Cross section of the main house.
Cross section of the main house and the house at the back.
The outside wall facing the alley, showing the iron cross ties.
View into the small inner court at the back of the building.
Since Amsterdam is located on a bog, houses are built on a typical foundation of wooden poles. Long wooden beams, basically entire trees of 13 to 20 meters long, were drilled into the soil to reach the firmer sediment layer of sand. The poles were placed in pairs, next to each other, with a distance of 80 cm between the pairs. The poles have to be kept under water to maintain an anaerobic environment and avoid rotting. The water levels in the city have therefore always been carefully maintained. Heavy foundation beams were nailed on top of the poles, which were first cut at the same level. These formed the basis for the house.
On top of these beams, several layers of stone were built with loam (in Dutch ‘leem’). 5 to 6 layers of bricks were laid on top with a tough mortar of sand, and lime, with the purpose of blocking rising damp.
Then the walls were built in brick (Amsterdam bricks were 18/19 x 9 x 4.3 cm), using lime mortar. Walls were either 1 or 1.5 bricks thick (i.e. 18/19 - 27/28 cm). The walls were built up to the first level, where pine beams were placed to create the floors. What is exceptional in this house is that the beams were placed vertically on their shorter side, rather then laying flat on their wider side. This is unusual for the time period. It was known that beams placed this way were stronger, but beams were usually placed flat, in order to have a minimal loss of height. The exposed wood inside was later painted with linseed oil based paint. The beam heads were covered with tar to avoid wood rot. At the beam heads, iron cross ties were placed to counteract the natural outward bending of the brick walls and to create a strong joint between beams and walls. When reaching the intended height of the outside walls, the wooden roof construction was built. Last but not least, the roof tiles were put in place. Lead lined gutters and downspouts are used to deal with precipitation.
Until 1570/1580, oak wood was the type of wood used in Amsterdam for building houses, but by the time this house was constructed, oak was becoming scares and expensive. Softwood (pine) from the Netherlands, but also imported, was then gradually introduced. In the 17th century, oak wood was still considered superior and was therefore used in parts that are visible, in this house e.g. in the windows of the sael. Construction elements were built using pine. Sometimes pine beams were used, which were covered with oak – this was done in the cassette ceiling in the sael.
The brick walls were not plastered on the outside. At the back of the houses on the Heintje Hoekssteeg is a small inner court – its outside walls are plastered. On the inside the walls were as normal in those days plastered with lime plaster. The original plaster survived in the sael.
First form of central heating in the church (located in the fixed benches for dignitaries) .
Original stairs covered with new steps.
Canal room after restoration
Museum during the 2005 roof restoration.
Following is a brief list of known maintenance, repair and restoration work to the building in chronological order:
Damage to one of the beam heads
Condensation on the windows and consequent damage to the window sills
Canal houses in Amsterdam suffer from sagging (listen to the architect), because the poles have a certain amount of spring. Immediately after construction, the poles compress slightly, caused by traffic (historically these were carriages) and people walking, but also due to natural compression of the soil, which clings to the poles. The house on the Oudezijds Voorburgwal is built on the corner of an alley, the Heintje Hoekssteeg. Corner houses are prone to sag away from the corner towards the adjacent alley, in the direction of the long side of the building. On the outside one can often observe the walls of these corner houses curving out into the adjacent alley. This also happened to this building, but the deformation was treated during the restoration in the 1950’s.
There has been an issue (first mentioned in the 1970’s) with the rotting of beam heads in the north wall of the building at the church’s third level floor (the 6th level of the building). The wall at this level is exposed to the weather (there is no connecting building at this level). No other rotting has been found in other walls except one with an obvious rain infiltration problem. The beam heads were impregnated with an epoxy resin, the walls were stuccoed and painted. The reason for this rotting might have been twofold, but which of the following reasons is the most likely cause of the damage remains uncertain:
The windows in the building are single pane. In winter, there is often condensation on the inside of the windows, resulting in rapid decay of the window sills.
Sheets of lexane have been installed on the inside of the northeast and southeast facing windows in order to reduce UV levels and also as a protective measure against burglary and to avoid damage by broken glass in case a window is smashed in.