TIMBER FRAMING · 2020. 4. 23. · TIMBER FRAMING 233 SEPTEMBER Thfi24 15 2 2 Test-fitting and...

Rebuilding a Viking-Age Frame

TIMBER FRAMINGJ O U R N A L O F T H E T I M B E R F R A M E R S G U I L D

Number 133, September 2019

TIMBER FRAMING 133 • SEPTEMBER 201914

Denmark’s Largest Viking-Age Timber Structure Rebuilt

THIS is an account of my involvement in the ongoing reconstruction of a 9th-century mead hall at the Sagnlandet Lejre open-air museum, eastern Denmark. Since carpentry

work commenced in the spring of 2018, I have contributed over 2000 hours to this effort, subcontracting for carpentry firm Julius Nielsen & Søn of Copenhagen, specialists in historic carpentry with prestigious restoration projects to their credit, such as recent work on the Fredensborg and Amalienborg royal palaces.

Background Excavations led by Roskilde Museum in 1986–2009 uncovered rich archeological material from the late Iron Age, shedding new light on mythical records of a local prehistoric power center around Lejre, in eastern Denmark. Among the findings were the postholes of a 62m-long building that Sagnlandet Lejre received funding to rebuild in 2015 ($10.5 million from A. P. Møller og Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal and $1.5 million from Augustinus Fonden). The project also features a 21m-long longhouse in similar style, not presented here.

Postholes mark the essential plan of the original structure, but leave much to qualified guesswork (see also “Building Customs in Viking-Age Scandinavia,” TF 128). The reconstruction at hand incorporates as many pieces of the original puzzle as possible, while also satisfying modern building code requirements. Nonetheless, traditional joinery predominates, with the exception of a few lag bolts and steel rods.

The spectacular outer “hogback” shape leads to a rather challenging oak frame, its nine bents varying in size, from the 12m-wide central bents, 10m- tall to the ridge, to the smaller gable bents, 7.5m wide by 6m tall. All longitudinal members are curved —ridge beam singly, purlin and wall plates doubly—and span up to 10m between bents (Fig. 1).

A stave wall encloses this structure, similar to those at the Hedared church in Sweden and Greensted church in England, where thick

So his mind turned to hall-building: he handed down orders for men to work on a great mead-hallmeant to be a wonder of the world for ever. —Beowulf

Olle Malling

1 Wall plates installed. Joinery in the upper ties awaits purlin plates of similar double curvature.

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15TIMBER FRAMING 133 • SEPTEMBER 2019

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2 Test-fitting and predrilling a bent in the workshop.

3 Positioning a bent on the floor layout prior to horizontally scribing the upper tie beam—lower interrupted tie beams have already been joined to the posts. A makeshift battering ram beats a stubborn stick.

4 Chalk lines on the floor define key references of the timber frame, typically top and outside faces. When laid up on the floor, smaller timbers are centered on larger ones. One could say the reference plane is centered, rather than locating one or two faces of timbers, as in the square rule system. However, a rough position within, say, 5mm of center will do. Snapped centerlines on timbers are not strictly necessary; no joinery in this frame is marked from such lines.

5 Facade post in bent, slightly rotated in the layup to match outer wall curve.

vertical planks, with either tongue-and-groove joints or loose splines between, are tenoned into a groove in the beam spanning above them. Oak shingles clad the roof. All timber—from around 200 oak trees (Quercus robur) and a few large Douglas fir (Pseudotsuga menziesii) for the ridge beam and purlin plates—were sourced and milled locally on Zealand, Denmark’s large eastern island.

In the shop The layout of this frame was done with full-scale lofting on the shop floor (known in Denmark as opsnøring), with measurements from a set of drawings. Timbers were positioned and scribed directly from these lines. The majority of the layout, cutting, and test-fitting happened in a workshop space large enough to mark

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Magnus Frimer-Larsen


Magnus Frimer-Larsen Magnus Frimer-Larsen


6 Raking timbers buttressing the assembled building.

7 Separate test-fitting of facade post and raking timber.

8 Ridge assembly layup—plywood triangles fixed to the layout floor facilitate positioning of curved ridge beam.

9 Horizontal line transfer—tie beam positioned at correct height, but a known “drop distance” away from the post. A strip of hardboard is cut to this drop distance in width, typically 20–40mm wider than the tenon length, and held up against the post to mark the shoulder cuts on the beam.

10 Scribing curved braces vertically with straightedge and spirit levels. I prefer using a plumb bob for improved visibility.

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Ole Malling


Ole Malling




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half of the building’s plan on the floor at once. Certain parts of the structure, nevertheless, were fabricated on-site, scribed and fitted directly into the partly installed building.

The nine bents each have a single reference plane to orient their principal members. The floor layout for each bent also includes reference lines such as top of tie beam, outside of posts, etc. (Figs. 2–4). Only facade posts break out of these reference planes, rotated in the layup to match the outer wall curve (Fig. 5).

Each raking timber (see Figs. 6 and 16) buttressing the wall joins a facade post. Even where facade posts are located in bents, however, raking timbers were not included in bent layups, as they stand perpendicular to the wall, not in line with the bents. To avoid stacking them awkwardly to achieve the correct angle, they were instead joined to facade posts in separate layups (Fig. 7).

Though curved, the entire ridge assembly—kingposts, braces, and ridge beam—was also situated in one (longitudinal) reference plane, allowing standard layup, scribing, and test fitting on the floor layout (Fig. 8).

The substantial section of most members (posts and upper tie beams are 400mm x 400mm) encouraged us to avoid stacking timbers where not necessary—scribing horizontally rather than vertically. Apart from reducing the amount of heavy material lifting, a benefit of this choice is that the timbers do not bear on each other and can be knocked around one at a time without affecting the entire layup.

For precise scribing of irregular hewn faces, horizontal line transfer was accomplished with hardboard strips of a certain “drop distance” width—matching exactly the distance an edge has to travel to arrive at its reference line on the floor (Fig. 9). The distinction between vertical and horizontal transfer, as well as the line transfer marking method, are thoroughly described by Ulrik Hjort Lassen in “The Invisible Tools of a Timber Framer” (see also “A Carpenter in the Academy,” TF 129).

Scribing members one at a time requires multiple test fittings, but allows for a bit of “independent” kerfing in between steps. This reduces the risk of error from scribing an entire assembly at once. Braces were scribed in vertically, using either a spirit level or a plumb bob. Either way the technique is the same: registering the shape of a face against a plumb reference and transferring it onto another piece to define the adjoining shoulder (Fig. 10).

11 Neatly scribed shoulders on a curved brace. The timbers were delivered with a hewn finish on visible faces.

12 Wall plate being stacked and connected to interrupted tie beams, positioned in plan and elevation. Due to space limitations, the floor layout comprised only half of the building’s plan and longitudinal framing was developed in two mirrored halves. The traditional scarf joint specified for the wall plate, called uforkilet skråt hageblad in Danish, is not wedged, has square abutments, and was fixed with lag bolts on site.

13 Purlin plates in the making. Upper tie beams are positioned in plan and elevation relative to the floor layout, the purlin plates stacked on top and vertically scribed to the ties. Scarf joints are placed at the tie beam intersection, and the entire assembly—purlin plate scarf joint, tie beam, and post—bolted together with barrel nut anchors.

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Ole Malling



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14 Aisle brace layup (here, for the 21m-long longhouse). Braces positioned at an estimated angle to follow the doubly curved purlin plate. The purlin plate end is left wild for on-site marking with jigs.

15 Chainsaw joinery.

Diligence in scribing really does enhance the results—these hewn timbers are not only highly irregular, but also of such large dimensions that drawboring cannot fix much if the fit is sloppy (Fig. 11).

The wall plates are doubly curved, sawn to shape in conversion. We tackled joining them in a two-step process, first scarfing together one continuous piece, then connecting it to the lower, interrupted tie beams (stikbjælker) with cogged joints (Fig. 12). The same process was used for the large purlin plates, also doubly curved, lapped into the upper tie beams (spændrigler) (Fig. 13).

Doubly curved timbers require a “three-axis layup,” in which members are positioned at specific heights as well as horizontally on the floor layout, where bent fabrication requires only a two-dimensional reference plane. Though more involved, this is not complicated, as the heights of relevant bent members (lower and upper tie beams, as they meet the doubly curved longitudinal members in question) are already set out in the bent floor layouts. These bent members are thus positioned in plan and elevation, leveled on a level mark defined during the prior bent layup (to preserve the fit of existing joinery). Longitudinal members are then positioned offset above and vertically scribed into the bent members.

While conceptually straightforward, this approach has the obvious disadvantage of requiring the painstaking knocking around of big timbers, sometimes stacked at considerable height, to hit the correct position in space. As a result, this becomes a rather time-consuming step, the average layup taking about as long as the scribing and cutting of the involved joinery combined.

Again, however, this is a working method with a low risk of error. Apart from heights, no measurements are in play—and even heights might just as well be marked from the bent floor layout directly onto a story pole, further reducing the risk of miscommunication. With lengths tangibly defined, and plumb and level as the only other references, what you see really is what you get. Potential errors should be clearly visible before any marking, let alone cutting, is done.

Note that, while faces level in the bent layup turn plumb when installed, in this longitudinal layup all members are oriented as in the final configuration.

Tackling the longitudinal aisle braces in the workshop would have required another large layup of the curved aisle “wall frames,” which would have had no other purpose than fitting these braces, as all other members involved were already finished. Aisle braces were therefore joined only to aisle posts—canted an estimated angle—with the purlin plate end left wild for later on-site marking and cutting (Fig. 14).

The substantial volume and scale of joinery made efficient cutting crucial, offering an opportunity to evaluate different tool setups. While circular saws, chain mortisers, and hand tools were in the mix, we ended up using electric chainsaws fitted with 14-in. or 18-in. bars for the majority of joinery (Fig. 15).

The chainsaw becomes quite a Swiss Army knife with practice. Besides cutting to any depth needed, it can pare shoulders down to a line like a chisel and plane surfaces rather smoothly. Scoring lines prior to cutting, to avoid tearout, can help achieve a high finish.

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a.b.

d. e. f.c.

h.i. k.j. g.

16 Structural overview, with Danish terms in parentheses:a. ridge assembly: ridge beam (rygås), ridge post (dok), braces (kopbånd)b. upper tie beam (spændrigel)c. purlin plate (mellemås)d. lower, interrupted tie beam (stikbjælke)e. aisle post (tagbærende stolpe)f. aisle brace (kopbånd)

g. interrupted sub-plates (hammerbånd)h. wall plate (fodås)i. raking timber (skråstolpe)j. facade post (facadestolpe)k. wall planks (vægplanker)

Photo: Ole Malling, graphics: Magnus Frimer-Larsen

Ole Malling17 Hammerbånd installation with the wall plate temporarily removed.


Perhaps most important, a chainsaw is not restricted to straight cuts indexed to flat surfaces like a circular saw, which was appreciated when working with roughly hewn surfaces. Its versatility makes the chainsaw fast: it saves switching cords, picking up and putting down tools, and adjustment of depth and angle settings. However, without the pauses between using different tools and the setup time for each, I find cutting joinery by chainsaw more fatiguing than with circular saw and chisel.

On-site When installation commenced in August 2018, the four months of prefabrication had left certain parts of the structure to be dealt with on-site, and some prefabrication continued in the workshop until October.

In principle, the potential of heavy timber frame prefabrication off-site probably has no limit. However, in a scribe-cut-prefit workflow, the time-consuming precise positioning of members prior to actual fabrication in the workshop has to be weighed against the benefits of often more effective on-site lifting equipment and working on a fixed, partly installed structure.

Hammerbånd, interrupted sub-plates (see Fig. 16), constitute an essential element in the stave wall system of this structure—the grooved lower face receives the tenoned end of wall planks, themselves matched with grooves and loose splines, and holds the wall in place. The hammerbånd are in turn tenoned into the facade posts on either side, and the facade posts are held in place longitudinally by the continuous wall plate.

To fabricate the hammerbånd, the ever-changing angles of plumb shoulder cuts along the curved wall had to be registered with the wall plate temporarily installed to firmly locate facade posts. Once the hammerbånd had been marked and cut, their installation required the wall plate to come off again (Fig. 17).

That the heavy wall plates were lifted three times during installation, in addition to many lifts in the workshop, leads me to suspect that some original tricks of the trade have been lost, or were

18Magnus Frimer-Larsen

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Ole Malling

18 On-site aisle brace scribing, phase one (picture from the 21m-long longhouse): With purlin plates temporarily fitted, jigs are attached to aisle posts. Battens are screwed to the jig, fitted tightly up against the purlin plate where the brace shoulders will go. A reference mark, like a “two foot mark,” registers the position of the jig on the purlin plate for the purpose of mortise layout.

19 Phase two: The purlin plate is lifted off, the brace is lowered into the jig, and lines for the shoulder cuts transferred from the battens. The distance between the point where the battens intersect with the brace (that is, its nosing) and the aforementioned reference mark is used to locate the mortise in the purlin plate.

20 Purlin plate installed on a pair of aisle braces.

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21 Rafter half-lap joints increasingly skewed toward the gables. The canting results from the rafters standing perpendicular to the wall plate (to which they are clamped prior to scribing) and tilting the rafter faces from plumb.

22 Positioning rafters prior to scribing birdsmouths. 21

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Ole Malling

overlooked here. Certainly, if nothing else, a craneless installation would have motivated alternative joinery solutions or procedure back in Viking-Age Denmark.

As noted earlier, longitudinal braces in the two aisle “wall frames” had only been joined to aisle posts, with the purlin plate end left wild for on-site marking and cutting. The purlin plate was therefore initially installed without braces. Jigs were attached to aisle posts at brace locations, and brace shoulder cuts were registered with battens fitted tightly against the lower face of the purlin plate, screwed to jigs (Fig. 18).

With the purlin plate removed, aisle braces could then be inserted into the jigs, and their shoulder cuts transferred (Fig. 19). Registering the point at which braces intersected the “shoulder battens,” the corresponding mortises could be precisely marked onto the purlin plate and conveniently punched out on the ground.

Again, the historical accuracy of this procedure is questionable, given the many “extra” crane lifts. However, using jigs in this fashion, directly transferring lines from one piece of wood to another, is an intuitive method with a low risk of error (Fig. 20).


On a regular gable roof, all cuts are worked out on the first rafter—the rest are duplicates. The “hogback” roof, however, has no identical rafter pairs—they vary in length and birdsmouth location, and are canted at different angles to keep the top faces in plane with the curved roof. Toward the gables, this canting generates radically skewed lap joints at the peak (Fig. 21).

These unusual rafters were fabricated in a four-step process. First, with half laps for the peak joint provisionally cut, rafters were located in plan of the roof, offset vertically above their final location. The skewed top joint was then scribed and cut in the air, often kerfed and repositioned a bit with winches attached to purlin plates to pull

rafters upwards (Fig. 22). Next, clamped firmly at top and bottom, rafters were vertically scribed to ridge beam, purlin plates, and wall plates (Fig. 23). They were then flown down, cut on the ground, and flown back up. Two carpenters produced and installed an average of 11/2 rafter pairs per day, out of 55 total.

Conclusion Facing the playful geometry of the drawings and truckloads of enormous timbers at first humbled us as much as Beowulf ’s warriors when “the timbered hall rose before them, radiant with gold.” I have outlined some of the processes that led our work from that point through the successful fabrication and installation of this frame, though careful positioning of its members and diligent transfer of their shapes sums up the development of this timber frame.

Positioning happens in the workshop, where segments of the structure are solved in isolation, guided by floor layouts and, in some cases, also elevations. Later on, this happens on-site with the installed structure at hand as the direct basis for further development.

Once positioned, members can be joined via direct transfer of their shapes. Whether the layup involves exotic measures or not, scribing is done at the level of individual connections—the overall complexity of the structure hardly spills over into this task.

The ways in which our Viking predecessors arrived at this generous building design, and how the curved geometry was practically developed at full scale, are outside the scope of this article, but I look forward to learning more from the archeologists behind the project.

At the time of writing we are still working on interior finish carpentry, and the opening date has not yet been announced.

—Magnus Frimer-Larsen

Magnus Frimer-Larsen is a Danish carpenter specializing in historic timber buildings. With experience timber framing in the UK and the American Midwest, he is involved in the newly formed Scandinavian timber framing network, Stolpverk Norden.

ReferencesHeaney, Seamus (trans.), Beowulf (London, Faber and Faber, 1999).Lassen, Ulrik Hjort, “The Invisible Tools of a Timber Framer—A

Survey of Principles, Situations and Procedures for Marking,” PhD dissertation, Department of Conservation, University of Gothenburg, 2014, https://gupea.ub.gu.se/handle/2077/35598.

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23 Scribing birdsmouths at the peak with a short spirit level.

See back cover for a photo of the massive scale of the hall, nearly complete.

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TIMBER FRAMING · 2020. 4. 23. · TIMBER FRAMING 233 SEPTEMBER Thfi24 15 2 2 Test-fitting and...

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