Increasing height of timber frame need advice

[windfall]

First post, so forgive me for the run on questions....
Increasing the height of a 24' by 48' high post timber frame from the Fox Maple book.  The book calls for 8'4" to top of loft floor, and the exterior posts to be 12 ft.  I would like to increase both of those heights equally by 2'ft.  I'm hoping that by keeping both numbers the same I'm not increasing the outward thrust on the exterior post joints? With everything else staying the same does this seem logical?  The other change would be just making 8x10's versus the 7 x10's they call out for exterior posts.  Next question, can I extend the purlins through the end wall principal rafters to have gable end overhang?  Or is there another way?  Thanks for any ideas and or advice.
   

[Jim_Rogers]

If the distance between the loft floor and the top of the post doesn't change then the thrust will be the same. If you're adding 2' to this distance than it will put more bending stress on the post.
Increasing it to 8" would be better for the frame.

It maybe better to create the gable end over hang by extending the roof decking materials out over the rafters then to cut the top surface of the rafter to allow the purlin to extend out. You could add another "flake" purlin to the outside of the rafter which would be held up by the roof decking if you just want the look.

Extending interior timbers to the outside environment isn't the best as there will be gaps and thermal bridging that will invite trouble into the frame.

Jim Rogers

[windfall]

Thanks Jim,
I will not change heights in an unequal fashion so as not to increase the outward thrust on the exterior posts.  I like the purlin system however I'm having second thoughts due to no rake or gable end overhang for weather.  I am thinking of using the first floor bent system out of the book but a continuous plate on top versus the english tie joints.  Then rafters versus the purlin system allowing me to have some sidewall weather protection.  Does this sound okay? Questions..... When attaching summer beams, are they pegged as well?  If one uses lapped rafters at ridge, are they pegged into the top plate through the seat or not pegged at all? Thanks again, from nails to pegs lots of fun, but a definite mind shift.

[Jim_Rogers]

Can you post the page number of the plan you are looking at in his book? I'll review it before i give you any advice on modifications.
Thanks

Jim Rogers

[windfall]

Thanks again Jim,
The book is Chappell's "A Timber Framers Workshop".  Page's 198-201. I'm keeping same width, increase length to 48ft. 5 bents, 12ft apart.  Increase height of beam ties and ext post 2ft.(no outward thrust change per your advice). The confusion for me on the summer beams is due to the explanation in the book that when you have two summer beams on either side of tie beam(same location) you need a post under it, but in the drawing it shows no post. It also seems as though not much tie beam would be left? No mention is given to pegging the summer beam? Again, a huge thank-you...the information I am learning via your help and this site is priceless!

[windfall]

Forgot to say, its the High Post Cape Frame.

[Roger Nair]

To create overhang on a purlin system is shift the principal rafters downwards to the extent that a one inch passing notch to nestle in the purlins without notching the purlins.  Use timberscrews to secure.

[windfall]

Roger, Thanks....I think I understand what you mean...I hope..any ideas for the rake ends?  Which system or design do you favor, Rafters or purlin roof system?