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

 

[handirifle]

LD1
Hopefully I can answer most of your questions. I should have mentioned up front that the pic was not a finish plan drawing, it was originally made (by me) to give the truss co. an idea of what I had in mind. Knee braces were always in the planned construction. The posts are to be 8' high, with the header on top. The reason I mentioned the heavy duty header (6x10 or 6x12) was IF I decided to go with a glulam beam down the ridge with rafters down from that. The heavy header was theoretically to replace havine a center post support all the way to the foundation, in the front.


I still would use a 6x for the header, purely for looks.

The center post, in the rear, is on the same plane as the rear corner posts are. How could I extend this all the way to the top of the truss without cutting the trusses? I think I know what you're saying but could you elaborate a bit more on that? Please?

So, you believe a 2x4 16" O.C. spanning 9ft would support the roof load? Since I nevermentioned it, snow load is almost non existant here. Central coast of California. We see about one storm a year, and it usually drops a few inches. The roof is 6-12 pitch with 5/8 (or heavier if needed) sheathing and 15lb felt under comp shingles.

And lastly for the tripple in the front, I THINK, their original design had the third truss with vertical memembers for nailing on siding, since that is how they would do it for a house. I didn't ask that question, but it's my guess based on a later conversation, via email.

Would single trusses in the three areas, be made of 4x lumber? Remember we do not have snow loads here, but we do have to engineer for earthquakes, that might be it.

 

[LD1]

Typically aroundhere the end truss is on the outside of the posts and dot directally on top or them. this would keep the 3 posts on the back on the same plane. This is also to keep the 2" wide truss on the same plane as the 2x4 nailers if you were adding a wall. But the reason it needs it be extended is because you have to have something to add lareral strength to the open truss design you are wanting.
Example. Imagine taking 3 or 4 peices of 2x12 lumber and stand on end. Then nail a peice of plywood to the top. Now stand on it and rock back and forth. It wont take much at all to lay the "top heavy" 2x12's on their side and bend the nails. This is what you are trying to fight with trusses. Floor joists are the same way, that is why they have x-bracing between them. If want an open design with no cross braces, you have to extend the post onn the back.

As to the trusses. Using 4x lumber doesnt gain much at all. The strength comes from the depth. Example, a 4x4 truss would not be as strong as a 2x6 trusss built the same way. Typically that is how they add strength. By going to larger 2x lumber and not 4x. The only thing a 4x would gain would be lateral strength. Which may be required in your area due to the quakes you mentioned. I have no exp. with that. Just ask a few builders in your area if you can get trusses to span 18' on 9' centers. I'm sure someone can.

As to the 2x4's, yes you will be fine on 16" centers.
Here is a span table.http://www.msrlumber.org/spantables.pdf

I refrenced chart 10. with a 20psf live load and a 10psf dead load, and a l/240 deflection, a 2x4 will span the 9' no problem.

 

[MarkV]

My comment would be that I don't find standard manufactured trusses very esthetic left exposed. If I were building it I would build a conventional gable roof frame on 2' centers with 2x6 rafters and use collar ties every other rafter set above the 8' wall height for a taller ceiling feeling. The collar ties are also a great place to mount a fan light combination. One thing I have done in this type of structure is run a double layer of roof sheathing. For the first layer use T-111 with the finish side facing in and then layer it with 1/2" ply or OSB. It will give enough nailing surface to put shingles on the roof and leave an unmarred interior finish. You can sort of see the affect in the attached photo from our weekend house.

I have given up on open pavilions in my area. Between the birds, spiders and wasps we find a screened enclosure much nicer for the hot tub.

MarkV

 

[Kays Supply]

I used a cathedral truss system on my open back porch. It let me close it all in but still had the high ceiling. I put white washed pine tongue and groove boards on the ceiling. I put foam board above that. It keeps the heat from coming through in the hot summer. The gable is sided to match the house. Like they said, all screened it keeps the bugs out. I can pressure wash it all and it looks like new in short order every spring.

 

[Kays Supply]

I used a cathedral truss system on my open back porch. It let me close it all in but still had the high ceiling. I put white washed pine tongue and groove boards on the ceiling. I put foam board above that. It keeps the heat from coming through in the hot summer. The gable is sided to match the house. Like they said, all screened it keeps the bugs out. I can pressure wash it all and it looks like new in short order every spring.

 

[6sunset6]

You can get PT glue lams. I just priced some for a small bridge. Pricey but sometimes it is the way to go.
http://www.ilevel.com/literature/TJ-7102.pdf

 

[magicheater]

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

Building uses change, perhaps in the future it would be. When building plan for everything, you are in Maine, don't you?

 

[nickel plate]

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.

If you go with the grooved (4", 8" or 12"oc) plywood siding, do note that the sheathing span value is determined at the depth of the groove to the back side of the panel. 5/8" thick panel with a deep groove leaves you about 3/8" +- sheathing value. Not enough there to pass code as the thinnest roof sheathing starts at 7/16" thick.
Using stringers for nailing the roof sheathing does not take into consideration the required 8" oc edge nailing of the panels. Read the stamp on the back of your selected roof panel and you will probably see that the field needs to be nailed at 16"oc abiet this is for vertical sidewall application but again, stringers won't work. There used to be an 1-1/8" 4x8 grooved plywood panel decking that was made exactly for your application that spanned 48" thus no unsightly stringers at all but you will have to set the trusses at 48"oc.
Since your trusses will be exposed and if you do not paint them, tell the truss company not to spray paint your job name on the bottom chord of the truss package as that will give you another unsightly look once installed.
For what they do and the limited amount that you need, trusses are cheap. You can probably get a set of engineered single ply trusses with a larger bottom chord (2x6 or 2x8) that will span 48" oc.
Watch out for "shiners".

 

[LD1]

I would shy away from the gluelams unless you want to spend big $$$ and like the looks.

Gluelams do have their advantages such as being able to clear span greater distances without supports. And rock solid floors in new houses.

But for what you are doing, an 18' span with trusses is not hard to do with conventional lumber. Neither is the 9' span between posts and trusses.

Save your money cause gluelams are about 3x's the cost.

If you like the open look, get a scissor truss. Finish with your grooved plywood on the underside. It will give a vaulted ceiling look and yet it will still hide the trusses. Cause I agree with others that exposed conventional trusses dont look the greatest. If you still want the exposed truss look, and are willing to spen the $$, you cant beat the looks of large timber trusses IMO.

 

[handirifle]

My comment would be that I don't find standard manufactured trusses very esthetic left exposed. If I were building it I would build a conventional gable roof frame on 2' centers with 2x6 rafters and use collar ties every other rafter set above the 8' wall height for a taller ceiling feeling. The collar ties are also a great place to mount a fan light combination. One thing I have done in this type of structure is run a double layer of roof sheathing. For the first layer use T-111 with the finish side facing in and then layer it with 1/2" ply or OSB. It will give enough nailing surface to put shingles on the roof and leave an unmarred interior finish. You can sort of see the affect in the attached photo from our weekend house.

I have given up on open pavilions in my area. Between the birds, spiders and wasps we find a screened enclosure much nicer for the hot tub.

MarkV

MarkV

Nice looking setup there. I have given the rafters and collar ties some serious thought lately. You can even adjust them a bit higher from what I have read, anyway. Is your stained? Was that a spray on or brush on finish? If brush on, that would be a LOT of upkeep.

I could possibly end up enclosing this whole rig in the future, so really insulating the ceiling, or having the ability to, is not out of line in this case.

LD1
I do not recall ever seeing that type of setup here, interesting. Thanks for the span table info.

Kays supply
I have also considered the cathederal or scissor truss and enclosing it all. My wife is not super keen on the open beam idea, because of the spiders and webs.