Normally we supply a wind beam at this point, this can vary in size and strength according to the wind category and spans. Generally use smart frame to calculate this member, can be a number of laminated 90x45 MGP12 on flat or up to Hardwood GL18.
http://www.tilling.com.au/smartframe/Software-SmartFrame-Tilling-House-CAD
Example of a porch roof using the hip roof and shed roof primitives. I’m wondering if it might not be worthwhile to add in a feature to create this type of combination roof automatically. Shed Roof w/ ledger & hip ends.
View updated model here:
I probably should have checked the numbers first. Given the high wind loads in our area (155 mph ult.) a 3-1/2 x 9-1/2 PSL loaded in the weak axis will deflect almost a full inch with a clear span of 10’-10" and a trib. length of 9’. However, a 5-1/4" beam will pass with flying colors, so I’ve updated my detail to:
The eccentricity is small enough that I think it makes sense to just sandwich them together and make sure they act as one unit. I still like the idea of disallowing any splices in the members in this region of the wall and will keep my notes specifying that.
Started the manual as a MS Word document however that did’t work so well for hyperlinks. Starting over with an html manual page:
http://design.medeek.com/support/trusspluginmanual/commontruss.html
Couple of pages up, only about 25 more to go…
Version 1.2.9 - 02.12.2015
A typical application might be a clerestory roof with a upper shed roof and lower shed roof with a ledger board:
View model here:
[url]https://3dwarehouse.sketchup.com/model.html?id=u0b2dd5bc-605d-467c-a6bb-449bb54e76e6[/url]
Version 1.3.0 - 02.14.2016
View model here:
I have shown 3 configurations of the same roof to display the differences with non-structural vs. structural outlookers (horz. & vert.). I am not exactly sure how to treat the gable end truss for this truss type since I have never dealt with this type of truss before. Any sample outputs showing the gable end truss with a dropped top chord for a tail bearing truss would be very helpful.
Theoretically, one could forego the gable end trusses altogether and just balloon frame up to the roof diaphragm but I would like to provide the option for gable end trusses if it is a typical method used in real construction of this type of roof.
I am currently investigating the best method to construct the gable end wall and truss with a tail bearing truss. Show below are 3 different possible configurations:
This is just one possible method of framing the gable end wall into the gable truss with a 2x4 outlooker. Option 3 shown above is somewhat of a question, not sure how that heel joint would come together.
View the model here to analyze the different configurations:
Alternatively one could balloon frame the wall at the gable ends and attach a ledger for the ceiling:
View model here:
In my opinion a partially sloping wall gets complicated to frame. From an engineering standpoint the balloon framed wall is also the strongest option.
Yes, I’ve also considered running the gable end truss down to meet the top plate of the common trusses however this method is typically discouraged for scissor type trusses per the recommendation of the BCSI-B3 Summary Sheet:
http://support.sbcindustry.com/images/publication_images/b3.pdf
A raked gable end wall or balloon framed wall is preferred otherwise a hinge is created and it hard to brace laterally for out of plane loads (wind) to the gable end wall.
One could argue that a tail bearing truss is not a scissor truss but I would say it is very similar especially as the height of the bottom chord from the top plate increases.
Version 1.3.1 - 02.15.2016
View model here:
I’ve been looking at a number of garage designs recently that employ an attic or storage truss. I’m finding that a lot of them tend to use raised heels to allow for more head room while having a lower roof pitch (ie. 6/12 - 8/12). I’m thinking about adding in raised heels for the attic truss type in the plugin.
A quick mock up would look something like this:
View model here:
Ignore the unbalance in the panel lengths, in practice and in the plugin they will be properly balanced.
What I do have a question on is the use of a top chord splice as shown in the above image so that the overhangs do not have to be as deep as the top chord in the non-triangulated region of the truss. I have never seen a splice used on a attic truss with a raised heel, I don’t see why it can’t be done but it is always nice to have a confirmation that someone else is doing this sort of thing in practice.
Version 1.3.1 - 02.17.2016
I’ve also addressed a number of bugs for rafter roofs when metric units are being used. I highly recommend everyone download the latest version, especially if you are using metric units.
Started to code in the dual pitch truss, the top chords, king post and bottom chord are there just need to add some webs:
Just an FYI, my previous post in Nov. had a sign switched in the last step of the derivation for Span 1, corrected in the plugin to a minus sign and everything is comes out perfect.
Here is a Dual Pitch 2/2 - 3/3 truss with a 12:12 pitch and a 4:12 pitch.
Still working on the gable end trusses and the advanced options involving structural outlookers.
I will be looking at raised heel scissor trusses next, those sound challenging and interesting. Please post or send me examples of any raised heel scissor truss examples or shop drawings. The combined pitches of the top and bottom chord with a wedge, slider or vertical web and strut will require some serious calculations and ample logic.
Version 1.3.2 - 02.23.2016
View model here:
Version 1.3.3 - 02.28.2016
View model here:
I’m not sure how common place this truss type is anymore so I will add the advanced options at a later date if requested by a user. I can also add in other configurations with more panels if needed (ie. 8/8, 10/10).
