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Joined: Fri, Sep 6, 2013
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When we're working up a project at planning-design stage, using Autocad we design so our wall positions incorporate a tolerance of 20mm. When we go to construction, we take this 20mm off, this allows for the construction to be slightly out of alignment but to still achieve wall areas.
It's worth noting we see this as our design contingency, we don't tell anyone else about it, if they did know about it they might well take the 20mm into their calculations are use it.
How should this be dealt with though in Revit? When we set walls out at planning stage, using the wall face interior as the alignment, this goes to someone i.e. a tenant, who will see it and work to it, but who can't be allowed to know about the extra 20mm. At some stage though we have to claim our 20mm back....whats the best way of doing this?
Moving the walls is obvious but an autocad-level approach. I've thought we could instead set walls out to wall Core Face:Interior, and allow a finished zone on top of that, but it presupposed we know what the internal finishes buildup will be.
Any alternative views?
Apologies if this is slightly confusing but we get caught on things like this.
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Joined: Fri, Sep 6, 2013
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teafoe and WWHub, we have two problems.
Firstly at an early stage in the design we don't know what it is that we are designing for, whether the structure will be concrete blockwork or timber or steel stud. We don't know how much insulation we will need as we won't have any target U-Values to work to (that's a long way down the line), and we won't know the cladding systems with 100% accuracy. All we can do is guess, and it's probably going to be wrong.
Our bigger problem is we've been caught by clients seeing our drawings, deciding that if we've drawn 100m2 of floor space that they are going to get it (WYSIWYG). If we don't allow for a tolerance however and the 100m2 comes out as 99m2 because a few walls will be slightly out of place, we'll get it in the neck, not the contractor....we'll be told we should have allowed for a tolerance. But if we allow for a tolerance, and given them 101m2, then applying WYSIWYG again they'll expect to get it.
Question is thus how are tolerances best allowed for? We can differentiate between two stages, where they need to see and expect to get 100m2, and a later stage where they don't see 100m2 but 101m2, but at this point having signed up to 100m2 the slightly bigger area is not a problem, they haven't contracted for it so if we provide say 100.5m2 we're still fine. It would be if we only provided 99.5 m2 we'd be in trouble, but by making the provision over the requirement we (usually) avoid this.
Making a wall thicker is no help, we have to measure usually to the inside face, but if we do that and allow an extra 20mm in the buildup, we're no better off as taking 20mm off just moves the outside face, the wall is still where it was.
Moving the wall is easy (and obvious) enough, but we could be doing it to a substantial scheme, and doesn't offer a controlled solution.
Now, if we were doing it in Autocad we would draw a polyline around the inside of our measured area and say that is the measured line. We would then offset that by 20mm and then draw our walls (again) from there. We leave the orginal measurement on a locked layer, frozen off, but we can turn it back on again...thats our check area.
Question is how best to go about it with Revit?
To put it another way, its like allowing a contingency (time or money) on a project. If proper project management processes are used, then someone owns the contingency. If everyone knows about it but no one owns it, and it gets used up by just anyone, it'll be gone likety split. Regardless however, contingencies have to be allowed for and factored into a project, just not used; they are for exceptional issues only and only to give breathing space if all else has failed.
Problem for us we have to allow for a contingency (space) that no one can see but which is ours, and how best to manage that in Revit?
Sorry if its confusing but that's commercial work for you, and we do get caught by this problem too often as it is, where no tolerances have been allowed and areas have come in too small, with a consequential loss of rental value and ourselves being asked whether we're going to make up the difference.
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Joined: Tue, May 16, 2006
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Walls can be drawn using one of several reference points and that reference can be changed at any time. This is one of the places where Revit excels over CAD.
I often draw our structures using the exterior as the reference because of site limitations or maybe because I want the exterior to masonry course. In some cases like hotels, the interior dimensions must hold.
So what do you do when you must hold a dimension but the exterior walls change.
- Pick the exterior wall type to change from somewhere in the model,
- select all instances in the model,
- set the wall location line appropriately (hotels - interior),
- then change the wall type.
All walls change and the dimensions accordingly but the walls are now right and in the right place.
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