Timber Frame Water Mill Reconstruction Project, UK Part 1

Written by Guest Author, Gavin Sollars, Timber Frame Carpenter, UK

The village is the token and pride of England; there are usually found in it vestiges of earlier life – cottages, manor-houses, farm-houses, with buildings of more or less historic interest; and who should understand them, their origin, their peculiarity of structure, better than the local carpenter?

Walter Rose, The Village Carpenter 
The reconstruction job site as seen from across the River Test. Notice the green netting installed to prevent things from falling into the environmentally-sensitive river.

Introduction 

I became acquainted with Stan early in 2019 when I decided to look at buying an Ootsuki Nomi. During my search I became skeptical of many of the Japanese tools that are widely available to the European market and, after a lot of research, I came across Stan’s contact details and sent him an email. Stan took a great deal of time to discuss with me what really motivated my purchase, the kinds of things I should take into consideration when looking at Japanese tools and went into detail about the intricacies of Japanese craftsmanship. The information he freely provided was invaluable, and with his help I feel I made a very good choice, and now have a tool that will serve me for my entire career.

I recently updated Stan with some pictures of buildings I had worked on and he asked if I would be willing to share them with the readers of his blog. The overall aim of these ramblings is to describe to you (who Stan calls his “Gentle Readers”) the general outlines of the reconstruction of an 18th century traditionally-jointed timber frame structure in a beautiful area of the English countryside in the summer of 2019. I hope that this article will give you an understanding of the work that was undertaken and also the enthusiasm I have for this archaic variety of building craft and carpentry as a whole. 

Project Background

Timber framing in the UK has enjoyed a resurgence in popularity over the last 30 or so years, with quite a number of small to medium sized specialists in the craft building new ‘post and beam’ style buildings that emulate the traditional frames of the past. These companies are mixing time-honoured design details and timber framing techniques with more modern methods of production: chiefly circular saws and portable chain mortisers to rough out the work. This deep understanding and appreciation of historic building vernacular made my employer (The Green Oak Carpentry Co.) well placed to undertake the reconstruction of this Project.

The Mill prior to 2018 fire

The company was awarded the contract to reconstruct the building as close to the original as possible.

The Project is situated to the North of the Test Valley in Hampshire County in Southern England on the banks of the beautiful River Test, famous for trout fly fishing and “gin-clear waters.” The original waterwheel powered a grain mill. It was later converted to paper production, and even later housed a generator serving the nearby Manor House. Unfortunately, the original structure was completely destroyed by fire in early 2018.

At 21 metres (68.8’) long and 5.7 metres (18.7’) wide, the main structure is situated on a small island created by a man-made diversion in the River Test. The river flows from the north and is then diverted via a sluice gate to the right. The river then widens into a pool and bubbles quickly along the west side of the building. The diversion along the east flank drives the turbine, and passes underneath a wing that links the main structure back to the existing dwelling and also houses the turbine and mill workings. 

Historical & Structural Considerations

The original building was “listed” with the Historic Buildings and Monuments Commission for England confirming the historical importance of the building on the one hand while placing restrictions on how any work to the building can be performed on the other. What remained of the original building after the fire was still subject to the Commission’s rules and regulations, of course. It once featured shorter posts sitting on top of a brick wall from approximately first floor height. In the wake of the fire the surviving outer brick walls were deemed too structurally unsound to bear a load – however, due to the walls being “protected” under UK law, they had to be preserved. To get around this issue we installed two outer plates running around the perimeter of the building with the lower of the two (D – below drawing) supported on metal brackets (C) connected to the back of the timber Jowl posts (B) by lag bolts. The full weight of these two plates, as well as the softwood stud wall with conventional insulation and weatherboarding is carried by these brackets transferring the load to the jowl posts (B).

A detail drawing (drawn by myself) of the steel bracket, showing how load was removed from the fragile existing wall. The drawing also explains the interplay between our frame and the other elements in the building.

Design & Construction Details

Framing work started in July 2019 with a team of eight carpenters framing the bulk of the structure over a period of five weeks in workshops off-site. A team of four transported the fabricated components of the timber frame to the jobsite, assembled and raised the frame, framed the hips and valleys, then fitted the common rafters and cut and assembled the jack rafters.   

Constructed entirely from European green oak, the structural frame is very utilitarian by design and lacks the aesthetic details like the curved braces typical in many historic timber structures in the UK. Nonetheless, it has some nice detailing that might not be obvious at first glance. 

The main posts (wooden structural columns) are mostly jowl posts (aka “gunstock posts”) that flare at the top with tenons that fit into both the top plate (beam running along the top of and connecting the exterior posts) the column and tie beam. Historically, jowl posts were cut from the flaring grain of the base of a tree. These butts were often quartered and each post placed in the building adjacent to its sibling. I believe that this is a similarity historic English carpentry shares with its Japanese counterpart.

Here you can see the cross frame construction 

The dominant style of cross frame (or bent in North America) features a bridging beam (the large beam that spans the first floor and carries the common joists), a tie beam which spans the top plates. This beam stops the wall frames from spreading under the load from the roof. And then a simple truss design consisting of two vertical studs and an upper collar with short stub ties jointed horizontally between the principle rafters and studs. The purlins (the members that run the length of the roof) are ‘clasped’ between the stub tie and the principal rafter.  

The main roof frame is comprised of bridled common rafter pairs, a pre-Georgian (prior to 1714) hip gable at one end and a standard gable at the other. A pre-Georgian hip is the English name for a hip rafter that is usually square in section and canted so that one edge is in the plane of either the gable or the main roof. Hip roofs were historically framed in this way until carpentry methods changed and more of a ‘hip board’ set plumb with jacks pitched onto the sides became the preferred method of hip framing. 

The pre-Georgian hip gable. The effect of canting the hip rafter in this way means that the jack rafters pitched from the two walls have a side cut angle on top and a square cut on the edge, but the jack rafters on the gables have a more complex (and comically named!) ‘nuns crutch’ or ‘lip cut’.

The adjoining wing has a wider span and a higher apex to the main building, and the roof meets the main roof in a valley. These valleys are similarly canted into the plane of the roof like the hips. In the same way the hips produce two different jack rafter cuts so does the valley. You’ll notice that on the main building there is a square jack cut and on the linking building the jacks have a compound cut onto the valley rafter. After running into the valleys, two small hip rafters pick up the opposite slope of the main roof. All of these angles were found using the framing square. 

The junction between the wing and the main building looking back down the east wall.

The main building is split into two clear halves; one which is vaulted floor to ceiling, and the other which has two floors of joists.      

Green Oak Timbers

What sets this type of carpentry apart from other woodworking is its use of timbers that are rough-sawn and often of irregular dimensions, requiring an understanding of how to deal with imperfections. For example, timbers are often significantly out of square, and dimensions only approximate: according to the European standard allowable tolerances are +9mm ~ -3mm in section. 5mm of deflection per metre is also allowed. These significant irregularities complicate the carpenter’s job.

Moisture contents can be in excess of 60% in fresher felled stock and during the summer months the warmer weather can cause problems with drying and shrinkage – we often keep our stacks covered with hessian cloth in an effort to shade the timbers and reduce warpage and cracking. 

Timber framing using this challenging material teaches a carpenter much about the nature of wood as a living thing, the characteristics of the timbers, how they are likely to behave and what can be asked of them.  

The Layout Process

Carpenters have developed various layout systems over many centuries to overcome the difficulties of working with irregular timbers. In my company we use lofting, for example. According to this method, we draw out entire layups on the floor and align the outside edges of each member to these lines with any sectional irregularities placed on the inside of the building, whilst any crowning (deflection or bowing) is oriented upwards and outwards.

Once the layout is drawn full-scale on the lofting floor, the timbers are placed on blocks in alignment with their corresponding grid lines on the floor. The various members are then laid one over the other so carpenters can accurately mark out lengths and scribe the shoulders of the joints using levels and plumb bobs. 

The plumb bob is an ancient tool that you are doubtless familiar with – its importance in carpentry cannot be overstated. Plumb bob scribing, or ‘scribe rule’ layout, is a difficult thing to describe without actually seeing it done. What it boils down to is using a perfect reference in a less than perfect situation. By sighting down the plane of the timber by eye and comparing it at the same time with a plumb line a carpenter can gauge to what degree that face is out of plumb and then accurately replicate that plane on the shoulder of the intersecting timber. The shoulders of tenons and widths of mortices are carefully marked using this technique.

Once a frame is cut and fitted back together, a plumb bob can be used to accurately transfer and mark additional details up from the floor. In the case of this watermill I used a plumb bob to mark the theoretical positions of the purlin housings on each truss. The result was that, regardless of the amount of deflection or variation in thickness of each principal rafter, the purlin housing was maintained in a consistent level position down the entire length of the building.

A plumb bob being used to mark the principal rafter to tie beam joint. On the floor you can see the layout lines. We mark out each individual frame in a building full size on the floor with chalk lines, and then set up the timbers to those lines. This plumb bob belonged to my great grandfather who was also a carpenter. 

Frames are generally made up of wall frames (running the length of a building) and cross frames (spanning a building). Many of the timbers are therefore used repeatedly in multiple layups. In the case of main posts they are first framed into the exterior walls of a building. Once the walls are completed they are framed in the ‘cross frame layups’. To ensure that the posts return to the right height and rotation that they were in during their previous layups, we use scratched datums (often a set distance from the top of top plate) and rotation marks that allow us to wedge the timber to return it to plumb or level. 

Ensuring that a designated point on each timber is plumb and level is essential, particularly for those in multiple layups. It guarantees that a timber has been returned to the correct plane each time it is fitted up so that when it is stood up and connected to multiple beams, the rotation of each individual shoulder scribe is correct.   

Once the bulk of the main structure is framed we laid-up floor joist and ‘cogged’ the tie beams into the top plates. Traditionally tie beams were dovetailed into the plates but because the shrinkage of dovetails (green oak, remember) tends to cause the building to spread, it is now more common to see a simple cog used. A cog also slightly outperforms a dovetail in green timber when under tension.

Assembly and Erection at the Job Site

The building enclosed two concrete pads differing in elevation by about 200mm (8”). The base of each post therefore was designed to accommodate this change maintaining the design elevation of the building. This and other variables made laying-out of the building one of the most challenging I have ever been involved in.


This photo shows the “jowl posts” and the boom of the spider crane as assembly work is underway.

The only access to the site was a track through a field at the rear of the building and a small trackway and bridge over the river too narrow for a mobile crane to cross. The solution we employed was to bring in and set up a small spider crane in various places inside the building. The limitations of this machine required us to be very methodical about the assembly sequencing to ensure we didn’t obstruct subsequent lifts. 

Space was at a premium. Without a large area to unload the piles of timber, we had to unload the timbers and other materials in the field behind the property and then use a remote-controlled tracked carrier to ferry timber across the narrow access bridge.  

And, to throw one more element into the mix, the river is an extremely well-protected ‘Site of Specific Scientific Interest’, meaning we had to be very careful when cutting roof members to prevent sawdust from drifting into the water course. The scaffolders installed netting around the entire perimeter to prevent anything from falling from the scaffold. We also did the majority of our cutting away from the edge of the scaffold on a plywood deck we laid on the joists.

As the building began to take shape its scale became more apparent. At nearly nine meters high, it’s an impressive structure. 

Lessons Learned

I took away a lot of lessons from this building project such as managing levels on-site, and the importance of every trade singing off the same song sheet, as it were.

We had issues with the initial layout of the structure as it became clear that the structural steel that effectively served as the starting point for everything above it had not been installed at the correct elevation. The work was delayed while we sorted out this problem.

I also learned valuable lessons about effective joint placement. Because of the space constraints mentioned above, we were forced to erect the structure by lifting and placing each cross frame and then linking it back with its purlins. However, because the scarf joint landed on the wrong side of each truss, every time we craned a purlin into position, it was left temporarily unsupported at one end. These decisions were admittedly made early on before any proper site visits were made. A proper method statement was in place, of course, but the experience taught me that starting with the end in mind is important when planning.

I hope that you, Gentle Reader, gained some insight into the work that I am involved with and found it an interesting read. If you would like further information about historic timber framing in the UK, I recommend a small book titled Discovering Timber Framed Buildings by Richard Harris. 

– Gavin Sollars

Gavin Sollars hard at work

Thank you for your reading this article. It is rare to find a craftsman like Gavin with the skills and inclination to write about his work and a willingness to share it freely with others. Gavin did not write this to promote his company, but if you like this sort of thing as much as we do, please visit his company’s website and sign up for their newsletter.

In the next post in this series Gavin will outline the construction of the roof frame. Please stay tuned.

YMHOS

If you have questions or would like to learn more about our tools, please use the questions form located immediately below. Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.”

5 thoughts on “Timber Frame Water Mill Reconstruction Project, UK Part 1

      1. Gavin is finishing up the second in this 2 Part series. I hope he will share with us in future posts his techniques for using a plumbline to layout joints from lines on a lofting floor.

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  1. I am posting a question Tom sent as a message, with his permission, because I think many will find it informative. I have also posted my answers. Stan

    >Tom’s Question 1: Love the story and would like to know more about your tools, especially chisels. A question I have on both Japanese chisels and pull saws: Are there any differences in the cutting angles/edges or metallurgy of Japanese tools when working on softwoods vs. hardwoods. Or oak which is a kind of soft hardwood? It seems like most of the Japanese carpentry and woodworking I see involves softer woods.

    >>Stan’s Answer 1:
    Regarding metallurgy, there is no difference between tools intended to cut hardwoods and softwoods.

    There is a difference between solid wood and plywood/mdf/LVL etc. and other synthetic materials made with adhesives and sanded to thickness. High-speed steel will resist the damage the glues, and especially sandpaper grit embedded in these materials wreak better than plain HC steel.

    Regarding angles, depending on the hardness of the wood, one may need to change angles. A chisel edge sharpened at 20 degrees to cut paulownia wood will fail if used to cut ebony. But 27.5~35 degrees will handle most woods. The user needs to match his bevel angle to the job and his technique. This is often a trial and error process. Same applies to plane blades.

    If tearout is a problem, a plane with a higher bedding angle will help.

    Most Japanese saws sold nowadays are intended for softwoods and not hardwoods since most consumers nowadays use Japanese saws to cut softwoods. A market-driven decision. The philosophy of Japanese sawteeth directly contradicts that of their simpler Western counterparts. They are sharper, more aggressive, and cut more efficiently. They are more fragile and more difficult to sharpen, but assume the user has some skill. Please see Zetsaw’s webpage that explains the details in English. Notice the rake differences. https://z-saw.co.jp/en/reference.html

    The teeth of Japanese saws have more rake, are longer, and more fragile than Western counterparts. One needs to keep the saw straight in the cut when using fine-toothed Japanese saws. Failure to do so can break/bend teeth. Of course, anyone with a bean’s worth of brains knows this, but there are many who flail around with the saw like it’s a shovel instead of a cutting instrument and then blame the saw for their failure to pay attention.

    But the problem you imply of using saws intended for softwoods to cut hardwoods is valid. I recommend using induction-hardened kaeba (exchangeable blade) saws with rip teeth when cutting hard woods (versus “hardwoods”) for both rip cuts and crosscuts. Sounds strange I know, but you will be pleasantly surprised.

    I hope this answered your questions.

    >Tom’s second comment: I have heard from some of the more careful woodworkers I know that they never use their edge tools on wood once it has been sanded, for the same issue you mentioned of grit left behind in the sandpaper swarf.

    >>Stan’s response: The resistance some woodworkers have to using their valuable edged tools such as planes, saws and chisels to cut wood that has been exposed to sandpaper is warranted and wise, IMO.

    Have you ever seen plywood being made? In a previous life I bought it by the container-load from factories in Canada and the US and shipped it to Japan. Factory inspections were part of the job.

    Plywood is made from several sheets of sliced veneer. In quality plywood, each layer of veneer is passed through a thickness sandpaper prior to lamination. Both sides of each sheet of veneer, not to mention both surfaces of the final product, are sanded and absolutely contain large amounts of embedded sandpaper grit, and not the weak-as-water sandpaper sold in hardware stores, but very hard industrial-grade stuff tough enough to grind stone.

    LVL and MDF and OSB are often thickness-sanded to final dimensions. More hard grit.

    Ask the manager of a plywood Plywood/MDF/OSB/LVL factory what he thinks of sandpaper grit’s impact on his equipment. It ain’t pretty and costs a lot of money to remedy.

    But don’t take my word. Sharpen a western chisel sharp and bright as a mirror. Use it to make a few cuts in solid, clean wood. Examine the flat and bevel of the blade before the cut and after using a loupe or powerful magnifying glass. Note the new scratches.

    Next use the same chisel to make the same cuts in solid wood which has been sanded. Examine and note the scratches. You will discover a notable difference.

    Repeat the same test and examination on a piece of cabinet-grade plywood. All will be clear.

    The sandpaper grit dulls and wears out cutting edges to no purpose. It wastes the tool owner’s time and money for several reasons. 1. Because a tool subjected to sandpaper grit must be sharpened more frequently; and 2. Because time is money and time spent sharpening is time a professional craftsman is not making money; and 3. Because sharpening stones and steel cost money too, money sandpaper grit burns fiercely.

    Imagine what the grit does to the sole of a plane or teeth of a saw. Neither wood nor steel nor pocketbook need the grief.

    A wise man will avoid using his valuable edged tools on sandpaper grit-contaminated wood just as he will wood with embedded stones. Unless, perhaps, if he is rich, has too much time, loves sharpening, and hates his tools.

    Stan

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