The Forestry Forum is sponsored in part by:

iDRY Vacuum Kilns


Forestry Forum
Sponsored by:


TimberKing Sawmills



Toll Free 1-800-582-0470

LogRite Tools



Norwood Industries Inc.




Your source for Portable Sawmills, Edgers, Resaws, Sharpeners, Setters, Bandsaw Blades and Sawmill Parts

EZ Boardwalk Sawmills. More Saw For Less Money!

STIHLDealers.com sponsored by Northeast STIHL


Woodland Sawmills

Peterson Swingmills

 KASCO SharpTech WoodMaxx Blades

Turbosawmill

Sawmill Exchange

Michigan Firewood, your BRUTE FORCE Authorized Dealer

FARMA


Baker Products

ECHO-Bearcat

iDRY Wood Lumber Vacuum Drying for everyon

Nyle Kiln Dry Systems




Author Topic: ideas for spreading roof load and maintaining continuous purlin plate  (Read 2484 times)

0 Members and 1 Guest are viewing this topic.

Offline mrbrb

  • Full Member
  • **
  • Posts: 62
  • Location: CT/NY
  • welcome to hard times
    • Share Post
Hello,
Im looking for some feedback/ideas on alternatives to this continuous purlin plate design with vertical posts:
 

  

 

Wondering about the possibility of placing the posts at a 60 degree diagonal, thus spreading the load out towards the walls and creating a wider alley. Seems like roughly the same amount of joinery, but this is not something I have seen done- and there is probably a reason why:




Offline Brian_Weekley

  • Senior Member
  • ****
  • Posts: 701
  • Location: N. Stonington, CT
  • Gender: Male
  • I am Batman!
    • Share Post
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #1 on: September 02, 2014, 08:34:34 AM »
Although your design might give you a "wider alley" at the base, those slanting posts take up a lot of room.  You lose a lot of working space on either side of the alley.  I think overall, you'll end up with much less usable space.  I think my head would be full of bruises from manuvering around all of those slanting posts rather than ones that were straight up and down.  Just my two cents...
e aho laula

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 7316
  • Age: 67
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • Share Post
    • jrsawmill.com
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #2 on: September 02, 2014, 04:38:13 PM »
If you have a heavy snow load that's one thing. But you haven't said where you intend to build.
Larger common rafters closely spaced may eliminate the need for a principal purlin plate.

It all depends on the load, the span, the type of wood.
Lots of things to consider.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline D L Bahler

  • Senior Member
  • ****
  • Posts: 611
  • Age: 2015
  • Location: Central Indiana - Berner Mitteland
  • Gender: Male
  • Hopp Schwyz!
    • Share Post
    • Traditional Swiss Carpentry
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #3 on: September 02, 2014, 05:04:06 PM »
If you would push the canted posts clear to the ends of the tie beams, then have them support the collar beam just under the purlin (the purlin is lodged on the collar with a shallow cog and a heavy wooden peg) then you have the Liegender Stuhl which has been used thousands upon thousands of times, in Europe and North America. It exists for precisely the reason you are looking for, to create more room in the middle of the structure. It's considerably less complicated than what you have shown here, and more efficient.

You'll need to add some braces in your roof structure too.

Offline timberwrestler

  • Full Member x2
  • ***
  • Posts: 129
    • Share Post
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #4 on: September 02, 2014, 08:34:24 PM »
Yes, I'm with DL on this one (believe it or not).  You need to move the struts out.  And I'd say you need a principle rafter at each bent, that in turn supports the purlin plate.  This is also akin to French jamb de force.

Offline mrbrb

  • Full Member
  • **
  • Posts: 62
  • Location: CT/NY
  • welcome to hard times
    • Share Post
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #5 on: September 02, 2014, 11:19:00 PM »
Thank you for the feedback and ideas. Mr Bahler, is this along the lines of what you were suggesting? Pretty sure I know what you mean by 'cog'- basically a lap joint.

This building is sited in Northern Connecticut- snow load is 30psf for my town, so I would be designing the roof for a total of 40 psf.

I am using mostly no.2 white pine, with oak braces when I can. All of the calculations are for no.2 ewp.

The main idea here is to get the roof load out toward the walls, as the main tie beams just squeaked by with my original design (vertical queen posts), with a good deal of the roof load going straight to the mid point of the tie beams.  Even though the original design passes, I would feel a lot more comfortable directing the roof load to the periphery of the tie beams.

-  total floor load of 35psf (clear span first floor), with calculations taking into account the self weight of the oversized tie beams.

How would you work braces into this type of roof system?

Thanks and all the best!

  

    

Offline D L Bahler

  • Senior Member
  • ****
  • Posts: 611
  • Age: 2015
  • Location: Central Indiana - Berner Mitteland
  • Gender: Male
  • Hopp Schwyz!
    • Share Post
    • Traditional Swiss Carpentry
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #6 on: September 03, 2014, 12:19:41 PM »
Like this:
 

[/img]

The photograph above has an upper truss used to support a ridge beam. I doubt the size of your structure merits doing this. The design you have is pretty good, I would just recommend to add some bracing like shown.

Offline routestep

  • Full Member x2
  • ***
  • Posts: 219
    • Share Post
Re: ideas for spreading roof load and maintaining continuous purlin plate
« Reply #7 on: September 08, 2014, 07:45:46 PM »
Somewhere on this site I have a gallery of pictures.

I made a barn that uses 6 by 8 inch struts very similar to your second set of pictures. They were about 110 inches long. Total of four pair. Your drawing shows many more!

The struts were mortised into the cross ties about thirteen inches from the tie/post connection and angles up to a collar tie in principle rafters. The angle was 52 degrees.

The principle purlins were in the roof, mortised into the principle rafters and supported the common rafters.


Share via delicious Share via digg Share via facebook Share via linkedin Share via pinterest Share via reddit Share via stumble Share via tumblr Share via twitter

xx
Purlin /roof load questions

Started by shinnlinger on Timber Framing/Log construction

13 Replies
3850 Views
Last post October 10, 2012, 12:15:43 PM
by shinnlinger
xx
purlin size and spacing, other roof sheathing ideas?

Started by hawth on Timber Framing/Log construction

3 Replies
5114 Views
Last post October 23, 2011, 01:11:41 AM
by Raphael
xx
Scarf Joint location in load bearing top plate

Started by Hackermatack on Timber Framing/Log construction

7 Replies
1727 Views
Last post January 15, 2016, 12:12:26 PM
by jimdad07
xx
How to spread roof load evenly over a box beam?

Started by captainprog on Timber Framing/Log construction

10 Replies
707 Views
Last post January 13, 2019, 06:13:00 PM
by Dana Stanley
 


Powered by EzPortal