SIZE OF ROOF SPARS?

[Kody]

Hi everyone,
I almost have the drawings for my TD ready to start cutting the materials but have run into a snag. A problem down here is the availability of suitable size timber. I note that all of you in the US use 1"x2" timber for the horizontal spars that hold the roof and support the side panels. I can't get 1" x 2" timber, I can only buy 42mm x 19 mm. This is 3/4" x 1 5/8". Would this be suitable for roof spars, the 1 5/8" is actually 1.653". If I want /need 1" x 2" I will have to buy 70mm x 35mm (2 3/4" x 1 3/8") and have the timber machined down to 2" x 1 3/8" or even 1' thick. This is a lot of wasted timber and adds greatly to the cost. What size timber would you fellas recommend or what would you do?

Kody

[KCStudly]

Dimensional lumber in the US is based on the nominal size of the rough sawn boards, so by the time that the shapes have been planed and sanded they are actually only 3/4 x 1-1/2 inch. So when some one says 1x2 they are referring to a nominal size (unless they specify "actual"), what they really mean is 3/4 x 1-1/2 measured actual dimension.

Kind of like pipe sizing, the nominal size is not the same as the actual measured size.

You will be fine with the 3/4 x 1-5/8 providing that you are not spanning too great a distance. On edge is stronger, of course, due to the deeper section height.

Are you installing insulation board and what thicknesses are available? When the foam and wood don't match it is a lot of work messy work to get them even. The foam is not super consistent in thickness from sheet to sheet, so if your are doing torsion box construction, or even skeletonizing, you should expect to have to fair some foam.

[danlott]

In the US a 1x2 is really .75" x 1.5", this can be confusing, but here is something I copied off the web to help explain it.

Nominal vs. Actual

The label put on the lumber you buy is called the “nominal” lumber size. The actual size is always a little bit smaller. Nominal refers to the dimension the lumber was sawn. When a 2×4 is cut out of a log it is 2″x4″. After the board is dried and planed it becomes its actual size of 1 1/2″x3 1/2″.

Here is a quick conversion chart:

Nominal - Actual
5/4″ - 1 1/8″
1″ - 3/4″
2″ - 1 1/2″
3″ - 2 1/2″
4″ - 3 1/2″
6″ - 5 1/2″
8″ - 7 1/4″
10″ - 9 1/4″
12" - 11 1/4″

[Lgboro]

You can go with even smaller woods if you make your spars into a T shape with opposing grains. I glued up (dowel pinned and biscuit joined) all my wooded members for walls, ceiling and floors and used wood planned to 3/4 inch. I would go with 1/2 inch if I were to build with this method again and would not have any worries about strength.

[terryjones1]

I used 3/4" H x 1" V (actual measurements) clear pine on the roof of my TTT.
The roof spans 78" in width.
The spars are approximately 10" apart.
I, also, used "sandwich" construction with 1/4" plywood for ourside and inside.
I used epoxy as the glue.
The roof holds my weight (220 lbs)

[48Rob]

Joe,

Your available lumber will work just fine, but be aware that the size alone isn't as important as correctly grouping size with spacing.

A series of 3/4 x 1-5/8 spars will support a great deal of weight if placed on 6" centers, a bit less if placed on 12" centers, and so on.

Rob

[doug hodder]

Depending on how "tooled up" you are, you can always purchase larger material and rip it down to whatever size you want. Just buy accordingly so that you don't end up wasting a lot of material. If you are going to do an insulated wall or ceiling, just make sure that you rip them down to accept what available sizes of insulation is available. Just an idea. Doug

[Kody]

That's wonderful info and a huge help for me. I will use the standard off-the-shelf sizes here for the build. The roof spars with now be 19mm x 42mm, - 3/4" x 1 5/8". Thanks again for your replies. The begining of the start is getting closer each day. I am well under way to having all the fiddly jobs around the home nearly finished.

Kody and Joe