20 WOODEN CHURCHES IN VIKING AND

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WO O D E N C H U RC H E S I N V I K I N G A N D M E D I E VA L N O RWAY:
T WO G E O M E T R I C A N D S TAT I C S T R AT E G I E S
Jørgen H. Jensenius
The question of the ‘origin’ of medieval wooden churches has not yet been
solved. It may be because the question is vague, because answers are thoughts
which do not carry the weight of arguments, or that facts are seen isolated from
contexts. In the available literature it has been claimed there was a sudden leap
from posts set in the ground to staves placed on the ground, to prevent moisture damage to the posts/staves. To question the claimed relation of cause and
effect, this paper describes two foundation strategies. Geometric and static consequences for the superstructures are discussed, and I ask how roof spans and
loads affect the choice of footings.
Background
It has been assumed that Norwegian craftsmen – accompanying Viking wintering expeditions in central Europe – designed transportable and easily assembled buildings. 1 With the evangelisation of Norway, foreign customs and attitudes came to influence local ways of thinking. Travelling craftsmen brought
with them knowledge of how to plan, design and prepare buildings; the clergy
may have proposed what they were accustomed to. 2 The Church was protected
by the king, who governed by force and fiat. One could become a church owner by inheritance, by purchasing property with a church standing on it, or by
building a church oneself. Landholders ordered churches to be built on their
demesnes and paid for the work in order to legitimise their rule and prove their
loyalty and faith to the bishops and kings. 3 Gradually the administrative project of establishing bishoprics produced results. Estimates give a figure of more
than 2,000 wooden churches in Viking and medieval times in Norway. The vernacular vocabulary of suitable wooden designs had to be adapted to ecclesias-
Fig. 1: Oseberg chamber,
dated to 834 (University
of Oslo: Museum
of Cultural History)
tical specifications. The nineteenth-century art historian Lorentz Dietrichson
named 322 wooden churches; for him all seemed to be ground-set buildings. 4
Church planning and design
There is no specification in the New Testament for a
sacred space. Descriptions of a sacred space in the
Old Testament are reinterpreted by Paul as the
assembly of true believers in Christ. 5 A thousand
years later, there was no universal blueprint for
building wooden churches – planning seems to have
been a mixture of conformity to tradition and local
diversity; design followed need, funding and the
properties of the materials. The building process
was not secret, difficult or mystical: If there was a
‘trade-secret’, it was the years of meticulous practice.
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Guiding principles were pragmatism and simplicity,
designs were shared by rules of thumb, and orally
and visually through the apprentice system. General practice was known and the details may have
been easy to learn and remember. 6 The building
and its parts were shaped by measures and ratios,
without resort to Euclidean theory. 7 Some ratios
can be reconstructed, but theoretical assumptions
and how the design was understood is probably lost
in history and irretrievable.
The function of a church is liturgical practice, and
a variety of local buildings may have been accepted
as potentially suitable. Buildings made of wood or
stone, large or small, earth-fast or ground-set, wattleand-daub or palisade construction were all consecrated in northern Europe. 8 Abundant and readily
available in Norway, pine (þelliviði; Pinus sylvestris)
could be locally sourced and delivered quickly. An
embedded footing is termed earth-fast, an independent one is ground-set. In terms of durability, performance and cost, the earth-fast construction may
have been seen as a viable concept of church building for hundreds of years.9 Many problems are associated with wooden building designs, relating to thermal breaks and leaks,
Fig. 2: Map with earthfast churches
water penetration, moisture and freeze/thaw cycles. Direct or indirect traces
of some twenty-five presumably earth-fast churches have been documented in
Norway over the last 60 years; roughly dated as from the year 1060 and later.
All that may be left are pits with a bottom stone, infill and the lower stump
of a post. In addition, negative forms of building remnants like post-holes, impressions of door posts, wall plates and flooring can be traced. Yet, even from
meticulously documented foundation remains one cannot deduce the original
superstructure of the buildings. Valid insights and formulated hypotheses by
a building archaeologist notwithstanding, any description of missing parts of
a church building will be nothing but speculation without tangible evidence.
Fig. 3: Drawing, pit with
post
Earth-fast churches
On the building site the oriented ordinates stipulating walls were marked on the
ground. A typical building would have a series of roof-bearing posts along its perimeter, set into pits. If the ground was soft, pits could easily be excavated, but
it could not support heavy earth-fast posts and so settling could occur. On the
other hand, stony ground would prevent transmission of the load through the
posts to a deeper soil stratum to avoid uneven frost heave or thaw weakening in
spring. The inevitable spoils from the pits could easily damage markers, making
it difficult to verify the accurate placing of posts, as may be deduced from excavation plans. 10
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To prevent settling and avoid moisture and fungi from attacking the wood, it
was necessary to ensure drainage for water run-off by putting sand and a stone
slab at the bottom of the pits which would act as a moisture-resistant barrier
and by charring the end of the post. Later, roof overhangs may also have been
created for the same reason.
No precise levelling may have been done in the pits, so the top of the posts
would be at slightly different elevations. To help keep the post plumb after
erection, its lower end was fixed by bracing with heavier stones, before being
packed tight with backfill of smaller stones and earth.
Fig. 4: Post-hole Høre
The use of 89 bracing stones has been recorded in 160 excavated post pits
in Norway. A post with a diameter of 0.3 m and a length of 5.0 m weighs in
excess of 280 kg. Even with considerable bracing a depth of 0.3 to 0.9 m will
not give the posts lateral stability. When a church was disassembled, the posts
might be lifted from the pit, leaving behind post-holes, negative impressions
in the rammed infill. As I have shown elsewhere, preserved fragments of 66
posts from 17 excavated churches have diameters or width of 0.2 to 0.4 m. 11 The
cross-section can be squared, rounded or rectangular, although the shape above
ground may have differed. Empty post-holes in Kaupanger II, Eidskog, Høre I,
Ringebu I and Bø I indicate that posts were lifted out when the building was
disassembled.
Builders may have preferred to work with right angles, but, despite adjustments
to make a better fit, the posts would often have been placed with undesirable
deviations from the planned design. To nullify differential settlement and variation in centre distances and alignment, short, adjustable wall plates may have
linked the posts. Therefore to make the wall a rugged construction, lateral stability in all directions was provided by inserting tie beams and diagonal braces
Fig. 5: Arson in Fantoft
Stave Church 1992
at the upper ends of the posts. Even if excavations in Norway have not revealed
wooden floors in earth-fast buildings, we cannot rule out suspended floor solutions. A tamped earthen floor is cheap, would require little transport and produced no waste which
could rot. Substrates of pebbles and sand would act
as a capillary break from moisture in the ground.
A floor may be flat even if tilted. A slightly sloping
earthen floor was perhaps regarded as merely a minor inconvenience. An earthen floor is easy to fill in
and smooth over after an indoor burial. Accumulation in floor level may gradually have covered the
lower part of the sills. As time went by, thresholds
had to be raised and doors trimmed. Local conditions of climate, maintenance, demography, economy, use and abuse and changing requirements
made the durability of the embedded posts difficult
to anticipate. A church had to be replaced when it
was burned or swept away by inundation, landslide,
avalanche or heavy wind.
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Fig. 6: Post-hole
and raft beams in Lom
Fig. 7: Uvdal Stave
Church
Another reason to replace a church was when maintenance costs equalled the
expense of rebuilding. This could explain why the earth-fast buildings at Urnes,
Mære and Kaupanger were replaced by others with similar foundations and area.
The earth-fast design may still have been appreciated as a time-honoured viable
church concept. Liturgical practices could change with little impact on the fabric of a building, except where nave and altar room had become too narrow for
practical use. Earth-fast churches in Lom, Høre, Ringebu and Kaupanger were
replaced by ground-set buildings in the later 1100s, at the same time as earthfast structures in Mære, Bø and Kinsarvik were superseded by stone buildings.
When the Archbishopric of Nidaros was established in the years 1152–53, the
options available were small earth-fast, ground-set and stone churches, medium
ground-set and stone churches, and large stone churches. None of these solutions is objectively better, though they may all have been appreciated as adequate constructions in their own way. In spite of foundation variants of old and
new, buildings had a common base in design and craft, in social and economic
practice. Earth-fast construction may have continued alongside ground-set for
a long time, and both are still in use for certain purposes today.
Planning the ground-set church
A tall roof was not prescribed liturgically nor was it a requirement for the practiceof faith. Grand loftiness in a church may have been seen as a cultural asset, a
social want, a powerful political sign or have been inspired by the architecture
in vogue.
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To prepare for a new edifice on a site, the builders
had to refill older pits, then level and compress the
ground. On a stony site, embedding posts evenly
could be difficult; one solution was to reduce the
number of pits. This, it was hoped, would prevent
differential settlement of the building from heaving and thaw weakening in frost-susceptible soils
during the spring.
The roof is a sloped structure transferring loads
to the walls below. The first measurements set out
on the site would be the span of the central roof;
the ratio of span to height in known churches gives
the gable an angle of 55–58°. A heavy-duty base was
required to support such a superstructure with substantial weight and a substantial potential overturning moment. The roofing was thus the cause
and the ground-set footing an effect.
Fig. 8: Borgund Stave
Church, roof
The ground-set footing
The builder would set out coordinates for the pits. A pit was dug for the first
bed stone in the nave, to provide adequate transfer and distribution of building
loads to the underlying soil. Three more pits were dug and the other three bed
stones were roughly placed and adjusted to the same level. The four bed stones
would, in rugged terrain, provide fulcrums for a solid cut lumber floor, a levelled
rectangle of four raft beams of equal thickness.
Thus the raft beams had an independent bearing and did not hang on the sill.
On the contrary, the beams extended out to carry the outer wall sills and thereby keep the walls together as well.
The floor
Fig. 9: Bed stone and raft
beams
To install the roof, a flat base surface has to be provided, upon which upright
staves can be secured, spaced apart in rows. Simple spanning half-round timbers
were laid flush with the beams, usually without floor joists. Underneath was
the crawl space, an underfloor space that was not habitable. As a structural system, the floor would have an adequate capacity to resist lateral loads by constituting a horizontal diaphragm, being a spread footing. Prior art differs substantially from this solution. The floor would be the reference plane, the working
platform, from which width and angular base dimensions were derived, both
horizontally and vertically.
All components had to be built to required standards; the floor was level, staves
were plumb, joints were tight, and finished dimensions were as planned. The
predictability of the position of joints made it possible to measure, cut and finish
most elements of stave churches in advance, prior to the assembly of the parts
and erection of the building. Critical connections are where the roof system
connects to the supporting walls, where walls connect to each other, and where
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walls connect to the foundation. To assemble the centre volume, heel tenons in
the staves were inserted into cut-outs in the surface of the raft beams. When
erected, the staves would be kept in line at the same level, with even distances
in two directions. Scribed lines, cut-outs and pegs would give permanent relative
positions of elements and datum points for joints at any horizontal cross-section in the vertical plane, including the roof framing. Structures could then be
located in reference to the floor and the nearest intersection of the arbitrary
axes. It seems from Lomen Stave Church that the carpenters made use of a predetermined modular dimension. When initially marked in the floor, it would
give the spatial relationships between the parts, and their absolute dimensions.
Ratios thus defined may be either rational or irrational; dimensional accuracy
would generally be highly self-consistent.
In addition, sequences of dimensions, determined as multiples of an elementary modular unit, are explicitly incorporated following a prescribed formula.
This method would give approximation of some irrational proportions, using a
direct geometric construction as the initial design basis. This coherence is documented and discussed elsewhere, in an analysis of Lomen Stave Church. 12 In
the centre of the nave only limited shear reinforcement was required to make
the construction sideways resistant. Open bays between the columns were
Fig. 10: Borgund Stave
Church, protecting
gallery
Fig. 11: Borgund Stave
Church, floor
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created and internal adaptability was provided. To ensure that the incomplete
structure was stable during assembly, the erection had to be carried out in the
right sequence. Staves were kept in plumb with bracing elements like props,
brackets, knee brackets and diagonal braces. In all four walls in the centre room,
‘St. Andrew’s Crosses’ of braces between the upper and lower wall plate function
as lattice girders.
The outer walls transferred lateral loads to the frame through in-plane shear
stress, secured by braces. There are still 28 medieval ground-set wooden churches left in Norway. Some of them have been described, like Kaupanger, 13 Nes, 14
Lomen 15 and Urnes. 16
Conclusions
Rafter span may have been cause, and choice of footing the effect, for the design
of the high-rise construction of the ground-set churches. The parallel traditions
of footing constructions may have been looked upon as good solutions in their
own right. The earth-fast footing was probably gradually replaced by the groundset approach in wooden churches after the year 1100.
325
324
164
355
356
16
3
501
Fig. 12: Elevation of
Lomen Stave Church
Fig. 13: Borgund Stave
Church, nave, north-east
corner
502
27
Notes
1 Chouquer, G., F. Favory, Les arpenteurs romain. Théorie et pratique, Paris: Éditions Errance,
1992; Lucas, A.T., ‘The Plundering and Burning of Churches in Ireland, 7th to 16th Century’,
in: Rynne, E. (ed.), Essays in Commemoration of Monsignor Michael Moloney, North Munster
Studies, Limerick: Thomond Archaeological Society, 1967, 172–229; Keynes, S., ‘The Vikings in
England, c.790–1016’, in Sawyer, P. (ed.), The Oxford Illustrated History of the Viking, Oxford:
Oxford University Press, 1997, 48–82; Zimmermann, W. H., ‘Pfosten, Ständer und Schwelle
und der Übergang vom Pfosten – zum Ständerbau – Eine Studie zu Innovation und Beharrung
im Hausbau’, Probleme der Küstenforschung im südlichen Nordseegebiet, 1998, 25: 9–241.
2 Higham, R., P. Barker, Timber Castles, London: Batsford, 1992; Milne, G. (ed.), Timber Building Techniques in London c.900–1400, London & Middlesex Archaeological Society, Special
Paper 15, London, 1992; Shirley, E. A. M., The Construction of the Roman Legionary Fortress
at Inchtuthil, British Archaeological Reports, British Series 298, London, 2000; Jungmann,
J. A., The Mass of the Roman Rite, I–II, Dublin: Four Courts Press, 1950/1986.
3 Wood, S., The Proprietary Church in the Medieval West, Oxford/New York: Oxford University
Press, 2006, 918.
4 Dietrichson, L., De norske stavkirker, Christiania: Alb. Cammermeyer, 1892, 96–97.
5 I Corinthians 3:16.
6 Coyne, R., A. Snodgrass, ‘Is Designing Mysterious? Challenging the Dual Knowledge Thesis’,
Design Studies 12, 1991, 3: 124–131 (129ff).
7 Shelby, L. R., ‘The Geometrical Knowledge of Medieval Master Masons’, Speculum, 1972,
47: 395–421; Evans, G. R., ‘The “Sub-Euclidean” Geometry of the Earlier Middle Ages, up to the
Mid Twelfth Century’, Archive for History of Exact Sciences, 1976/77, 16: 105–118; McCade,
J., ‘Problem Solving: Much More Than Just Design’, Journal of Technology Education 2, No. 1,
1990, 28–42.
8 Meeson, R. A., C. M. Welch, ‘Earthfast Posts: The Persistence of Alternative Building
Techniques’, Vernacular Architecture, 1993, 24: 1–17; Zimmermann, W. H., 1998.
9 Ahrens, C., Die frühen Holzkirchen Europas, Vol. I–II, Stuttgart: Konrad Theiss, 2001.
10 Jensenius, J. H., Trekirkene før stavkirkene. En undersøkelse av planlegging og design
av kirker før ca. år 1100, Con-Text 6, Oslo: Arkitekthøgskolen i Oslo, 2001, 91–100.
11 Ibid., 121–171.
12 Jensenius, J. H., Lomen stavkirke. En matematisk analyse, Oslo: Riksantikvarens Skrifter
5, 1988, 25 ff.
13 Bjerknes, K., H.-E. Liden, ‘The Stave Churches of Kaupanger’, Norwegian Antiquarian
Bulletin, No. 1, The Central Office of Historic Monuments, Oslo, 1975.
14 Christie, H., Nes Stavkirke. The Stave Church of Nes, Riksantikvarens Skrifter nr. 3,
Riksantikvariatet, Oslo, 1979.
15 Jensenius, J. H., 1988.
16 Christie, H., Urnes stavkirke: den nåværende kirken på Urnes, Oslo: Pax, 2009; Krogh,
K. J., Urnesstilens kirke. Forgængeren for den nuværende kirke på Urnes, Oslo: Pax, 2012.
All illustrations are by the author except where noted.