How to Find Sleepers

We at The Charles A. Weyerhaeuser Memorial Museum have been on a weeks’ long hunt for sleepers in our Archives.

Lest you think we have somnambulant creatures hiding amongst the boxes, documents, ledgers, and photos, fear not! The sleepers in this case are 2 x 4-inch boards between the hardwood floor planks and 3/4-inch underlayment and the concrete foundation. The sleepers are spaced 16 inches apart and allow for moisture between the concrete foundation and the wood floor to escape. The sleepers provide breathing space, keeping the wood floor from warping or buckling.

Why on earth would we need to find the sleepers? Why not let sleeping sleepers lie undisturbed?

Because we are upending the entire Archives this year in order to install high-density mobile shelving and those sleepers aren’t going to have the luxury of lazing about. They’ve got work to do.

We’ve received a Legacy Grant through the Minnesota Historical Society (thank you, Minnesota taxpayers!) to install mobile shelving in our Archives in order to expand the room’s capacity for storage. As one of the conditions of the grant, we had to have a structural engineer examine the floor to see if it would be able to handle the extra weight of the mobile shelving.

Mark Hallan of Widseth Smith Nolting came to the museum to check out our blueprints and look at the floor. The blueprints indicated that the sleepers in the Archives ran north-south, parallel to the floorboards, at 16 inches on center. Because the rails of our mobile shelving are going to be running north-south as well, we needed to locate the sleepers so we could place the rails directly on them or very, very close to them so the floor would handle the weight of the shelves.

Blueprint drawing showing ends of sleepers in Archives at The Charles A. Weyerhaeuser Memorial Museum.

Blueprint drawing showing ends of sleepers in Archives at The Charles A. Weyerhaeuser Memorial Museum.

Based on this blueprint drawing for The Charles A. Weyerhaeuser Memorial Museum, it appears that the sleepers should run in a north-south orientation in the Archives

Based on this blueprint drawing for The Charles A. Weyerhaeuser Memorial Museum, it appears that the sleepers should run in a north-south orientation in the Archives

The hunt for the sleepers was on.

It was suggested that we try drilling into the floor to find them. Eek! Drilling holes in our hardwood floor? There had to be a better way.

First I tried a stud-finder, but the results were inconclusive. In looking at the blueprints, we realized that the 3/4-inch underlayment allowed for the floorboards to be screwed down more often than every 16 inches, with the thickness of the underlayment and the floorboards making it impossible for a stud-finder to locate the sleepers. Stud-finders typically pick up the metal in a wall or floor, not the wood itself.

It was suggested that we pull a baseboard off the south wall to see if we could find the ends of the sleepers that way. But, in thinking about the underlayment, we realized we probably wouldn’t be able to see the sleepers underneath it.

Blue tape in southeast corner of Archives, prepping for drilling the first 2 holes, The Charles A. Weyerhaeuser Memorial Museum, 2019.

Blue tape in southeast corner of Archives, prepping for drilling the first 2 holes, The Charles A. Weyerhaeuser Memorial Museum, 2019. There wasn’t this much space available when we drilled the initial holes.

So, with the wood repair and refinishing expertise of my husband Erik, we chose a far corner (southeast) to drill a couple of holes into the floor. We figured if we worked within a 20-inch square, surely we would find at least one sleeper and be able to figure out where they started. Because, of course, the room is not evenly divisible by 16 inches (the spacing of the sleepers), so that meant one of our sleepers would start/end at a point that wasn’t exactly 16 inches from the east or west wall.

We drilled two 3/4-inch holes in order to mimic the 3/4-inch wood plugs that cover the screw heads in the floorboards. As we drilled through the floorboard and the underlayment, we could feel the drill give and we knew we hadn’t hit a sleeper but were in a space between sleepers. This happened for both holes, so we stopped for the day, partially out of frustration for not finding a sleeper (not even by poking a wire into the holes) but also because Erik was trying to work in an area between a shelf and the south wall, so he didn’t have enough space to maneuver.

We needed more space and time to think about the problem before we drilled any more holes.

With the help of Morrison County Historical Society board members and staff, we emptied an entire shelving unit plus half of another, dismantled a shelving unit, and moved a floating wall out of the Archives. This opened a significant portion of floor space so we could continue our search.

We drilled a couple more small holes (1/4-inch) along the same path as the first two, thinking surely we should be able to find a sleeper running north-south along the line because that’s what the blueprint showed. I poked a wire in, but it didn’t hit a sleeper no matter how I twisted and pushed it around.

I had a small pen light that I was able to drop into one of the larger holes and, with the overhead lights off, realized I could see light shining through all of the holes we had drilled, which meant we were in a channel with no sleepers intersecting it, as there should have been.

Stymied again and not wanting to unnecessarily drill any more holes, I contacted our architecture firm, Miller Dunwiddie, Inc. One of the partners, Foster Dunwiddie, who is now retired, designed our building. Perhaps there were notes on file that would help us in our search for sleepers. Denita Lemmon at Miller Dunwiddie now handles Foster’s legacy projects, including our museum.

As she and her team were looking through our building information, I decided to see if the sleepers were running east-west rather than north-south. I took the trusty drill, measured 16 inches over from the south wall, and drilled a 1/4-inch hole. And, lo! The drill bit did not break through into open space! It was drilling into solid wood all the way down. Emboldened, I drilled three more holes, one more on the same east-west line to ensure the sleeper was running that direction, then two more 16 inches north of that. I hit sleepers with all 4 holes and also smelled cedar as I was pulling the bit up. Erik said it would make sense if the sleepers were made of cedar because it is rot resistant.

Blue tape grid to help us find sleepers. We drilled 5 holes before striking the first sleeper. The additional 3 holes confirmed the east-west orientation of the sleepers. The Charles A. Weyerhaeuser Memorial Museum, 2019.

Blue tape grid to help us find sleepers. We drilled 5 holes before striking the first sleeper. The additional 3 holes confirmed the east-west orientation of the sleepers. The Charles A. Weyerhaeuser Memorial Museum, 2019. We put steel wool in the holes to keep critters out. These holes will all be filled with wood plugs and finished to match the floor.

As soon as I had completed my hole-drilling, I received an email from John Mecum at Miller Dunwiddie. He suggested we have a company use ground penetrating radar on the floor to find the sleepers. While I was pretty sure I had found the first two, I wanted to confirm my findings without drilling more holes, so we contracted with American Engineering Testing, the firm John recommended for ground penetrating radar.

On July 26, 2019, Brandon Mikelson from AET paid a visit with his handheld ground penetrating radar (GPR) machine. He said that it can be difficult to get readings from wood using GPR and he had to use the sleeper holes I had drilled in order to calibrate his machine to find the rest of the sleepers. (Which made me feel better about drilling these holes prior to hearing back from the architect.) He ran down the length of the room and marked the sleepers using blue tape. Wouldn’t you know it? The sleepers all ran east-west and were 16-inches on center, regular as regular could be.

Brandon Mikelson from American Engineering Testing, Inc. using ground penetrating radar to find sleepers under the floor in the Z.N. Barnes Room at The Charles A. Weyerhaeuser Memorial Museum, July 26, 2019. He is marking the sleepers with blue tape as he finds them.

Brandon Mikelson from American Engineering Testing, Inc. using ground penetrating radar to find sleepers under the floor in the Z.N. Barnes Room at The Charles A. Weyerhaeuser Memorial Museum, July 26, 2019. He is marking the sleepers with blue tape as he finds them.

As long as Brandon had his machine handy, we had him check for the sleepers in the other 3 rooms in the museum that have wood floors, the Rosenmeier Research Room, the J.C. Patience Room, and the Z.N. Barnes room. All of them have their sleepers running east-west, perpendicular to the floorboards.

Sleepers marked with blue tape in the Archives at The Charles A. Weyerhaeuser Memorial Museum, July 26, 2019.

Sleepers marked with blue tape in the Archives at The Charles A. Weyerhaeuser Memorial Museum, July 26, 2019.

Because the sleepers are oriented east-west, the placement of the rails on the mobile shelving doesn’t have to line up perfectly with specific sleepers because the rails will be running across the sleepers and will thus be properly supported the length of the Archives.

And that’s how you find those elusive sleepers.


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