• Blog posts


    By Dennis Collin

    Part One , Part Two and Part Three can be found by clicking on the respective links.

    Previously on repeating details in Revit, I mentioned a problem about dragging a line of repeating elements where if the number of items is less than two, Revit reports an error on how it can’t create geometry.


    At the time of writing, Revit will not permit an Array amount of one item, but this is what is calculated when drawing shorter lines of repeatable components. However, this situation can be avoided by placing a conditional IF statement ensuring that the number of items will have no less than the required minimum of two items in the list.

    The conditional if statement is placed in the formula section of the Family Types dialogue within the Family Editor. We need to create another Integer parameter which says the equivalent of; “if the number of bricks is less than two, the number is two bricks otherwise leave the number of bricks as it is“.

    Mathematically speaking it is a Boolean statement, with one value for True and another for False. In terms of syntax: if (Condition, Value if True, Value if False) spaces do not matter but spelling, commas and sentence case for parameter names do.

    A typical repeating element would have some formulae like below.


    If after doing this errors still result, it will usually be the result of too many constraints being applied, or an error in the formula itself. If this is the case just reassemble the nested family and apply constraints one at a time, testing as you go. It is all too easy to make mistakes, even if you are a Revit user of many years! Frequently testing and saving progress can prevent frustration and a lot of hair pulling!

    In this example, I was referring to detail components, but the same principles can be applied for MEP equipment families, fixings or model repeating model wall details such as stone corbelling or cornices.


    These kinds of examples are very similar to tutorials used in our two-day family creation course. Whilst a little daunting to a new user, Revit is logical in how it works and processes learnt in creating one example can easily be applied to other similar components.

    Details of Cadline Training courses can be found here: https://training.cadline.co.uk/