Yesterday we began building the main stairs at Mission of Hope, our first permanent concrete stairs. Like all ‘first days’ of a new phase in the work, it goes very slow and the miscommunication is rampant. It takes us about three hours to determine where the stairs will start and stop, which we determine by measuring along the beam at the first floor slab and then dangling a straight 2×4 to the transit mark at the ground floor slab. Haitians seem to have a predisposition for taking measurements and suspending building elements, just as they determined the initial square of the building by floating a framing square. It seems sturdier to me to measure things from ground up. Perhaps they do not trust the solidity of the ground, or they like the challenge of establishing equilibrium and plumb in space, or maybe they just don’t like to crouch down. In this case the method, however precarious, yields a result I consider exact enough. We determine the total height of the stairs to be 10’-3 ¾”, only a quarter inch off our ‘drawn’ dimension of 10’-4”.
There are two factors that determine the comfort level of climbing a set of stairs. The first is the relationship between the vertical face of each step, the riser, and the horizontal plane where we place our foot, the tread. These must lie within a proportional range; the steeper the rise, the narrower the tread. Monumental stairs have long treads, as much as 14”, but very shallow risers, as little as 4-1/2”. Steep service stairs can have risers as tall as eight or nine inches, but the treads must be correspondingly narrow for any comfort. The rule of thumb architects use is rise times tread equals 72+/-.
Seven in eleven are the most common stair dimensions in the United States. I want to use 11” treads on the main stair at MoHI, narrower treads are not advisable for exterior stairs and we don’t have enough space to make them more grand. Since I have to cover over ten feet of vertical distance, I could make 17 risers at a hair over 7-1/4” each or I could make 18 at 6-7/8” each. The shorter rise will be both more comfortable and more appropriate for a school full of children.
The second factor in stair comfort is that all the risers be exactly the same height. The human gait can differentiate changes in riser height as little as 1/8”. Uneven stairs force us to look down and concentrate on our feet, rather than allowing us to ascend stairs with grace and certainty. Stairs in Haiti are notoriously erratic, and if Renee has made one firm demand this project, it is that she wants perfect stairs.
I explain to the carpenters how I want us to create the ‘reverse’ formwork on the inside face of the stairs, where they meet the vertical wall. This goes over easier than I expect and within a few minutes they have tacked bits of 11” x 6-7/8” plywood cascading diagonally along the block wall. Now I have a problem. There is nothing wrong with that they are doing, but the opportunity for small mistakes is great. If each plywood rectangle is only 1/16” inch off, I will have a one inch discrepancy by the time I lay out the entire stair. I fetch Renee, whom I rely on for the most subtle translations. I tell the workers that what they have done is not wrong, but is more prone to cumulative error than cutting multiple stair teeth out of large pieces of plywood. Words like ‘cumulative’ do not exist in Creole. Finally we say that what they have done is good, but if we use larger pieces we will be ‘plus exactement.’ They seem to buy that idea.
Now I get a full sheet four foot by eight foot plywood sheet and score it in 6-7/8” increments along one line, not by measuring 6-7/8” over and over again, but by measuring from the same datum 6-7/8” and 1’-1-3/4”, then 1’ 8-5/8”, etc. and repeating with 11”, 22”, 33”… in the opposite direction. Datum dimensions are more accurate in total than sequential dimensions. I am not sure if the workers go along because they understand the benefit of what I explain or because they are humoring me, but we lay out the first stair with only four separate sections of saw-toothed plywood. The second stair is even more accurate; we use only three pieces. When both sets of opposing risers are outlined against the walls we verify level across the future landing between them. Everything is quite square. Other work goes on in the meantime, but these two lengths of formwork are the major accomplishment of six men over the better part of two days. We may be getting better at our work; but we are not getting any faster.