birds mouth

[TROYL]

Is the birds mouth cut on a rafter suppose to be the full width of the top plate? I'm using 2x8 rafters and 2x4 wall. i'm planning on cutting them a full 3.5" or is there somthing i need to know. i have never cut one before.

[NM_Shooter]

Good questions.  I want to piggyback on another question...

I am planning on cutting my rafters off-site.  I won't be able to measure them in place.  In order to make up for a little bit of the top plate wandering, I was planning on cutting the birdsmouths with 1/4" of "slop" 

Comments?

[ScottA]

If the wall has sheathing on it you'll want to add for that making your notch about 4" deep.

Shooter I'd cut them exact and push or pull the wall to line them up.

[Don_P]

You need to maintain a minimum of 3-1/2" of the wood remaining above the birdsmouth if there is an overhang. with that 2x4 of material left you are allowed up to a 2' overhang. The seat cut (the horizontal line) must provide a minimum of 1-1/2" bearing on wood framing (sheathing isn't a bearing, 1-1/2" min on the top plate), 3" minimum bearing on concrete.

You can overnotch but you'll need to snap a straight line down the plate and make a registration mark on the rafters to align them to the same point each time. I cut exact, I have had to customize cuts if I'm bearing on a bowed beam.

I like to run a string down the center top or underside of the ridge and keep an eye on it as we nail the rafters. I typically work high and my wife works the wall. She nails the bottom first and then I nail the top, I have some ability to adjust at the ridge but if I lock there first she's stuck. More people notice the bottom than the top.

If I have a cathedral ceiling I typically make the bird full width so the wall flows into the ceiling plane... WARNING; there is an often misunderstood verse that states that you cannot notch the end of a member more than 1/4 depth. I've seen many people and in fact trade magazines apply this to the bird. If you have a hard case inspector this is worth remembering, in that case do not notch more than 1/4 depth and mutter under your breath.

In no case should the seat cut extend inboard of the wall line, it can cause the rafter to split.

In no case should the rafter plumb cut at the ridge dangle beneath the ridge, it may cause the rafter to split.

http://windyhilllogworks.com/Calcs/rftllclc.htm

[TROYL]

thanks guys,  I upgraded may rafters to 2x8's after using your calculator a month ago on this sight and held my sheeting down a 1/2" to hold the foot cut to 3.5".  I has exceeding the 1/3 of the 2x8 with a 4" cut according to the calculator. i'm also plannning on ripping the rafters down from the birds mouth to the rafter tail.( not sure of the proper term for this). but it will eliminate the heel cut and short the size of fascia board i will have to buy.  i just wasn't sure i was suupose to cut them that big or not. sure seems like it would help making the interior work a little easy to finish off. thanks again for the help.

[Jens]

please make sure to measure your walls first, in several areas.  A difference of even 1", is very easy to have happen, and will ruin your day, and waste your money on rafter stock.  Like Don said, if your ridge is smaller than the length of the plumbcut, put it at the bottom of the plumbcut instead of the top.  Its nice if it is the right height, but the world isn't always ideal, is it?  The steeper your pitch, the shallower the seat cut in the rafter can be, because of the 1/4 or 1/3 rule.  A minimum 1.5" on the framing is needed, 2-3" better.  Anyway, like I said, check in many spots before you cut all of your stock, or you may end up having to build a deck with those rafters!

[bayview]

Don't forget to tie it all together with some Simpson connectors . . . Worth the extra time and money.

http://www.strongtie.com/products/highwind/TrussRafter-WDTP.html

[Jens]

yup, I don't think modern building codes have benefited old man Simpson enough.  The feds need their kick backs too

[diyfrank]

I'm using 2x10 rafters. How does ripping the overhang from a 2x10 to more of a 2x6 sound? 2x10 hanging over will look ugly.
I'm thinking about doing this unless theres a better way.

[Jens]

it is not uncommon to have the tails ripped to 4 or 6 inches.  4 is more common, gives that old look if you have open eaves. 

[PEG688]

I'm using 2x10 rafters. How does ripping the overhang from a 2x10 to more of a 2x6 sound?

I'm thinking about doing this unless theres a better way.

You can even go down to a 2x4 look , just don't cut past . Finish the rip and cross cuts with a jig saw or hand saw don't run by the intersection of the two cut with the Skilsaw. 


 

[NM_Shooter]

Hmmmm...

Ok.  Good idea on pulling the walls in with a strap or come-along to draw them plumb if necessary.  Is there an easy way to push them out?  maybe with a brace pushing off of the floor deck?

As small as my cabin will be (14X20), I think it should be easy (Ahem...  ) to get the walls within 1/2" of consistent span.  I'm building panels off site for speed of assembly, so sheeting will already be on.  No panel will be longer than 10'.  I'll probably sheet the gable end walls after installation though because of the off-width of the cabin.

I'll probably get one wall as perfectly plumb as I can, make it linear with a top plate, and then set up the opposite wall and use a tape measure to get the top plates as parallel as possible.  I can either adjust for plumb or adjust for parallel.  I'll probably adjust for parallel given the short span and hope for the best.  I can't imagine it will be too far off. 

-f-

[firefox]

Simpson has VPA and VP brackets to substitute for cutting the birds mouth. I used the VPA brackets on a garage roof and they seemed to work pretty good. I am curious as to whether they are better or worse than the standard birdsmouth from a structural view point. They have code reports on their site, but I don't realy know enough to evaluate them.
Bruce

[Don_P]

Generally we set a tight stringline 1-1/2" inside the top plate on nails at each gable end then walk along the wall with a scrap 2x checking the string to wall gap. If the wall needs to go out a 2x pusher from near the top plate at a stud to a block in the middle of the floor will shove it out. We then nail a brace to a floor block and the wall to hold it. To pull in a similar setup, the flatways angled 2x is naile to the floor and to the top plate. A short post (~3-4') is then put between the angled 2x and the floor and used to bow the angled 2x upwards by pulling it towards the floor end. This effectively shortens the hypotenuse of the triangle formed and pulls the top plate in. Again brace solid. We nail a diagonal brace on all unsheathed walls. The bracing is left in place until the roof sheathing is finished forming a rigid diaphragm, only then does the bracing come off.

The brackets are frowned upon by carpenters and do not meet the letter of the building code. I would check before using if it is to be inspected. The weight is bearing on nails and a very fine corner of the plate, not much if it gets heavily loaded. It does have an ESR (engineering services report) which most inspectors would respect... but ask first  .