CAD packages for building design

June 17, 2016

Last weekend saw us attend our 2nd Build It Live home building show, this time in Bicester, Oxfordshire.  We went along having pretty much decided that since the turn key builder we had identified had fallen through, we would have to go it alone, and werte looking for CAD packages that could help us.

There were several CAD packages being exhibited at the show, and we wanted a real world demo of each (i.e. don’t start from carfully crafted example files).  I had phoned up one supplier and arranged for the aforsed demo.  We turned up on the stand and met our contact, where we dove streight into the package.

The salesman was very confident in his product (a really good sign – he wasn’t nervous that we would find somthing nasty), so we started by drawing some walls, and adding a window.  Imagine my supprise when I asked where do you tell the package about the amterials used in the wall, only to be greated with bewilderment.  Now I am no architect or builder, but I would like to know what materials a wall is built from, if only because I need to know how thick the walls are.  NO this package can’t do that.  walls are a preset thickness; internal thick or thin, external thick, standard or thin.  you can adjust the exact thickness but you can’t specify the materials.

So we looked a little deeper, the package draws floorplans, and even renders a 3d “model” of the house, but it doesn’t really do anything more than the free packages (sketchup for example) can do.  So what did I think a house design CAD package should do for me?

Build from known materials.  Start by specifing dimentions of materials like beems, blocks, morter thickness, stand off gaps, plaster sheets, etc.
Once I have defined these I can create a ‘wall’ template if you will.  the sandwich of the walls compesition.  i.e. skim coat, plaster board, standoff, blockwork, standoff, plasterboard and skim coat would be a reasonable internal solid wall.  Now if I were to draw a wall using this template the CAD package knows (A) how thick the walls are and (B) can keep track of the Bill Of Materials (BOM).

Better yet I would then expect the system to suggest / optimise the positions of adjoining walls, and opinings (i.e. for doors and windows) to minimise wasteage, the number of cuts blocks etc.  after all materials are relativly cheep, but labour is expensive.  if I only have to cut every 2nd brick for a window opening then I have just saved a considerable amount of time!


So we went and looked at another package, from a differant vendor and lo the same again.  This time however I could buy a companion package that appeared to be a spreadsheet front end that would at least do the materials estimates, and wall ‘template’, so we could at least now go back into the CAD and set walls at the correct thicknesses.  nasty itteratve process but at least I should be able to fit a bath into the bathroom without  it colliding with a wall that was infinatly thin on the drawing but for some reason is 150mm thick in the real world…..

The salesman for this package seamed genuinly supprised when both my wife and I claimed thatthis was one of the reasons we wanted to look at a specilist CAD package, stating that’s not how the building industry works.  “Drawings look nice but it is upto the builder to actuly make them”  WTF!  if that really is the way that building industry works then there is a LOT of money to be made by introducing twentith centry engineering practices  (design rules etc).  Still we are only 16 years into the twenty first centry…