Timber Framers Guild Forums General General Forum Questions Shrinkage

Hi everyone.
Have a question regarding shrinkage. If you have several tie beams connecting post on a exterior wall will the wall shrink in length

Tie beams run across the building from one wall to the other, so I am assuming you are referring to girts. Not enough shrinkage to be concerned with.

Mikey:
Every timber in a frame gets it's name by its location. A tie beam is called a tie beam because it does actually "tie" the two broad walls together.

Timbers in a wall, as mentioned are usually called girts and sometimes even connecting girts.

And most timbers do not shrink in length, very much if any at all.

It may appear that they shrink if there is a gap between the girt shoulder and the post. But most likely the post has shrunk, some.

Jim Rogers

Sorry. Your right my mistake. I understand that the girls don't shrink in length but the post do. So if you had for example 8 post that were 12x12 green they would probably shrink about a 1/2" each this would add up to approximately 4" overall. If the joints didn't separate at all wouldn't the wall shorten up by 4". And if you stick framed the outer wall that wall wouldn't move. Or the joints at each post would separate approximately by 1/4" on each side. Any thoughts

Yep, a whole lot of shrinking going on. But don't despair. The length of the wall is regulated by the sills and the top plates and if the sills and plates are joined end to end by scarfs, you can expect shrinkage on the overall plate and sill lines to be .01% of wet length to dry. If you follow the same reasoning and join intermediate girt with splines or free tenons, the girt line should shrink consistent to the plates and sills. If the girts are housed in, the shrinkage of the posts will not show dramatically nor pull against the girt line.

Oops, longitudinal shrinkage has a misplaced decimal point, it is approximately 0.1% not as I typed .01%.

Ok. Get that but if you have shouldered joints for the girts and the top plate and the sill plate prevent movement you will end up with big gaps on the 12x12 post and possibly break tenons or pegs wouldn't you.?

I would say no, but there are a number of details that need to be attended to. Shrinkage considerations can vary by species and degree of seasoning. First tangential shrinkage is greatest. Radial shrinkage is less than tan. by a factor of 2 to 2.5. So if you are using green boxed heart posts you will encounter the least amount of shrink if the free tenon passes thru the center of the post and the girt centers on the post. I would fully house the girt as deeply as practical but I would not hollow the post face abutment with the girt. I would favor not putting pegs thru the free tenon and rely on braces to hold the centered positions. By using free tenons the post will not forcefully pull on the girts. Long sill to girt braces will hold position without being strongly effected by post shrink. If you come from the land of huge timber and have free of heart posts, place the radial grain in girt line to keep the shrink limited.

Thanks Roger. Very informative. Much appreciated.