Joined: 25 Jun 2005
Location: River Forest, Illinois
|Posted: Sun Jan 29, 2006 1:01 pm Post subject: Davenport House Construction Photos - 2
|One of the most challenging tasks on the restoration of the Davenport House was a structural repair of the north facade compound bulge. This structural problem was due to the following:
1. The ribbon windows were basically just a big slice out of the balloon frame, without studs extending through the window mullions. Basically this created hinge action at the top and bottom of the window. FLW fixed this on the next iteration of this t-shaped house type, the Ward Willets House. FLW was a practicing architect at this point in his career. The rookie carpentry crew that constructed the Davenport House was still learning.
2. The peak of the roof above cantilevers out 5' perpendicular to the wall. 2x4 angled lookouts supported this large cantilever. The 2x4 lookouts exerted a horizontal force on the wall above the window. This created a 3/4" bulge in which peaked at the weakest point, the top of the ribbon window.
3. The north facade beneath the ribbon window has a cantilever that is scabbed onto the wall. This had sagged badly and part of it was in danger of falling off of the house. It exerted an outward thrust on the wall creating an unsightly bulge out, approximately 1". This peaked at the weakest point, the bottom of the ribbon window.
4. To make a bad situation worse, the election bored 1" diameter holes in the studs beneath the window early on in the restoration process. This further weakened the overloaded studs beneath the window. The electrician is excellent, but he made a bad choice.
The result of all this was that the second floor ribbon windows bulged in at the top and out at the bottom. The center window was approximately 1 3/4" out of plumb.
We repaired it this way. First we installed Horizontal and vertical string lines to measure the problem and to act as a reference point as we applied force to the structure. Simultaneously we did the following:
1. Jacked up the north facade cantilevered low roof.
2. Pushed out with 5 ton jacks on a diagonal to the top of the window.
3. Pulled in with 1 1/2 ton lever hoists, aka come alongs, in a horizontal orientation.
We did the work incrementally and we measured the change against our horizontal and vertical string lines. We over compensated slightly because from our experience we knew that the modest deformation of the wood structure would return. Once we had the structure in place we proceeded to make the structural repairs. The cantilevered low roof structure was repaired first then we lowered the jacks there only to check our compensation assumptions. We then adjusted our work to get the cantilevered roof in the desired position. We then made the repairs to the balloon frame studs and their connections to the windows. The structural engineer wanted to put long steel plates horizontally above and below the window and vertical steel plates in the wall from the foundation up the wall and through the window mullions. This posed enormous challenges to build which I was not willing to accept for budget reasons.
We worked with him to come up with Plan B. Plan B was much more buildable and was "likely" to work, but it was not a guaranteed fix. Plan B involved: reinforcing the wall horizontally and vertically with additional wood members; installing shop fabricated steel brackets at the wood connections to the windows; creating a wood diaphragm with the new 2x6 ceiling joists and plywood. This was designed to hold the wall above the windows, at approximately its unsupported mid-point in place. We made the repairs and partially released the jacks and the lever hoists to check the results against our string lines. We tightened everything up and made further adjustments to get the proper alignment. We repeated this a second time. When we took down the jacks and hoists, we continued to monitor the wall. After approximately a week a small increment of deformation had returned. However this is only noticeable if one knows what to look for and carefully studies the wall. We were thrilled with results to a perplexing and challenging compound bulge. This structural repair took approximately 5 weeks for a highly skilled carpenter aided by two architect carpenter assistants.
These photographs were taken right before we took down the jacks, lever hoists, and temporary framing.
Paul Harding FAIA Owner and Restoration Architect for FLW's 1901 E. Arthur Davenport House, the First Prairie School House in Chicago | www.harding.com | LinkedIn