof £140 - £182/m2 [Erisco Bauder green roof system on waterproofing membrane]

□  Roof Garden £330/m2 [Including provision of planers, pot plating, shrubs, irrigation,
lighting, paving, waterproofing, feature artwork, seating; excluding any edge treatment, assuming existingparapet is of sound structure and 1100mm high; assuming roof slab is able to take extra load and access to roof space already existed]

□  Planting roof £210/m2 [assuming 60% areas for planting and 40% for circulation]

Funding opportunities:

Also see:

□  Landscape

□  Ecological value of site

□  Create space for a garden

More information:

□  Case study; Canadian green roof

□  Case study: Rooftop Revolution - Russia

□  www.greenroofs.co.uk

□  www.livingroofs.org



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Install Photovoltaics


Photovoltaic technology uses light energy to generate electricity (photo denotes light and voltaic denotes the generation of electricity).

There are three main types of photovoltaic technologies available i.e., mono-crystalline [deep blue colour], poly-crystalline [multicoloured with sparkling blue tones] and amorphous [black thin-film]. Mono-crystalline technology is the most efficient however and it’s also the most expensive.

Individual solar cells are interconnected, embedded on glass or plastic, and framed to form a module. Modules are strung together in an electrical series with cables and wires to form a PV array. Direct or diffused sunlight on the solar cells creates the photovoltaic effect, generating unregulated DC electric power. This DC power can be used, stored in a battery system, or fed into an inverter that transforms and synchronises the power into AC electricity. The electricity can be used in the building or exported to a mains electricity company through a grid interconnection.

There are two basic ways to install PV on the roof of tower blocks i.e., flat mounting and rack mounting.

Flat mounted installation is cheaper but less efficient. Rack mounted installation relies on a simple metal frame to orient the PVs towards the most optimum angle to face the sun.

Other considerations


PVs do not require much maintenance other than occasional cleaning of the surfaces to remove dirt and grime [similar to windows]. However, they must be kept clear of snow, weeds, and other sources of shading to operate properly. PV cells are connected in series, so shading even one cell in a module will appreciably decrease the output of the entire module. Typically PVs have a life of 25 years however, the invertors and batteries have a much shorter life [approximately 3-5years] and therefore will need regular replacement.

Orientation and Shadowing
The orientation and the tilt angle of the PV panels must be considered relative to the geographical location of the building site. Typically, in the UK, the panels must face south at a tilt of about 15 degrees higher than the site latitude.

Shadowing from nearby buildings and trees will decrease the efficiency of the energy generation. Therefore these factors must all be taken into account during the design stages.


Integration to mains

In a typical application, a building is served simultaneously by photovoltaics and the mains electricity supply.


Source: Power-Technology, USA


  • The roof of typical 20-storey tower block with PVs can generate approximately 10% of the total energy required or provide enough to light 60-70% of the common areas within the building.

  • The renewable energy generated helps reduce 45-60kg of CO2 emissions per year for every square meter of the PV roof.

Energy generated | required | available

Typical Cost

□  Monocrystalline £920/m2 - £1,440/m2
□  Polycrystalline £550/m2 - £1,300/m2
□  Thin film amorphous £330/m2 - £490/m2

Funding opportunities:
  Solar PV grant

Also see:

□  Wind turbines

□  PV on facade

□  Electrical

More information:



□  Solar Century

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Install Wind turbines


Wind is a form of energy and exists over the earth surface as a result of variations in air pressure. Windmills are used to generate electricity and the quantum of electricity generated depends on the wind speed.

Wind Power = air density x area of blades x speed3


Wind turbines on top of tower blocks could potentially generate more energy than the ones at ground level. This is because, wind speeds increase with increasing height from the ground. For tower blocks with more that 15 storeys, the wind speed at the top can be more than double that at the ground level.


There are two main types of wind turbines i.e., vertical and horizontal axis turbines. Horizontal axis turbines are more efficient, widely used and cheaper. However, safety concerns, noise and aesthetics has lead to increasing interest in the vertical axis turbines.

Other considerations

Integration to mains

In a typical application, a building is served simultaneously by the wind turbine and the mains electricity. If the wind speeds are below cut-in speed there will be no output from the turbine and all of the needed power is purchased from the mains. As wind speeds increase, turbine output increases and the amount of power purchased from the mains is proportionately decreased. When the turbine produces more power than the building needs, the extra electricity may be sold to the utility.



Wind turbulence in urban settings is fairly high due to the interaction of wind with the built environment.



The rotation motion of the turbine can induce vibrations and noise into the structure of of the tower block, therefore necessary precautions need to be taken.


Source: Battle McCarthy, UK


  • A typical 20 storey tower block with integrated wind turbines could potentially generate approximately 20% of the annual electricity required in the building. This will require four turbines [4m dia each] located on the roof of the tower block.

  • One option is to size the wind turbines to meet the electricity demand for all the common areas of the tower block.

Basic options

Typical Cost

□  Wind turbines: £2,500 - £5,000 per kW installed

Funding opportunities:
□  Clear Skies Grant  

Also see:

□  Electrical

□  Photovoltaics

More information:

□  WEB

□  Lockergnome

□  Bradford Feasibility Study

□  Urban Turbines

□  British Wind Energy Association

□  Hugh Piggott: It’s A Breeze, A Guide to Choosing Wind power. CAT, 1998


□  UK Green Power

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Project partners:           | Price Myers: Sustainability |Battle McCarthy | Architype | STBI | Franklin Andrews |            


Copyright 2004  Price & Myers Sustainability                                 last updated: 11/25/11

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