Tidal Build, a design-build firm in Mystic I have worked with before, brought me a seven-sheet permit set for a residential elevator addition on a 1951 cape in Dover, Massachusetts. The owner wanted a home elevator running from the basement to the first floor. That meant a small hoistway bumped out the back of the house, about 4 ft 7 in by 4 ft 9 in inside, a small control room beside it, new foundation walls, a raised roof section over the hoistway, two new doors and a relocated window in the existing rear wall, and a pit cut into the basement slab.
Most of the structure was already on the set. What Tidal needed was an engineer to review the structural content, design the items the set left open, and seal it for the building department. I practice in Connecticut and held a Massachusetts temporary permit for this project.
Reading the set produced the usual short list for the kickoff call: which ridge LVL and rafter spacing the architect wanted where two sheets differed, where the structural general notes would live, and the elevator manufacturer’s loads, which no permit set carries until the elevator is picked. We settled those on a recorded call. What the set could not tell anyone was what was under the house.
That last one mattered most. The ridge beam over the new roof lands on two posts, and those posts land on an interior bearing wall that the drawings neither show nor dimension. Below that wall is a basement carrying beam, and the basement is fully finished with a flat drywall ceiling. Nobody could see the beam.
The contractor did the legwork. He found a dropped box in the ceiling running along the center line of the house, in line with the ridge and with a bearing line visible at the attic floor. He taped the box at a doorway and came back a day later with a magnet. No pull anywhere, so wood and not steel. The box bears on short wall segments between a line of cased openings and doors, and it stops about 17 ft short of the far wall. Which end of that run the elevator corner sits on could be read from the plans and the photographs, but only as an inference, and the beam itself, its size, span and condition, was never measured.
The attic had its own surprise. Every rafter was buried in spray foam, so the size and spacing the set relied on could not be confirmed from any photograph.
The design was written so that none of those unknowns had to be resolved before sealing.
The new roof is a raised 5:12 section standing over the existing roof, closed on each side by a short triangular wall. The new 2x12 rafters at 12 in o.c. span 20 ft from a three-ply LVL ridge beam down to the outer hoistway wall. The drop beam the set drew at the line of the old rear wall is made non-bearing, so the new roof puts no load on the 1951 wall. On each side, the existing rafter under the triangular wall gets a 2x10 sistered full length, and so does the next rafter out, which takes the snow that drifts against the wall. The builder had floated a knee wall on a tripled rafter. The sealed design uses a doubled one.
The ridge beam posts are 3-1/2 x 5-1/4 in PSL, placed in the field directly over the bearing wall once the contractor has found it from the attic. The letter spells out what that wall has to be: continuous in one plane from the second-floor plate to the basement beam, solid blocking through every floor so the joists are never in the load path, and at least two full-height studs under each post at each level. The contractor confirms it in writing with photographs before the beam is loaded. That is an ordinary pre-framing confirmation of an existing condition the drawings do not show, not a condition on the letter.
Under the second post goes a new 3-1/2 in steel column on a 3 ft 3 in square footing, cut into the slab, its cap plate set tight to the underside of the existing beam without jacking. The point is that the existing beam’s size, span and condition are never relied on. If no beam is found at the posts when the ceiling is opened, the sheet says what happens instead: block solid up to the first-floor wall, add a second column under the first post on a footing no deeper than the gable wall footing, and call this office.
The rest of the package is the kind of detail an elevator addition needs and a permit set usually leaves out. Two new door openings and a relocated window in the rear wall, on (2) 2x10 headers, with the wall treated as bearing for the full roof, attic and upper floor. New 10 in foundation walls on 2 ft footings, 48 in below grade, doweled into the 1951 wall with No. 5 epoxy anchors at 16 in, with an underpinning detail for the case where the old footing sits more than 12 in above the new one. The control room walls retain the uphill grade and were designed as a closed box tied to the old foundation, good for a retained height up to 4 ft 6 in. The pit, the rail wall pads, the lifting beam and the hoistway shear walls all came from the manufacturer’s drawing and the wind and seismic numbers for the town.
Design snow was the Massachusetts flat-roof minimum of 35 psf on a 40 psf ground load. Wind was 120 mph, Exposure B. Seismic Design Category B.
Kickoff call on a Wednesday, recorded with the architect’s consent, to settle the open questions in the set. Photographs and the elevator submittal arrived the next day, and the contractor’s basement investigation ran over the following week while the calculations were being written. The package went out twelve days after the call: a five-page letter, the redlined architectural sheets, S-1 and S-2, and the calculation book, all signed and sealed.
If you are an architect or builder with a set that needs a structural review and a stamp, that is a service line I run, and I am happy to look at a set and tell you whether it needs me before anyone spends money.
| Item | Detail |
|---|---|
| Building | 1951 single-family cape, one and a half stories, full basement, finished throughout |
| Framing | Existing 2x10 rafters at 16 in o.c. as drawn, hidden under spray foam; an interior bearing wall under the ridge that the drawings do not show; a boxed wood carrying beam on the basement center line |
| Foundation | Existing poured concrete, 1951. New 10 in concrete walls on 2 ft by 12 in footings held 48 in below the lowest adjacent grade, pinned to the old wall with epoxy dowels |
| Existing condition | A finished basement with a flat ceiling, the carrying beam boxed in and the interior bearing wall not shown on the drawings. Nothing about the hidden framing could be measured without opening finishes |
| Scope | Review of the structural content of a seven-sheet permit set for a rear hoistway addition and a small control room, plus design of everything the set left to the engineer, delivered as a letter, redlined sheets, two structural sheets and calculations |
| Hoistway inside | 4 ft 7 1/4 in by 4 ft 9 1/4 in |
| Elevator travel | 7 ft 11 1/2 in, basement to first floor |
| New rafter span | 20 ft 1 1/2 in, ridge beam to outer hoistway wall |
| Load at each ridge beam post | 2,100 lb snow plus dead, 540 lb dead only |
| Control room retained height | Up to 4 ft 6 in, grade to top of slab |
| New column load, upper bound | 12,600 lb |
| Ridge beam | (3) 1-3/4 x 11-7/8 in LVL 2.0E, top beveled to 5:12, rafters in sloped-seat hangers |
| New rafters | 2x12 SPF No. 2 at 12 in o.c., single piece, 24 ft stock |
| Ridge beam posts | 3-1/2 x 5-1/4 in PSL, strapped to the beam, over an existing bearing wall located in the field |
| New basement column | 3-1/2 in listed adjustable steel column or Schedule 40 pipe, on a 3 ft 3 in square by 12 in footing, cap plate set tight to the existing beam without jacking |
| Rear wall headers | (2) 2x10 at each of the two new doors and the relocated window |
| Foundation pinning | No. 5 epoxy dowels at 16 in o.c., 8 in embedment, alternating faces; hoistway corner holdowns on 5/8 in rods |
| Hoistway walls | 2x6 SPF No. 2 at 12 in o.c. full height, 7/16 in wood structural panel one side, blocked at mid-height |
| Lifting beam | (2) 2x12 SPF No. 2 across the top of the hoistway, through-bolted eye marked for 1,000 lb |
| Load path | New rafters bear on the ridge beam at the top and on the outer hoistway wall at the bottom. The ridge beam lands on two PSL posts set directly over an existing second-floor bearing wall, through solid blocking at every floor, down to the basement carrying beam, with a new steel column and footing under the second post |
| Loads carried | new hoistway roof and the snow that drifts against it, elevator rail, pit and lifting beam reactions, retained soil against the control room walls, wind on the hoistway shear walls |
| Ground snow load | 35 PSF |
| Design wind speed | 120 MPH |
| Seismic design category | B |
| Code basis | Massachusetts State Building Code 780 CMR, 10th edition (2021 IBC and IRC base), NDS 2018, ACI 318-19, manufacturer values for LVL, PSL and connectors |
On a job like this one, yes. The architect's drawings, the contractor's photographs and measurements, and the manufacturer's data were the basis, and the letter says so. Everything the drawings did not show, the bearing wall, the carrying beam, the rafters under the foam, the old footing depth, is written as a condition the contractor confirms as the work opens up, with a fallback detail where the answer could go either way.
Because it was not necessary to seal the design. The new column goes under the second post on its own footing, set tight to the beam without jacking, so the post load reaches the ground whether the beam is big or small, sound or tired. If no beam turns up at the posts at all, the sheet says what to do instead. The owner keeps a finished basement until the crew is there anyway.
Less than people expect in weight and more in detail. The car and its drum drive put a few thousand pounds into the pit with impact, the rail brackets pull on the hoistway walls, and the lifting beam at the top has to carry a rated load for service. Then there is the roof, the shear walls, the foundation pinning and the retaining wall at the control room. None of it is heavy. All of it has to be specified.
Independent review and stamped calculations for a rear addition where 44 ft of first-floor bearing wall came out in two spans on a four-ply 20 in LVL, plus a sealed revision when the framing changed.
Call or text Travis at (860) 519-6009, or send the details below. Site visits are typically scheduled within a week, stamped letters follow within three business days of the visit, and you always talk to the engineer who stamps it.
This page describes engineering performed for a specific structure under conditions verified on site. Spans, member sizes, and connection details are particular to that building and its loading. Nothing here is a design for any other structure. Every project requires its own analysis by a licensed engineer.
