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Revit, BIM and existing buildings

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    Revit, BIM and existing buildings

    We are about to start some major projects with a large contractor that we work with. They are sold on the BIM process and want all their new jobs to be carried out in this way. No problem on our new builds, but I am a little stuck on the ones where we have existing buildings as part of the project.

    We dont want to get into having to draw the existing buildings up from survey data, but I cant see any other way around this. I have some fairly raw cloud point surveys that are very good and clever, but in terms of data that I can use... fairly rubbish..! They are messy, dont seem to accurate (well, they are at 1:200 detail) and in fact once loaded into Revit are dumb objects.

    I probably know what the answer is, but I would love to hear how some of you guys carry this process out. I dont think we mind converting data over to evit, but there will of course be a cost involved.


    I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it

    Hi Andy,
    Do you have the existing buildings in autocad format?
    We have done this before. Use the cad files, even the elevations for the existing and just modeled the new work. It does remove the ability to show any 3d info of the existing, but workable for transition projects.
    If you do have dwg files, it doesn't take top much tp model the existing shell. I guess it all comes down tp how much time and how much the client is willing to pay?
    Andrew Harp
    BIM Manager GHD
    If you are not willing to learn, no one can help you.
    If you are determined to learn, no one can stop you.


      Hi Andrew,

      No we dont have the existing in any detail other than the outline. So any internals etc would need to be surveyed. I do kno wthat there are companies that will point could / survey it for you and then convert it to a usable revit model. Im not sure of how expensive this is, but it does make liabilities much simpler.

      I would assume as you say above, that the most cost effective way to do this, would be to get a standard survey carried out, ie 2D, and then add the required 3D elements in Revit. If you wanted a true BIM process that is. That way you could still take measurements, schedules etc from any alterations / additions in the existing building.

      Im sure this may sound like a simple question, but I cant afford to get the answer wrong with this client, as we are carrying out quite a few projects with them. Like I say, I think I already know the answer, but you can always do with a little extra input..
      I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it


        BIM & Existing buildings


        If they are committed to BIM then they will understand the need to invest in a good measured survey.

        Almost all my work is on existing buildings and I have tried the following:

        1 Get an autoCAD survey moddelled in India by a 3rd party - partially successful, low cost, but i would nto do it again.
        2 get an autocad survey done, and add in a revit survey - this was a good workflow as we needed the CAD anyway. the revit was OK but clearly put together by someone who did not understand edwardian construction, so there was a fair amount of changign the model later on - but then I had the CAD underlay and it got me going really quickly. Added about a 3rd onto the survey cost.
        3 Get CAD survey done and only model what you need - while rotating the CAD survey to create 3D elevations. I find this works really well - and allows a quick move to BIM with the cad survey just there in the background. It allows planning drawings to be prepared for elevations, sections etc, and it is only when you want to show the 3D in context that you need to model more of the rest ........ if ever.



          I'd go with the survey and then remodel the whole thing in Revit (for as far as needed to delete the dwg's again). Let me put it this way: using dwg's in your project will cost you throughout the whole work process in terms of time needed to regen on everything you do.
          Martijn de Riet
          Professional Revit Consultant | Revit API Developer
          MdR Advies
          Planta1 Revit Online Consulting


            The cost is mostly in the survey, the model can only be as accurate as the survey

            You have only really talked of the building structure, but just as important are any existing services, this obviously adds more cost to an existing model, but can be extremely valuable.

            For projects where the model is required only for co-ordination in the new construction you obviously only model a high level of detail for the interface extent. But I am seeing more projects where the client wants a fully coordinated model for new & existing

            I think a combination of quality site survey along with an initial site visit followed by further site visits to check areas which are unclear following development of a model is the best approach. Point Cloud data is obviously useful for comparison and particularly for facades
            Revit BLOGGAGE



              Could you not also take a ton of pictures and for a point cloud? Would be much quicker then doing a true survey, much less expensive than a scan, and much quicker to get it into Revit using a point cloud overlay.



                Thats a very good point as well.. M&E. I did speak about this to my boss, as one of the things they will be doing is upgrading / overhauling some pipework, heating etc. Problem is, people hear BIM and think "great.. coordinated building models.." but dont think about what has to happen in order to reach that point..

                I have a phone call booked in this pm in order to try and flush out what we are required to do to meet their needs.. Will let people know how the contractor see's this working.
                I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it


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