BIM-Based LCC

Across Europe, there is a real and urgent demand for deep renovation of the existing building stock and transformation of vacant, obsolete, or vacant buildings into dwellings. Due to the enormous scale of such operations and the need for the attainment of energy efficiency goals, a systematic approach is required to inform any decision-making in the process of renovation with respect to the monetary and environmental consequences of the choices. However, several challenges must be overcome prior to scaling up the renovation process resulting in energy-efficient buildings. One of the challenges is the lack of tools and methods for quickly estimating the costs, benefits, and expected return on investments for each proposed renovation strategy at an early stage of decision-making. As detailed in Directive 2014/24/EU of the 2014 to identify the most advantageous tender, the decision should not be only based on non-cost criteria. Qualitative criteria should therefore be accompanied by a cost-effectiveness approach such as life-cycle costing. Simple “payback time” is a quick way of evaluating the financial attractiveness of EE measures and sufficient evidence-based information on the costs and benefits (Liu, Meyer, and Hogan 2010). The main purpose for developing this use case is to propose a systematic and quick Life Cycle Costing (LCC) calculation to be able to compare different renovation strategies. 

Aim: The “LCC tool” was developed to:

• Provide insight into the financial performance of each renovation strategy
• Reduce the time and consequently the cost of LCC calculation using the automatic quantity take off
• Streamline and standardize the process by providing a systematic approach, which makes the results of the comparison between different scenarios more reliable

Scope: In principle, the LCC analysis can be applied to different stages of the life cycle of an asset, however, as shown in Figure 1, the potential for value improvement is much greater in the planning stage compared to other stages. Up to 80% of the operation, maintenance, and replacement costs of a building can be influenced by the first 20% of the design and planning process.

The LCC analysis normally gives insight into the following questions:

• Will the future expenses for maintenance and management considering the capital cost related to a renovation investment be in balance with the rental benefits?
• If there is not a good cost/benefit balance will that then be compensated by an increased market value?
• Is a renovation investment needed and what will the effect be on the future market value by the end of the life cycle?
• Will the quality of the real estate stay on a level, during the life cycle, which can facilitate refinance of the outstanding loans?
• Is it worthwhile to invest or better to just maintain? Is it better to sell now or to wait and do that later?

Figure 1: Different scopes and the extent to which they influence LCC savings over time based on NEN-ISO 15686-5

The objectives for the use of the LCC tool may include time reduction and consequently, cost reduction as well as improved accuracy of calculating the financial performance (KPI) of a renovation scenario.

• The accuracy of the calculation depends very much on the availability of data whether acquired from the BIM model or external databases. This is especially important when we are comparing different alternatives; in order to be able to rely on the results of the comparison we need to make sure that the alternatives contain the same level of information details
• Currently, the quantity-take can be performed properly if the building is modelled based on NLsb standards

Future improvement:

The BIM model is currently enriched according to project specifications, although the values used are fully compliant with existing NL/SfB and NE2767-2 standards (‘BIM Loket - NL/SfB’ n.d.). Mapping of NL/SfB onto IFC and vice versa are, however, active areas of research. Developments in this domain could further enhance the efficacy of the BIM-based LCC. Additionally, since LCC calculation requires assumptions about future behaviour, sensitivity analysis (such as Monte Carlo analysis) can be added to allow for the identification of a distribution of possible costs and a range of more and less probable figures for use in calculations.

• NEN-ISO 15686-5

Figure 2: UML Sequence diagram of interaction between LCC tool components

All LCC functionalities are integrated into the RE Suite. The tool can be accessed with any web browser by visiting https://demo.demobv.nl and logging in using provided credentials.

The calculation requires a different category of costs based on the scope and level of analysis for each project. This can be specified in the tool and a user can tailor their calculation by adding/deleting rows. The cost items are mainly divided between Capital Expenses and Operational Expenses. In principle the LCC table has the following columns to fill out:

Description, a recognizable name for the line item in the LCC

Quantity, an optional field that can be used to compute the Cost

Unit cost, an optional field that can be used to compute the Cost

Cost, which can be automatically computed as Quantity * Unit Cost if both are filled or manually filled out otherwise

Start year, the first year the expense occurs

Cycle, how often the expense reoccurs, e.g., every 3 years

Duration, after how long the expense stops reoccurring, e.g., after 10 years

A bidirectional connection between the BIMSpeed platform and the RE Suite has been established. Users can navigate between the two platforms, and exchange data between them. When a user is on the BIMSpeed platform, it is possible to reach the RE Suite through the User Interface of the BIMSpeed platform. There are two ways to do this:

1 - Through External Services: RE Suite is always accessible through ‘External Services‘, which can be reached by clicking the External Services button on the top of any project homepage. If the user clicks on ‘Go to the service’, the service is triggered.

2 - Through IFC’s:  RE Suite is registered as a service relevant for IFC files. Any IFC file on the BIMSpeed platform can be directly opened in RE Suite by clicking on the ‘3 dots’ menu of the IFC file, selecting ‘Access to services’, and clicking on ‘Go to the service’. In the background the webservice of RE Suite is called. After successful login the file is automatically downloaded and shown in the RE Suite 3D viewer. From here multiple BIM related applications are available.

Demonstration: 

One of the BIM-Speed project demonstration cases pertains to four three-story residential apartment blocks in Warmond, The Netherlands. Constructed in 1969, these complexes are owned and managed by the social housing corporation Stek. The apartments are positioned above a semi-sunken basement where people find their own personal storage rooms.

Within the BIM-Speed project renovation options for these complexes are considered, such as:

• Add insulation to (some of) the cavity walls
• Disconnect from natural gas
• Use sustainable energy sources for meeting heating demands

The BIM-Speed LCC tool is applied as proof of concept to one of the complexes to gain insight into the financial impact of the renovation options in both expenses and returns.

Figure 3: demonstration case in Warmond, The Netherlands

Enriching the BIM model

Requirements

For the purpose of demonstrating the LCC tool, the BIM model had to be enriched with additional information, needed to perform the LCC analysis. Besides the geometrical information of elements, which can easily be read from the BIM model, it was also required to have information about the material and element description, following the NEN2767 and NLSfB standards. The goal was to add 5 new parameters to the elements, which are going to be included in the renovation process, namely the:

• NEN2767_material_code
• NEN2767_material_description
• NLSfB_element_code
• NLSfB_component_code
• NLSfB_decomposition_description

Additionally, it was desired to have a parameter which will specify whether the element is going to be renovated or not, so the 6^th parameter was added, and that is:

• Renovation_option

An example of an external wall with cavities, which is made of bricks, is going to be renovated and has the following classifications

• NLSfB classification is “21.22 External walls, load bearing, cavity walls”
• NEN2767 classification is “03 Brick”

the parameters would be filled as follows:

Table 1: Example of parameters and values

  Implementation

The implementation of enriching the BIM model was performed in Autodesk Revit software. The first step was to define six new project parameters. The type of parameters was defined as “Text” and they were grouped under the section “Text”. Parameters were assigned to Floors, Roofs, Walls, and Windows, as these are the categories which are going to be included in the renovation scenarios. An example of the definition of the parameter “NEN2767_material_code” can be seen in Figure 4.

Figure 4 Definition of one of the parameters

By clicking on one of the elements, to which the parameters were assigned, the new parameters can be visible under the Properties section. They are located under the group “Text” as exhibited in Figure 5.

Figure 5 Newly defined parameters

For each element in question, the new parameters had to be filled in with values, as seen in Figure 6 for an example of an external wall.

Figure 6 Parameters with values

To better monitor the process of filling in the values, a schedule was created, which offered an overview of all the elements from a category. This way no element was left out. From a wall schedule in Figure 7 it can be seen how values were entered for each element. Additionally, adding the parameter “IsExternal” to the list was helpful to differentiate the internal walls, which are not included in the renovation, from the external wall, which are included in the renovation and therefore have “Yes” as a value for the “Renovation_option” parameter.

Figure 7 Wall schedule

The same process was repeated for the windows, floors, and roof. The below table includes all the different parameter values which were used in the model.

Table 2 Parameter values

Once the model was enriched with the information, needed for the LCC analysis, it could be exported as an IFC file. When choosing “Export Revit property sets” as an export option, the newly defined parameters will be exported, but they will be grouped under “Text” as seen in Figure 8, where BIMvision software was used as an IFC viewer.

Figure 8 IFC model with “Export Revit property sets” settings

Since it was desired that the group of parameters, which is now called “Text” would be associated with the BIM Speed LCC, a User Defined Property Set had to be first composed, to be used as export options. This was done with a TXT file, which includes instructions for the Property set naming. The TXT file specifies, that the property set name is going to be “BIM_Speed_LCC” and that it will apply to Instances and to every IfcElement. After that, the parameters are listed, together with their Data type and their Revit parameter name. The TXT file can be seen in Figure 9.

Figure 9 TXT file for User Defined parameters

This TXT file was used in the IFC export settings, under the tab Property Sets, where “Export user-defined property sets” was selected with a tick and by clicking on the Browse button, the TXT file was selected as shown in Figure 10.

Figure 10 IFC export options

With these settings, the newly defined parameters are now grouped under “BIM_Speed_LCC” as seen from the IFC viewer in Figure 11.

Figure 11 IFC model with “Export user-defined property sets” settings

Scenario comparison

To evaluate the efficacy of the BIM-based LCC two renovation options are considered for the complex Woudestraat in Warmond, The Netherlands. The renovation concerns applying façade cladding with thermos-acoustic insulation panels. The type of material is in question.

For the purposes of this proof of concept, the financial impact of installation and materials are offset against subsidy and reduced energy costs.
The complex has a BIM model available, and it is enriched as described in chapter 1.1, denoting building decomposition and material specifications as well as which elements are relevant for renovation.
These relevant elements are imported into the LCC Tool as described in chapter Error! Reference source not found.. This results in generally available building information.
For each strategy, an LCC is created and pre-filled with default categorization as depicted in Error! Reference source not found. The LCCs are now filled out with details regarding the specific scenarios.

The quantity of the elements marked for renovation can be imported from the BIM model.
The main difference in cost is the choice of insulation panel. By specifying the product name in the LCC and importing unit costs from the BIM-Speed Catalog the total financial impact is immediately calculated.

Upon estimating the reduction in heating costs this yields a cumulative total life cycle costing graph for the two strategies as depicted in Figure 12. As can be seen, while the initial outlay for a more thermally isolation material is higher, the costs are eventually recaptured due to reduced heating costs.

Figure 12: Strategy comparison for different isolation materials. The red line depicts a strategy with more thermal isolation

To compare how the strategies respond to different scenarios the inflation, interest, and income index parameters can be adjusted. If one of the strategies is only viable in a narrow range of scenario parameters, it can be considered high risk.