REFURBISHMENT OPTIONS

 Basic

■ Overcladding

■ Add thermal insulation

■ Replace windows

Good

■ Provide solar shading

■ Increase size of openings

■ Enclose balconies

 Exemplary

■ Install photovoltaic cladding

Overcladding

Overcladding options for tower blocks include, insulation render and rainscreen cladding.

Rainscreen cladding

This comprises a resilient outer screen, usually a decorative cladding panel, supported on a vertically aligned timber, aluminium or steel sub-frame, which is fixed back to and supported by the primary building structure. A continuous void is maintained immediately behind the cladding panel and the entire system is ventilated at the base and head as well as at all penetrations.

Any moisture penetrating through the various joints in the cladding can be effectively removed by the provision of uninterrupted ventilation paths for the full height of the façade. Insulation and breather membranes can be incorporated into the cladding system, which provide the added benefit of eliminating both cold bridging and interstitial condensation, and enhancing the thermal performance of the structure.

Rendered finish

This typically has a rigid slab insulation directly mounted or pasted on the external surface of the the existing wall with an in-situ decorative coat of render on the outside.

Other considerations

Disturbance to residents

Overcladding process can take months to complete and requires the use of scaffolding. This may become an irritant to the residents in the building. Noise due to drilling may also become a nuisance. The disturbance could be minimised by restricting the time period; providing advance notice to the residents and providing alternative accommodation as retreats.

Balconies

Balconies and walkways can be fully enclosed to create buffer zones. If external wall insulation is not considered then enclosing the balconies etc. will also reduce the effect of the thermal bridges associated with them.

Vandalism

External wall surfaces are prone to vandalism and graffiti. A more robust cladding may be required on the ground floor from the one above.

Maintenance

Some overcladding systems require frequent maintenance and access platforms need to be provided. Replacement of purpose-made parts may be expensive. Provision must be made to monitor the performance of all overcladding systems over time.

Access to the structure of the building i.e., columns, beams and slabs may be required to check for deterioration at regular intervals.

Building Life

Overcladding will not reinstate the structural integrity of the tower block nor prevent further degradation in buildings that have a problem with assembly or production of the existing components. Therefore, decision to overclad should be taken only after careful investigation of the existing condition. Overcladding may not increase the building life as much as expected [Harrison et al, 1986].

Benefits

The benefits external cladding of tower blocks include;

• Restoration of existing facade

• Extending the life of the building

• Improving appearance and image

• Provide thermal insulation & weather-tightness

• Improve acoustical performance of the building

• Lower maintenance cost

• Preventing pedestrian injury from falling external surface.

□  Timber cladding on existing external walls: £100/m2

- kiln dried un-treated larch rainscreen cladding; including breather membrane & fix to existing walls; excludes cost for repairing existing walls

□  Permarock External Wall Insulation System:

£100/m2

□  Aluminium cladding: £200/m2 -£240/m2

□  Galvanised steel cladding: £190/m2 -£220/m2

□  Terracotta cladding: £350/m2 -£400/m2

□  Rannila ‘Nordicon’ Large Panel with Render £160/m2

-All costs include 70-100mm external insulation

Also see:

□  Wall insulation

□  Innovations in Façade Technology

More information:

□  Energy efficient best practice

□  Harrison et al, 1986, Overcladding external walls of large panel system dwellings, BRE Bookshop, Watford, UK.

□ www.bath.ac.uk  

Suppliers:

□  www.eclcontracts.co.uk

□  www.rannila.com

□  www.permarock.com

To register as a supplier click here...

Wall Insulation

The purpose of re-insulation is to reduce the heat loss in the building. In addition to smaller heat losses the indoor climate will be improved at the same time. The indoor climate will be improved because the insulated outer walls reduce the heat loss through the fabric retaining inner room temperatures.

The preferred method of insulating facades is externally [overcladding]. This can be achieved  through Rainscreen cladding with insulation or insulated render. Overcladding can also help in reducing thermal cold bridging.

Internal insulation can be also considered if a thin layer of insulation is required, as this has an impact on the internal accommodation area. It can  be an economical option. However, whilst considering internal insulation, the following issues need to be taken into account:

• the reduction in thermal mass, 

• risk of interstitial condensation and thermal bridging

• reduction in room size

Internal insulation will make the building perform like a light weight building [due to reduced thermal mass] and thus reducing the heating time lag. This can be an advantage if the heating services are being updated to an electric heating system from a gas system.

Insulation beyond a thickness of 150mm is not advised unless convective heat gains are controlled [e.g., heat recovery ventilation].

Other considerations

Structural

Typically, internal and external insulation do not  add much load [30-60kg/m2] to the building structure therefore, structural issues should not be a barrier to its installation.

Removal and reinstallation of fittings

Disruption to electrical and plumbing work on the internal surface will need to be considered. Fittings and services such as, rainwater & overflow pipes, windows, radiators, water pipes, switches, window sills, toilet and kitchen fittings will have to be removed and reinstalled.

Disturbance to residents

Temporary re-housing may be required especially whilst considering internal insulation.

Heating system

As the heat loss through the facade will decrease with additional insulation, the capacity of the heating system will have to be re-assessed.

Planning permission & regulations

Planning permission may be required where the building appearance has been changed.

Building regulation on u-value of walls do not apply for refurbishments and only apply to areas such as extensions. However, change in fire performance must be considered.

Benefits

For a tower block building, 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 losses through the fabric.

However it has substantial impact on the residences 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.

Heat loss through a typical tower block

Embodied energy: insulation

60mm internal insulation

□  Sheep wool: £33/m2

□  Extruded polystyrene £30/m2

□  polyurethane boards £13/m2

Also see:

More information:

□ Energy efficient best practice

□ Building green

□ EST: Insulation solid walls

Suppliers:

□  Knauf Insulation

□  Kingspan Insulation

To register as a supplier click here...

Replace Glazing

The importance of improving the thermal performance of windows is well know in the building industry.

Double glazing greatly enhances the thermal and acoustical performance of the building.

Window replacement tends to have a long payback period, however it is a crucial step when overhauling the thermal envelope of a structure.

Replacing windows tends to be laborious principally because of the difficulty in finding windows to fit the building’s existing rough openings. There are three approaches to fulfilling the task:
 

Secondary glazing: This involves added an extra inner layer of glazing. This can improve the insulation to the same standard as double glazing without replacing the existing window.

Custom-built frames: This approach involves completely knocking out the original window frame and starting from scratch with the rough opening.

Change opening size: This involves removing the entire existing window and frame and then begin hacking away at the rough opening to fit a larger standard sized window. This approach, clearly, only makes sense if the damage or decay has extended past the confines of the window into the building its self, in which case cleaning up the rough opening might as well entail making it appropriate for an enlarged but standard fitting.

Custom sized glazing: Especially appropriate when the frame is in good condition, but perhaps, the glass panes are separating from a warped weather sash, installing a custom-sized window into an existing frame can be another alternative. Though the least expensive initially, such measures are usually short-lived and aesthetically unappealing.
 

Other considerations

Provide trickle vents

Trickle vents are small adjustable ventilation openings to provide controllable background ventilation. These should be provided whilst replacing windows.

Draught proofing

Draught proofing of windows and doors should also be considered. Draughts are caused by cold air forcing its way through gaps around windows or doors causing heat loss.

Environmental impact of frames

Timber framed windows are the most environmentally friendly. However, durability concerns require them to be treated or painted which tends to reduce their environmental credentials. Wood from sustainablely forested sources must be specified. uPVC and aluminium windows must be avoided.

Building regulations

The Part L of the building regulations do not apply to refurbishment works. However, as major refurbishments to the facade are rarely done and windows have a lifecycle of 20-30years, it is important to consider meeting the current U-value [thermal] requirements.

Security

Ground floor windows and those easily accessible above ground floor, must be successfully tested to BS 7950:1997 'Specification for enhanced security performance of casement and tilt/ turn windows for domestic applications', at an appropriately accredited UKAS test house, or if otherwise tested must be independently authenticated, in writing, by a test house suitably approved by UKAS.

Ground floor windows and those that are easily accessible to entry must have key operated locks. Where necessary, opening restrictors or similar built-in mechanisms will be required.

Benefits

□  Double glazing can improve thermal comfort for the residents in areas of the rooms near to windows and save energy for space heating by 25%. It can also result in better noise insulation.

Heat loss through a typical tower block

U-values: window frames [12mm gap]

□  Softwood timber & uPVC - £120/m2 

□  Hardwood & aluminium  - £200/m2.

□  Secondary glazing - £60-£100.m2

Also see:

More information:

□  Energy efficient best practice

 □ www.securedbydesign.com

Suppliers:

□  Knauf Insulation

□  Kingspan Insulation

To register as a supplier click here...

Increase size of openings & enclose balconies

As the majority of the energy used in the tower blocks are for space heating, maximising any ‘free’ heating helps to reduce energy consumption.

In the UK, approximately 1400kWh of solar radiation falls on every square meter annually and the typical heating requirement is about 140kWh/m2. Therefore, it’s at least theoretically possible to completely heat a home using just 10% of passive solar gains.

Passive solar measures can be applied to existing buildings to good effect. To maximise passive solar gains the size of south facing windows of the tower blocks can be increased to allow more direct radiation in winters [up to 40% window to wall ratio]. The high thermal mass of the concrete floors can 'soak up' radiation during  the day and release into the building at night. Windows within 30 degrees either side of south are most appropriate.

Alternatively, the south facing balconies can be use as a conservatory. This can provide an extra unheated living space which also provides significant free solar gains. However the positive energy gains of a conservatory will be lost if the space is heated like the rest of the building.

One possible solution is to create an external skin to the existing façade. The double skin façade captures heat which can be recovered [at the top] to heat the flats.
 

Other considerations

Double skin facades:

DTI research on commercial buildings has shown that double skin buildings are able to reduce energy consumption by 65%, running costs by 65% and cut CO2 emissions by 50%, in the cold temperate climatic prevalent in the United Kingdom when compared to advanced single skin building. Cost exercises have shown that buildings employing a double skin may cost as little as 2.5% based on gross internal floor area.

Over heating
In order to avoid over heating in summer, appropriate shading devices that permit winter gains but reduce summer gains are recommended.

Heat loss through glass
In passive solar heating applications, windows should have a low U-value to reduce winter heat gains and summer conductive heat gains. Low-E coated double-glazing is recommended.

Controls
A responsive, zoned heating system [which takes into account passive gains] to automatically cut in when and where necessary can be incorporated to optimise heating.

source: www.bentech.se

Benefits

• Passive solar heat gains

• Reduced energy cost

• Reduced CO2 emissions

• Better views and daylight

Double skin facade

source: Battle McCarthy

□  n/a

Also see:

More information:

□  Energy efficient best practice

 □ Double skin facades

Suppliers:

□   Bentech

To register as a supplier click here...

Provide solar shading

Flats with large windows facing south, east and west can over heat during summers due to excessive solar gains.

Horizontal shading devices: Consider using horizontal shading devices such as, overhangs, light shelves and external louvres over the windows facing south. The shading must be designed to let direct winter gain but must protect against the summer sun.

Vertical shading devices: These can be used for the windows facing eastern and western directions.

Overhangs can be solid or opaque, and use flat or sloped designs. Fixed and movable exterior louvres running horizontally or vertically across windows can also be used to reflect and diffuse sunlight.

Fixed and movable interior features such as drapes, blinds, louvers, and baffles, can block and reflect direct sunlight entering through windows.

Blinds and curtains also help reduce heat gains, but generally are not as efficient as exterior features.

Other considerations

PV panels could be mounted on top of the solar shading to generate electricity.

horizontal overhangs

Vertical louvres

Benefits

• Prevent over heating
• Avoid thermal discomfort in summer
• Prevent glare

Sun path diagram: London

□ 

Also see:

More information:

□  Energy efficient best practice

□  Dutch case study with solar shading

Suppliers:

□ 

To register as a supplier click here...

Convert the lower floor wall into a 'Green wall'

Transforming the façade of the lower floors of the block into a green planted wall can be an effective and environmentally sensitive way dealing with some of the common social and environmental problems affecting the lower floors of the tower.

Infrequently accessed service areas at the base of the tower can result in blank and functional facades that attract anti-social behaviour such as graffiti, vandalism and create a negative impression of the tower at the point of arrival. Dwelling spaces on the lower levels of the tower are often unattractive to residents due to real and perceived risks from crime, and there are clear organisational reasons why the ground floor of the tower has to accommodate at least some service and plant areas.

Consider turning the lower floors of the tower into a green façade as a cost effective way of transforming the image of the tower and increasing biodiversity while also repelling vandalism. A green wall can help to integrate the base of the tower into the surrounding landscape and reduce the visual scale of the building.

Traditional wire rope frameworks or metal lattice support systems for vegetation have a reputation for being expensive and complex to install and can require a large number of fixings into the background wall structure. Modular three-dimensional trellis cladding panels that are pre-assembled in the factory can have benefits over wire or lattice systems as they provide their own support structure, potentially reducing the number of fixings and speeding up on-site installation.

It is important that the chosen supporting system is of a robust construction and resistant to climbing. As with all landscape elements regular maintenance is critical to the success of the solution and should be considered at the outset. Installing façade planting systems on lower sections of the tower simplifies access arrangements and specifying low-maintenance planting schemes can reduce the maintenance burden.

Benefits

• Cost-effective way to enhance the appearance of the tower

• Can reduce the risk of anti-social behaviour and vandalism

• Makes a strong and positive environmental statement and contributes to local biodiversity

□  n/a

Also see:

More information:

□  www.greenscreen.com

Suppliers:

To register as a supplier click here...

Install photovoltaic cladding

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 [multi-coloured with sparkling blue tones] and amorphous [black thin-film].

Mono-crystalline technology is the most efficient however; it is 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 three basic ways to install PVs on the facade of tower blocks:

• flat mounted on the wall as cladding

• as overhangs on windows

• integrated in to the glazing system

Other considerations

Maintenance
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 PV have a life of 25 years.  The invertors and batteries have a much shorter life [approximately 3-5years] and therefore will need regular replacement.

Orientation and Shadowing
The use of PVs on the facade of the building can  only be justified on the south facing surface.

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 decease 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 the Photovoltaic and the mains electricity supply.

PV cladding system, Sandwell

PV integrated overhangs, Northumbria University

Glass-glass PV system, Ideal for atriums and enclosed balconies.

Benefits

• The south facade of a 20-storey tower block with PVs can provide enough to light most 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

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

Also see:

□  Wind turbines

□  PV on roof

□  Electrical

More information:

□  PV-WEB

Suppliers:

□  Solar Century

To register as a supplier click here...