The church Jan Hartman had installed in his house from 1661-1663 required major building work. Just imagine what it must have been like to adapt the existing attics into a church that could accommodate a congregation of 150 people and to remain hidden from the outside.
Lamp of God, hanging from the opening in the ceiling
church; additional beam along the long side of the first gallery (lap joint)
The structural floor beams carrying the floors of the 5th and 6th level were cut in the middle to create an open space in the center - 2.65 meters wide with galleries along three sides. The floor beams are fairly thick and strong as their original function was to carry the weight of goods stocked on these 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, because of the loss in height.
To increase stability of the galleries, beams were positioned along the long sides of the galleries, perpendicular to the original floor beams. Each long side has 2 beams joined together by a lap joint.
To prevent the galleries from flexing, 2 cast iron rods connected the galleries to the roof construction. These rods are positioned near the joints in the long beams, in order to reduce the load at these points. There are also 2 horizontal rods between each of the galleries (4 in total), their function being somewhat unclear. Some say that they moderate the sideway pressure from the outside walls and prevent sagging of the outside wall towards the alley. If this is true, then the rods only provide strength under tension not under pressure.
Grabowsky & Poort engineering firm, who carried out an assessment of the construction in 1988, argues however that the rods are ‘pressure rods’ – installed at a later stage, but possibly already during the construction of the galleries, to avoid the long beams positioned at the long side of the galleries from twisting.
The painted wooden and plastered ceiling has a 0.55 m diameter opening leading to the attic above. The ‘Lamp of God’ is hung from this opening. The opening was most likely used for ventilation.
Damage to the fixed wooden benches for dignitaries.
There is specific damage (recorded in a condition assessment in 2006) that appears to have been caused prior to the time the building became museum, when it was still in use as a church. Examples are the heavily worn away areas of wood in between the balusters of the balustrade and, to a certain extent, the abrasion of wooden floors. On the floor there is a built up layer of dirt in areas less walked over. In addition in several areas of the wooden floor there are modern nails, which were possibly used during events to tack down cabling. At present, the house rules forbid this kind of action. There are also signs that the handling of tripods and stands during events resulted in scratching of surfaces.
More recent damage can be observed in the severe abrasion of paint layers and build up of grime on balustrades railings and doorposts caused by people touching these elements for support as they walk through. Damage caused by bumping and scratching has resulted in localized paint loss or dents in surfaces.
The fixed wooden benches for dignitaries on either sides of the altar are not commonly used, but are still in use during events. The bench on the SW wall is shorter and narrower than the one on the opposite wall. Both benches show many signs of use: the wood is deformed and the balustrades are unstable from people pressing against them. There is paint loss, dents and scratches caused by use. The SW bench is especially unstable and the back seat of the bench is dislodged by people pressing their backs against it. This bench is also at a narrow pathway on the left hand side of the altar.
The slight bending and dipping of the galleries towards the altar.
The movement in the galleries caused by their own weight and when loaded with people is believed to be mitigated by the vertical tension rods. However the galleries dip slightly closer to the altar. One rod (near the altar, on the SW side) was broken at some point in the past. This damage was first noticed in the 1970’s and not repaired until 2001. At this location the SW 1st gallery is sagging more, which could be an indirect result of this damage. The gallery on the opposite side also has a bend, but to a much lesser extent. There is obviously some movement in the SW 1st gallery (recorded in a condition assessment in 2006) – the plaster underneath is crumbling away and there is damage to the beam heads.This movement may also be affected by traffic outside, especially heavy garbage trucks and street cleaning machines, which are believed to cause vibration in the building.
There has also 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).
The carrying capacity of the church galleries was reassessed in 2007 by the engineering firm De Prouw BV.
One of the balustrade on the first gallery (on the northwest side, close to the altar) was covered by a piece of leather and stuffing, attached to the railing. The exact purpose of this upholstery is unknown, but because it was in poor condition and badly damaged, it was removed in 2005. The upholstery may be reinstated during the forthcoming restoration of the church.