Whole-House Structural Evaluation in Bristol, CT: a Gutted Hewn Frame

What the client wanted

A design firm brought me this one. The town had stopped work on the rehabilitation of an old house in Bristol and, before it would release the permit, it wanted a structural evaluation of the entire building by a licensed engineer, followed by stamped drawings showing the existing deficiencies, the proposed repairs, member sizes, connection details and calculations. The building official’s list cited a history of water in the basement, a long vacancy and visible rot in the basement framing.

The evaluation is the first half of that. One visit, the whole building, what condition it is in, and the repairs required in order of priority. The drawings are a second submission.

What we found

A two-story hewn timber frame with a one-and-a-half-story rear wing, about 34 ft across the front and 28 ft deep, on fieldstone over a dirt-floor basement. Posts in the walls, 6x6 girts at the second floor, and three 6x6 beams running across the house carrying the second-floor joists, which tenon into them. Two hewn girders in the basement carry the first floor and bear on the base of the main chimney. The inside had been stripped to the frame, new windows and headers were in, and the outside was wrapped.

The frame itself is in good condition where I could examine it. I read two of the three beams with a pin moisture meter against a control reading on known dry wood and got 8.4 to 13.5 percent, which is dry. Probing with an awl found no active rot on any of the beams or the wall girts I could see. What looked like rot on the bottom of the rear beam was bark. There is minor flaking and some wood loss along the bottom corners, all dry and shallow. Nothing in the frame or the foundation is moving.

The biggest problems are the ones the work created. The three second-floor beams had been carried by the partitions, posts and chimneys under them, because a 6x6 does not carry a second floor across a 34 ft house on its end posts alone. The gut took most of that away. The rear beam still bears on a chimney that is slated for removal, the middle beam has the stair framing under it, and the front beam has nothing between its end posts that I could find. Nothing was shored.

The middle beam has two empty rectangular pockets in its underside, about 4 in deep, where knee braces once ran up from the wall posts. The braces are gone. On one side of that same beam the joists do not tenon in at all. They sit on a bolted strip of wood on the face of the beam with no other connection, which is weak. At most of the tenoned joists elsewhere the shoulder stands about an inch off the beam face, so the joints are not tight even though nothing sags.

Smaller items: the top of the rear beam cut down about 3 in at one joist seat, four or five round holes that look like old insect damage, with a crack beside them, in the right wall girt, and a thin, triangular original stud in the rear wall.

In the basement, a section of the original stone wall had toppled inward and a brick wall had been built inside it. The sill now bears on the brick. That sill has old dry rot and notches where wires have been passed through it; the wood is dry and the rot is not active. The toppled stone lies against the foot of the brick carrying nothing. There is one short length of minor active decay at the base of the framing on the stone wall. One girder is helped along by a full-height post standing on a flat stone with a wood shim and a piece of brick packed under the beam, and by a stub post about 2 ft long on the stone ledge. Neither is a permanent support. A photograph the client sent before the visit shows the underside of a girder pitted and decayed over about a foot or two, with a split along the bottom, where it bears on the chimney base; I did not examine that bearing separately. At the front right corner the mortar is gone from the top course under the sill, a stone has moved, and daylight shows through from inside. Outside, the mortar on the stone walls is weathered and gone in places; inside, the walls are tight with light mortar loss in a few areas.

The engineering

An evaluation is not a design, and the letter says so. What it does is sort the findings into what matters and put them in order.

Priority one is the three second-floor beams. Keep the chimney under the rear beam and every other support in place until the repair drawings are approved and the permanent supports they show are in. Shore the front beam now, snug, without jacking. The drawings have to locate every original and required support point along all three beams and detail a post or a bearing wall on a footing at each one, the contractor’s double 2x10 at the middle beam included if it goes ahead.

Priority two is connections and bracing: face-mount hangers with structural screws at every joist on the ledger side of the middle beam, the tenoned joists fastened where their shoulders stand open, knee braces restored at the two empty pockets or equivalent bracing shown, the right girt reinforced, the thin stud sistered.

Priority three is the local repairs to the beams, a bearing plate or hardwood block at the notched seat and fitted hardwood blocks or plates at the brace pockets. Priority four is the basement: shore, then replace the two added posts with posts on concrete footings and solid shims, give the girder new bearing on a footing beside the chimney base so it bears on sound wood whatever the decay turns out to be, no jacking, repoint the stone with a lime mortar inside and out, reset the corner, leave the toppled stone where it lies. Priority five is water: gutters and downspouts, with the downspouts carried at least four feet from the foundation, and the grade falling away, because every repair above depends on the basement staying dry.

Can a double 2x10 beside the middle beam carry the joists?

The contractor asked that on site, with the joists hung from the new beam. The letter calls it a design question, not a repair in kind. That beam would carry the second floor and possibly part of the roof through the framing above it, so it gets sized on the drawings once the loads on it and the supports under it are settled. The joist hangers at the middle beam are the right repair either way.

How it got delivered

A Thursday evening visit, about two and a half hours, the whole building from the outside walls to the attic knee walls, with the client and the crew there and the owner at the end. I told them to plan on a week. The evaluation was signed and sealed the following Tuesday and in the client’s hands two days after that, with the photographs and my first-floor sketch bound in so the building official could follow the findings to the pictures.

If you are working on an old house and the town has asked for an engineer to look at the whole thing before you go on, I do that work. One visit, then a letter that says what is there and what has to happen first, and the drawings after it if you want me to do those too.