How to Square a Post Frame Building Roof

Many builders believe if they have a building correct in width and length at ground, diagonals at ground are equal (footprint is square) and columns are plumb, then when they get ready to run roof steel everything will be perfectly ready to go.

This might be close to true for a small footprint building with a low eave height, however in most cases making this assumption will lead to a world of grief.

Today we will steal from Hansen Pole Buildings’ Construction Manual to achieve a perfectly square roof.

Note – ease in squaring a roof is one reason I frame my roof and install roofing prior to framing any walls. Everything moves far easier.

Figure 13-1: Squaring Roof

1. Check both endwall trusses for straightness (against a string line) from side to side.

1. Make certain endwall truss is plumb at each column. Properly set columns are either plumb or lean out slightly. To pull in, attach a cable from this column top to column base at the opposite endwall. Using a “come-along” move column top inward until plumb.

1. Using a stringline align all eave struts (purlins) to straight. Any nonaligned column tops can be pulled into place using a “come-along” also, using the same procedure as outlined in the last paragraph. This is critical as this building line will be a noticeable one.

1. Make certain the roof is square by checking diagonals from peak at one end to eave at the opposite corner. Refer to Figure 13-1 where diagonals AD and BC, AF and BE are equal.

Be certain to measure from the same “point” going each direction. Serious errors have been caused by lack of consistency. If uncertain, double check.

If any roof diagonals are “long”, run a cable and come-along from truss peak to opposite corner column (along purlin underside). Pull slowly until dimensions are equal. For best results, the difference in diagonals should be no greater than 1/8”. A very small “tug” can change a diagonal drastically.

NOTE: One side only may be squared up at a time. Place roofing on squared side, then repeat the process for the opposite side.

When Your Pole Barn Roof Grows

While one’s love might grow, it proves less than ideal to have this occur when it comes to overall length of a post frame building roof. To follow, a case study of why not:

Our client writes:

“Our roofing installer has come up 6” short on the roof steel on both sides.  He has requested one additional roof panel, and also 4 flat charcoal sheets 4’ x 10’ to break for some of the trims.  He said the gutter sides of the roof trim are also coming up short.  I went back and rechecked the plans, and it looks to me like the roof steel was 6” short on both sides per the take off.  Can you check the take-off on your end too, and help us get these pieces out to him quickly?”

Mike the Pole Barn Guru writes:

This client’s building should measure 60 feet in length from outside corner to outside corner. Building has 18” overhangs past each endwall. With a Hansen Pole Building, this causes ideal overall roof length to be 63’3”. Client’s roofer provided a photo, including tape measure, of overall length being 63’4” and roof steel running out of coverage about three inches before there.

Here (from Hansen Pole Buildings’ Construction Manual) how it should have been done:

“First roof panel positioning is critical. This panel establishes alignment and layout for installation balance. Accurately position and square before fastening.

Starting at roof edge, hold first steel sheet “overlap” edge even with end truss top chord siding backing center.

Important hint – Keep panels from stretching or compressing in width as they are installed. Panels cover 36” from major rib center on one panel side to major rib center at other side of panel. Measure each panel as installed or pre-mark building frame (or underlying reflective radiant barrier) every 36” to check panel width.

Why would this be important? If roof plane is square, endwall is straight and a 36” panel coverage is maintained, eave edges of each panel will come out straight. If eave edges begin to “stair step”, this is a sign one of these has occurred: roof plane out of square, eave strut boards are out of straight alignment, or each panel net coverage was other than exactly 36”.

Provided overall roof length is a three foot multiple (plus 3” to allow for framing), upon roof plane completion, last panel should not require trimming.”

As I advised client: With first panel of roof steel beginning at center of varge/fly rafter (3/4″ in) and a net panel coverage of 36″, with extra distance gained from overlap of panels (approximately 1-1/2″) other end should have ended right in center of opposite varge/fly rafter from beginning.

This is why it is essential to confirm each panel, as installed, covers exactly 36″.

Also, since you need two steel panel overlaps, it will require two more roof panels. As an alternative, we can supply (for rake trims) two “Richard Corners” (named after one of my 1990’s crew chiefs who needed them all too often) custom bent with a longer leg in order to cover area left open.

Today’s worthless trivia answer: Edison Lighthouse, remarkably they still tour despite only having a single hit and no original band members!