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How short can timber frame braces be?

Started by Roachven, May 25, 2015, 01:37:35 PM

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Roachven

Results from this forum often come up in my google searches and I've found a ton of very helpful info here over the past couple years.  I've been building our homestead on 60 forested acres in northeast Minnesota for 4 years now, learning as I go.  Most of the buildings/sheds I've thrown together here in the last few years have been very crudely built with round logs, poles and polebarn nails.  We got a bandsaw mill 2 years ago and I am trying to refine my building techniques and learn more about timber frame joinery.  I imagine I will be turning to this forum often with questions in the next few years as I see no end to my building projects.

My question is project specific.  I'm currently starting to build a 7'x14' screen porch addition onto our house.  I have all the materials milled and the concrete tubes poured.  I am pretty much ready to build except I keep second guessing aspects of my design.  The eaves of the existing building that I am building off of are very short (7 ½ feet) so that even with just a 2/12 pitch, the bottom of my outer top plate beam will only be 5 feet tall (see pictures).  The clear span of the beams is only 7 feet. 

My question is this.  How short can my corner braces be?  I would like them to be as short as is reasonable to improve visibility out the screen window. 

Other details.  I'm using 4"x4" cedar posts, 4"x6" spruce beams, 3"x3 1/2" cedar braces, 2 1/2"x6" spruce rafters 2ft OC and 1 1/2"x5" spruce purlins 15" OC.  All dimensions are rough cut actual measurements. 

Also I know this topic has been covered before, but does anyone know any formula or rule for figuring ideal length for braces?  I would assume that the shorter your post are and the sorter the clear span of you beam, the shorter your braces need to be?

Thanks for any help in advance!

I'm having trouble trying to get my drawing on here, will try to post it soon...
2001 Baker 18m Bandsaw Mill
Husky 543xp, 372xp, Echo CS-352
2001 Skandic SWT Snowmobile (winter log skidding)
Beat up 94 Toyota
3 kids and the best Wife ever
shutterflyoffsitephotosnotallowed.com
www.youtube.com/user/Roachven
www.ic.org/directory/long-haul/
www.workaway.info/618479233977-en.html

Roachven

 

 


By the way, I consider myself relatively computer literate, but posting photos on here is very confusing.
2001 Baker 18m Bandsaw Mill
Husky 543xp, 372xp, Echo CS-352
2001 Skandic SWT Snowmobile (winter log skidding)
Beat up 94 Toyota
3 kids and the best Wife ever
shutterflyoffsitephotosnotallowed.com
www.youtube.com/user/Roachven
www.ic.org/directory/long-haul/
www.workaway.info/618479233977-en.html

Ljohnsaw

Welcome to the Forum!

You didn't state what the floor is going to be.  Concrete slab so as not to loose any more head room?  Do you have snow loads to contend with?  If not, you could up-size your beam and do away with the center post (if you have a long enough beam stock).  What is the shear strength of spruce vs. Doug Fir/Pine?

Since this is tied to your house, you don't need a lot of bracing (IMO) and could go fairly small - perhaps a foot down and a foot over.  That is a pretty low beam - is there any way you could tie in to your existing roof either at the eve/fascia or up the slope a bit to pick up another foot or two?  I think you would be much happier with the outcome.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

witterbound

Is the bottom going to enclosed and covered with cool siding?  If so, that will add stiffness. Even if not, ther are a lot of shed roof porches built with 2x4s that don't have any bracing.  If it we me, I wouldn't use any bracing.

beenthere

Welcome to the Forestry Forum.

Even those of us who are not computer literate can post pics here.  ;D

It's easy when you know why it is done the way it is... the gallery is for posterity and we don't like the dreaded red x's when pics on other sites are taken down. Hope that eases the pain. ;)
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Roachven

Thanks for the replies.  The floor is going to be an after thought if anything....  it will be dirt for now with pallets to put the stove and freezers on.  I might eventually put down either gravel or some kind of tamped earthen floor or perhaps some scrappy cedar straight on the ground.  Either way, I won't loose much to the eventual floor. 

Our house is really just a cabin that came with our land and it won't be our house forever, I hope to start construction of our log home within 3 years or so.  Although, in the meantime, with two young kids and a 300 sq ft house, we need all the extra room we can get and I need to keep the building relatively fast and simple.  I also want to be able to learn from my mistakes on projects like this and become a better builder in the process.  Tying it into the eaves would complicate things especially concerning ice dams, since the building it will be attached to is heated and it will be an unheated space.

I'm definitely going to keep the middle beam for several reasons.  As I mentioned before, I have all the materials already prepared and the concrete tubes for all three pillars poured.  I also would have to increase the beam size by at least a few inches which would block more of the screen which I am trying to avoid.... My screens are 7 feet wide too, so I need the post to frame them to.  Also handling smaller material is nice sometimes.  For the siding, I just plan to do horizontal lapped cedar boards.  This will only cover the bottom 2 feet because the rest will be screens. It will also be easier to just nail the siding to the posts since the span will only be 7 feet.  However, I don't think doing the siding this way will add much stiffness?

We do have significant snow loads here 60lbs/sq ft plus it is a very shallow pitch on the NW side of our house, so I expect it to need to hold 2-4 feet of snow from December until April some winters.  I guess I should have mentioned these snow loads in my original post.... 

I know that shear strength spruce is not as strong as Doug Fir but I thought it was comparable to pine, but I'm not sure, anyone know?

Anyhow I was originally thinking two feet down and two feet over, but I might go with a foot down and a foot over unless there are any opinions against this?

Thanks again for the thoughts and opinions!

2001 Baker 18m Bandsaw Mill
Husky 543xp, 372xp, Echo CS-352
2001 Skandic SWT Snowmobile (winter log skidding)
Beat up 94 Toyota
3 kids and the best Wife ever
shutterflyoffsitephotosnotallowed.com
www.youtube.com/user/Roachven
www.ic.org/directory/long-haul/
www.workaway.info/618479233977-en.html

Roachven

By the way, in case it is confusing..... The stove in the drawing is a wood cookstove for summer cooking.
2001 Baker 18m Bandsaw Mill
Husky 543xp, 372xp, Echo CS-352
2001 Skandic SWT Snowmobile (winter log skidding)
Beat up 94 Toyota
3 kids and the best Wife ever
shutterflyoffsitephotosnotallowed.com
www.youtube.com/user/Roachven
www.ic.org/directory/long-haul/
www.workaway.info/618479233977-en.html

beenthere

Apparently you do not have building codes that you must follow.
That can be good for you while building.



south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Roachven

No codes, no inspector around here, and miles of wilderness, that's part of what I like about it.
2001 Baker 18m Bandsaw Mill
Husky 543xp, 372xp, Echo CS-352
2001 Skandic SWT Snowmobile (winter log skidding)
Beat up 94 Toyota
3 kids and the best Wife ever
shutterflyoffsitephotosnotallowed.com
www.youtube.com/user/Roachven
www.ic.org/directory/long-haul/
www.workaway.info/618479233977-en.html

beenthere

Then you are going to rely on yourself to make it hold up for your family to be safe. That is ok.

I wouldn't splice the beam over the center post. You give up beam strength (has to do with moments, etc. ) when splicing over a post which you likely know. Also, I'd go 16" OC for your rafters rather than 2'.

The strength of your spruce joists will depend on the grade (quality) of your dimension stock. Too many knots and the quality as well as strength will not hold your heavy snow load, I'm thinking.

After your build, you can make winter-time measurements of the sag in your structure and make temporary structure adjustments if needed to keep the roof up until summer comes for additional construction. Likely it will not cave in unexpectedly without bending or sagging first.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

kgb12158

Forgive me if someone has already answered your question on how you calculate the length of a brace.  It is actually quite easy if you have a framing square.  On one side of the 1 ½" area on the square are a series of #s. You will see 30 over 30 or 48 over 48 in 3"or 4" increments from 24" up to 60".  Next to each pair of #s is another # this represents the hypotenuse of the right triangle.  Next to the 30,30 should be 43 and a raised 43.  This actually means 43" and 43/100 th. of an inch.  Translated a 30" brace needs a 43 7/16" hypotinuce form shoulder to shoulder.  The tenion is beyont this dimention.  This is tough to describe without a square to show you.  I'll try to get a picture of the square and brace to share. 

As to what is the shortest brace you should use.  Boats used small corbels that may be only 12-18" long.  The brace function is to prevent the structure from racking.  You may get away with an 18" brace but put them on each post rather than in the corners.

Good luck
Kim Balfour Timber Framing since 1986, Woodmizer LT40 HG, and 52" Lane 00 circular Mill.
Only 23 months to full time timber framing

Roachven

Thanks again everyone for the thoughts and opinions.  I ended up talking to a timber framer friend of mine and he suggested going two feet down and two feet over for the braces.  While talking to him, I realized I failed to mention on this forum that I was actually planning to use timberlok screws or pole barn nails to fasten all of the joints.  So I guess this is technically not a timber framed structure but more of a post and beam where I played around with a little bit of notching and joinery.

Anyhow, I got the skeleton up and roofing on so I figured I would share pictures for anyone who might be interested. Thanks again for all the replies.



  

  

  

  

  

  

 
2001 Baker 18m Bandsaw Mill
Husky 543xp, 372xp, Echo CS-352
2001 Skandic SWT Snowmobile (winter log skidding)
Beat up 94 Toyota
3 kids and the best Wife ever
shutterflyoffsitephotosnotallowed.com
www.youtube.com/user/Roachven
www.ic.org/directory/long-haul/
www.workaway.info/618479233977-en.html

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