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Pavilion in FL

Started by MishaZ, December 22, 2020, 06:13:35 PM

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MishaZ

Need help locating a local yard that caries timber other than PT Yellow Pine (unless PT is what you recommend in FL?)

Hello all, new to the forum and am a DIY. I'm always hunting for a new project, just can't sit around idle. Not to mention I have three kids under 10 in the house, projects are a good distraction. In fact i just finished building from scratch a large playground for those three kids as part of my COVID project. Will attach a pic to establish baseline credibility 

I'm writing to you all as i am looking to start another backyard project. Looking to build a Pavilion around 14'x16'. I'm was thinking of doing Timber Framing using mortise and tenon joinery for the first time. Alternatively would use Post and Beam with metal braces. Never built a pavilion before, but doing something for the first time is not a deterrent. Love to build with my hands and figuring things out.

The issue I am having is selecting the wood for the project. I live in Tampa, FL and would like to keep the project somewhat cost effective. Most abundant material is Pressure Treated Yellow Pine. But talking to one of the mils, was told that it's not best for Timber Framing as it will work and check as it ages due to weather (rain and heat). From my research Douglass Fur and Cypress are other commonly used woods for timber framing. Cypress being closest to native ??? I read on another site that FL Cypress (Pond Cypress) is not that good for structural work.

Need your advice on wood to use, framing style to use and advice on local place (or close enough) where I could get something other than PT Yellow Pine. I'm thinking of using 8x8 posts, so the place would need to carry large dimensions.  Recommendation on Post and Beam vs Timber Framing is also welcome.

Sorry for the long intro!  You don't know what you don't know and I want to know ;) 

Mike



 




 

Don P

Really, yellow pine is one of the lesser checking species and for the posts treated is not a bad thing. Large timbers will check, that's just part of it. You can lessen the checking by drying a bit slower, out of the sun but with good airflow so that the core can lose moisture and size at a closer rate to the rapidly shrinking outer shell. I've had luck reducing checking when I had to put something up green and exposed if I put on something breathable but that would slow the surface drying, even something like Thompsons. You don't want an impervious film like varnish or paint on green timbers or it'll trap moisture and cause rot.

Within reason just about any species can be used, simply size the pieces correctly for the loads and strength of the material.

Personally I'm not a purist, either method will work, do what makes you happy.

ellmoe

We do sell some untreated pine for pergolas , etc. , cypress is what is most commonly used by our customers in Florida.
Thirty plus years in the sawmill/millwork business. A sore back and arthritic fingers to prove it!

MishaZ

So everything aside, I'll ask a more direct question.

Pressure Treated Pine or Cypress ???

PC-Urban-Sawyer


Raider Bill

The First 70 years of childhood is always the hardest.

kantuckid

Cypress story: My wife & I canoed the Okefenokee Swamp in the early 1970's. There in you canoe and camp per assigned routes that are color marked in the swamp. The only solid ground overnight spot we had in our 4 days there was on an island which had a hunting camp (logging camp before that with log haul routes outbound) with a nice but basic lodge left for before WWII, I think it was said to have been built during the depression, like 1930's. It had cypress heartwood shingles on the roof and outer walls, cypress floors and framing. They looked like they'd been done recently in spite of the hot, humid swamp environment.
Cypress is your wood of choice if optimum figures into this project.
Google Cypress lumber/logs and FL sources with websites will pop up. 
Kan=Kansas;tuck=Kentucky;kid=what I'm not

MishaZ

Well, Cypress it is.  I found a local place that can get it sourced within three days.  Can get it rough or S4S delivered for a flat rate of $75.  It is going to be green.  I have read many of threads on Green vs KD framing and there are many of opinions.  I don't really have the luxury of waiting around for months to let it dry naturally and the place I'm getting it from does not do KD.  From what i have read, green is easier to work with, but Cypress will lose quite a bit of moisture.  

That stated, here is the next "simple and direct" question.  Which framing style should I go with:

* Post and Beam (hardware) - If so, there are follow-ups on hardware; external plates, internal knife hidden plate, etc.  Any brands you recommend?  I'd probably still do a diminished haunch or shoulder so the post would take the brunt of the load and not the mechanical joint.

* Timber Framing (mortise & tenon) - full disclosure, never done this before, but really wanted to try as final product looks something to be proud of for long time and I get to learn a new trade.  But is it too much too soon?!?!?!  I have no specialty tools.  Will need to get framing chisel and slick, not too big of a deal.  I don't know if I can justify spending the $$$ on the chain mortiser.  So will have to drill out and carve out the mortises by hand.  Don't have 15" circular saw, but 10-1/4" are reasonable in $.

Ohhh, and there is a matter of this being in FL where there are hurricane code requirements...  Will M&T be sufficient to comply with hurricane code requirements?  Hurricane rafter ties are not the most attractive looking things.

Don P

It sounds like you would like to do timberframe, go for it. There is no need for expensive tools, they make it faster is all. When people comment on my 16" saw I tell them that I have a hand held 28" one too, their eyes get big and I reach over and grab a handsaw  :D.

kantuckid

I see no reason unless (it's your own desire to play at timber frame joints) to not simply use good carpentry construction details such as the pictures show above? Hot dipped galvanized bolts installed via hand tools and some way to saw wood and make the holes. 
If your not fixed on the source mentioned, look at CRACKER SAWMILL / D&J LUMBER - Cracker Sawmill - Home in Williston, FL. 
Kan=Kansas;tuck=Kentucky;kid=what I'm not

Don P

Quote from: MishaZ on December 28, 2020, 11:41:43 AMOhhh, and there is a matter of this being in FL where there are hurricane code requirements...  Will M&T be sufficient to comply with hurricane code requirements?  Hurricane rafter ties are not the most attractive looking things.
That depends on what the requirements are, please post them or a link to those codes.

I can get to the strength required of a hurricane tie here by using a concealed structural screw or lag. Most of these types of codes require a level of performance rather than a certain product. Also see if this is small enough to be viewed as an exempt accessory structure.


kantuckid

Is this a playground? I read pavillion which I think of as a shelter house roof sort of thing? but I see pics of a kids playground which is it?
Kan=Kansas;tuck=Kentucky;kid=what I'm not

MishaZ

So bringing this thread back as I'm trying to get this project back on track.  I'm a notorious overthinker (the engineer in me) and anytime I'm doing something for the first time (which tends to be every project) I spend a lot of time doing research.  Some of my light reading consists of: Learn to Timber Frame, Timber Frame Construction, The Very Efficient Carpenter, Complete Book of Framing...

I've decided to go with a 14'x14' pavilion.  I have cleared the yard to get flat surface and dug footer holes and pored with reinforcement 24"x24"x18" footers.  I then laid CMU 16"x16" column block four high (one below grade and three above grade).  I pored the column with concrete and wet set a wood column bracket (this picture to come).

I have not done any calculations on the size of timber I plan to use, as I'm going off of combination of different plans I have found.  I would not mind a check from those here if you see any issues.  If you feel something can be upsized or downsized, let me know.  This is Florida, no snow load (Tampa), just the uplift from wind (120 MPH wind velocity per FBC).

Intent is to go with:
Post/King Post: 6x6 (8'x5)
Plate/Ridge: 6x8 (18'x3)
Tie Beam: 6x8 (16'x2)
Rafter: 4x4 (10'x16)
Knee Brace: 4x6 (8'x6)

I was considering going up to 6x8 or 8x8 on post and possibly doing 2x8 on rafters...

I'll have a Part II to this to discuss options I see on wood now that I got pricing in.  Biggest issue are the 6x8 beams that are 16' and 18' (most don't have 18' and jumps to 20').

  


 

 



 

 

 

 


Don P

A quick walk thru of some checks I see;

The ridge is a uniformly lo0aded beam with a 14' span. The tributary area in square feet is the length of the roof x half of the width of the building. The load per square foot is ~10 psf dead load + ~20 psf (wind... min?).

Each end of the ridge is on a post center point loading the tie beam. Half of the ridge uniform load is now a point load at midspan on the tie. Since this is a square building and because a center point load creates twice the bending force of a uniformly distributed load... even though the load on the tie is half that of the ridge, they are equally stressed in bending, kinda cool.


MishaZ

As mentioned, this is a picture of where I'm at with the post base.

Anymore input on my post above and thoughts on size selection of timber???



 

MishaZ


logman

You definitely don't want to downsize anything.  
LT40HD, 12' ext, 5105 JD tractor, Genie GTH5519 telehandler
M&K Timber Works

Don P

Quote from: Don P on August 12, 2022, 04:04:04 PM
A quick walk thru of some checks I see;

The ridge is a uniformly lo0aded beam with a 14' span. The tributary area in square feet is the length of the roof x half of the width of the building. The load per square foot is ~10 psf dead load + ~20 psf (wind... min?).

Each end of the ridge is on a post center point loading the tie beam. Half of the ridge uniform load is now a point load at midspan on the tie. Since this is a square building and because a center point load creates twice the bending force of a uniformly distributed load... even though the load on the tie is half that of the ridge, they are equally stressed in bending, kinda cool.
Let's walk through the ridge;
Tributary area to the ridge is ~7'x~14'=~100sf x 30psf (20LL,wind+ 10psf DL)=3000lbs uniformly distributed along the ridge by the common rafters.
Go Here and start plugging in numbers;
Design for Bending (forestryforum.com)
In #2 cypress I'm getting a 6x10 for the ridge.

For the tie beam with the kingpost delivering half the 3000 pound ridge load to the midpoint of each tie go here;
Midspan Point Loaded Simple Beam (forestryforum.com)
enter 1500 lbs, Fb=625, E=1, Fv-175 for #2 cypress
As expected it requires the same size as the ridge. Although the load is half the ridge load on a similar span, a center point load creates twice the maximum bending moment in the beam. Instinctively we all know this one. If you hear the ice crack, spread out!

Plate has ~5.5' x 14' of trib area x 30 psf=77sf area x 30 psf=2310 lbs load, use the uniformly loaded beam calc for that check.

Rafter, span is 6.5', trib width is ~3' =20sf area tributary to the rafter x 30psf= 600 lbs load uniformly distributed... but a different calc for lumber 2-4" thick, it uses higher design values than heavy timber
Design for Bending (forestryforum.com)
I get a pass in full dimension 4x4

MishaZ

Thank you Don P for your quick calcs and backcheck!  Very helpful.  What are your thoughts on the columns? 

Don P

They are more than adequate for vertical loads, you'll have to satisfy yourself on lateral.

MishaZ

Quote from: Don P on August 14, 2022, 05:25:18 PMTributary area to the ridge is ~7'x~14'=~100sf x 30psf (20LL,wind+ 10psf DL)=3000lbs uniformly distributed along the ridge by the common rafters.
Go Here and start plugging in numbers;
Design for Bending (forestryforum.com)
In #2 cypress I'm getting a 6x10 for the ridge.
Don P, when calculating the load on the ridge (transfer load off the rafters), would we want to take in to account that the rafters are at an incline?  Would the load distribution between ridge and plate be equal (excluding the overhang)? 

Don P

That is the way it is conventionally done, on the horizontal projection. There is always room to stare deeper into the hole  :D. I do think it is reasonably conservative.

I'm not worried about the beam or rafter dimensions, and it is easy enough to secure the roof together so that it stays together in the wind. Whether it will stay on its perch is another matter. From any wind direction there are only 2 relatively small braces in compression keeping it upright. 

MishaZ

Quote from: Don P on August 15, 2022, 08:21:57 PM
That is the way it is conventionally done, on the horizontal projection. There is always room to stare deeper into the hole  :D. I do think it is reasonably conservative.

I'm not worried about the beam or rafter dimensions, and it is easy enough to secure the roof together so that it stays together in the wind. Whether it will stay on its perch is another matter. From any wind direction there are only 2 relatively small braces in compression keeping it upright.
Small change of plans on the roof framing type.  I decided to go with Hip Roof (5:12 Pitch) instead of Gable Roof.  Will be 1x6 T&G roof instead of plywood. Looking for similar feedback on rafter sizing.
As mentioned before, overall dimensions of structure are 14.5'x14.5'.  
Posts: 6x6
Tie Beams: 6x8
Knee Braces: 4x6
What I'm contemplating is dimension of Hip and Common Rafters.
Option 1:
Hip Rafters: 2x8 x(11'-9")
Common Rafters: 2x6 x(8'-8")
Option 2:
Upsize Hip or both to 3x


 


MishaZ

Comments?  Really want to put the order for the timber with holidays coming up.

Don P

Whatever it was, the fever has broken, but I've already lost this post once, better check this. You can check rafters with the code, I think you are fine there. Design the hip as a beam, if you've read that section of code, yup, I'm being more conservative, I've fixed code work there. The trib area is a little different than we are used to seeing. The load on the hip is what is inside the black box. A uniformly increasing load to one end (basically). Stare at it and it'll make sense, half of each jack is bearing on the plate, half is supported by the hip. Your trib line goes right up those jack midpoints (red) to the king common (green).



 

I'd use 20 psf LL + 10psf DL unless you have local design numbers.

Hmm, I need to write that calc... or find it. The equations are here go to fig 5;
DA6-BeamFormulas.pmd (purdue.edu)

Edit;
I'm not up to coding. Let's try to do a quick and dirty check.
Max moment on the hip is going to be .1283Wl
~30 sf x 30 psf... W= 900lbs
I'm going to back up a bit from what I normally say. Snow falls vertically so typically we use the horizontal projection of sloping roof members. Wind is your control and can act normal to the plane of the roof, I'm going to use actual hip length for l ~128"

So we have .1283 x 900 x 128 =14780 inch lbs of bending torque on the hip.

Section modulus on a nominal 2x8 is 13.14"3. Fb for #2 Baldcypress is 825 psi
13.14 x 825=10840 in-lbs max allowable moment... fail. I have no strength numbers on pondcypress, you mentioned it is weaker.

IMO go for a 3x8, double 2x8 or a 2x10 (S=21.39... notice the diff in section modulus between a 2x8 and 2x10, "deeper is cheaper")

Edit/edit... I see tie beams but not plates. I think we have a thinking/word problem. This puppy is still thrusting. It either needs ties or a ring beam or all the thrust is on the tenons and joinery you've been asking about in another thread. We do need to be clear there.
Building a Strong Cathedral Hip Roof (homeadvisor.com)

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