Cement Attic Floors


South attic.

Many Longwood Gardens employees and volunteers who have access to the nooks and crannies of the Peirce–du Pont House are puzzled to find a cement floor in the south attic over the old part built by the Peirces in 1730. Why would anyone put such heavy material over a living space? Everyone seems to have a theory and all are different.  Certainly someone at Longwood Gardens knows for sure, but I have not yet found them.  Meanwhile, I am free to speculate on my own just for fun.

For a while, a window sash was missing from an attic dormer window that was noticed by an occasional observant visitor. We were told to tell them Longwood management was aware of the situation, and that rain coming in would do no harm, no doubt because the cement floor would not warp or rot. That’s the advantage of cement. I suspect the sash was purposely removed to provide ventilation from the outside through the doorway that opens into the third-floor balcony overlooking the central conservatory.  (I was standing in that doorway to take the photo above.)

When I did a Google search on cement attic floors, I found they were not as unusual as I expected. Several references were questions from people living in very old houses who were asking how to insulate a cement attic floor.  (Answer: not easily.) After my shift, I went up to the attic with my flashlight to investigate further.  (I am using “cement” and “concrete” interchangeably, but I think it is all concrete for strength and economy.  “Cement” was used in the Google references.)

Around the opening of the stairs going up, I could see the edge of the cement, covered with wood molding, which appeared to be a couple of inches thick. The slab seems to be bonded tightly to the brick walls on the sides. (I was looking for a slope and a place for drainage.  I found neither.)

The roof over all of this is of wood shakes, but there is no underlay of plywood or tar roofing paper. (I am using the common meaning of “shake” for wooden shingles. “Shake” properly refers to the horizontal boards the shingles are nailed to, prominent in the photo, not the shingles themselves.) Looking up, I was seeing the underside of the shakes which fit together very accurately. No sunlight came through any cracks. Wood shakes are expected to swell as they get wet, closing off any cracks, but I could see no cracks even on a dry, sunny day. The shakes were recently replaced and still look new on their underside.

So, my theory is that the cement floor is really part of the roof system. Small amounts of water are expected to get through the shakes where it simply pools on the floor as on a sidewalk. The water soon dries with a little ventilation.

The floor, presumably dating from the original construction in 1730, has no visible cracks, although they may have been repaired when the House was repurposed as a museum and office space in 1995. (On the photo. you can see the Y-shaped steel cables added at the restoration to keep the north-south walls from bowing out. The square of railings on the right are around the tightly-wound stairway coming up from the floor below.)

Cement must have seemed high-tech in those days before waterproof plywood, Tyvek, water-impermeable polyethylene sheets, and even simple tar paper.  Pouring all that by hand up on the third floor must have made for a busy and exhausting day.

My next step is to go up again with a level and examine the edge more thoroughly. Is it tilted to one side to drain off any water that accumulates more than a puddle? If I am ever there during a downpour, I will certainly go up to see what is happening.  I will take a small brush to see if it is properly concrete (cement with stones) as I would expect from the thrifty Quaker Peirces.  I would also like to know if the cement was poured over a wooden sub-floor.  We occasionally get visitors very knowledgeable about old house construction, and I will discuss it with them.  Part of the fascination of old houses is guessing what is original construction and what has been renovated even a hundred years ago.

I will also look for books on old house construction.  I do not believe the features of the Peirce House, as it was then in 1730, were unique.  Building a house by hand with a family waiting is no time for experimentation.

Maybe I should call Dave Hall from our class.  He became a successful architect in St. Paul.  His specialty was designing jails, so he must know a lot about cement.

W. C. Fields once said, “Women are like elephants.  I like to look at them, but I wouldn’t want to own one.”  I feel the same about old houses.  Volunteering at Longwood’s Peirce-du Pont House is perfect. I feel as if I own it, but I am grateful not to. I am encouraged to explore all over it, but I am never expected to fix anything or even pay for any maintenance.

Sometime this summer, I hope to visit the Owen House in Lansdowne (see posting) that was also built in the 1730s, and see if I can find out about their roof, although from the photos, it seems now to be of standard three-tab asphalt shingles.

I would be glad to hear from anyone with special knowledge of very old house construction.


About Roger Walck

My reasons for writing this blog are spelled out in the posting of 10/1/2012, Montaigne's Essays. They are probably not what you think.
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