Roof Spar Construction for 5' TD

[asianflava]

I started out with pine but it ended up getting used elsewhere. Instead of making a trip, I would remove one of the spars I had mocked up and use it for whatever I was working on at the time.

In the end I used 1X2 poplar because it held the short brads better than pine. The brads were only there to hold the skins until the glue setup. I also laid my spars wide side down so my roof is only 1 1/8in thick.

[Geron]

I may regret it but I'm using 1x2 yellow pine (knotless) and I'm 5' wide. Where panels join I'm using 2x2 white pine (ripped from selected 2x4's) to give more "nailing" room for each panel end. Got a 2x2 in the tight radius curve up front and will use 2x2's to frame in the vent -- nailing room again. Doubled 1x2 popular or red oak only for the hatch hinge area. I'll skin with 1/8" baltic birch inside and out.

Once glued with poly I don't believe it'll go anywhere.

Geron

[Gerdo]

I used 1x2 maple, 8"-10" on centers. I did double up a couple by my vent, and hatch hinge. Maple is strong but not brittle. It is also easy to find straight ones, they also tend to stay straight. I probably used too many but that seems to be the theme of my TD. There is alot of surface up there and it gives me piece of mind. We have had some big snowfalls this winter and all seems to be good.

[Keith B]

Gerdo-HOLY SMOKES - MAPLE???? Now that is very nice wood, very strong, very hard, but crazy heavy and even crazier expensive. I use Maple when building furniture, it's wonderful to work with; my budget will not allow that, epecially for something you "wont see".. but to you for using some great stock. Mine are 1x4 Pine glued to 1x3 Poplar, 12"oc/6"oc on the radius, finished size should be 1.5"x2.5".
I'll do the hatch in doubled 1x3 oak.

[Esteban]

One of the follies from my youth was buying and tearing down a WWII era warehouse for it's salvage lumber. I have a big stack of old growth douglas fir 2x8 rafters taking up room in a garage I need to clear out. I'll cut some of them down to use for my roof spars and wall frame. The well seasoned, tight grained, lumber should be much stronger than any newly purchased wood from HD. They'll be "free." I'm willing to share my bounty if you're building a TD nearby.

I'm wondering, is a 2x2 roof spar stronger if it's glued up from 2 peices of 1x2?

Steve B.

[Keith B]

Steve B... yes it is. That's why laminated beems are so popular for floor trusses in homes and they got away from 2x12's from the 40-70's building codes. Grain will run "diagonally" when looking at the end grain. If you can glue up the boards where the grains go away from each other you'll also minimilize twisting. Also.. 1 board could have a slight split in it.. .that spilt WILL go the full length of the board in a given time, if you use two boards you stength that. They also state, the most stength is when width is 1/2 of the height or greater... i.e. a 1x is actually 3/4 x 1.5. The strongest truss you could build for a TD would be 1/2" osb encased in "real" lumber, much like they use for door headers in homes, but there just isn't enough room to do that, plus, I don't think it's AT ALL necessary. The TD egg shape will resist sagging in itself, just by design.. I'm just "beefing" mine up because I have about a 6' flat section. Oak is strong, but thanks to the advise of this forum I am comfortable with the pine/poplar combination. I can build a home, but the TD is kind of an art in my opinion.. maximizing weight, material and shape to = strength, so I REALLY trust the guys on this site... they've done it and it's my "newbie" luck to hopefully benefit from their successes. I don't wanna build a house, I wanna build a TD

[Wood Tick]

Just a quick thought. To increase structual integrity and reduce deflection often a piece of 3/4 plywood was added between window headers that were oversized. I would think that adding a 3/4 rip glued and screwed to a pine 1x4 would be cost effective and adequate for that span.

[Geron]

Just a quick thought. To increase structual integrity and reduce deflection often a piece of 3/4 plywood was added between window headers that were oversized. I would think that adding a 3/4 rip glued and screwed to a pine 1x4 would be cost effective and adequate for that span.

I always put 1/2 ply between the 2 bys even on standard size headers. I'm also from the old school and break the top plate on a stud and double nail the bottom plate at doors, etc, etc. Ever walk through a development an note some the the "framing" that's done nowadays by the "quickie" framers?

The idea of ripped ply sounds reasonable across the board to lam to the spars. Good ply gives very good lateral strength. There's usually plenty of drop to get the ply from making it virtually "cost free"

[Keith B]

All good ideas... just remember.. ply, osb, etc has very poor screw holding power - thus it's good to have ply "sandwiched" between two pieces of real wood. On house windows, doors, etc, it's mostly done to get the proper depth of a framed wall with just strips of osb, etc., but on LVL beams, the piece has to be 100 solid, no joints, must be glued and incased in wood top and bottom - basically building an I-beam out of plywood... just make sure your plywood has wood around it to glue/screw to. That's how I built my front bulk head. I put a Dado in oak, top/bottom/sides and slipped 1/2" ply in it..it made the ply straight, ridged and gave me a good place to glue and screw the walls into. Another strong "beam" idea is what's called the box beam.. basically think of it as a hollow core door or a wall w/ plywood on both sides or your typical floor truss with plywood on both sides - basically a solid wood frame of some type encased in plywood....the reason they don't really use these is they're rediculously heavy and manufacturing costs are expensive...thus why cheap builders don't sheet 100% of houses w/ plywood anymore.

[bobhenry]

I used Douglas Fir. A couple 1" thick boards won't set you back very much $ and you can cut them down to make spars. It's way cheaper than oak and still a pretty dense, heavy, strong material.

I cut my roof spars from #1 grade Southern Yellow pine 2x12's . One 10' board will give you 70 feet of 1 1/2 x 1 1/2 spars at $11.00 for that 10' 2x12 . That's cheap ( like me ) ! I did space them 12" o/c I felt that would smooth out the curves and gave all the support needed. Extreme fiber in bending is rated at 1000 for #2 SPF (YOUR STANDARD 2X4 ) The #1 syp is rated at the same test at 1450. Not quite 50% stronger. If you are overly cautious make them 1 1/2 x 3 the vertical depth is what gives the strength. Think of stepping on a 8' 2x4 placed on a couple of blocks laid flat it will bow or break with your weight but with the 1 1/2 top and bottom it will support you with minimum deflection. Good clean lumber with very few tight small knots are the key.