Standard envelope insulation – ‘light’

Building Characteristics

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Embedded Technologies


• Windows change
• Roof and loft insulation



Energy management

Technology readiness

actual system proven in operational environment (with competitive manufacturing)


This package consists in the very first step of the thermal insulation of a building and includes the following components:

  • Roof insulation, using either an insulation panel/roll or a spray foam under the roof. External roof insulation is also possible (i.e. built-up roof insulation under waterproofing)
  • Energy efficient windows (double or triple glazing)


Without proper insulation, as much as 25 to 30% of the heat in an uninsulated house is lost through the roof, and 10 to 15% through the window. Those two points are usually addressed first (i.e. before the walls – 25 to 35% of losses, and the floor – 10 to 15% of losses) as they are the most easy to deal with and the  most profitable in the short term.  Loft insulation and new windows act as a barrier, slowing the movement of heat out of the building during the winter and into it during the summer.

On its own,this package will not increase the performance of a building sufficiently for this building to become energy-efficient, but it can be complemented at a later stage with additional technologies so as to generate more substantial energy savings.


Roof / loft insulation


Different types of materials can be used for internal and external insulation, either in a roll, panel or spray foam form, each having its own benefits and limitations: wool (glass, rock, sheep or hemp), polyurethane, expanded polystyrene (EPS) or extruded polystyrene (XPS).  The recommended uses are the following:


There are two main ways to insulate a loft or a roof: at the joists or at the rafters.

Insulation at the joists (Source: ADEME)

Cold loft insulation at the joists

The insulating material is laid (or sprayed) on the floor of the cold loft.


Warm loft insulation at rafter or externally

For the insulation of warm and occupied lofts under a pitched roof, two techniques are available:

Internal insulation

Insulation at the rafters with panels (Source: ADEME)

Loose fill insulation (Source: ADEME)

The internal insulation can be done with semi-rigid panels or rolls, whose layout will depend on the structure of the building frame and the available space.

A loose-fill insulation can also be injected in an air-tight cavity under the roof cover.

External insulation

Insulating from the outside avoid loosing living space but requires to remove the existing covering. Load-bearing panels can be used, or insulation can be added between the rafters and the roof covering, with a roof sarking (i.e. a protective and waterproof second skin under the roof). This last solution requires raising the roof line.


Flat roofs insulation

For flat roof, external insulation (“hot roof”) is recommended. Insulating from the inside can cause damage as it will inevitably lead to the formation of condensation. In this case, a rigid insulation is fitted outside, above the existing weatherproofing. This is then covered with a further weatherproofing layer.


Energy-efficient windows


The performance of the windows depends on the glazing and the frame. The level of performance is expressed by the thermal transmittance coefficient Uw. Performant solutions exist with timber, PVC or aluminium (with thermal breaks) frames.

Double glazing

Double glazing is made of two glass layers separated by an air gap. It is more performant than simple glazing and reduces the condensation and heat losses through the windows. The new generation of double glazing includes argon instead of air, as well as a fine transparent layer with low emissivity, usually silver-based: its insulating capacity is 2 to 3 times that of standard double glazing.

Triple glazing

Triple-glazing is made of three layers of glass separated by two layers of argon or krypton and two low-emissivity metallic layers. The Uw value is excellent, however the ligh transmittance can be lower than for a good double-glazing.



Windows can be changed with two main techniques:

  • By keeping the existing frame: this a simplest option, however the performance and the glazed area are slightly reduced
  • By removing the existing frame: this is the most performant option, however it requires more work and some finishing

As double or triple-glazed windows will be more airtight than the original single-glazed frames, condensation can build up in the building due to the reduced ventilation. If there is not a sufficient level of background ventilation in the room, replacement windows should therefore have trickle vents incorporated into the frame, that let in a small amount of controlled ventilation.


Design and implementation


  • Thermal properties that can be adjusted to climate and regulatory requirements
  • Different available materials, including bio-sourced ones (hemp and sheep wool, timber framed Windows)
  • Easy to install
  • Low cost solution
  • Common retrofitting solutions, well established in building codes and with extensive references
  • Benefits in terms of acoustic comfort


  • Disturbance to building occupants (however no longer than a few days)
  • The installation of windows should be done with care to avoid heat losses through draughts and termal bridges.
  • The installation of insulating material should also be handled with care to prevent skin irritation during installation (for mineral wool) and minimise the risk of condensation (which would reduce the performance).
  • Some of the insulating materials (e.g. hemp fibres) need to be treated with chemicals to give the insulation resistance to fire.
  • Wooden frame windows require maintenance


  • New thermal regulations
  • Important market in Europe
  • New insulation materials more environmental-friendly


  • Fire regulations for EPS (e.g. phase out of flame retardant HBCD in Europe)
  • EPS, XPS and PVC meet growing criticism (with regard to hazardous substances and combustibility)

Related Business model

One-Stop-Shop / Step-by-Step approach

The Step-by-Step renovation model is a widely diffused model of building refurbishment that consists in the repairs or replacement of different building components, such as the windows, plasterwork, roof covering, boiler etc. according to their life duration. One of the benefits of such an approach is that it gets the most out of each building component so that the initial investment is taken advantage of to its fullest.

The need of repairs or replacement of various components arises at different points in time. Inevitably, in the case of a complete retrofit building components that are still intact are renewed unnecessarily before time. In the step-by-step approach this can be avoided.

When applying a step-by-step approach, at least a rough overall plan should be made for all measures including those which lie in the distant future, before starting the work. In this way it can be ensured that an optimal end result is achieved in terms of cost-effectiveness, energy efficiency and quality.

The building owner, being it a private or public owner, in collaboration with the designer (planner) defines a planning for the renovation measures to be carried out and a timeline of implementation. The different contractors are involved by the owner in the renovation project in successive phases, according to the initial plan. The design risk is shared between the owner and the designer, while different contractors assume the construction risks associated to their tasks.

The following points should be included in such forward-looking overall planning:

  • Chronological order of the measures: besides the expected time-point for the renewal of the individual components this also depends on the functional context. For instance, for window replacement with airtight windows, the installation of a mechanical ventilation system will also be necessary at the same time. Similarly, a heat pump with low temperature heating can only be installed if the heating load has already been largely reduced by means of insulation measures.
  • Energy-relevant quality of individual building components: if the future quality of thermal protection of all building components is determined in advance, then the energy standard of the building that is achievable in the future can be ascertained by means of an energy balancing software program. The future energy costs and savings can also be determined with this. The transparent final goal provides motivation for implementing the necessary building component quality at each step.
  • Building envelope – position of the airtight layer and insulation layer: if the approximate location of the airtight layer and insulation layer in the building component structure is specified, then it will be possible to find out whether the two layers can be continued without any gaps at the component connections as far as possible – even in the case of adjacent components which are not being modernised at the same time. This is the only way to achieve a building that is airtight and thermal bridge minimised as a whole.
  • For subsequent measures, clarify in advance the points that must be given attention now: a good standard of thermal protection can only be achieved easily and cost-effectively if the interrelationships between measures that are not being implemented at the same time are kept in mind in advance. A typical example is that of a new balcony which is already joined to the (as yet) uninsulated wall of the house with a thermal separation. What at first does not seem to make sense in terms of construction prevents a massive thermal bridge at a later point in time when the wall insulation is carried out, and therefore makes it possible to realise the full potential for saving energy.
  • Economic efficiency analysis (optional): if the energy savings achievable over the useful life of the measure are compared with the investment costs which are necessary for improving efficiency going beyond the level for maintenance alone, then it will be easy to recognise whether a measure is successful in economic terms as well. As a rule, this may support the building owner‘s decision to implement ambitious efficiency measures. In addition, the building owner can already plan for the necessary investment funds in the long term.
  • The step-by-step renovation model was deeply studied and standardised within the EU project EnerPHit that developed the EnerPhit Standard based on the Passive House methodolgy and concept.

In conclusion, step-by-step modernization permits to building owners with limited financial resources to spread the investment costs for modernisation measures over a longer period of time. Moreover, the model permits to avoid unnecessary renewal or repair of components that are still good in terms of appearance and function. The extra costs for improving the level of thermal protection will often be moderate if energy saving measures are carried out at the same time as repair work that is necessary in any case. This speaks in favour of energy-related modernisation of each building component only when it needs to be repaired anyway.


This package will soon be illustrated by an example