Spars (roof supports)

[Ira]

1 by 2 poplar doubled up/laminated, for a 1 1/2" square spar.

Well, she survived Wilma.

[GPW]

We have a nice rot/insect resistant cypress here , I was planning on doing all my framing with that ... it is very light , and holds nails/screws much better than pine (alot of the old boat builders around here have used it for many years ... ) Any problems , you guys know of .... using oak for galley lid X spar.

I noticed on the GBP that the spars are screwed directly to the 3/4" sides , no blocking or framing (slots) for them ...I was thinking of filling in between each spar with some of the ply scraps , cut to fit ... is this really too much ... it would save alot of work ... on the other hand , if I did it , it would provide a nice "nailer" for the interior roofing panel ... I dunno ???

Also in the GBP, the roofing /outer sheeting wasn't discussed (or I missed it).... 1/4" ply , Masonite (the old timers seemed to like that )... what ??? how was it attached .. glue and nailed I'd guess...
So many questions , so little time .. All Help greatly appreciated!!!!!!

[Ira]

The Cubby plans call for framed walls, 3/8" ply (if I remember right), but the framing is more for your insulation and to have places to run wires and such.

So those plans call for the interior walls to be notched out at the top, to sit the ends of the spars in.

I didn't do it...a lot of other Cubby builders didn't do it...and we just screwed from the outside of the wall into the ends of the spars.

[GPW]

That sounds good to me !!!! Survived Wilma, eh?... Probably would survive a Katrina with a bit more insulation ....

ps , you should see what's not left of this place...

[madjack]

GPW, we used 3/4 ply walls and screwed thru them into the ends of the spars, we also installed 3/4 ply blocks between each rib as much as extra nailer support and glue surface for the roof skin...1/8 luan would be a beter choice than masonite for the skin...also if you use .032 or heavier AL, a wooden skin is not necessary
madjack

[GPW]

Guys, Thanks for the info , That surely is alot easier than an inner frame or worse a laminated curved profile ... Should save mucho' time ...
Now about those nailers ... if the spars are wide enough (1 1/2") and the ceiling was attached , either interior or exterior , onto the ribs (glue and screw) and side edges (end grain ?)would we really need those nailers on the ends... in the old Kustom Van days we'd just run a plastic trim strip along the interior ceiling edge and attach the panels at the ribs only , never on the edges .. that way the finish was just a simple moulding at the mating edges... it would have to be precisely cut for max "neatness"... but not too critical .. I'm trying to save as much weight as possible , so I can spend it later on fun stuff , like a small TV,sound system , or a jaccuzi...

[GPW]

Trying to simplify things even more , I'm going to have some small cabinets in the front and back , Using 3/4" birch ply .... if I run the cab frame all the way to the roof line, I can use it to replace a spar/bow and by adding a nailer on the outside of the cabinet (towards the cabin ) on each wall I can run the roof from cab to cab ...so the only roofing (interior ) I'd have to do is overhead directly , and the small piece on the front , below the cabinets... saving material (cost and weight ) , the cabinets would be larger inside , uninsulated , but a few towels/clothes /blankets should take care of that ...stronger too since the 2"x2" is replaced by a 3/4"x2'(Deep Spar ) What do you think ????

[GPW]

Judging from the reaction , I guess that's a bad idea...

[mikeschn]

GPW,

I'm not sure why you got no response...

Technically what you describe will work. The top of the face frame can replace a spar, and the bottom of the front cabinet can replace a spar. But if you have 1/8" plywood roof, it wouldn't take much of a rock to put a hole thru your roof at that point.

Check out unscientific test in this thread...
http://tnttt.com/viewto ... 3783#53783

And in that test the plywood is backed by EPS. Without EPS you'll get a hole in the plywood even quicker...

Mike...

[bobinohio]

Derek,

I haven't built yet but my thinking was poplar. It is the cheapest (in my area) of the hardwoods and is stable, holds fasteners and takes paint and glue well.

I checked some weights and found, unless you're very concerned with a few ounces, there's not a lot of difference.

Figuring a 4'x3/4"x1 1/2" spar (maybe... ceiling joist or rafter??) the approximate weights are:

Western White Pine, Spruce, Ponderosa Pine, Redwood: 13.5 oz.
Poplar: 15 oz.
Shortleaf Pine ( one of the major Southern Yellow Pines): 18.4 oz
Birch, Maple, Red Oak: 22oz.

These are based on CabinetMaking and Millwork 2nd. ('82). Other sources will differ. For example: new growth fir is on the market. It is both lighter and weaker than old growth. Fir, btw, falls halfway between SYP and Poplar in weight.

Some others-Ash is just a bit lighter than Red Oak and looks almost the same with a little more shock resistance. Red and white cedar are not listed.

The best "Pine" I've come across is Southern yellow Pine.
It is used extensively for roof trusses, headers, and other weight bearing applications in home and industrial building...because of its strength.

Also because its cheaper. The biggest problems are it is slightly less stable and the density difference between growth rings really tends to turn brads, nails, and to a lesser (but very annoying) extent- small diameter drill bits.

Always pre drill!!
And when choosing/using lumber, leave the pieces with knots at the store.
It costs more for premium lumber that doesn't have knots, but a structural rib with a decent sized knot will snap like a match stick with only minor pressure applied.

I'd have made the whole quote bold, big and red but that gets annoying. Knot free pine is difficult to find in my area. Much of the clear pine I see appears to be sugar pine- lighter and weaker. It is also at least as expensive as poplar. Most hardwoods are clear- and that is the most importand thing.

BTW, maple and red oak are usually the next cheapest after poplar.

Bob

[48Rob]

Couple thoughts,

Nailing (fastening) the paneling at the ends is perhaps not nessesary, but adds much strength and rigidity to the structure.
Think "twisting forces" such as when you drive a car through a small ditch at an angle less than 90 degrees.

Or, when you take a long rectangular cardboard box, and holding an end in each hand, twist it, one end oposite the other.

In the trailer scenario, if you have nailed/fastened only along the ribs and seams, much twisting of the structure can occur.

The weight savings of a handful of fasteners and a bit of glue isn't enough to be concerned about.

As for a "larger" rib, yes, using a piece of plywood "as" a rib will result in a much stronger trailer, though the "extra" rib, attached to a regular rib will make a heck of a strong roof support.
I did this in two areas in my trailer to provide some sense of protection against falling objects crushing me/mine inside the trailer (think tree limb in a storm). Mine run from floor to ceiling.
Using plywood, in a structural sense, instead of framing, and then tacking thin paneling on will be far stronger, in the application you're considering.
Sandwich construction, done correctly, is actually stronger than a solid panel, but, in replacing a rib as you're considering, more rigidity will be gained by securely fastening the plywood panel to the sidewalls...now, if you also attach it to a roof rib, you have created a very rigid structure.

As far as installing a ceiling panel in only the visible areas, yes, it is an acceptable method, but will result in a very warm cabinet.
You could insulate that area, but then you'll "see" the insulation each time you open the doors.
Perhaps not a big deal...


Rob

[GPW]

Gentlemen , Thanks for the info .... my problem is compounded by the fact that I'm building a 12'Lx6'Wx5'H... same setup only a bit larger ... so I must think about 50% larger in the materials .... planning on 2"x4" (true sized) spars and 3/8" roof/front with Aluminum skin on the roof /front/hatch ...painted sides...spars on 16" centers , and from what I gather , the frames and spars combined would be better/stronger...The weight be durned' cause I'm probably going to end up with way more trailer than I need anyway ...

not to digress , to get the height/lengths I need , I'll have to join pieces of ply for the proper width , etc.... was planning on a lengthwise half lap join with a router , but would a buttjoin /batten be as good , or again the combination of both .....I appreciate the help , This is going to be my escape pod , so I have to "do it right "

[48Rob]

Hi Bob,

Your post was very informative, thanks for doing the research!

You wrote;

BTW, maple and red oak are usually the next cheapest after poplar.

It is difficult for me to remember to include when speaking of different species, but I should point out that ones location is all important in regard to which species is commonly available, and which can be had for the lowest price.

In my area, Illinois, Oak is relatively inexpensive, with Poplar being next in line.
Here, Maple is like an exotic African whatever wood...just completely unreasonable.

So, point is no matter what advice we give or receive here, always consider that one species or another may be more/less expensive in your area.
A potentially large savings...

Another point is "knot free Pine"

Knot free Pine is not a common thing here either...
Most of us would like to think that we can just go to the lumber yard and "pick out" some really nice lumber for our project...

Well, most of us have been conditioned to shop at the big box stores, because of the convienience and cost savings.
Wood can certainly be had cheap there, but it is usually cheap wood and we're the ones being "had".
Most weekend project people don't know or care about what they get...they just want a "board" for that shelf (or whatever) project.

It costs more, but buying from a true lumber yard will net you much higher quality lumber.

For those that may not know, lumber is graded according to quality.
Higher the quality, higher the price.
Can you guess which grade the big box stores sell you??

If you're slapping together a temporary box to store something in the garage, the lower quality lumber will suffice.
If you're building an heirloom curio cabinet for your daughters wedding present, you'll probably want a little better quality.

So, you live in a place devoid of a "real" lumber yard...
Choose a piece(s) of lumber bigger than you need, that the proper sized parts can be cut out of.
You end up with no knots, and straight grain.

Rob

[48Rob]

GPW,

Will your trailer have a curved roof?

If so, 3/8" plywood can be quite difficult to bend...

If the plywood you're joining isn't a structurally important panel, a butt joint with battens will be fine.
It would obviously be stronger though if you did a half lap and battens.

Rob

[GPW]

Rob , you built a Big one ... did you oversize your lumber ??? Saw the build pics (TUB???) but no narrative ....