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Log valley

Started by cloair, December 08, 2007, 02:04:17 PM

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cloair

Does anyone have good source of information on how to create log valleys in a log home? Particularily the joinery and correct sizing for weight. I have the log construction manual from Chambers but it only shows how to cut the valley rafter groove.
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

Don P

Welcome to the forum cloair.
Joe Bartok is a wiz with log and timber joinery math and tutorials;
http://joe.bartok.googlepages.com/logroofframing
http://ca.geocities.com/web_sketches/

I wrote this log beam calc quite awhile ago, its not the best but may get you started
https://forestryforum.com/members/donp/logbeamcalc.htm. That calc is from Tom Hahney's math in the "Log Span Tables". It is for full or nearly full round logs. There are newer design values available. I suspect this is going to get a bit deeper than all that.

cloair

Don
Thanks for the information that is very helpful I am building a log house that is L shaped main roof is 40 by 26 with an 14 by 16 "addition" if you want to call it to make the bottom of the L 40' also both with a 10/12 pitch. The next ? I have is the order of log placement ridge logs, valleys then purlins or what would be the correct order.  If I new how to use a CAD program I would upload a drawing. Our neck of the woods requires a 42psf roof snowloading.  I would like to keep the area under the valleys free from as many posts as possible.  But there can be as many as needed at the bottom of each of the 2 valleys "under the purlins". Is there any more information available that you are aware of? Hopefully this makes sense. Thanks.
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

Don P

Google sketchup is a free download and a pretty good drawing program.
From my understanding I think you have the right assembly order.
How far apart are the purlins from each other?
Are they spanning the full distance from the far wall to the valley ~40'? Some heavy trusses to break up the span?
I'm a bit lost, an el has one valley, a T would have 2. A plan view (birds eye view from above) sketch even in "paint" would be a big help.
What species are the beams?
I think we might be able to get some very rough dimensions together. I do think this is a job for a very good, log oriented, design/ engineer before you build. Detailing this strong enough won't be easy. The closer you get it, hopefully the lower that bill  :).

Edit, I'm following you on the 2 valleys now  :-[ :)
Ridge of Main roof, then supporting valley all the way from plate to ridge. Then supported valley from plate to supporting valley (narrower building/same pitch so lower ridge on the "addition"), Then its addition ridge, then purlins all around. That's my story tonight  :). I'm envisioning a main ridge beam that's feet in diameter without some other support though  ???



cloair

Don
I have attached a pdf file of the roof layout from ms paint.  The purlins will about 5'5" apart with a 10/12 pitch. The purlins will be supported with posts at the intersecting interior walls. I plan to use a 21" mid span white pine for the main ridge, and the rest will be approxiamately 18" mid span white pines.
Thank You
Quinten
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

Don P

Quinten,
I've sketched on your drawing one way that it can be done. I've put a supporting valley in red on the side with the least supported area. This bears on the ridge and wall. The supported valley in blue bears on the wall and supporting valley. Would this work in your plan?

As I see it the purlin just above the intersection could also be sized to bear the supporting valley rather than the ridge, this might look better. Can you sketch and dimension in where the other roof supporting walls are?


cloair

Don
I think what you drew in will work. In the attached pdf, the circles indicate a post that will support the purlins, and the line I drew next to C will represent a wall to support the purlins. I also have another question in regards to wall log layout. Round 1 will start with a butt at A taper down to B then use the rest of the log at D taper down to C(tip) then a full log with butt at E tapering down to F(tip). Round 2 will start with a butt at E taper down to D then use the rest of the log at B taper down to C(tip) then a full log with butt at A tapering down to F(tip). Round 3 will start with a butt at C taper down to D then use the rest of the log at B taper down to A(tip) then a full log with butt at F tapering down to E(tip). Round 4 will start with a butt at C taper down to B then use the rest of the log at D taper down to E(tip) then a full log with butt at F tapering down to A(tip). I figure this will keep log waste down to a minimum, and keep a BB-TT arrangement at the corners. What are your thoughts on this.
Thank you
Quinten
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

Don P

Still ruminatin  :),
If the lower purlins on the main roof could go to 4' spacing they would "shake hands" across the valley. The header supporting the valleys could then be the second purlin rather than the ridge, this would be simpler and stronger I think. That cleans up the valley detail, it would make the span to the ridge roughly 4'8" is the downside.Would that work?


cloair

Don
Very good idea, I think that would work fine the first purlin could be a little smaller and find a little larger second purlin that will support the valley and it would probably not be noticeable.  The purlins I am using are fairly large for instance the main ridge is a 21" midspan diameter white pine the rest are anywere from 17-20" midspan diameter whites.  What size do you think the valley logs should be?
Thank you
Quinten
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

Don P

While figuring I generated some numbers, here's some to tuck away;
10/12 roof pitch=39.8 degrees
Valley slope angle=30.5 degrees (you'll bump into this as a plumb cut also)
Heel level cut angle 59.5 degrees (compliment of the hip slope angle)
Valley line length (192" width, this is the imaginary center lines)=157.58" the span is a bit shorter but I'll work it from this as span.
valley backing angle 26.9 degrees

I've painted in green what I consider to be the tributary area bearing on the valleys, about 156 square feet, 78 sf supported by each valley. Multiply that by 42 snow+15 dead, 78sf*57psf= 4446 lbs.

It could get fancy but trying to keep it simple, the purlins are putting the most load on the valleys at one point in midspan. I'll figure it as if the entire load is sitting at a point midspan of the valley.
https://forestryforum.com/members/donp/beamclc_ctrpointload.htm
I come up with a 12.25"x12.25" beam required. That's fine for a square beam but we're round. One log home engineer told me his secret, I've since had others confirm that this is one conservative way to size a beam. Inscribe that square on the end of a log, using Ron W's calc;
https://forestryforum.com/calcs/log_size.htm
A 17.3" dia will do that.
Before we leave it, I went conservative at every turn. Treating the load as uniform halves the max bending moment and reduces the beam size to 9.75" square
https://forestryforum.com/members/donp/beamclcNDS2.htm
Using Ron's calc again-13.8". This is too small just showing the far end of thinking. The truth probably lies a little better than halfway between.

That is an initial raw walk through, there's connection damage to think about. Backing the valley is going to potentially hurt it bad depending on how deep you sink it, I haven't given that much thought yet. Bigger is definitely safer than smaller if it can meet up well.

Let's quit here for the moment to let anyone correct me so far. We need to check that purlin bearing both valleys next, its got some load on. I hear a cookie calling my name  ;D



cloair

Don
This is starting to make sense to me, I revised the pdf drawing to show there is also a supporting wall in the addition(bold line).  So looking at your drawing the valley should be supporting less than the area in green.
Thanks
Quinten
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

Don P

QuoteCan you sketch and dimension in where the other roof supporting walls are?
Your turn to bring us back to this point  :D

One question. With the wall across the addition imagine yourself in the main house looking towards the addition, I'm visualizing an exposed valley and a gable wall immediately behind it seperating the main room from the addition. Its an aesthetic question I guess, do you want to look at the valley and gable or would you rather just see more expanse of the main roof.

We're working towards making an exposed valley, you can also make an overlaid (or california, or blind,) valley by building the main roof then overlaying the addition onto it, the valley shows outside, inside it doesn't. Just ruminating.

If you want exposed then figure trib load and get us back to here, if its a calivali we need to switch gears  :).

cloair

Don
The addition upstairs will be a bedroom, this will be a story and a half house with a loft and master bedroom upstairs, thus the wall.  I still want an exposed valley in the loft area I think it would look great.
Thanks
Quinten
Woodmizer Lt 30, Ford 555d Backhoe, JD 450B Dozer

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