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Refurbishment: Key issues of over sheeting

9 November 2010 No Comment

Over sheeting of a building can significantly reduce its energy consumption through improvements to the insulation and air-tightness of the building envelope. In many cases refurbishment offers a practical alternative to new build or re-cladding and it also offers significant social, economic and environmental benefits.

Energy consumption

What are the main advantages of over sheeting?

Over sheeting an existing system has many advantages:

  • It is less expensive than re-sheeting.
  • It is quicker to install.
  • It offers minimal disturbance to building occupants.
  • It can reduce the need for internal protection.

It also provides an opportunity to incorporate additional insulation which if considered at the design stage can give air-tightness levels similar to those found in re-sheet or new build projects. It is also easy to change the appearance of the building through the use of contemporary colours and materials such as those available in the Colorcoat product range.

The use of such pre-finished steel provides a long-term solution with guarantees of up to 40 years which are attractive to both building owners and clients.

What technical issues need to be considered?

As the old roofing is retained for use as a liner there will be a need to incorporate a new vapour control layer (VCL). This prevents interstitial condensation build up in the cavity if the old roof cannot be adequately sealed. At junctions and points of penetration a sealed VCL or liner will also minimise air leakage from within the building and with care, can provide air leakage rates similar to those found in new build.

What issues need to be considered at the design and planning stage?

A refurbishment project will always encounter the unexpected and therefore it is essential to undertake a thorough structural and environmental survey of the building to minimize any risks. Specialist contractors should be involved at the earliest opportunity and employed to carry out the installation based on a robust Health and Safety plan developed before work starts on site.

Will over sheeting provide a sustainable solution with long term cost savings?

A recent theoretical study conducted by the SCI highlighted that renovating a pre 1985 warehouse, to Part L 2006 thermal and air-permeability standards, using an assessed cladding system with Colorcoat pre-finished steel would lead to a 55% reduction in CO2 emissions and a corresponding reduction of 65% in the total annual energy demand.

The same study showed that a typical warehouse built during the 1990’s and upgraded to the current best performance U-values and an air-permeability of 3 m3/m2/hr would reduce CO2 emissions by 65% and provide a 73% reduction in total annual energy demand. So upgrading your building in line with legislation has clear sustainable benefits.

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