Renovations are essentially the art of compromise. New space planning, lifestyles and work practices need to be fitted around existing load bearing structure and styles of a different era with elegance, efficiency and at minimal cost and inconvenience. In this article I will be discussing firstly the architectural issues of renovation and then how BIM facilitates the methods of documenting and dealing with these issues.
Reasons to Renovate
There are several reasons driving a decision to renovate old inadequate or dysfunctional buildings in preference to demolition and new construction. The following list gives the main reasons that come to mind but is by no means exhaustive:
- Preserving heritage buildings
- Modernising outdated buildings
- Upgrades to reduce energy costs
- Conserving resources through reuse
- Alterations with changed use
- Alterations with building extensions
- Alternative to new construction for lower building cost
While a renovation usually involves more than one of these motivations, it is important to understand which is the primary driver in order to adopt the right strategy for the renovation.
The preservation of historical or heritage buildings has become a strong priority around the world since the building booms of the 70's and 80's obliterated much of the old inner city building stock. This is frequently enforced through town planning conditions on redevelopment projects. It rarely leads to reduced building costs, and usually involves stringent conditions of approval, where very thorough and detailed documentation is required. These often include requirements to replicate the original building methods, fixings, and colour schemes in restoration work. Conversely new additions in many cases have to be distinctly differentiated to avoid confusion as to what is genuinely historic. New extensions also sometimes have to have reversible connections to the old, i.e. which do not mar the original building fabric if the new extension should eventually be removed. Figure 1 shows one such design solution. In this case the added awnings were not allowed to obstruct the view of the building above.
When an old building has no historical significance and no redeeming aesthetic qualities, but has a sound structure, a decision is sometimes made to renovate and modernise its appearance, usually in conjunction with changes to the internal functional planning. The assumption behind this decision is often that this is a cheaper alternative to new construction, but the need for continuous occupation could also be a major factor. Below Figures 1, 2 and 3 show various stages of one such house renovation.
Our increasing awareness of sustainability issues has for many years now been driving a wave of building renovations with the aim of upgrading to reduce energy costs and eliminate adverse health issues. This often involves a strong focus on increased insulation, resolving damp-proofing issues, providing adequate ventilation, replacing and improving building service runs, and replacing components found to be toxic.
Sustainability through recycling is increasingly becoming a strong motivation for renovations in order to limit the dependence on new building materials. However, reuse of building materials, while lowering the cost to the environment, will almost always lead to higher labour costs and need to be carefully evaluated as to the net benefit before going down this path.
The first and greatest challenge when undertaking a renovation is the unknown and hidden condition of the existing building. Over time all buildings deteriorate, and all old buildings can be expected to have deteriorating drainage, plumbing, and electrical service runs that need replacing. A cursory inspection would also easily reveal sagging or cracking structure, either due to inadequate bracing, or foundation movement. Such issues are fairly easy to predict and budget for in the renovation program.
However, a building that at first may appear sound will, once a renovation gets underway, almost inevitably reveal latent problems that are costly to rectify. Such hidden issues are often specific to particular climate zones and building vernaculars.
In Cold and Temperate Climate Zones some of the more common old building problems are:
Poor insulation, draughty windows and doors, incorrectly placed vapour barriers in walls and roofs causing ice build up in wall framing, inadequate ventilation or damp proofing giving rise to mould growth, spalling concrete beams and columns because of rusting reinforcement.
In Mediterranean Climates old buildings are traditionally of masonry construction. Often built to sub-standard building practices, they frequently reveal problems of: Rising damp in walls and floors at grade, cracking walls due to lack of reinforcement or inadequate footings, termite infestations in joinery and roof beams.
In Tropical and Sub-tropical Climates the vernacular is commonly lightweight framed construction. Old buildings in these zones usually have these problems: Inadequately heat-insulated roofs and walls, leaky metal roofs, dry rot in structure and cladding, mould growth in poorly ventilated spaces, and termite attack.
In addition to the problems of deterioration, rectifications are often needed due to changing building standards (e.g. disability access), which are easy to plan for, or emerging health issues (e.g. asbestos, lead paint, CCA), which will only be revealed in a thorough building audit.
In order to minimise the risk of cost and time overruns it is crucial that as most of the latent problems are identified at the outset, and the optimal methods for dealing with them determined and factored into the program. Some problems can not be discovered at the outset, and a time and cost contingency allowance should be set aside for these commensurate with the risk of them occurring.
It is readily acknowledged among AEC professionals that BIM greatly facilitates the whole process through design to completion for new construction. For renovation projects there are several additional benefits in the BIM process. The first step of a renovation project is a full survey and a building audit by each of the consultants in their area of expertise.
One emerging technology that is beginning to revolutionise the building survey is the use of laser scanners. Laser scans from strategic points in and around an existing building generate what is called a PointCloud data set. Faro, one company making laser scan equipment give a good presentation of how this works through their online video in their website . A PointCloud can best be thought of as a 3D bitmap which can then be inserted into BIM software such as ArchiCAD, Revit, or Microstation. Using this as the accurate dimensional guide, the various BIM components are then generated to make up the Building Information Model.
A Building Information Model of existing conditions facilitates the analysis and efficient coordination of data gathered by the consultant team in their building audit. It becomes the database where this information is collated and problem areas highlighted. Points of deterioration and dilapidation, as well as essential load bearing structure, can be identified. This information base in the form of a Virtual Building becomes an easily readable logical framework from which the design and program for the renovation can then be developed.
The visual feedback through the use of BIM also makes it easier to make sound strategic decisions regarding the staging of the renovation program and the logistics of achieving the end result within an already existing structure, a significant problem in large buildings on crowded sites.
The various BIM software packages now have features that facilitate renovation documentation: Thus the Renovation filters in ArchiCAD are tools specifically used to identify and colour code Existing components to remain, Components for demolition, Temporary work, and New construction (see figures 5 and 6 above). Timelines can be applied to this and construction animations generated to highlight issues of site logistics. Likewise the Phasing filters in Revit can be used to advantage in a similar manner. For more thorough explanations of how these filters work, visit the instructive videos for ArchiCAD and Revit.
These filters are mainly intended for broader documentation such as space planning and design changes, but in theory they could also be applied at the detail level, where many of the critical issues of renovations crop up, e.g. how to temporarily support a beam to replace a corroded seating bracket.
With the help of BIM, collaborating designers and engineers can in short order make more informed and better coordinated decisions about to what extent a dysfunctional old building should be preserved, remedied or replaced. Without BIM, construction professionals in Pisa have been grappling with this very question for just one building over the past 850 years!