Greenhouse spreadsheet explained

Assuming you have downloaded the spreadsheet and opened it… I generally use Open Office but saved the spreadsheet in .xls (Excel) format. Hopefully you don’t encounter problems, but if so, email dave@twinsprings.com and I’ll try to help.

Spreadsheet overview. There are two Sheets

  • Designthis is the sheet we will use
  • Shading – I am working on a method of putting horizontal boards across a panel to let in winter light and block summer light. It is not ready for prime time

Using the design sheet for your project. This sheet calculates the pieces to be cut for each “bay”. The idea is that multiple “bays” will be bolted together to form the greenhouse. The picture on the first page shows two bays bolted together. You may have large pieces of glass that are not the same dimensions.

The spreadsheet has some cells colored CYAN, GREEN, and YELLOW. The design assumes that the framework is built with 2x6s, 2x4s, ans 1x2s. The actual measurements of these items are shown in B3-C5.  If the lumber yards start selling smaller versions of these pieces, adjustments may need to be made in these cells

The CYAN cells (B6, B7, B8) are specific to the pane of glass in each bay. You will change these for each pane of glass. The bays will all be the same height (so their roofs line up) but the glass in each may have different heights, as well as widths. And varying thicknesses (for single and double paned glass) will affect some trim and other pieces. You should run the calculations with the longest pane first; this will set the roof height.

The GREEN cells will apply to all the bays you build. You will set these values once for the entire greenhouse and be used for all the bays. They include:

  • (B1) designed “sun slant” – for winter use, sites like http://www.solarpoweristhefuture.com/how-to-figure-correct-angle-for-solar-panels.shtml recommend 65 degrees if your latitude is 40º. This is cell B1 (initially set t0 60). To be honest, I used 60 degrees and I do live at about latitude 40º
  • (B9) slop – This value is used in several of the calculations. The idea is if you have a piece of glass that is 80″ x 40″, and create a frame with those exact dimensions, due to imperfections in the wood, the glass may not fit. I had good results using slop of 0.25″ and using store-bought lumber. The computed opening will be 80.25″ x 40.25″
  • (D15) difference in height between the front and the back. This foundation in this design requires one build a level line for the front of the greenhouse and a level line for the back. The two lines do not have to be level with each other. This cell is where to specify how much higher the back is than the front. (If it is lower, use a negative number.) Since building the foundation lines is the next step, do not worry about this value until they are built. Then come back and update the value in the spreadsheet (before you start cutting the boards.)
  • (D3). This will be the length of a standard 2×6 to be used in the slanted verticals. It must be long enough to have a angle piece be cut off the bottom (for the solar slant) and to hold the longest pane of glass. There is intended to have excess space at the bottom. I recommend buying and using standard lengths like 92.5″ or 96″ or the next size, but this cell would allow one to choose other lengths.  Cell (E10) will tell you if the length you choose will accommodate the glass pane.
  • (C12) and (F12). These cells are used to determine the size of the roof. The glass panel is framed by 2x6s. C12 will be the length of the roof from the 2×6 to the back of the back wall. F12 is how far you want the roof to overhang the back wall. You will want the overhang to at least cover whatever siding you expect on the back wall, and preferably extend a couple inches beyond that so that precipitation does not easily drip on the back wall. The longer you make the roof (not counting the overhang), the deeper the greenhouse will be and the more inside area it will have.
  • (H10). There is bracing between the slanted front wall and the roof. If the bracing is short, it will be closer to where the front wall and roof are connected; this offers less bracing strength. Longer bracing will offer greater strength but reduce headroom. 36″ seems a good compromise, but you can alter it if you like.

The YELLOW cells tell how to cut the various pieces.