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    By Stuart Tanfield

    I can never get it to work”: This is a common response from our customers when discussing the import of a gbXML file from Revit into TAS or any other analysis software.

    Importing a gbXML file into an analysis software provides lots of benefits including; data consistency, integrity and importantly it will save you time, however importing the gbXML file into your analysis software can be a challenge in itself. This is quite often not something the user trying to import the file is doing wrong, but can stem from the techniques used with the model originator.

    Taking the common scenario where we have an M&E consultants looking to import a gbXML file from the architect’s model, they often face difficulties in validating that the model has been built correctly. Often models appear on the surface to look accurate, but having a closer look reveals some of the reasons why your gbXML file will not import as you would have hoped. Frequently, the model originator is unaware that the file is to be used in this way by the M&E consultancy, so communication on this needs to be clear from the very beginning, before the commencement of any modelling.

    Working extensively with EDSL who develop TAS, the team have developed a definitive guide in how to produce an accurate gbXML. The guide provides insight in to understanding how the Revit model is required to be built. This does not require any special practices to be followed, just some good old common sense! The guide can be found at the following link;http://edsl.myzen.co.uk/downloads/misc/EDSL%20Revit%20gbXML%20Guide.pdf 



     Figure 1. Rooms correctly defined for gbXML export

    In specific terms, overlapping walls, and roofs that do not fully cover the building are typical issues that tend to crop up. In addition, making sure external elements are marked as “exterior” will also help to alleviate some of these common problems. It’s not to say that all the everyday issues lie entirely with the model originator, but the physicality of the building components does. When the gbXML space definitions are required, then this is something that may need to be carried out by the M&E consultant.

    Defining rooms or spaces is critical in capturing all the building data. Again one of the common challenges is making sure ALL areas of the building have been captured. Simply defining a habitable space will not be enough to produce a full gbXML model. Areas to think about include ceiling and floor voids as well as risers and wall void spaces. Atriums can catch users out, be sure to extend the height of your rooms far enough. Each of these needs to be defined before the export of the file. (See Figure 1.)

    EDSL have included within the gbXML export guide, refer to the checklist of things to bear in mind when producing a model for gbXML export below: 

    • Turn on the “Areas and Volumes” option.
    • Make columns non-room-bounding.
    • Assign rooms to all areas, including lifts, risers, and voids.
    • Ensure room limits are sufficient for each room to have a bounding element or another room at the top and bottom. (In general, set upper limit to floor above.)
    • Remove all room separation lines that do not separate two areas.
    • Ensure that two or more room-bounding walls have not been placed in parallel and in contact with each other. Do the same for floors and roofs.
    • Resolve any warnings about overlapping walls and room separation lines.
    • Resolve any issues with overlapping rooms.
    • Change function of external walls and ground floors to “exterior”.
    • Ensure all areas have a floor.
    • Make half-height internal walls non room bounding. If there are different rooms on either side of the wall use a room separation line to mark the boundary between them.
    • Ensure that roof footprints are sufficient to cover the areas below.
    • Where possible, replace bay windows with windows directly in the main wall.
    • Use the “Automatically Imbed” option to place curtain glazing within walls instead of making holes in the wall’s profile.

    In summary, if lines of communication are clear, when models are produced, they will be sympathetic to the ongoing use of the file. With a small amount of work in defining spaces from the M&E consultants, we should be producing far more gbXML ready files with the help of the EDSL guide and we should start to see much clearer and more defined results.

    For further information on this article please contact your Account Manager or call our Sales Team on 01784 419922 or emailsales@cadline.co.uk