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Author Topic: First Outdoor Pavilion Build (Planning)  (Read 2119 times)

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Offline huntandfish88

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First Outdoor Pavilion Build (Planning)
« on: July 07, 2020, 01:17:46 PM »
Hi All,

First time posting and planning an outdoor pavilion. I've attached some drawings I did in Autocad and asking for some feedback from the professionals.

Quick overview,
All lumber will be pressure treated SPF.
The posts will be 6x6
I will notch the tops of the posts to accept the 2 ply 2x10 beam so it has full bearing.
The trusses will also be built fully with 6x6's and screwed together with 10" timberlok screws.
The ridge post will be part of the truss and will be notched for the 2x8 ridge beam to create a 16" overhang on front, and 3" overhang on back.
I will use 2x8 joist on 24" centers.
2x8 Fascia on the 2 eaves
2x8 collar ties on every other joist
The pavilion will have a open rafter appearance with 5/8" Tounge and groove pine screwed to the top side of the joists.
I will install 3/4" plywood over the 5/8" T&G so no roofing nails penetrate the t&g.
I will finish with architectural aspahlt shingles

The posts are 8'-3" to underside of 2 ply 2x10 beams

The span between the 2 posts on the front elevation will be 13' from outside post to outside post

The span between the 2 posts on the side elevation will be 13-8" from outside post to outside post

I estimate the entire dead load of the roof to be approximately 3400 lbs

The roof will be built in southern ontairo, Canada where specified snow load is 1.3 kPa

I'm planning to use a 12" sonotube for each post with an embedded post bracket OR put the 6x6 directly in the ground with 4 bags of concrete. Concrete will be 28 mPa.

Please see plans and let me know if you have any questions. Everyones thoughts are greatly appreciated!!!

thanks in advanced



 

 

 

 



Offline huntandfish88

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Re: First Outdoor Pavilion Build (Planning)
« Reply #1 on: July 07, 2020, 02:48:35 PM »
Photo I found online of the look Im trying to achieve. Sorry if its rotated 

Offline swmn

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Re: First Outdoor Pavilion Build (Planning)
« Reply #2 on: July 07, 2020, 04:26:37 PM »
I play with it a little after work tonight.  Seat of the pants I will first look at deflection on your 2x10 beams with a full load of snow on it.  It seems (I am n00b at beam calcs) like a lot of weight to put on a pair of 2x1s with a 14 foot span.  Once I get your snow load converted to antique from metric I'll have a change.  

It will be  few hours, but it is an interesting problem.

Are your 2x10 ply beams drop in replacements for #2 SPF 2x10?

Offline Hilltop366

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Re: First Outdoor Pavilion Build (Planning)
« Reply #3 on: July 07, 2020, 08:57:19 PM »
Greetings huntandfish88,

I'm thinking I would call your ridge beam a ridge board as it does not look heavy enough to hold  of the roof or prevent outward force on the 2 ply-beam, to me either increasing the size of the beam or lowering the collar ties would be best.

Offline swmn

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Re: First Outdoor Pavilion Build (Planning)
« Reply #4 on: July 07, 2020, 10:23:47 PM »
The beams supporting all the rafters don't work for me.  

Let me walk you through my assumptions before we get carried away.  I come up with 182 square feet of roof.

1.3 kpa snow load internet searched for me to 27.157 pounds per square foot snow load, which I rounded up to 30 psf just to make the math easier. 

30 psf of snow x 182 sqft of roof, you are wanting to park 5460 pounds of snow up there.

3400 pounds of roofing materials divided by 182 square feet of roof puts you at 18 pounds per square foot of roofing material; reasonable I think, I am used to calculating on 20psf roofing dead load.  

3400 pounds of roof + 5460 pound of snow = 8860 pounds on your two beams with the 13' 8" span,  and I don't have the dimensions for your overhang at the front.  

Eyeballing it your overhang looks like maybe 40-50cm?  That could help with the deflection problem I see, but it won't help your bending problem.

Without the overhang on the end, I ran with a single 2x10 for each beam which failed miserably, and then noticed you have doubled 2x10 beams in your drawings and tried again with a single 4x10 on each side to hold up all the rafters.  In general (I am a n00b without a bunch of dinero to waste) a single 4x10 will (most of the time) be cheaper than fastening two 2x10s together well enough for them to act like a single 4x10 under load.  If you just set the beams in the notches a single 4x10 is stronger than 2 adjacent 2x10s - and a single 4x10 for each of your two spans doesn't cut it.  If you have a bunch of epoxy and nails laying around you could epoxy two of 2x10 together and plant 642 nails while the epoxy is wet.

With a  #2 SPF 4x10 on those 13'8" spans, you got trouble.  Your section modulus provided is only 53, to pass on bending your section modulus required is a bit over 78.

Fully loaded that thing is going to deflect (droop in the middle of the beam) 0.73 inches, according to the tools here on this website.  You would want to limit your deflection to 0.68 inches for a 1/240 roof, or 0.46 inches for a 1/360 stiffness floor.

But it isn't hopeless.  The beams are almost strong enough.

One thing you could do that would probably be enough is put in another pair of posts in the middle, so you got three posts down each side with an open front and back.  That would cut your beam's spans in half which solves you beam problem on bending and deflection using single 4x10s - but I don't know how you are planning to use the building.

Another option, since you have 6x6 posts, is call around to your local sawmills to see what you can get 6 inches wide by (what depth is available?) x 16 feet long.  Or 18 feet long, or whatever you need for the overhang.  There is no point in me running hundreds of possible scenarios to find out you local saw mills make toothpicks and axe handles.

I am not experienced enough to comment on your roof framing, but I have been hanging around here long enough to know Hilltop is not a moron.  Click the red tool box icon at the bottom of the left column of clickable things.  Scroll to the bottom of that page and click on the beam and column calculators.  

Also, you will need to know the weight bearing strength of your dirt.  If you only sink four posts, each of those sonotube footprints are going to have to support 8860 pounds of snow and roof, plus the posts and the beams.  How many square feet, how much area of footprint are your planned sontube bases going to cover, and how much weight will the underlying dirt be able to support?  Don't forget the wight of the concrete in the sonotube, the dirt will have to support that too.

For this much effort and expense I would _absolutely not_ sink the posts into postholes.  Personally.

Offline Don P

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Re: First Outdoor Pavilion Build (Planning)
« Reply #5 on: July 07, 2020, 11:08:10 PM »
Actually building up a beam by nailing pieces together vertically  gives a 10% increase in strength for 2 plies and 15% for 3 or more. The distribution of defects compared to a solid sawn beam is the reason.
As long as the loading is spread out across the top like here with the rafters sitting evenly on top of the pair of 2x10s, the nails are simply holding the pair together, they are not load carrying elements, so no special nailing callout there.

Remember depth is the quickest and cheapest way to increase section modulus, bending strength. The equation for figuring out section modulus is bd2/6, breadth x (depth squared)/ 6. Depth is squaring as you increase in that dimension. In stiffness equations depth is cubed.
Add depth first when you need more strength if possible.

Hilltop is seeing this correctly. The collars are too high to be considered thrust restraint. The ridgeBEAM needs to support 1/2 of the roof load. Each ridgepost supporting that ridge is delivering 1/4 of roof load to the midspan of an ~12' clear spanning tie beam/"bottom chord". So two things to check there, the 1/2 roof load uniformly distributed along the ridge beam, and 1/4 of the roof load as a point load on the center of the tie beam.
Then,
1/4 of the roof load +the eaves overhang weight is bearing uniformly on each of the plates.

I think that will change some of the sizes.
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Offline huntandfish88

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Re: First Outdoor Pavilion Build (Planning)
« Reply #6 on: July 08, 2020, 11:13:49 AM »
Thanks for the replies everyone! This is very helpful.

I should clarify, the slope of the roof is a 5/12, and based on my research a 5/12 slope does not technically require a "ridge beam" so Hilltop yes you are correct it would be more considered a ridge board. I believe ridge beams are only technically required on slopes less than 3/12?? Maybe someone could clarify that for me. 

The grade of lumber i will be using is #2 SPF. 

From what I understand collar ties are for wind uplift resistance and rafter ties are for live/snow load resistance, Would I be able to incorporate both into my design and add the rafter ties to every other roof rafter similar to the collar ties?

swmn, if I upsize the beams to a 3ply 2x10, would that meet the necessary l/240 deflection and section modulus? 

I'd prefer not adding an additional post along the mid span of the beams but I can if absolutely need be. 

Without doing a soil test, I found some information online from my city council that states:
"For design of footings on the native sand, silty sand, or silt till below depths of about 1.0 to 2.3 m below existing grades, the following allowable bearing pressures (net stress increase) can be used for design of footings:
Serviceability Limit States (SLS) 150 kPa (3,100 psf) 
 Ultimate Limit States (ULS) 225 kPa (4,700 psf) 

I'm assuming each post/column would support 1/4 of the weight of the structure. The roof is actually closer to 230 sq ft total (each slope is roughly 8.25 feet x 13.66 feet long) so 3400lb dead load plus 6250 live/snow load = 9650 lbs. /4 = 2412 lbs per post or 10.75 kN. Does that sound correct? 

I ran some quick numbers and found that the required footing size is 280mm x 280mm or 11" x 11" based on the loading. Can anyone comment on this? 

Looking forward to some more responses. thanks again! 

Offline huntandfish88

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Re: First Outdoor Pavilion Build (Planning)
« Reply #7 on: July 08, 2020, 11:26:06 AM »
Sorry 1 more thing I wanted to add, if I put the posts on a concrete peir above grade, would it not be weaker when lateral force (ie wind) is applied to it vs putting directly on the footing 4 feet below grade? 

My footing must be 4' below grade for frost purposes. 

Online btulloh

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Re: First Outdoor Pavilion Build (Planning)
« Reply #8 on: July 08, 2020, 11:53:11 AM »
Better in the long run to put them on piers and use adequate bracing for wind load, etc.  Posts in the ground will eventually fail.  It's always a big debate here, and some people like the posts in the ground, but . . .  

This question will probably stimulate a lively discussion.  There have been many discussions you could find here if you search the forum a little bit.  It only comes up about once a month.   :D
HM126

Offline swmn

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Re: First Outdoor Pavilion Build (Planning)
« Reply #9 on: July 08, 2020, 11:55:08 AM »
Actually building up a beam by nailing pieces together vertically  gives a 10% increase in strength for 2 plies and 15% for 3 or more. The distribution of defects compared to a solid sawn beam is the reason.
As long as the loading is spread out across the top like here with the rafters sitting evenly on top of the pair of 2x10s, the nails are simply holding the pair together, they are not load carrying elements, so no special nailing callout there.

Remember depth is the quickest and cheapest way to increase section modulus, bending strength. 
Ok, I am still learning.  I don't know what materials the OP has access to.  I first thought he was using built up, engineered 2x10, the kind with the plywood vertical web and laminated top and bottom to make a wooden I beam, but I think now having looked at the illustration more closely he is using #2 SPF 2x10s and the " 2 ply" text description means the 2x10 are doubled, not engineered product.
I tried a simple beam uniformly loaded with the updated weights on tripled 2x10, that is 4825 pounds on a beam that is 4.5 x 9.5 inch actual, span 164 inches, nominal SPF 2x10, repetitive yes, 3 or more members, and it still fails in bending and fails in deflection.
When I moved over to heavy timbers calculator and put in an actual 6x10 of #2 SPF it passes on deflection but still fails on fiber stress in bending.  Was I wrong to lift the values for fibersteress in bending, modulus of elasticity and allowable shear associated with #2 SPF from the lumber results and use them as inputs on the heavy timber calculator?
Also @Don P , once we have the dimensions of the overhang and move to the calculator for beam overhanging one support, should I use the overhang  length of the ridgbeam/pole/board as the overhang, or figure out how much weight is on the overhanging roof and apply all of it to the length of the overhanging beam?
I can't really help with the dirt work question, much.  A 12" diameter circle has an area of 113 square inches, a square foot is 144 square inches, so each 12" diameter pier has a foot print of 0.78 square feet.

Offline swmn

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Re: First Outdoor Pavilion Build (Planning)
« Reply #10 on: July 08, 2020, 12:20:45 PM »
I did try it again with a 6 x 9.5 actual timber - which would be like putting a 4th 2x10 up there since three of 2x10 is 4.5" thick.  Then I went back and added a fourth 2x10 on the lumber calculator and the results are pretty close. 

I think the ah-ha moment for me was recognizing 6x10 actual timber is like having a fourth nominal 2x10 on the team.

 6x9.5 #2 SPF on all that span is just not quite enough whether it is one piece or four piece beam

Offline Don P

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Re: First Outdoor Pavilion Build (Planning)
« Reply #11 on: July 08, 2020, 05:18:23 PM »
It sounds like you have read some code but need some clarifying. You correctly understand the difference between a collar and rafter tie.

Below a 3/12 any ridge, hip or valley shall be designed as a beam. Above 3/12 any rafter couple that is not properly tied must be supported by a ridge beam. Properly tied is tie in the lower third of roof height preferrably at plate level and properly connected.

If you tie the rafters (code now calls for a tie on every rafter couple but it wasn't always that way and there are ways) Anyway, if you tie the rafters and use a ridgeboard each built up plate carries 50% of roof load. If you don't tie and use a ridgebeam then that ridge carries 50% of roof load and each plate carries 25%.

So reboot, which way are you leaning?

Quote
Was I wrong to lift the values for fibersteress in bending, modulus of elasticity and allowable shear associated with #2 SPF from the lumber results and use them as inputs on the heavy timber calculator?
Oh yeah. Heavy timber has a different set of base design values (lower) and fewer adjustment factors, so do not interchange them. The reference document for all that is the "Supplement to the NDS, wood design values" it is under the publications tab at awc.org. It never hurts to read it for background, well and the NDS right above it as well.

For "normal" overhangs, <~2', I add the load to the main span and use the simple beam calc. That is going to be slightly more conservative than using the overhanging beam calc which technically is more correct, I've seen engineers doing the same thing. As loads, spans and overhangs get larger correct does become more serious.

H&F, you've got it on the soils/footing size required thinking, I didn't check your math. A buried post is going to pick up lateral resistance from the soil, if it is properly compacted as the hole is filled, if you haven't built long term fence chances of that aren't good. I see lots of posts dropped in, soil shovelled in and we're done, that has pretty much zero lateral. If you know how to tamp a post in to contain a bull then there is a chance, most people don't understand that when the wind blows on a structure it makes that charging bull seem pretty low horsepower  :D.

Buried posts don't rot in your lifetime if you buy the right kind. Foundation grade, UC4, use category 4. The words "ground contact" are pretty worthless, the UC is the key to the treatment level.
I see bracing in one plane only in the drawings, need it in both but that bracing probably does not do as much as people would like to think.

Both sides of that argument are kind of like watching the wizard of Oz at work. Don't look behind the curtain  :D



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Offline swmn

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Re: First Outdoor Pavilion Build (Planning)
« Reply #12 on: July 08, 2020, 09:44:45 PM »
If I downloaded the correct .pdf the F sub b (fiber stress in bending) for #2 SPF drops from 1000 in 2-4" thick dimension lumber, to 600 for timbers 5x5 and up.  Jiminey Cricket!

OP, I have no idea how big your beams need to be, but it is going to be money.

Offline Don P

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Re: First Outdoor Pavilion Build (Planning)
« Reply #13 on: July 08, 2020, 10:20:07 PM »
It is a large drop with most species when you go from dimensional 2-4" thick material to 5x5 and larger, that's another big bonus with built up beams of dimensional material. 

Let's hang on and see which direction H&F wants to go and I'll talk through this one. I think it might be a close enough example that you can use it to work the one in the other thread, it's mostly thinking through the loading and then just some practice.
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Offline swmn

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Re: First Outdoor Pavilion Build (Planning)
« Reply #14 on: July 09, 2020, 01:02:31 AM »
Thanks Don.  I look forward to learning some more.  

I do see in the WWPA grading guide a #2 SPF 6x10 could have a sound knot 5 5/8" centered on the wide face and make grade as a timber, where max knot on a #2 SPF 2x10 centered on the wide face is 4 1/4 inches.

I have a queasy feeling my new woodshed might be blown over by an anemic geriatic toodling over on his walker and having a smoker's cough against one of my posts.

OP, you might as well download the Canadian lumber grading guide, it is a free .pdf, at nlga dot org.  Whatever you and Don come up with, you want to be sure the beam you buy has the correct stamp inked on it somewhere.  I am thinking specifically of section 13, "grade stamps"

Good luck.


Offline huntandfish88

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Re: First Outdoor Pavilion Build (Planning)
« Reply #15 on: July 09, 2020, 11:10:27 AM »
Hi gents, 
Thanks again for responses! 

So I think I'm going to install a collar tie and a rafter tie on each roof rafter (every 24" o/c) just to be safe. I'd also prefer to stick with dimensional lumber for everything, for availability purposes (and cost). Fir timbers in my area start at $20+ per linear foot !

With regards to the beam I would prefer to use 2x10s as I have some left over from a job. If a 3ply (or even 4ply) doesnt work, then worst case scenario I could add an additional 6x6 post at midspan, which I assume would solve any deflection concerns? Don if your able to lend your expertise on this I would greatly appreciate it! I know  this isnt a typical "timber" construction that most people are used to seeing on this forum lol 

With regards to the post being in the ground, my plan was this: 
-Treat all 4 sides of each post to 1 foot above grade with a liquid rubber water proofer (bottom 5' of post)
-Pour a proper concrete footing 4' below grade, (12"x12" seems  to be acceptable based on my calcs)
-Install a 12" dia. sonotube sitting directly on top of the footing
-Drop the post inside of the sonotube sitting directly top of the footing.
-Pour concrete which will fully encapsulate the bottom 4' of the post. 
-Slope the top edge of the concrete so water runs away from the post.
Thoughts? 

I know this is a timber forum but wondering if the concrete and wood with the water proofing membrane in between will stand the test of time? Keep in mind I don't believe this post/pier/footing will see much water anyway since it is going under a covered roof.


Offline Andries

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Re: First Outdoor Pavilion Build (Planning)
« Reply #16 on: July 09, 2020, 11:23:03 AM »
The footing and sonotube are the best way to go. However, wood that is encapsulated will not do well when below grade.
Use a little more concrete, fill the tube to a bit above grade and place an attachment for your post in the wet cement. A few rebar rods in the cement will keep it all lined up.
There are many posts on the Forum discussing fixes for pole barns. Most start with a regret at having placed wood below grade.
Nice project you've going going on - please keep us updated as you move forward. 👍
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Offline Don P

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Re: First Outdoor Pavilion Build (Planning)
« Reply #17 on: July 09, 2020, 09:19:39 PM »
We have a viable plan now. Thinking about it, step one before trying to check beam sizes is "Do we have a buildable plan?" The original plan needed a little work which could have changed the load path. We now have that clarified and can proceed. 

This is the direction swmn was going so lets walk through it. I think I'll just be rehashing what he did but let's see what comes up along the way, we might get lucky and root up an acorn.

Snow load at 30 psf. Roof width+ eave overhangs, I'm going to call 16' x 13.66' long= 218.56 square feet loading the plate beams x 30 psf =6556.8 lbs. I'm guessing I added more eave overhang than swmn. 

Add your dead load of 3400lbs  and I'm at 10,000lbs, 5 kips uniformly distributed along each plate.

It's all dimensional stock, so using this calc for lumber 2-4" thick;
https://forestryforum.com/members/donp/ddsimplebeam.html

Inputs; load 5000lbs, span 156 (inside to inside of posts + an inch or so each end),3 wide x 9.25 deep, #1/2 SPF, duration: snow, yes: 2 or more (we'll be bumping that up to yes: 3 or more directly), size factor 2&3x10, no wet service, no incising. Click "show result" and it fails miserably.
bump up to a 3 ply so 4.5x9.25 and yes: 3 or more members, and click show result again, fail, but less miserably. 

try 4 ply so 6x9.25 and it passes. So there is one way.

Explore going deeper, try a 3 ply 2x12 so 4.5x11.25,  size factor:2&3x12, and it passes with higher section modulus (strength) than a 4 ply 2x10 and less deflection, it is stiffer. That is a superior beam and probably easier to get on that post.

For adequate bracing, I'd like to hear good ideas. This is the other side of the coin. When the building cannot get any bracing from medieval earthfast construction that lateral resistance needs to come from somewhere. Simpson does make some bracing connectors. Take a look at their KBS1Z, kneebrace stabilizer. At least there are some numbers that could be plugged in. 
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Re: First Outdoor Pavilion Build (Planning)
« Reply #18 on: July 10, 2020, 02:41:41 AM »
For adequate bracing, I'd like to hear good ideas. 
I have seen 30 psf on many roofs.  I get that sail height is going to vary with the moisture content of the snow.  But if he gets wind in Southern Ontario like I have seen in Minnesota or Buffalo, NY, gosh, the side thrust is probably best expressed in tons.
One thing I would not do is cut away part of one of the 2x10s in the beam to make a mortise.  With 4 2x10s side by side up there to make the beam it just barely passes on section modulus to pass on bending.

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Re: First Outdoor Pavilion Build (Planning)
« Reply #19 on: July 10, 2020, 10:51:34 PM »
Well I got some bracing questions.  

In my mind's eye I have the front opening with the long overhang facing south.  Up the east and west sides we have quadruple 2x10 plate beams.  Wind is from the north.

I think I need to know the side thrust I am trying to control before I can pick a brace system.  I am thinking 4x4 is probably not quite enough but 6x6 might be.  I am more worried about the end of the brace punching into the post than I am the brace collapsing.

But with only four posts if we use compression bracing the only braces help we have to resist all the wind thrust from the north start somewhere on the north face of the south posts , head north and up, and then fasten to the bottom of the plate beam.  Each of those two braces will have to be stout enough to handle I think half the wind load.

We could bore some 1" holes, and then line them with short pieces of black iron pipe for a bushing, then thread 3/4 steel cable which ought to be enough, and then use turnbuckles to make tension braces.

I did check my Atlas, I have never been to Ontario.  I went, early 1990s, to three Habs games in Montreal, but that is a ways east from Ontario, and I have driven through Manitoba to the west.  A cubic foot of water weighs about 63 pounds, so pure water up there about 6" deep would match the weight load, but I don't know how tall a pile of snow we are talking about to plan for windloading.  Fairbanks, Alaska is famous in the cross country ski community for our dry fluffy low moisture content snow, I am used to seeing 3-4 feet accumulation coming in at ~35 psf roof load.  

So something like 2-3 feet of snow, plus 1.5 inches for decking and a bit for the thickness of the asphalt shingles, and the end truss is specified as 6x6, I would be comfortable I think with something like 3 feet to one meter to 4 feet (times length) for the sail area.   And I got nothing for wind speed.

I did look at the simpson kbs1z.  I would be comfortable using the higher values for wood at and under 19% MC, but that is as far as I can go.

If the magnitude of the side thrust is high enough we may have to think where on the posts we can safely locate the braces.

Given that wind comes from all points of the compass we might need a tension brace and a compression brace in every corner.

PS: I think I was 8, maybe 9 years old when I started using "dang" as part of the name of the tamping rod.  No bulls, but we had saddle horses that liked to lean on fence posts to rub their winter coats out, plus pigs and a steer almost every year.  I have seen fence posts sunk by non-farm kids that chickens could knock over.


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