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Frame design question for you experienced types

Started by moorerp, March 18, 2012, 04:28:44 PM

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moorerp

Howdy,

I'm designing a square frame, 29' on a side, with a principal rafter, common purlin hip roof.  With any luck, I'll be able to attach the sketchup file below.

My simple question is this: given the basic design shown on the sketchup figure (8x8 ridge beam, principal rafters joining above the ridge, 6x8 support post under the principal rafter/hip rafter confluence), how big do the principal rafters need to be?  The ones perpendicular to the ridge are 6' apart OC.

They're roughly designed as 6x6 in the attached sketchup file, but they're like that only because I figured A) 6x6 is probably big enough, and B) 6x6 will be easy to mill from the timbers I have on hand.  But I do have access to some 6x8 timbers that would serve, as well as some 4x9's.  Although it makes intuitive sense to me that 4x9's laid on edge might be superior to 6x6's, it's only a gut feeling.

(Just as a potentially important aside- I have no idea how to use rafter span tables or any other standard method for calculating rafter size because I'm an inexperienced framer.  My usual approach is to achieve safety by making things bigger and stronger than they need to be.  Trouble with the roof is, I don't have enough experience to know what overbuilt is!)

thanks for your help as I begin to figure out how to build myself a house that'll last 200 years....  Please feel free to ask questions about important bits of info I'm sure I've left out.

 

randy

  Success!

Brian_Weekley

Randy,

I'm no expert, but have a few questions for you... The roof pitch looks very shallow.  What part of the country will this be built (snow loads)?  Why are you choosing to build a hip roof vs. a traditional gable style? 
e aho laula

witterbound

Seems like Jim just answered this for someone else.  Your principal rafters have to be bigger than you think because you'll be cutting some of them out for the joinery for your purlins.  If you start with 6x6 and cut out 2 inches on each side for your purlin pocket /joinery, then you've just got a 2x6 left.

moorerp

hey Brian,

The pitch is pretty low, but the frame is going up in extreme southern AZ, so snow loads are negligible.  It's at 4,000 ft. so it does snow from time to time (in fact, it's snowing there right now), but rarely, and very rarely more than a few inches.

The frame is also going up inside of some existing walls- it's a renovation of an 80 YO adobe with walls that are so wonky that I don't want to put any load on them at all- thus the frame roof.  And also thus the hip- I need overhang all the way around the building, and a simple hip roof seems the easiest way to achieve that.  I also like the simple elegance of it, and it's also a pretty common design on older ranch houses down there.  And last but not least, I'm trying to cut down on the volume of space above the plates- it actually gets quite cold in winter here, and old adobes are notoriously hard to stay warm in unless they're situated to take advantage of solar gain (which this one is not). 

Thanks for the input-
randy


Quote from: Brian_Weekley on March 18, 2012, 09:51:14 PM
Randy,

I'm no expert, but have a few questions for you... The roof pitch looks very shallow.  What part of the country will this be built (snow loads)?  Why are you choosing to build a hip roof vs. a traditional gable style?

moorerp

My plan is to leave the purlins proud of the principal rafters on purlin cleats (see Figure 27 in volume 5 of Jack Sobon's Roof Historic American Timber Joinery for an example, http://tfguild.org/joinery/part5.pdf) so there won't be very much removal from the principal rafters at all.  At least that's the idea so far....

Quote from: witterbound on March 18, 2012, 10:59:55 PM
Seems like Jim just answered this for someone else.  Your principal rafters have to be bigger than you think because you'll be cutting some of them out for the joinery for your purlins.  If you start with 6x6 and cut out 2 inches on each side for your purlin pocket /joinery, then you've just got a 2x6 left.

witterbound

Timber frames get a lot of their strength from the walls that are built around them.  My frame swayed and flexed when we were putting the roof on...we added the walls later.  If your walls are wonky ......

moorerp

My walls are unbelievably wonky- charmingly so (I keep telling myself that).  But the walls won't bear on the frame stability at all in this case, as the walls aren't going to be attached to the frame at all, except at the eaves, and there just to keep the weather and the critters out.  I'll attach a picture of the working model below so you can sort of see what I'm talking about.

Quote from: witterbound on March 19, 2012, 02:12:55 AM
Timber frames get a lot of their strength from the walls that are built around them.  My frame swayed and flexed when we were putting the roof on...we added the walls later.  If your walls are wonky ......



 

witterbound

Three more things for you to think about.  Footers, if your posts are going to carrying the entire weight of the roof, you're going to need some good footers.  Braces -- I don't see any in your drawing and you're going to need some.  Raising -- think about how you are going to raise a frame inside existing walls, as one typically must spread posts out to accept a tenon during raising.  My hunch is that no engineer would give you a stamp of approval for a timber frame w/o attached walls to strengthen the frame.  You might not need an engineer's approval, but they do exist for a reason and you should talk to one about this before you spend your time and money on a frame.

Jim_Rogers

There are several things that I see that jump right out to me.

First is that you have a scarf right over a post. This is not the best.
You are asking the load on the beam to be the strongest right there, and then you cut half the beam away. Not good. There are many threads here on this forum about scarf placement. You should do a search and read them and understand the correct location of the scarf. If you can't move the scarf then you may have to do something else to support it like a bolster block.



You don't show any braces. If your frame is to be a self standing structure then you need to brace it in both directions, front to back and left to right.
You show a supported ridge and only one support post.

If you want advice on the complete plan/frame, post the sketchup file in the plans section of the forum so we can download it and look at the frame.

Also, in that section is a review I did for dukndog of his frame. Read that to understand how an engineer is going to look at your design, and determine the loads and size the timbers necessary to hold up the roof.

Hip rafters even supported at the ridge hip rafters have some thrust at the plate. The proper support has to be done there to hold up the rafter and reduce the outward thrust.

One way it is done is with a joint known as the dragon and cross. It is not real complex but it has several pieces. I can post a drawing of one if you think you may like to look at it.

You say you need large overhang but none of your rafters show any. How are you going to overhang your adobe walls if not with the rafters?

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

timberwrestler

Besides the timber sizing and thrust issues others have mentioned, there are some hip specific things worth pointing out. 

First, doing an irregular hip (not 45 in plan) is quite doable, but it's not exactly straightforward.  There are a lot of angles involved and they'll be different for each side of the hip.  I would get Will Beemer's articles from the TF Guild called 'when roofs collide.'  Sketchup is a great resource, but you'll need to know what to draw first (the various clip angles and such), and how to calculate the working points. 

Secondly, if you have an irregular hip, and you want your overhangs to be equal, you're going to have to move the hip off of the corner of the building, and make some adjustments for that. 

Thirdly, irregular hips or valleys are often backed unevenly, that is, the backing angle is not centered on the beam.  Shifting the backing angle off of the center allows for the even reveals on the two plumb sides of the hip.  It just looks better.  I'm not sure whether Will's articles show how to do that--I can always draw something up if you'd like.
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moorerp

Thanks for the input Jim; the scarf-over-post thing I had not heard before.  That's especially good info because it seems intuitively obvious, to someone with little experience, that the scarf, being the weakest part of the plate, should be supported best from underneath.  Your perspective makes perfect sense, though- so much for intuition.  Unfortunately, I may have to go with a bolster block because of the length of my available beams, but that also may not be such a bad thing; that intersection looks kind of cool that way.

I don't have wood long enough to provide the overhang I want from one-piece rafters, so my plan is to use a sprocket, like in Figure 8 of the roof joinery section of "Historic American Timber Joinery."

The obvious things that are missing from the frame (like braces, peg holes, and miscellaneous posts and rafters) are missing because I just haven't gotten that far yet.  And you better believe I'll be posting this entire sketchup file on the design forum (which I didn't know existed- oops) for you guys to dissect- what a great resource!

And lastly, I'd love to see a dragon and cross if you'd be kind enough to post a figure.  But a quick question- if the hip is housed and supported at the ridge just like the other principal rafters (and birdsmouthed into the plate), why is there thrust at the plate for the hip and not the principals?  Or am I misinterpreting what you were saying?

I'll go immediately and check out your evaluation for dukndog-

thanks,
Randy

p.s.- I love my alpha protractor even though it'll be awhile before I can put it to use; it's just fun to play with.


Quote from: Jim_Rogers on March 19, 2012, 11:02:34 AM
There are several things that I see that jump right out to me.

First is that you have a scarf right over a post. This is not the best.
You are asking the load on the beam to be the strongest right there, and then you cut half the beam away. Not good. There are many threads here on this forum about scarf placement. You should do a search and read them and understand the correct location of the scarf. If you can't move the scarf then you may have to do something else to support it like a bolster block.



You don't show any braces. If your frame is to be a self standing structure then you need to brace it in both directions, front to back and left to right.
You show a supported ridge and only one support post.

If you want advice on the complete plan/frame, post the sketchup file in the plans section of the forum so we can download it and look at the frame.

Also, in that section is a review I did for dukndog of his frame. Read that to understand how an engineer is going to look at your design, and determine the loads and size the timbers necessary to hold up the roof.

Hip rafters even supported at the ridge hip rafters have some thrust at the plate. The proper support has to be done there to hold up the rafter and reduce the outward thrust.

One way it is done is with a joint known as the dragon and cross. It is not real complex but it has several pieces. I can post a drawing of one if you think you may like to look at it.

You say you need large overhang but none of your rafters show any. How are you going to overhang your adobe walls if not with the rafters?

Jim Rogers

moorerp

I will toast to your health  smiley_beertoast if you draw me up a picture of what you're talking about, Timberwrestler!  I was with you right up to the "irregular hips or valleys are often backed unevenly, that is, the backing angle is not centered on the beam.  Shifting the backing angle off of the center allows for the even reveals on the two plumb sides of the hip" part. 

The hips are the only thing that have been holding me back on the frame design- I actually started my first thread on this forum to ask everyone whether they thought a timber frame hip roof was a really bad idea, especially for a beginner.  The upshot was "probably, but you could still do it if you were careful and kept it simple."  So I'm doing it. 

And thanks for the tip on the TFG article- didn't know about that one, but now I'm excited about it 'cause I find the articles at that place to be really informative.  Most of what I've got so far is pilfered from Jack Sobon's  "Historic American Timber Joinery" series.

randy



Quote from: timberwrestler on March 19, 2012, 01:42:19 PM
Besides the timber sizing and thrust issues others have mentioned, there are some hip specific things worth pointing out. 

First, doing an irregular hip (not 45 in plan) is quite doable, but it's not exactly straightforward.  There are a lot of angles involved and they'll be different for each side of the hip.  I would get Will Beemer's articles from the TF Guild called 'when roofs collide.'  Sketchup is a great resource, but you'll need to know what to draw first (the various clip angles and such), and how to calculate the working points. 

Secondly, if you have an irregular hip, and you want your overhangs to be equal, you're going to have to move the hip off of the corner of the building, and make some adjustments for that. 

Thirdly, irregular hips or valleys are often backed unevenly, that is, the backing angle is not centered on the beam.  Shifting the backing angle off of the center allows for the even reveals on the two plumb sides of the hip.  It just looks better.  I'm not sure whether Will's articles show how to do that--I can always draw something up if you'd like.

matt eddy

just a quick comment:  I personally don't like square rafters.  Looking into the frame quickly I would probably use either 6x8 rafters, or 5x9, or you can even go with like a 4x10.  I would have to consider my joinery options for the rafters.  typically my hips need to be much larger then the commons so you can join them good.  if your just housing/screwing them that probably won't be a issue.  Also consider a dragon beam for the foot of your hips.  I didn't read all the replies you got, just wanted to give a quick piece of advice.  good luck!  Hips can be tricky!

timberwrestler

Alright, you better start toasting. 

Here's the plan view method of locating the hip (be aware that this is completely different from shifting the hip to create equal overhangs).


 
Draw everything in plan view, with the eave lines, and the hip centerline (the eave lines are extra out of square in this case).  Draw a line square to the hip run at the eave intersection.  On either side of the eave intersection, measure out and mark the FULL width of the hip rafter.  Now bring each of those points back in towards the eave lines, parallel to the OPPOSITE eave.  Where those points intersect the eave line, run parallel to the hip run, and that will locate your hip.  The next pic shows what the hip looks like if you do this:


 
And the next pic shows what the hip looks like if you don't (if you keep it centered on the hip run):


 

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Brian_Weekley

Moorerp,

Sorry, didn't realize this was related to your previous thread on hip roofs...

I understand the hip roof is intended to provide the overhangs over your adobe walls.  However, couldn't you achieve the desired overhangs with a traditional gable roof design?  You could lengthen the top plates to extend the rafters beyond the gable ends.  You could also extend the rafters to provide overhangs over the side walls (e.g., sprockets).  I made a very crude sketch below (without braces, etc).  This just seems like it would be far easier to construct.  It would also give you ample room for a second floor or loft area above.  You could add queen posts and purlins for added support.  Just a thought...

e aho laula

moorerp

Hey Brian,

Man, you and my brother think exactly alike!  And for the record, I suspect that you're both absolutely correct, and I probably should just go with a standard gable design.  But I've got this stupid hip roof design in my head and I can't get it out, so I finally gave in and went with it.  But to be fair to my masochistic self, there are some compelling reason to use hips:  1)  The overhang at the gable is too high to protect the walls at the base of the gable end, and the walls are going to have earthen plaster that has to be protected from driven rain.  I realize that there are other ways to attach an overhang at the plate on the gable end that would protect the base, but that arrangement just looks funny to me- I like simple design (even though in this case it may be more complicated to construct).  2)  A gable roof maximizes space in above the plate that I'm trying to minimize because of heat loss issues that are already going to be bad because of the nature of mud buildings.  3)  I don't want to have to build up to the peak of the gable with adobe block- the walls in this building are wonky with a capital W, and building up with adobe would really be the only option besides hips if I wanted to keep the place somewhat traditional, which I do.

So basically, I decided that I'm going to make sure to take the time to figure it out properly and just build a hip roof.  I figure the fact that the building is square works to my advantage, because once I figure out 1 hip rafter with associated jack rafters, I've figured out how to do them all 'cause they'll be identical.

thanks for the input, and I'm happy to hear any opinions and observations that may counter any arguments laid out herein!

cheers,
randy

Quote from: Brian_Weekley on March 19, 2012, 07:51:15 PM
Moorerp,

Sorry, didn't realize this was related to your previous thread on hip roofs...

I understand the hip roof is intended to provide the overhangs over your adobe walls.  However, couldn't you achieve the desired overhangs with a traditional gable roof design?  You could lengthen the top plates to extend the rafters beyond the gable ends.  You could also extend the rafters to provide overhangs over the side walls (e.g., sprockets).  I made a very crude sketch below (without braces, etc).  This just seems like it would be far easier to construct.  It would also give you ample room for a second floor or loft area above.  You could add queen posts and purlins for added support.  Just a thought...



moorerp

Hi Matt, thanks for the input.  You're the second person to suggest a dragon beam (if that's the same as a dragon and cross) and I was only able to find exactly one image of this apparatus with Google images- couldn't make heads of tails of how it was supposed to work, though.  Do you know of any reference material that shows the ins and outs of dragon beams?

thanks,
Randy



Quote from: matt eddy on March 19, 2012, 05:57:26 PM
Also consider a dragon beam for the foot of your hips.  I didn't read all the replies you got, just wanted to give a quick piece of advice.  good luck!  Hips can be tricky!

witterbound

So, is your plan for the purlins to, in effect, lay on top of your rafters, and kinda encircle the roof every so many feet, kinds like the Inge of saturn?


moorerp

Who's the Inge of Saturn?  I'm picturing a svelte Swede in a cosmonaut suit....

But yeah, if I catch your drift, that's pretty much how I think it'll work.  They'll be 2x8-ish, gently cut perpendicularly into the tops of the rafters with big cleat stops on the downhill side.  Tongue-and-groove ceiling boards will go on top of the rafters, insulation on top of those and between the purlins, roof on top of that- I both want and need to keep it simple, and that's as simple as I could come up with.

Quote from: witterbound on March 19, 2012, 11:39:25 PM
So, is your plan for the purlins to, in effect, lay on top of your rafters, and kinda encircle the roof every so many feet, kinds like the Inge of saturn?

witterbound


matt eddy

ok, here's my secret:   I use the red tfg guild book (timberframe joinery and design workbook) starting on page 80 when I got questions with compound.  If you don't have the book its pretty cheap and I recommend owning it.  If I can't figure out something compound wise with this book in my finger tips I would then use my phone a friend.  (Ed Levin) or others.  Good luck!

Thehardway

I would like to see more detail on that center post and the intersecting joinery of the beams.  I just gave the drawing a quick glance and this is what jumped out at me, more may come later as I mull it over.  You have a lot of joinery coming together at the same plane on a very small post.  In addition to that, the beams coming into that post are going to bear the weight of the roof as well as the thrust of the rafters, working like tie beams for the posts/plates at the wall as well as load bearing.  I would definitely beef up the beam that bears the weight of the posts for the ridge beam.  Draw a picture of how your frame will distribute the weight forces from the top of the roof, down through the structures and determine in your mind what members are in tension  and what members are in compression and what the load path is to the posts.

I think you may be better served with two tall posts which ascend from the floor all the way up to the ends of the ridge beam.  An anchor beam between these posts with some braces would stiffen the whole structure from the center outward. Using three  bays rather than two adds to this as well. It

   allows for the use of smaller posts simplifies the joinery some. 

There were a lot of old train stations made with the same style of roof and frame you are depicting here.  You may want to do a little historic research,identify a few and visit them to see how they did it. 

What do you plan to use as your roof covering?  If you plan on using terra cotta tile which might be common in AZ and would look nice on this building, you will definitely need to size beams for this load as they are heavy.  An alternative might be to use a stamped metal roof that look like tile as it would be lighter than tile or asphalt shingle roofing and more energy efficient.

One enginnering error that has been commonly made in the past is designing based on current weather conditions.  Weather is cyclical in nature and we are currently at the apex of a warm cycle.  In the late 1700's and early 1800's we were in a cool cycle.  If you look back you will find records of deep snow in Virginia and the Carolinas as well as Georgia and Tennessee, areas that have not had more than a couple inches in the last century.
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witterbound

Why are you thinking purlins instead of more rafters? 

moorerp

Quote from: Thehardway on March 20, 2012, 11:10:13 AM
I would like to see more detail on that center post and the intersecting joinery of the beams.  I just gave the drawing a quick glance and this is what jumped out at me, more may come later as I mull it over.  You have a lot of joinery coming together at the same plane on a very small post.  In addition to that, the beams coming into that post are going to bear the weight of the roof as well as the thrust of the rafters, working like tie beams for the posts/plates at the wall as well as load bearing.  I would definitely beef up the beam that bears the weight of the posts for the ridge beam.  Draw a picture of how your frame will distribute the weight forces from the top of the roof, down through the structures and determine in your mind what members are in tension  and what members are in compression and what the load path is to the posts.

I think you may be better served with two tall posts which ascend from the floor all the way up to the ends of the ridge beam.  An anchor beam between these posts with some braces would stiffen the whole structure from the center outward. Using three  bays rather than two adds to this as well. It

   allows for the use of smaller posts simplifies the joinery some.

Hardway, THAT is a cool idea!  I love this forum....

That center post and it's 4-beam connection has been giving me mild fits for exactly the reasons you state- lots of joinery coming in at the same plane.  Just as a disclaimer, what you see in the sketchup drawing is the leftover of a rejected idea involving reciprocal overlapping joints that I just made up (looked cool, and probably would have been strong enough, but it made other elements of the frame go out of whack).  Two tall center posts under the ridge would solve the problem, and it would make a really much more interesting looking frame to boot.  With the dragon and cross that'll go in to support the hip rafters, this is gong to be a much more interesting frame without becoming much more difficult to cut.

One question that's been puzzling me (your advice on visualizing forces on the various members reminded me of it)- if the rafters are housed and supported at the ridge, and the ridge supported by posts to the floor, does this not do away with a great deal of the rafter thrust at the plate?


Quote from: Thehardway on March 20, 2012, 11:10:13 AM
There were a lot of old train stations made with the same style of roof and frame you are depicting here.  You may want to do a little historic research,identify a few and visit them to see how they did it. 

What do you plan to use as your roof covering?  If you plan on using terra cotta tile which might be common in AZ and would look nice on this building, you will definitely need to size beams for this load as they are heavy.  An alternative might be to use a stamped metal roof that look like tile as it would be lighter than tile or asphalt shingle roofing and more energy efficient.

One enginnering error that has been commonly made in the past is designing based on current weather conditions.  Weather is cyclical in nature and we are currently at the apex of a warm cycle.  In the late 1700's and early 1800's we were in a cool cycle.  If you look back you will find records of deep snow in Virginia and the Carolinas as well as Georgia and Tennessee, areas that have not had more than a couple inches in the last century.

I'm planning to use some form of metal roof. If I were going to be truly traditional for the area, I'd be using corrugated galvanized stuff, but I'm not sure I can bring myself to do that when there are other types of metal that will last much longer.  Not so concerned about the look, but I am concerned about using resources that are gonna require more resources sooner than later.  Anyhow, the roof is going to be light weight.

And I can hit the old Patagonia Train Station with a rock from my backyard- it's been updated, but there may be some visible joinery somewhere in there....

thanks,
Randy

Jim_Rogers

Securing rafters at the ridge will reduce the thrust at the plate, but not eliminate it.
When you get your finial design done, then we can look at it and make more comments.

You should consider getting a timber framing engineer involved to make sure you have all your eye's dotted and tee's crossed.

Just a suggestion.
I know several who can look at your sketchup drawing when you have it done.

I'm not the best on thrust, so that's why I hire them.

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

Thehardway

Randy,

Did a google search on the Patagonia train station and the pictures I pulled up were not a hip style roof.  Might be some confusion on my part.  Here is a picture of the Chatham Depot which is about 15 mi. from my new place.  A lot of history here.  The old #97 passed this building on the day of its famous and fateful wreck.  I think it is a great representation of a hip roofed building with large overhanging eaves.  Might be a good reference for you. It is currently undergoing restoration to become a veterans museum.  I am curious myself to see how the hips were framed on this.   

 

There are several more nearby here that use this same general style.

I like that dragon and cross joint but I'm not sure how it will work with the eaves you are looking to add.  I think the large brackets might be a good idea for you  to add the eaves on. I echo Jim's advice to get an engineers opinion after you have all your fun designing and drawing.  When dealing with spans, there is a limitation to the over engineering approach as the larger your timbers get, the heavier they are and they must bear their own weight as well as that of the structure, hence the idea of the truss sprang forth.  You can't always be safe just by adding girth to your beams and timbers. In some cases it may actually be worse to up size.  I'm sure you have already considered this but sometimes in the excitement of drawing big massive frames we focus too much on the dead loads, live loads, snow loads, wind loads etc. and forget the weight of the structural members themselves.  Being that this will be more or less two independent structures (TF and adobe) you  need to make sure settleing issues are addressed properly. 


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moorerp

hey Hardway, thanks for the input and the image.  That train station's roof is pretty much a carbon copy of the design I have in mind, even down to the slight flare of the overhang.  If you run down any info on how it was framed, I'd be much obliged to hear what you found (or see what you photographed, especially).

cheers,
randy

Quote from: Thehardway on March 22, 2012, 09:41:16 AM
Randy,

Did a google search on the Patagonia train station and the pictures I pulled up were not a hip style roof.  Might be some confusion on my part.  Here is a picture of the Chatham Depot which is about 15 mi. from my new place.  A lot of history here.  The old #97 passed this building on the day of its famous and fateful wreck.  I think it is a great representation of a hip roofed building with large overhanging eaves.  Might be a good reference for you. It is currently undergoing restoration to become a veterans museum.  I am curious myself to see how the hips were framed on this.   

 

thurlow

I pretty much don't understand hardly anything atall of what all y'all are saying and the terms being used;  I suppose that's cause I'm a barely literate, retired dirt farmer. Of course it could be 'cause I live here and y'all live 'there'.  Howsomever, I have built numerous buildings which are still standing and will continue to do so absent a tornado (the old folks usta call 'em cyclones).  The sketch of your roof looks very similar to the roof on my pavilion (24 x 30 or could be 32..........I disremember).  If I recall correctly it has 2 x 6 rafters on 24 inch centers;  that may not be an option for you..............



 
Here's to us and those like us; DanG few of us left!

moorerp

Heck, I just barely understand most of the terms used on this site, and have no idea about the rest.  I've built part of exactly 1 timber framed structure, and most of what I know comes from that project, plus a lot of reading stuff on the internet. 

Like moderator Jim says, though, if you're gonna discuss this stuff (or beg for help in my case), everybody needs to be on the same page language-wise, so I'm suckin' it up and learning the lingo.  It does make things easier, I have to admit.

That's  a nice looking pavilion, and it's pretty close to what I have in mind.  I'm gonna be using a lot bigger timbers, though.

cheers,
randy

Thehardway

Randy,

I'm jammed for time right now to get my house done and moved in as we close on April 30.  If it wasn't for that I would track the info down on the train station right away for you.  You might want to try calling the folks there and see if they could point you to some documents or photos of the reconstruct until I can get free to find you some info.

By the way, what you are calling a "flare" has a technical timberframe name.  It is called a sprocket.  A sprocket is a small wedge shaped piece of wood attached to the rafter to flatten the pitch and extend the roof at the eave.

This was done for more than just looks or a large overhang.  The purpose was three-fold.

1. It reduced the velocity of rain run-off before it came off the roof into the gutter (in some cases gutters were actually concealed and built into in the roof)
2. It served as a means of breaking up sheet ice that formed on the roof so that it would not slide off the roof in one big piece and kill someone below.
3. it kept water off the side of the building.

Another term associated with this type of roof is a rafter "tail". rafter tails were often used to form a sprocketed roof and extend overhangs.  They were frequently cut in a decorative design at the end and left exposed or in other cases they were used to support and attach the cornice.

Although sprockets and tails are different in cut, placement, and attachment, either can be used to give the same look to a building.


For a more comprehensive understanding of timberframing terminology the TF Guild website has a number of articles you can download with pictures and illustrations to help understand what they mean.  Interestingly though, both the terms here are not in their glossary but are found in the article on joinery.
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