Figure 2. Around 70 best practice retrofits of historic buildings have been collected up to now in the HiBERatlas– covering a wide range of building typologies and countries

Each case is presented with attractive photos to inspire users, a small teaser, an explanation of the building, its values and needs, and then goes on to describe the actual interventions implemented to reach these goals. Each retrofit solution is briefly described, and an explanation is given to why it fits this specific building.

Although when it comes to historic buildings and the conservation aspects that matter there are no standard solutions which are applicable everywhere, the experience from other cases can help to find the best solution for your own. If in 3encult there has been a very efficient new window developed which takes in the historic aesthetic and proportions for the Waaghaus in Bozen, this was in accordance with the heritage authority since the original windows had already been replaced and will fit other buildings where the original window is already lost, whilst in a building which still preserves the original windows one will opt for their renovation and enhancement. The HiBERatlas promotes a holistic approach; always consider the building in all its parts, the walls, the windows, the roof and floor, heating, domestic hot water, cooling and ventilation, and of course renewable sources. These are outlined in the retrofit solutions’ information on the website (see Figure 3). The photos from the construction site, and the final results help to assess the suitability of the solution.

Figure 3. The HiBERatlas promotes a holistic approach: consider the building in all its parts – respectively structured is the online presentation.

Within the HiBERatlas the single retrofit solutions are presented in the context of the overall approach for a specific building; the project teams felt that owners and practitioners also need more specific guidance to the solutions. To this aim, the HiBERtool was developed as an online decision guidance tool. Besides providing targeted access to the solutions collected with the best practice cases of the HiBERatlas, the HiBERtool makes available even more innovative solutions which have yet been implemented (or documented) in an overall best practice case.

The HiBERtool provides information which goes beyond the presentation in HiBERatlas, it provides more technical data and the evidence behind the potential solution.  Each record of a solution describes:

1. the energetic Improvement of the considered element
2. the technical functionality
3. consideration of the compatibility with historic structures.

For a coherent and comparable documentation of every single solution a set of questions was answered under these headings:

• What is the solution?
• Why does it work? (compatibility with conservation, technical function, energy improvement)
• Description of the context (What is special about the building and its surroundings?)
• Pros and Cons of the solution
• Additional Information (Publications, links to further information)

Figure 4. Screenshot of the pdf summarising the information provided for a single retrofit solution in the HiBERtool – here for the replacement of the glazing of the inner window of a box type window.

The written documentation is visually supported by drawings and photos. Some of the documented solutions have been studied in detail by means of numerical simulation and/or in-situ monitoring as part of research projects. All these data provide useful information in the appraisal of the solutions. Some of the options represent an innovative solution, and these are ones that although not yet commercialised, provide insight on future development.

HIBERtool: 4 categories of solutions

The user of the HiBERtool is guided step by step in finding suitable solutions by answering a number of questions. The decision trees standing behind these questions have been developed for each of the four categories of solutions, which cover (i) wall insulation, (ii) window solutions, (iii) solar systems and (iv) HVAC systems. The questions relate to two aspects: more information about the element to be refurbished (is it a solid wall or timber frame? Is it a box-type or single window? etc.), and more information on the characteristics to be preserved, or rather possibilities to intervene from the conservation point of view.

Figure 5. Four categories of retrofit solutions are available to date in the HiBERtool.

Solutions for windows

For windows, the user journey could look as follows. To the first question

1. Which kind of window do you want to refurbish or recreate?
   1. Box-type window
   2. Single window
   3. Coupled window

If the user selects a. box-type window, then the second question provides another four options:

2. Which impact on the appearance is allowed?
   1. Low impact
   2. Impact on the appearance from inside
   3. Impact on the appearance from outside (and inside)
   4. Impact on the whole window

If the user answered b. impact on the appearance from inside, four possible solutions are proposed:

1. Replacing the inner glass
2. Adding a layer of glass
3. Replacing sashes or window layer
4. Adding solar shading inside

Choosing a. replacing the inner glass leads to the description of the respective solution, presented with a picture, a short description and a link to the pdf containing more details. The ‘favourite star’ on the upper right allows the user to remember the solution if it is considered potentially interesting, and the user can go back with the button on the lower left in order to investigate for example solution b. adding a layer of glass, which again leads to a picture, short description, link to a pdf containing the details and in this case also the link to a Best Practice case in the HiBERatlas (the OSRAM building in Copenhagen).

Figure 6. User journey investigating possible solutions for a window renovation in the HiBERtool.

In total, 16 window solutions are documented. The first distinction was made on the

basis of the historic window type, (1) single window, (2) coupled window, or (3) box type window. With the classification according to the type of window to be retrofitted, the possible impact of the refurbishment on the historic appearance and character of the building as well as on the window itself was defined in a second level:

• Solutions for interventions with low impact are measures such as repairing the window, installing additional seals on the frame, additional foils on the glass or repairing the shutters. These solutions have no impact on the visual appearance and material, and also no spatial impact on the building.
• Solutions with impact on the internal appearance of the window, the glass, or the inner sash of for example box-type windows are replaced. Furthermore, solutions of additional modern windows on the inside of the original window are also documented. In total 6 solutions are documented for this category.
• The next level of impact of the intervention is an additional change of the exterior view. Changing the external glass can result in an important change of appearance, as the reflection of new modern glass is different from the historical glazing.
• The last category affects the whole historic window. In this group, solutions such as replacing the existing window with a replica are included.

Solutions for walls

In the group of wall solutions, a total of 39 solutions are documented. The solutions are assigned to different categories ranging from internal insulation over external insulation, external insulation combined with internal insulation and frame infill insulation to cavity insulation, reversible systems and innovative solutions. Especially when renovating historic buildings, the external appearance is in many cases of heritage significance. It is therefore not surprising that a large proportion, namely 18 of the 39 solutions, are assigned to the category ‘internal insulation’. Interesting renovation approaches for filling existing cavities are also documented. Innovative reversible systems show a completely different approach in preserving existing building fabric and unusual insulation materials such as aerogel, hemp concrete or reed mats show a range of possibilities for energetic improvement.

Figure 7. left: installation of internal insulation (Perlite) at Villa Castelli © Solarraum; middle: Blowing on the wet cellulose insulation material © HES; right: installation of wood fibre © Eurac.

As an example, here is a possible user path for the refurbishment of the walls of a farmhouse in solid timber construction. Starting from the structure of the tool, the question tree for the element ‘Walls’ is started. Figure 8 illustrates the course of the questioning and how this leads to the result category ‘internal insulation’.

Figure 8. Example for a decision path of a historic farmhouse with log walls

Figure 9. Screenshot of possible interior insulation solutions proposed by the HiBERtool with links to pdf with details and best practice cases in the HiBERatlas.

Figure 10 shows the single steps as seen by the user, and alternative answer possibilities. After selecting ‘solid wall’ with regards to the wall structure, the user is asked whether the external finish is worthy of preservation and answers with ‘yes, appearance’ (as compared to ‘no’, or ‘yes, for proportions’). The next questions checks whether the driving rain protection is fine (or at least there is a strategy to ensure it), followed by the question with regards to rising damp.

Having answered both with ‘no‘, the user is finally asked whether the internal finish is worthy for presentation. Answering ‘no’ here and selecting in the next step ‘internal insulation’ a wide variety of practically implemented solutions are given as results (perlite/aerogel for stone walls, calcium silicate for brick masonry, dense wood fibre for stone masonry, etc.). After reviewing the solutions, these are relevant for the farm described above. Cellulose for the log walls on farm Neuhäusl as well as sheep wool with vapour control layer Giatlahaus.

Figure 10. User journey for the refurbishment of the walls of a farmhouse in solid timber construction

Solutions for ventilation

Over the course of documenting the ventilation solutions, the focus is on different topics. A total of 18 solutions are documented, including some general descriptions of solutions that cannot be assigned to a best practice example. Three solutions about airtightness are integrated which deal with the planning and execution of airtight levels using practical examples. Three fact sheets for cascade ventilation, extended cascade ventilation and active overflow systems were created with regard to low invasiveness of air distribution and planning.

Another documentation includes the use of existing chimneys or shafts for the distribution of the ventilation pipes. The remaining 11 solutions refer to the location of the ventilation unit (central, decentralised) as well as to the possible distribution in the floor, ceiling and façade based on best practice examples.

Figure 11. left: supply air opening in a farmhouse in Tyrol © Michael Flach, right Ventilation pipes in the floor at Doragno Castle in Switzerland © L. Carugo.

Solutions for solar

The solar energy solutions documented mainly concerned solar thermal collectors and photovoltaic systems compatible with historic buildings. In total 37 solutions are documented. They are divided into the following categories: plants attached to the roof, roof integrated, attached to the wall, façade integrated and free-standing solar plants and solutions for integration into the landscape.

The case studies documented demonstrate that most solutions used in historic buildings are roof-integrated systems (22 solutions out of 37).

Many of the solutions are also documented on buildings in the HiBERatlas, as can be seen in the screenshot in Figure 12.

Figure 12. PV integration solutions in the HiBERtool

Besides finding the solutions in a guided way through the HiBERtool, it is also possible to study the whole range of solutions, over 130 of them, in the reports from IEA SHC Task 59. They have been divided into 5 parts:

• Part I - introduction
• Part II – windows
• Part III – walls
• Part IV – HVAC
• Part V – solar