Materials list appears to be off...am I misunderstanding?

[Chad Oftedal]

So, I purchased a set of plans for an 8x8 greenhouse which I am converting to a coop. Yesterday, I bought all the lumber (Qty: 46 - 2"x4"x8') that covered all the framing for the walls. This afternoon, I made my cut list based on all the measurements in the plans for the walls. I then went out to the shop and started cutting. I got down to the point where I needed 20 pieces at 39", and I could easily see that I was going to run out of lumber - note: I started cutting the longest pieces first, and saved my scraps to use for shorter pieces later.

Anyway, I could see it wasn't going to add up. So, I went back in the house, and triple checked my counts and measurements, and they were correct. I kept racking my brain trying to figure out how it could be so far off. So, since I had my cut list already in Excel, I converted all the lengths and quantities to inches, and divided by linear feet to get the total number of boards. It came out to 45.23 - 2"x4"x8' boards. The material list said 46, so that matched or double-checked that my cut lengths based on their plans was right.

OK, so the problem here as I see it, is that they way they came up with 46 boards was to assume zero waste and the sum of the total lengths needed, not the total boards needed when factoring in waste from cut pieces that are too short to be re-used in the framing due to being too short. To me, this seems like a problem (and not a small one) with their materials list, but this isn't my field of expertise. Am I off-base here? Can you not expect to make a cut list from a materials list?

 

[ChickenCanoe]

I'm guessing you are probably right. Perhaps they had a cut list to minimize waste. What I mean is, I sometimes have to do a little extra math and juggling what pieces come out of each board to maximize usable pieces. That requires mixing and matching lengths on a single board rather than starting at the beginning of the list and start cutting lengths in order.
You also have the length lost from the kerf width with each cut.

 

[Ohmyheart]

I don't know what your instructions said as to what materials you need. You should always cut wood in a way where you have no scraps left over. In other words use each board like it's your last. Scraps usually mean more wood is being used.

 

[Chad Oftedal]

I'm guessing you are probably right. Perhaps they had a cut list to minimize waste. What I mean is, I sometimes have to do a little extra math and juggling what pieces come out of each board to maximize usable pieces. That requires mixing and matching lengths on a single board rather than starting at the beginning of the list and start cutting lengths in order.
You also have the length lost from the kerf width with each cut.

Yeah, it feels like to me the material list was generated with some software that determined what number of boards (in common 8 ft size) would generate the needed length total, but didn't do the cut list to take in to account waste. For example, there are some boards that needed to be cut at 71 1/2". That leaves 24 1/2" left over from that board, but there are no other cuts to be made that can utilize that short of a left-over. So, they counted that 24 1/2" in their length total, but it can't be used in any of the structural framing because no piece needed is that short.

 

[ChickenCanoe]

There's your sign. That's a lot of waste. Even though they're more expensive, sometimes if you work it out before hand, it may be better to buy 10' or 12'.

 

[Chad Oftedal]

There's your sign. That's a lot of waste. Even though they're more expensive, sometimes if you work it out before hand, it may be better to buy 10' or 12'.

Exactly! My mistake here is that I was paying for plans that appeared to be well done - nice detail and drawings with measurements and fine details, etc., that I didn't really have any need to question the materials list. None of the cuts were any longer than what an 8' board could provide, so when it was a total of 46, 8' boards, that made sense. But, my assumption was the list was accounting for minimum boards needed and maximizing what you had to reduce waste, but unfortunately, that's not how they calculated it. Oh, well, I guess other than time to go back and get more lumber, it'll be OK. I'm sure in adding my extras and future projects, I'll make use of those scraps, but I would have much rather bought different lengths that would have minimized board count rather than all the same length.

 

[ChickenCanoe]

One can always make good use of scraps.

 

[aart]

My mistake here is that I was paying for plans that appeared to be well done - nice detail and drawings with measurements and fine details, etc., that I didn't really have any need to question the materials list.

Oh, If Only...sigh.

A materials list is all well and fine but...
.... I've often made cut diagrams in cad to reduce waste.