How to build a lean-to glasshouse
The wood and wood sizes
This project is written using both Metric (mm) and Imperial (inch) measurements.
The metric measurements are given first followed by the standard measurements in brackets ( ). For example: 50mm x 75mm (2x3).
The size (width and thickness) of the framing wood given throughout this project is the nominal size, that is the size of the wood before it has been dressed (surfaced, planed, seasoned).
When the wood has been dressed (surfaced, planed, seasoned), it becomes the 'actual size' or the true size.
The actual size of wood is less than the nominal size.
The wood I used for this frame was a treated softwood.
For the studs, top plates, rafters, and noggings I used dressed (surfaced, planed, seasoned) 50mm x 75mm (2x3). That is the 'called' (nominal) size. The actual size is less.
50mm x 75mm (2x3) is not a very common stock size in North America although it can be sourced from the odd place. Failing that, it can be obtained by ripping 2x6 stock in half.
For the bottom plate I used rough (actual size, fence post) 100mm x 100mm (4x4).
The stock sizes given for the framing wood in this documentation are the 'nominal' sizes as opposed to the true 'actual' sizes. why?...
Nominal size Vs actual size
When wood (nominal size) is dressed (surfaced, planed, seasoned), the width and thickness of it becomes less. It becomes the true 'actual' size. The actual size is less than the nominal size.
The actual (true) size can vary in different countries.
For example: Consider a piece of common 50mm x 100mm (2x4).
When dressed (surfaced, planed, seasoned) there is a discrepancy in the wood thicknesses between the British/Australasian standard stock size (being 45mm thick) and the US standard stock size (being 1 1/2" thick). There is a difference of around 7mm (1/4").
Hence why I will be referring to the framing wood by the nominal size rather than the actual size. The nominal size is more standardized.
If the wood that you source is a slightly different size (width and thickness) to the wood used in this project, it doesn't matter, Just make adjustments to suit.