Housing refurbishment & retrofit: What Should You Think About?

16 May


The overall guiding principle in design for energy efficient new build and refurbishment is to first conserve energy before having to generate it:
1 Insulate the building to the highest possible standard, make it airtight and ensure suitable levels of ventilation.
2 Install an efficient heating system that is sized correctly to match the anticipated space and domestic hot water demands.
3 Where possible, install solar collectors to provide a proportion of the hot water required.
4 Consider other renewable water and space heating systems
5 Consider renewable electrical power systems.

But first ….. understanding the existing structure

Fully comprehending how an existing building ‘works’ is key to a successful energy efficient refurbishment. Understanding how it has been constructed, how it has measured up to the elements and how it has used energy are the foundations to designing a strategy for its improvement.
As part of the overall initial structural and fabric survey, the designer should identify aspects of the building that will determine the eventual design strategy, including:

Thermal performance:

It is essential to understand how the building performs thermally. Understanding and quantifying energy useage, heat loss and air permeability will be critical in identifying performance targets and eventually measuring the degree of success realised through refurbishment. Assessing existing performance will include: – thermal modelling – air tightness testing – thermal imaging (useful if the budget allows) – meter readings will show exactly how much energy is currently consumed – understanding occupant behaviour will also identify how the energy is being consumed (eg space heating frequency, air temperature, bathing habits, use of appliances etc)


How does the building deal with rising damp and water penetration – is the house one that relies on an absorption and evaporation cycle where the walls become wet and then dry out, or is the house of a more modern construction that forms a barrier against moisture through using impermeable materials?


is the building in a particularly exposed location – is it subject to wind and driving rain? How has the fabric coped with any unusual conditions?


If the house is old, it will probably come with alterations and works that have addressed particular defects eg damp, draughts, leaks etc. These defects are a useful guide to how the building has performed in the past and will guide the designer to address the particular issues that are unique to the house as part of the refurbishment process.


The refurbishment is likely to alter the appearance of the building to some degree. It is important, particularly when involved with historically important buildings, to establish some ground rules in collaboration with Local Authority planners (and conservation officers if need be). What alterations that will be permitted by Planning will likely influence the degree of performance that can ultimately be achieved through the refurbishment.


Solid wall insulation

30% of the existing housing stock is of solid wall construction. Walls can be insulated internally or externally.
In designing an insulation strategy for external walls, it will be realised that not all buildings will present an ‘either/or’ scenario. Often the practicalities of adding insulation will force a compromise upon the designer. In these situations, it is likely that a combination of external and internal insulation will evolve to meet the needs of the brief.
An example of combined system might be where the appearance of the front façade is to be maintained to comply with Planning requirements, or, as in many cases, the façade borders a pavement. In these instances, it is common to apply internal insulation to the front wall and external insulation to other walls.
Note that where a terraced house is refurbished and the adjoining properties remain un-refurbished, the party walls will need insulating.
Each method of external wall insulation, whether insulation applied externally or internally has its advantages and disadvantages:

Internal insulation

Maintains the external appearance of the building.

The living spaces are quick to warm-up.

The adding of insulation reduces internal space, and, in historical buildings, will likely compromise decorative features.

The necessity to minimise encroachment on space will restrict the designer’s choice of materials and possibly restrict achievable u-values.

The occupants will probably have to re-locate during the period of the works.

External insulation

Applying insulation externally will change the appearance of the building. This might be an intended benefit, or it might be considered detrimental to valued historical building.

External insulation usually provides the designer with a greater flexibility in the choice of insulation materials and insulation thicknesses to obtain optimum u-values.

The majority of thermal bridges can be eliminated

External insulation will preserve the existing internal thermal mass. The thermal mass might be considered important in regulating the internal room temperatures.

It is likely to require planning permission.

The works will not unduly inconvenience the occupants.

External insulation options

Insulated render

Insulated render is the most cost-effective form of external insulation, though the system might be prone to damage and the selection of the render must be carefully considered in respect of a potential need for the existing wall to ‘breath’.

Timber, tile and slate cladding

Cladding offers the best performance characteristics by separating the thermal insulation from the weatherproof layers. It also offers the designer a wide flexibility in the specification of cladding material and façade design. On the other hand, it is likely to be expensive, require a higher degree of design input and present the greater depth of construction.

Rainscreen cladding

Rainscreen cladding is a common choice for buildings of over 3 stories. It is usually applied to high-rise post-war apartments.

Thanks to www.greenspec.co.uk


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