Heavy clay roof. Need some advice on the calculator

[Planeiron]

I had thought about using a pendant post which would give more room for windows and access but I'm using the king posts for attaching bracing as I don't want to brace in plane with the roof. Maybe a pendant would work for you? In my current shed the tie beams easily support a loft floor and probably a king post wouldn't be required for this purpose.

 

[BrentH]

I was imagining something similar, except instead using principal rafters, the pendant would be supported by the cruck, which then would rest on the tie beams. Though I was just making it all up in my head, so it is reaffirming to see your diagram and know that something similar already exists.

When you mention bracing in line with the roof, do you mean bracing the truss to the ridge beam? Or are you referring to bracing among the rafters? Or something else?

I hadn't really envisioned putting any bracing in the roof, it would seem logical to do so, but I have been basing most of my research off of examining old Norwegian buildings (with sod roofs and similar snow loads) and studying their plans, and none of the ones I saw actually had any bracing. Now, my Norwegian is lackluster so maybe I am missing something in the fine print, but I'd think I would notice a brace if there was one eventually.

[Planeiron]

Go on the timber framing guild website and publications of past editions. There's a picture of a cruck roof with braces from principal to purlin on page 23 of TIMBER FRAMING 81 SEPTEMBER 2006. There's a tonne of great info there generally. I intend bracing from king post to ridge beam.

I suppose when the building is sheathed and the rafters well sarked the building will be much more resistant to outside forces. I suppose it depends on individual situations and building intent. If it's for sleeping/living and the roof is potentially very heavy, then bracing would be at the least quite reassuring to have against racking.

Would love to read about the old Norwegian buildings as I spent some time there as a student many years ago. Some amazing Stave churches and fantastic joinery.

[Don P]

Yes, I'd like to see what you are planning.
That ridge detail made mymind wander. What is the king pendant doing? pretty much just creating a 4 way connection.

If the bolster is the "pinch point", the ridgebeam, which is passing thru continuously, can be spliced/scarfed over the bolster. Cruck framing could support or pinch the bolster underneath depending on how it is framed.

[BrentH]

I will try to post the drawings that I have soon. Most of my computer time right now is going towards doing the foundation pricing and calculations, and making sure I get all of the tools and materials I need.

[BrentH]

Hopefully these drawings come up clearly. The lower portion of the structure will mostly follow the instructions in Will Beemer's book, but with the roof I had to come up with something a little more sturdy. I think I am leaning towards the gable plan below. I haven't quite finished the design yet, so some dimensions will change, and the joinery is left vague for now. For example I am planning to reduce the size of the ridge beam, as all of my big trees are revealing themselves as rotten in the center. To compensate, I will add a post from the ridge beam to the tie beam in the middle bent. 

The dimensions are partially determined by the thickness of the walls. The walls will be log infill (mostly 6x6), so 8x beams and posts are 1" thicker on each side of the wall to protect trim boards that cover the gap left when the infill settles. The 8x thickness of sill beams will be tapered to shed water where the infill meets the sills. the south wall, gables, and small areas around windows, will be infilled with 6" of sawdustcrete (homemade version of hemp lime). So 6" timbers will be flush with the various infill techniques. Log infill requires braces to be eliminated, so the horizontal logs are pegged to resist racking.



 

 

[Don P]

 I will add a post from the ridge beam to the tie beam in the middle bent. 

Use the center point load calc for the tie, the tributary area is half the roof length x half the roof width x design load. The ridge load halves as does the span. 

[Planeiron]

Started work on this thing and have some posts in the making, sills and a joist. Quite pleased so far though still a lot to do.



 

Thinking ahead to the roof and the ridge detail. This will be 3 king post trusses sitting on the posts and plates. There'll be a ridge beam and then common rafters sitting on wall plates and ridge beam. 

I think it makes sense not to joint the commons at the peak as they should be fixed to the ridge only and that a gap should be left between the commons at the peak to allow for ridge shrinkage. Is that correct? 

[Don P]

That would confirm the load path is through the trusses. Angles across the grain become more acute as they season. I Think Jim has a ridge sketch showing the cuts beginning obtuse, open at the top, when green.

[Planeiron]

Thanks Don. @Jim, might you be able to post the picture? Thanks 

[Don P]

@Jim_Rogers 

[Jim_Rogers]

Thanks Don. @Jim, might you be able to post the picture? Thanks

 
To be accurate, you need to calculate the shrinkage of the ridge beam from left to right as well as up and down. And make sure your gap is bigger than that amount. If the ridge beam shrinks to the point where the rafters lift off the ridge then the thrust could be increased.
Jim Rogers

[Planeiron]

Thanks Jim. The picture is very helpful and the clarification to account for both horizontal and vertical shrinkage. I must admit, I hadn't immediately thought of the vertical component.

[Planeiron]

This is more of a venting exercise as I think I might need a day or 2 off from framing work. Moved 3 x 20 footer English oak 6 x 9" beams into my garage to work on as the rain just wouldn't stop. Using snap line square rule and thought I'd get 2 of these marked up in preparation for the wall plate joinery... Was completely busted after moving these and then a bit disappointed when there was more bow in the wall plate pieces than I had thought :-[. About 1/4 over 20' (maybe that's not much or maybe it is?): if I were to do the joinery and set the plate on the 3 jowled posts either the 2 post end tenons would fit and the middle not, or vice versa.  

Should have enough margin in the stock to account for bow. I had thought about using the persuader and leaving this in and letting the frame suck it up but I have concerns that additional outward pressure on the plate tenon could help split the jowled post between post tenon and teazle tenon.

Anyway, broke my chalk line >:(and thought I'd try using a laser line I already had. A lot slower as you have to draw in the line but worked quite nicely as a backup and much nicer than the photo shows. Unless you had a really expensive model, it wouldn't be much use in strong daylight though (green lasers apparently work better in strong light).



 


The previous day's work was test fitting sill members. You can see my beam transportation apparatus at the right  :D 



 


 

I made a slight modification of my boring machine to help get more consistent depths. I had been counting revolutions which was fairly accurate but found my mind wandering back to the roof details which continue to keep me awake and so kept loosing count. So instead I made some markings on the upright with zero corresponding to the top of the sliding guide and when the snail is fully engaged and the cutters just touch the surface. Originally just light penciled in but couldn't properly see so now lightly scored. Anyway, I feel a bit better having got that all out. Apologies for the ramble.


 

 
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[Planeiron]

I'm about to drill holes in teazle tenons in jowled posts. These will be offset down towards their shoulders but I read in a TFEC publication on drawboring that these should also be offset horizontally to anticipate post shrinkage and mitigate as much as possible post splitting. I assume that the horizontal offset is towards the plate side (towards center of post). Can someone confirm this is correct as per my crude diagram?

 

[Jim_Rogers]

The way to remember which way to offset a peg hole is put out your two hands. The drawing you showed the post is your right hand. The plate would be your left hand. To offset the peg hole, you want to move your left hand to the right because that is the way you want your timber to move, then that is the way to offset the peg hole. Offset the peg hole in two directions does take some thought. And if you do it wrong, you'll push the joint apart. Once you've pushed a joint apart, you'll learn how to offset the peg holes correctly. I would rotate the left arrow to the right.
Good luck with your project.

Jim Rogers

[Don P]

The horizontal offset is not a drawbore, simply a note to move the peg left as you indicate in the drawing so that when the post shrinks it is less apt to create tension perp to grain between the locked plate and tie in the post.

It's in a way the same admonition not to bolt a 2x12 deck rim to post wider than 5" apart on the bolts or it'll probably split as it dries.

[Planeiron]

Is there any merit in not pinning the teazle at all given the weight of the roof and siding should hold things snug 

or

pinning in a few years and not offsetting in any direction as it wouldn't be possible then anyway.