Skip to content


Home > About Us > What's New > Carpenters investigate structural movement at Gilman Garrison House

Carpenters investigate structural movement at Gilman Garrison House

February 22, 2012

Gilman Garrison wall
Historic New England carpenters removed the exterior wood cladding of the south wall of Gilman Garrison House to review the conditions of the original structure.

Historic New England's carpenters are investigating structural distress at the c. 1709 Gilman Garrison House in Exeter, New Hampshire. Severe cracking in the interior plaster suggested that the south-facing wall was bulging, or bowing, outwards, a potential sign of a displaced structural element or a too-heavy roof load. Carpenters removed the exterior wood cladding to review the conditions of the original rough-sawn log structure. Historic New England retained an engineering consultant to further review this area, provide commentary on its condition, and make recommendations. We decided to institute a structural monitoring program to determine how much, if at all, the building was moving.

We installed three systems to determine the type and severity of the structural issues at this critical rear wall:

  1. Measurements of the vertical movements: We established eight fixed points in the ceiling to determine vertical movements of the attic/roof structure. This data will assist in recording any attic or roof vertical settlements related to the rear wall bowing.
  2. Measurements of the bowing rear wall: Three steel-wire plumb lines were installed at the ends and center of the rear wall. We then took offset measurements from each line to the center of each rough-sawn plank in the wall. Tracking these offsets will assist in determining further bowing and its rate of progression, if any.
  3. Crack monitors: Our directional movement recording gauges were installed on the exterior of the building along the connections of the planks. These measurements will assist in determining the curvature of the wall and subsequent progress, if any.

The initial measurements were recorded in December 2011. Three additional readings will be completed in the spring, summer, and fall of 2012 to determine any movement of the wall and the need for repairs. Depending on the results, we will develop a plan for either stabilization or structural repair. This work is in conjunction with the long-term master plan for Gilman Garrison House, which includes roof replacement, cladding repair, and repainting.

Support preservation projects at our historic properties with a gift to the Preservation Maintenance Fund.

Directional movement recording guages

Posted by David Ottinger on March 1, 2012
I understand about establishing and using datum lines but am wondering what a "directional movement recording gauge" is? Are they available to the public?

Directional movement recording guages

Posted by Jodi Black on March 6, 2012
Thank you for your comment David! Yes, the crack monitors are available to the public. Our structural engineer supplied the ones at the Gilman-Garrison-- they used Avongard Crack Monitors
( but there are many sources online.

Good luck with your project.
Jodi Black
Preservation Manager, Historic New England

Test, just a test

Posted by TydrandmankPU on June 10, 2013
Hello. And Bye.

Add comment

You can add a comment by filling out the form below. Plain text formatting.

Please enter your name.
Please enter your e-mail address.
Carpenters investigate structural movement at Gilman Garrison House