TIMBER FRAMING JOURNAL OF THE TIMBER FRAMERS GUILD Number 133, September 2019

Rebuilding a Viking-Age Frame 1

Olle Malling Denmark’s Largest Viking-Age Timber Structure Rebuilt

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

HIS is an account of my involvement in the ongoing Postholes mark the essential plan of the original structure, but reconstruction of a 9th-century mead hall at the Sagnlandet leave much to qualified guesswork (see also “Building Customs in Lejre open-air museum, eastern Denmark. Since carpentry Viking-Age Scandinavia,” TF 128). The reconstruction at hand Twork commenced in the spring of 2018, I have contributed over incorporates as many pieces of the original puzzle as possible, while 2000 hours to this effort, subcontracting for carpentry firm Julius also satisfying modern building code requirements. Nonetheless, Nielsen & Søn of Copenhagen, specialists in historic carpentry with traditional joinery predominates, with the exception of a few lag prestigious restoration projects to their credit, such as recent work bolts and steel rods. on the Fredensborg and Amalienborg royal palaces. The spectacular outer “hogback” shape leads to a rather challenging oak frame, its nine bents varying in size, from the 12m- Background Excavations led by Roskilde Museum in 1986–2009 wide central bents, 10m- tall to the ridge, to the smaller gable bents, uncovered rich archeological material from the late Iron Age, 7.5m wide by 6m tall. All longitudinal members are curved­—ridge shedding new light on mythical records of a local prehistoric power beam singly, purlin and wall plates doubly—and span up to 10m center around Lejre, in eastern Denmark. Among the findings were between bents (Fig. 1). the postholes of a 62m-long building that Sagnlandet Lejre received A stave wall encloses this structure, similar to those at the Hedared funding to rebuild in 2015 ($10.5 million from A. P. Møller og church in Sweden and Greensted church in England, where thick Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal and $1.5 million from Augustinus Fonden). The project also features a 1 Wall plates installed. Joinery in the upper ties awaits purlin 21m-long longhouse in similar style, not presented here. plates of similar double curvature.

14 TIMBER FRAMING 133 • SEPTEMBER 2019 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 asopsnøring ), 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

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

3 Positioning a bent on the floor layout prior to horizontally 2 scribing the upper tie beam—lower interrupted tie beams have Magnus Frimer-Larsen 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.

3 3 Magnus Frimer-Larsen

4 5 Magnus Frimer-Larsen Magnus Frimer-Larsen

TIMBER FRAMING 133 • SEPTEMBER 2019 15 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.

6 Ole Malling

8 Ole Malling

9

Magnus Frimer-Larsen

7 Magnus Frimer-Larsen

6 Raking timbers buttressing the assembled building.

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

10 Magnus Frimer-Larsen

16 TIMBER FRAMING 133 • SEPTEMBER 2019 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, 11 and ridge beam—was also situated in one (longitudinal) reference Magnus Frimer-Larsen 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 12 the Academy,” TF 129). Scribing members one at a time requires multiple test fittings, Ole Malling 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, calleduforkilet skråt hageblad in Danish, is not wedged, has square abutments, and was fixed with lag bolts on site. 13

13 Purlin plates in the making. Upper tie beams are positioned Magnus Frimer-Larsen 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 barrel8 nut anchors.

TIMBER FRAMING 133 • SEPTEMBER 2019 17 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- 14 dimensional reference plane. Though more involved, this is not complicated, as the heights of relevant bent members (lower and Magnus Frimer-Larsen 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. 15 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 Magnus Frimer-Larsen for the majority of joinery (Fig. 15). The chainsaw becomes quite a Swiss Army knife with practice. 14 Aisle brace layup (here, for the 21m-long longhouse). Braces Besides cutting to any depth needed, it can pare shoulders down to positioned at an estimated angle to follow the doubly curved a line like a chisel and plane surfaces rather smoothly. Scoring lines purlin plate. The purlin plate end is left wild for on-site marking prior to cutting, to avoid tearout, can help achieve a high finish. with jigs.

15 Chainsaw joinery.

18 TIMBER FRAMING 133 • SEPTEMBER 2019 a. b.

c. d. e. f.

g. h. i. j. k.

16

Photo: Ole Malling, graphics: Magnus Frimer-Larsen 16 Structural overview, with Danish terms in parentheses: a. ridge assembly: ridge beam (rygås), ridge post (dok), braces g. interrupted sub-plates (hammerbånd) (kopbånd) h. wall plate (fodås) b. upper tie beam (spændrigel) i. raking timber (skråstolpe) c. purlin plate (mellemås) j. facade post (facadestolpe) d. lower, interrupted tie beam (stikbjælke) k. wall planks (vægplanker) e. aisle post (tagbærende stolpe) f. aisle brace (kopbånd)

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Ole Malling 17 Hammerbånd installation with the wall plate temporarily removed.

TIMBER FRAMING 133 • SEPTEMBER 2019 19 20

Ole Malling 20 Purlin plate installed on a pair of aisle braces.

18 Perhaps most important, a chainsaw is not restricted to straight cuts Magnus Frimer-Larsen 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 19 working on a fixed, partly installed structure. Magnus Frimer-Larsen Hammerbånd, interrupted sub-plates (see Fig. 16), constitute an essential element in the stave wall system of this structure— 18 On-site aisle brace scribing, phase one (picture from the 21m- the grooved lower face receives the tenoned end of wall planks, long longhouse): With purlin plates temporarily fitted, jigs are themselves matched with grooves and loose splines, and holds attached to aisle posts. Battens are screwed to the jig, fitted tightly the wall in place. The hammerbånd are in turn tenoned into the up against the purlin plate where the brace shoulders will go. A facade posts on either side, and the facade posts are held in place reference mark, like a “two foot mark,” registers the position of longitudinally by the continuous wall plate. the jig on the purlin plate for the purpose of mortise layout. To fabricate the hammerbånd, the ever-changing angles of plumb shoulder cuts along the curved wall had to be registered with the 19 Phase two: The purlin plate is lifted off, the brace is wall plate temporarily installed to firmly locate facade posts. Once lowered into the jig, and lines for the shoulder cuts transferred the hammerbånd had been marked and cut, their installation from the battens. The distance between the point where the required the wall plate to come off again (Fig. 17). battens intersect with the brace (that is, its nosing) and the That the heavy wall plates were lifted three times during aforementioned reference mark is used to locate the mortise in installation, in addition to many lifts in the workshop, leads me to the purlin plate. suspect that some original tricks of the trade have been lost, or were

20 TIMBER FRAMING 133 • SEPTEMBER 2019 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).

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 Magnus Frimer-Larsen

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Ole Malling

TIMBER FRAMING 133 • SEPTEMBER 2019 21 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 23 generous building design, and how the curved geometry was

Magnus Frimer-Larsen practically developed at full scale, are outside the scope of this article, but I look forward to learning more from the archeologists 23 Scribing birdsmouths at the peak with a short spirit level. behind the project. At the time of writing we are still working on interior finish See back cover for a photo of the massive scale of the hall, nearly carpentry, and the opening date has not yet been announced. complete. —Magnus Frimer-Larsen

On a regular gable roof, all cuts are worked out on the first Magnus Frimer-Larsen is a Danish carpenter specializing in historic rafter—the rest are duplicates. The “hogback” roof, however, has no timber buildings. With experience timber framing in the UK and the identical rafter pairs—they vary in length and birdsmouth location, American Midwest, he is involved in the newly formed Scandinavian and are canted at different angles to keep the top faces in plane with timber framing network, Stolpverk Norden. the curved roof. Toward the gables, this canting generates radically skewed lap joints at the peak (Fig. 21). References These unusual rafters were fabricated in a four-step process. Heaney, Seamus (trans.), Beowulf (London, Faber and Faber, 1999). First, with half laps for the peak joint provisionally cut, rafters were Lassen, Ulrik Hjort, “The Invisible Tools of a Timber Framer—A located in plan of the roof, offset vertically above their final location. Survey of Principles, Situations and Procedures for Marking,” The skewed top joint was then scribed and cut in the air, often kerfed PhD dissertation, Department of Conservation, University of and repositioned a bit with winches attached to purlin plates to pull Gothenburg, 2014, https://gupea.ub.gu.se/handle/2077/35598.

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