Subsequent Design and Detail Modelling

Based on the results of integral modelling, it is fundamental for building modelling that further modelling can be performed in two parallel activities, which are only loosely related to each other (see Figure 24). Thus, besides detailed modelling of the building construction, it is appropriate to model the user spaces as a separate activity. As stated, this distinction follows from the basic fact about buildings that user spaces and construction spaces are complementary to each other. The construction spaces consist of the construction components.

4.5.1 User Spaces

Modelling of the user spaces includes both outer and inner spaces. Regarding outer spaces, the terrain with coverings of the drive way, terraces and garden areas can be modelled. In practice, however, the primary emphasis is set on modelling of the interior to further detail as illustrated in Figure 26.

Figure 26 – Modelling of user spaces

For the interior, modelling will cover placement, size, form, etc.

of various components like:

Openings

Terminals for electricity, water, gas, waste water, antenna, etc.

Lightning, equipment

Modelling of the building construction includes further modelling of the identified building components including specification of attributes and subdivision i.e. identification of sub-components and structure.

Architecture

Primary construction, bearing construction Secondary construction

Electrical/electronic installations and equipment

Typically floors and walls are initially modelled as solids without considering their precise dimensions and contents. So, in this

activity, they are gradually modelled to sufficient detail, e.g.

with material layers, coverings, etc.

Figure 27 – Modelling of walls and floors gradually to greater detail It should be easy to subdivide an object into smaller parts of the same type without first having to delete the existing object and then create new objects and need to recreate missing attributes and relationships. In some cases, it would be suitable to be able to refer to the original object also as a collection of the subdivided objects⁷. For instance, a wall object may have been created first from corner to corner and a number of attributes are already added to the object. Then, if this object is subdivided into multiple wall sections, the attributes of the existing wall object should be transferred to the new wall objects and the existing wall object should be changed to a collection of the newly created wall objects (see Figure 28).

Figure 28 – Subdivision of walls into sections at intersecting walls Another kind of subdivision occurs when an object is subdivided into objects of other types, e.g. wall objects and floor objects into material layer objects. In this case new objects are created

7 In IFC, this is termed nesting.

but the existing object should be preserved and relationships should be created between this object and its parts. To consider these material layers as separate objects is necessary, because these objects are very often dislocated compared to its parent wall object (see Figure 28).

Figure 29 – Subdivision of walls into material layers

Similarly, a roof object may first be created as a simple object and afterwards detailed and subdivided. However, many roofs are rather complicated constructions so many sub-objects must be identified and created.

The relationships between the composite objects and its sub-objects may include relations or constraints between attributes.

For instance, the width attribute of a wall object must be the sum of the width attributes of its wall layer objects. Other relationships, however, may not be that simple. For instance, the width and height attributes of a composite wall object may be undefined if the corresponding attributes of the layer objects are not equal. This is often the case for external walls, i.e. walls that face the exterior. When such walls are built on top of foundations, the inner wall layer usually starts higher than the outer wall layer. Similarly, the attributes for horizontal dimensions of a composite floor may be undefined because the corresponding attributes of floor layer objects may be unequal.

4.5.3 Objects Belonging to Both User Spaces and Construction

Objects like windows and doors can be regarded as belonging to both activities, so they can be treated differently from project to project. In some projects, they can be modelled as part of the construction but, in other projects, they can be modelled together with the spaces. The design of size, form, colour, joints, etc. belongs most natural to modelling of rooms while modelling of thermal and acoustic properties most appropriately is part of construction modelling.

4.5.4 Model Evaluation, Consistency Checking, Constraint Specification, etc.

Different degrees of detail of models must be identified in connection with the different parties: clients, authorities, advisors, experts, constructors, etc. so that they match the required deliverables to these parties. This graduation must be related to specification of model content and is termed level of detail. Consequently, the required deliverables at the end of different intermediate stages must correspond to the content of the model at certain levels of detail.

4.5.5 Levels of Detail

Fundamentally for the building modelling framework, the identification of levels of detail must be divided according to the two parallel modelling activities. Further, the levels can be arranged differently depending on the project. For instance, if visualisation must be prepared early in the modelling process, greater focus may be put on modelling of rooms in the beginning.

Example of identified levels of detail regarding the rooms:

Level 1: Model is the result from integral modelling Level 2: Openings with windows and doors are placed Level 3: Banisters, fixtures, sanitary, terminals, convectors are defined

Level 4: Surfaces, colours, etc. are defined

Level 5: Lightning, furniture, panels, curtains, etc. are defined

Example of identified levels of detail regarding the building construction and installations:

Level 1: Model is the result from integral modelling Level 2: The primary geometry of the model is defined Level 3: The bearing construction is completed

Level 4: The primary installations are defined Level 5: Building products are defined

Level 6: Model is completed for exact quantity take off Level 7: Model is completed with details for construction work