How would you do this roof?

[handirifle]

I am building a gable roof over an 18' x 18' concrete pad that we have our spa on. I want a somewhat unusual look but at an affordable price. I pasted a MS Draw version of what it will look like. It will have 7, 6x6 posts, with a header going all the way around, size to be a 6x ? (yet to be determined). There are no walls. The front opening will be an 18ft span, but all the load bearing spans are 9ft.

This pic is NOT to scale, just a rendition

I have worked with a truss company to build me the trusses. I would do them my self, but do not want to use plywood for the webbing. I discussed that idea on another thread, but that was for an enclosed ceiling design. This design will be an open, cathederal type ceiling, and the trusses will be fully exposed underneath, and in the front and rear, as you see. What you do NOT see in the pic is the roof sheathing.

In the pic you can see three groups of trusses. according to the truss company, the front set (18ft span) will be 3 trusses ganged together, and the other 2 groups are 2 trusses ganged together, each.

In my pic you will also see semi horizontal white lines, between the groups of trusses. These are to be placed 24" OC, starting at the top and working down to the eves. These will most likely be 2x6 doug fir, nailed as you would a cripple in a verticle wall. These are what I picture to provide a stable nailing base for roof sheathing.

Is this the best way to frame for the roof sheathing, with those cripples, or is there a better way?

I am going to build this myself, with some hired help, but will also be getting professional assistance on the sizing of the header beam.

 

[bp fick]

Could you not simply build a conventional, stick framed walls? 18x18 is basically a small garage. Cut rafters out of 2x6 or 2x8 for roof and deck with OSB or external ply. Your cathedral ceiling would be very unobstructed.

Thoughts?

You didn't say, is this structure sided in any way? Did you mean no walls, ie, no siding?

 

[handirifle]

Yes, no walls is no siding. There will only be the 7 posts. I do not want walls, as it is to be simply a roof, albeit a nice one, over the spa area. Picture one of the roof structures you see in parks oever the picknic tables. That's what this will be. More like a gazebo with an open ended gable roof.

I could simplify with the trusses every 24" OC, but that will greatly clutter the ceiling, in my opinion.

I plan on using grooved plywood, with the groove side facing down, to give the appearance of tongue and groove boards. All of this will be painted so it doesn't have to be quite as nice as T&G would be, just the look.

 

[magicheater]

I have built roofs like this and insulated them with great success. PM me if you want some details and I can know more of yours.

 

[MikeInEburg]

If you want a nice look, go with heavy timbers instead of trusses.
Mike

 

[dstig1]

Glulam trusses are another good option. It will look a lot nicer than 2x trusses, and the glulam places can do all the engineering for you. If you don't know any glulam places, ask about glulam beams and trusses at a REAL lumberyard in your area. They'll either have access or know the firms that do them. They come regular or treated for outdoor exposure. The best way to handle these is to let someone with a boom crane hoist them in place. Way too heavy to handle otherwise.

This isn't the best pic, but it is the glulam ridge beam in the cathedral ceiling/roof of a screen porch I helped a friend build as part of his addition a few years back. It was finished with a simple Siikens 1-step stain/finish that is rated for outdoors.

 

[handirifle]

I would go with heavy timbers if they are available and not more money. We just moved into the new home we built, in March, and I JUST finished my 24x30 workshop. The spa pad and cover are the last (I think) building project. MANY landscape projects are on the horizon though, but that's another forum.

I wasn't aware glulams could be used outdoors. I was told they had to be inside a building. I really did consider them.

But using a glulam, would require a different approach. If I understand correctly, they are supposed to be supported from the ground up. Not possible in this design, since there is no center beam in the front of my pad.

Now if I could use say, a 6x12 header beam and place a verticle over it to support the glulam, that would work, but without paying an engineer, I'm guessing. I cannot afford an engineer.

That cathederal ceiling is beautiful, by the way. What I don't know either, at least not yet, is total cost, since in addition to the larger header, I would also need rafters every 24", and a ceiling paneling in addition to roof sheathing. I'd have to price that out compared to the trusses, and that is assuming it could be supported by just the header beam.

Anyone have thoughts on THAT issue?

 

[LD1]

Several things for you to consider here.

First, the center post in the back of you pic needs to extend all the way to the top of the truss. This provides lateral strength. unless you want some diagonal bracing between each truss, which would negate the open look you are going for.

Second, You dont need a 6x whatever for a header board. Since you are only going to do the trusses ever 9', that will put them right on top of the posts, thus the header wont be supporting any weight. It will simply be tying the tops of the posts together. a 2x6 or even a 2x8 would be sufficcent.

Third, Find a different truss company. You should be able to find trusses that will span that 18' on 9' centers without having to double and triple up. Unless you are predicting 80+ psf snow load or something. And the triple in the front with the other two doubles confuses me as well. Since each truss is setting on top of two posts, they are in a since carrying the same load. (actually the center will be slightly more.

Fourth, you didn't mention how high it was going to be. If you are going more tan 8'-10', I'd reccomend some knee braces on them posts. even a 6x6 has considerable deflection when sticking way up in the air. Knee braces help the lateral strength.

Lastly, If you arent expecting a high snow load (I am not sure where you live) you could probabally get by with 2x4's on end ever 16 or 24" for the purlins. 2x4's are typically used like that on 8' OC trusses every 24". So I'd probabally shoot for 16" OC with them.

 

[JDGreenGrass]

I have built roofs like this and insulated them with great success. PM me if you want some details and I can know more of yours.

Why would you insulate it.?? A building with no walls.?? Why insulate.??

 

[dstig1]

They make glulam trusses too. They can free span that distance. Trust me... Here is the local place that everyone uses. No idea where you are, but the info should be helpful. These guys include basic engineering in the cost, typically:

Structural Wood Corporation: Home Page

You would want to cross-fill in between the trusses with purlins to support the decking. No biggie, I'd think.

-Dave