Two part question:

1. I am in the process of planning my own home and have fell in love with heavy timber trusses. I am planning on using heavy timber trusses on ICF walls.It will be a 12/12 pitch roof, with a 24' clear span width. What is the "rule of thumb" optimal distance between trusses? I would like to base the floorplans footprint on it.

2.In the spirit of tradition I am considering using locally sawn native timbers taken from my property. They would be yellow (tulip) poplar. I know many old homes/barns here in VA were built with poplar beams. From what I have read it appears to be comparable to white pine in weight and strength when dry. Has anyone worked with poplar and if so what advise have they for or against?

Thanks!

I have seen trusses spaced at many different widths, usually between 8 and 12 feet. Larger spacing means larger timbers while closer spacing may mean smaller timbers. There is a minimium size for the joinery to work, however, so you may not gain anything by closer spacing after a point. That point depends on the type of truss and the local environmental loads. The distance may be set by what lengths your decking material comes in, or can span.

I recently finished my masters thesis on timber frame joinery, and I tested a large number of joints with yellow poplar. (it is available for download in the members only section). Yellow poplar actually preformed very well, better than eastern white pine. I am not sure why yellow poplar isn't more popular in modern frames; most covered bridges and upper timbers in barns where I grew up were yellow poplar. It works well, is inexpensive, and is quite strong. I think, because it has poplar in the name, that it gets mistaken for true poplars (quaking / lombardy / cottonwood, etc.) which is not a good timber framing wood. It is not the slightest bit rot resistant, however, so make sure there is some barrier between your ICF walls and the trusses.

Good luck with the project,

Yellow poplar is extremely easy to work when green, but in my experience, it actually checked worse than both white and red oak in the same frame. We haven't used it again because of the checking.

Keep us updated with your progress and good luck,

Gabel Holder

I noticed considerable checking when I cut my joints for testing; I thought perhaps it was because of the extremely low relative humidity where they were tested.

Has anyone else noticed this problem? Good end sealer help?

Thanks for the info, I will try to check out the members info area. One of the other reasons I am drawn to poplar is because of its unique color variations, I have seen everything from white and light green or yellow sapwood to dark purple in the heartwood. I don't mind the checking as long as the integrity of the joints is not compromised. I would guess that some of the checking could be done by controlling the rate of drying and sealing the ends of the timbers well both before and after cutting. I think I will build on a 8' bay standard. I have built some furniture items from poplar and it seems to be very stable once dry. I wonder if anyone has noticed a difference between winter cut poplar and spring/summer/fall cut. I know it makes a difference in moisture content of most wood. I also see advantages in the lack of knots and strightness of the timbers. I have some poplars that are clear of knots for 40+ feet and straight as an arrow.

I have worked with yellow poplar a number of times, in most cases it has been used as a secondary timber ie joist or rafters or as board stock.

In one case, poplar was cut along with mixed oak of the lot and sawn into mostly boxed heart 8 x 8, stacked together and air dried for about 9 months. The oak had minor checking, no wind and remained straight but the poplar had deep checking and troublesome wind and some bow. The checking presented difficulty in selecting joint location. I planed the wind out on two adjacent sides to form reference.

In another case, we used peeled poplar poles 8 in. butt for rafters in a open air structure, applied board sheathing and still experienced wind and seperation from the sheathing.

Another case we sawed and hewed poplar logs that was air dried with bark onthe log on bunks about 2 feet off the ground for about 3 years. The boxed heart 10 x 10 remained stable with moderate checking.

All cases were in unheated buildings.

My conclusion is when poplar dries very quickly dramatic checking and wind appears. End coating helps but evaporation from the side grain needs to be slowed. I expect green poplar beams in a heated building will be damaged by rapid drying.

From my observation of old buildings, poplar will weather rapidly if not well painted but poplar heart wood is more resistant to decay than red oak or red pine but poplar beams seem less stable than oak or pine.

Once I tried to convert poplar logs by riving into quarters results were poor due to winding cleave.