Blastoff!

Heck yeah! This week we successfully jacked up the timber frame off its foundation, building progressively taller stacks of cribbing to support it. Our trusses will suspend the timber frame in the air for several weeks while we install a 12-inch insulated floor underneath.

Ben arrived Monday morning with a shiny new bottle jack from Valley Rent-All, and we wasted no time positioning a jack at each end of each truss. We disconnected the timber frame’s six legs from the foundation angle brackets and then stationed a body in all four corners: Cillian the architect, Clayton the property owner, Ben, and myself. On Cillian’s count we pumped the four jacks in unison, lifting the trusses (and the timber frame with them) about an inch at a time. We paused frequently to check plumbness with a laser level; any low corners were resolved with a few extra pumps of the jack.

Jack setup.

Jack setup.

The jacks are supposed to have a range of about 10 inches, but one of them would only lift 5 inches and then quit moving. Therefore, we reset all four jacks every 5 inches. Resetting is a simple process: build up the cribbing tower to support the truss on its own, slowly release the jack (which lowers the truss onto the cribbing), then shim up the jack to a higher location and pump until it once again lifts the truss off the cribbing. Whoever took the longest to reset his jack received a good-natured ribbing. We are four young guys, after all.

Ben builds up one cribbing tower.

Ben builds up one cribbing tower.

The trusses and the bolted connections transfer vertical forces with ease, but they offer little help with horizontal forces (at least not in the direction perpendicular to the trusses). Shear stability is provided by the timber frame itself, via transverse beams at the second-floor level, and by two X-braces we built with dimensional lumber spanning across the first floor between the two trusses. This shear system protects the structure from racking in all but hurricane-force winds… which we don’t expect to encounter during the temporary 2-month load condition. Meanwhile, the extreme weight of the timber frame prevents uplift.

Around the 9-inch mark, Ben noticed the timber frame was “walking” – that is, instead of moving straight up, it was drifting away from the vertical axis. We solved this problem with a come-along. Cillian looped one end around a second-floor beam, I looped the other end around a tree, and we ratcheted the strap until the timber frame returned to center (as shown by our laser level). For the remainder of our lift, we constantly adjusted the tension in the come-along to keep the structure centered.

At last we came to a height of two feet above the foundation – we want plenty of extra space to build the floor system – and we built up the four cribbing towers one last time for a solid support. Ben removed the jacks and returned them to Valley Rent-All, as we won’t need them again until we’re ready to lower the timber frame back down. What a huge relief and validation that the trusses work!

End of day after a successful lift.

End of day after a successful lift.

Advertisements

2 thoughts on “Blastoff!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s