Truss Designs for an Attic

What you want is an 'attic truss'. You don't have to do the calculations. Your local lumber company has a truss manufacture they deal with. All you need to do is supply them with the total span, attic headroom, and possible extra point loading/weight. Then tell them what you want the roof to look like (hip, gable, mansard, whatever). They will figure out snow loads based on your area building code.

If your counter jock is not busy, you can get a cost per truss and possible delivery date before you have finished your coffee. Be prepared to have a decision ready when they ask about end trusses. What size window/door or just built for siding and a vent. A savy construction crew can work with a 24' span without a crane. even with the cost of a crane it is still the cheapest, fastest way to get a roof up.

thanks but this project is a "do it yourself." i was looking for designs for attic truss because i was thinking it would be fun to design them myself. it would cost to much to get a crane and a construction crew, i am probability going to get my friends together and do it between 8 of us or something like that. because i was looking at the attic truss in my cabin and my friends and they are just put together something like 20-30 years ago and they are pretty simple

"i just did these drawing on paint because i don't have ACAD at work but i got it at home"

the truss in my friend cabin look like this (above) 2x4 but there are actually 2" by 4" just as an idea of what there is. but i was surprised that the attic truss look like that and supported the snow loads, not much to them. dont know the spacing but that is just an ex.

i was thinking some thing like this for the attic room

so that the front (the side that faces the lake has a higher roof) the the side that faces the road has a steeper slope.

i was just look for some ideas on the how to brace the roof by truss that didn't take up much space. cost is a factor. so i might build the trusses on site.

just something that was wandering in my head. lot of ideas.

Your top drawing is just a collar tie, and I hope your friend's rafters are sized accordingly. You could also create a ridge beam sufficient to carry the load. Rafter size and collar ties included in the calcs.

Pre made trusses are cheaper than buying the lumber needed to build them. If you are not willing to check this out at your lumber company, then you're on your own.

Bye bye!

For your configurations, you might want to look at something like this:

I would also suggest you look at prefab trusses. They are made in factories, far more efficiently than you ever could. And the manufacturers buy materials in huge quantities, reducing their costs. And the products are extremely uniform. And they are quality controlled. How would you know if you have made a truss that is good enough? If you only use three nails instead of four at a joint, is that a problem or not?

i would think it would cost more to get the truss there then to builded them

i would think it would cost more to get the truss there then to builded them

Well it depends, of course. Trusses are delivered on a flat-bed truck, so it just depends if there is a road, and if the road is straight and flat enough for the truck. But it is true, you can't haul them up in a pickup truck, like you can plain 2"x4"s and nails.

And the major advantage of prebuilt trusses is the speed of construction. With a crane, three men can frame an entire house's roof with trusses in one day. The money you save by doing it so fast can makes up for the increased delivery cost. Or it might not. It just depends.

You might consider a "gambrel" type design.

My thoughts exactly! I vote for that.

oilcan13

Maybe a scissor truss would look good. If this is a DIY project, you might want to space them a little further apart, say 6' and use 1.5" deck to span between trusses. You can add more web members if you want to reduce the length of the top chords.

thks that gives me some great ideas about what to do.

GA to Ba/ael for the scissor truss design!

Even though I understand the principle behind those, part of my brain goes "But there ain't no daggone tension chord!"

Just one thing- it's the attic room's floor that will be taking the load of anything being hoisted in the garage, unless you were planning on hoisting things up and down through a trap door. In either case, I would recommend using a steel beam to span between the bearing walls.

If you're comfortable with the engineering, then you can also use a beam (wood or steel) to span either all the trusses or all the floor joists, so that they all carry an equal share of the load. My dream garage will have a homebuilt two-ton chainfall gantry crane so I can pick and set loads anywhere I want. The rails will be lag-bolted to properly sized studs.

I have built trusses before, and it can be done cheaper if you don't count the cost of your labor. You just need a flat concrete floor the size of the truss to work on.

When you build them yourself, you can take the time to pre-drill the nail holes to avoid splitting the wood, or even use bolts if you want to spend the money.

Personally I don't trust those 'nail plates' they use on commercial trusses. They cut a lot of fibers when they're driven in. They are pretty thin steel, also, and can corrode in a damp environment over time. And in a fire, they will fail long before the wood burns through.

Even though I understand the principle behind those, part of my brain goes "But there ain't no daggone tension chord!

If the joints were free-rotating pivots, there would be three chords in pure tension: the two lower ones and the vertical one. But since the joints are fixed, the chords will see a complex mixture of tension, compression, bending, etc.

I always wondered why trusses are built with rigid joints. Perhaps it is just cheaper.

Personally I don't trust those 'nail plates' they use on commercial trusses. They cut a lot of fibers when they're driven in. They are pretty thin steel, also, and can corrode in a damp environment over time. And in a fire, they will fail long before the wood burns through.

Commercial trusses are totally engineered, meaning they are as precisely as strong, cheap and durable as they are intended to be. That doesn't mean they are extremely strong, it just means they are meant to be just strong enough, and no more. Every material can fail if put in the wrong environment. A house might eventually fall down because the builders used the wrong tape for the vapor barrier.

Those nail plates do cut lots of wood fibers, but all those fibers are near the surface. And they create a tremendous amount of shear strength (they are extremely difficult to pull sideways, once nailed in.) That is what you want in that application.

I guess I grew up with the "If two nails will do, put in four screws" school of country make-do engineering. I remember when we built those trusses, my buddy's dad hunted all over trying to find 24' long boards for the bottom chord, to eliminate the joint in the middle. We ended up using two 12-footers, which he didn't like very much.

I personally don't like "reductive engineering" on things like roof trusses. Sure, they are just strong enough to support the design load for the design life of the truss.

I tend to think in terms of there being two layers of shingles and four feet of wet snow on the roof, an extra layer of sheetrock on the ceiling underneath, the house has settled (putting torsion stresses on the trusses) and now a 300 pound man climbs up on the roof. Yeah, it's expensive, and some call it wasteful, but I like to "over-engineer" anything that could conceivably fall on my head.

Ice-Man, I'm not clear on what you want, but some pointers:

Check with the Canadian/Winnepeg equivalent of a Code Enforcement Officer on the design load and minimum member size requirements, etc.

You will need to buy and study a lumber design manual, in some ways, wood is more complex than structural steel. If you build trusses, the connections can get pretty hairy.

Why not build the walls up to the eaves level and use simple rafters and ties from eave to eave?