How Not to Estimate For Materials

I remember when we built our garage many years ago.  Brian and I designed the garage and Dad came up with our supply estimate.  The cost to build the garage ended up being about 20% higher than the estimate.  The main reason – we changed our plans and went with 2 x 6’s for framing instead of 2 x 4’s.  We didn’t add this price increase to our budget, for some reason.  And our garage is about 1400 sq. ft.  Lesson learned, right?

We’ve completed a lot of projects since then and we always say – don’t forget to add 20%.  That’s 20% to the budget and 20% for materials.  I think this is the general rule of thumb for most projects.  When we haven’t done this method of estimating, we usually run into problems.

Remember this big pile of lumber?  The lumber we paid a few strong guys to carry up 2 flights of stairs?

Framing Lumber

Well, it turns out my estimate was wrong.  I didn’t follow our 20% rule of thumb.  And I know better!  Also, Brian didn’t help with the estimate, so I can’t blame him.  Ha!  So how did I estimate?

The Original Estimate

Basically, I made a spreadsheet with the running wall length for all walls and added that together.  For a grand total of 279.75 ft.  I rounded that up to 300.  Then I multiplied 300 x 12 and divided by 16 = 226.5.  A little more about this formula: 300 is the running wall length, multiplied by 12 inches per foot, divided by 16 inches – this is to get our 16 inches on center estimate.  Then I upped the 226.5 to 230.  This gave us the number of 2 x 6 x 8’s for our studs.

Next I figured the 2 top plates and 1 bottom plate.  So that was 300 divided by 12 ft = 25.  We planned to use 12 ft lengths for our 2 top and 1 bottom plates.  To get the number of 2 x 6 x 12’s, I simply took 25 x 3 for the 3 plates (2 top, 1 bottom.)  Here’s what I ordered:

  • 250 – 2 x 6 x 8
  • 75 – 2 x 6 x 12 (notice I didn’t order any extra here)

The Correct Estimate

What was I thinking?  Here’s what I should have ordered based on our 20% rule of thumb:

  • 275 – 2 x 6 x 8
  • 90 – 2 x 6 x 12

The problem is we ran out of straight 2 x 6 x 8’s earlier this week, so we decided to use 2 x 6 x 12’s.  This wasn’t our best idea because now we have a lot of waste.  So today, we are having more lumber delivered.  Here’s what we are getting:

  • 60 – 2 x 6 x 8
  • 20 – 2 x 6 x 12

Why do we need so many 2 x 6 x 8’s?  Because we used a lot of them for the top and bottom plates of shorter wall lengths.  Also, if we wouldn’t have started using 2 x 6 x 12’s and having so much waste, we probably wouldn’t need any additional.  Lesson learned and that’s why we stopped using them and started working on the second top plate.

Did I mention it’s very, very hot this week and working on the third floor with no air is not too much fun?  Luckily, we just have 2 walls to finish.  Only 2 walls!  The wall between the bunk room and the veranda and the wall between the master bedroom and the veranda.

The up side is we are getting the additional lumber delivered today.  The down side is we’re going to have to get it up 2 flights of stairs.  So now we’re looking for a few strong guys that would want to do some heavy lifting.

Thanks for joining our journey!


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