Thatching
Thatching
An Alternative Roofing Style
by Zach Miller of Davis City, IA
Thatch can provide a very durable and handsome roof. In the U.K., where thatching has a rich history, there are instances of a water reed roof lasting over 100 years. This example is exceptional. I would estimate a typical reed roof to last 50 plus years. The quality of the water reed, the skill in thatching, and the environment that the roof is exposed to would all contribute to the longevity or lack thereof.
Water reed (phragmitis communis) grows in low wet areas. It emerges in the spring as a sharp green spike. Green grass-like blades unfold as it climbs. This reed can grow up to 12 feet tall and grows a fluffy seed head. It looks similar to small bamboo, but is not as woody. In the fall the leaves fall off and the stem turns golden. At this point it can be harvested for thatch.
In 2014 we transplanted some water reed from Otumwa, Iowa, to a wetland field on our farm. Water reed harvested in 2019 and 2021 combined was enough to thatch a small house. As our reed bed continues to expand, one year’s harvest will provide enough yealms for a house.
Material Preparation
We wait until the ground freezes hard in December before we harvest it. A horse drawn sickle bar mower is used to cut down one swath at a time. Before the next pass, all the cut water reed is gathered and bundled with all the feathery top on one side and the cut ends on the other. Each bundle is spotted on a flat board to bring all the cut ends down flush. These bundles, also called yealms, are then tied by hand with a slip knot as tightly as possible. Yealms should be about 6 inches in diameter at the tie and 36–48 inches long. The really long reeds should be cut down to the right length. This means 12 foot long reeds would be cut twice into three 48 inch lengths. We bring all the tied bundles back to a barn to process into yealms of appropriate size. Each yealm is cut to the right length on a long table with loppers and then tied into bunches 6 inches in diameter at the tie, for a 12 inch thick roof.
Green, straight, tall willows about 1 inch in diameter at base need to be harvested just prior to thatching. All limbs need to be trimmed off flush and the top clipped off when it reaches about ½ inch in diameter. It is important the willows stay wet and green so that they can bend without breaking. The base ends of the willows can be submerged in a pond or water tank to keep them from drying and may even start them growing again. These willows are sharpened to a point and used as a sway for holding down each course of thatch.
We make our own thatch nails. There is currently no one that I know of that manufactures them. A ¼ inch diameter steel rod is cut into 9½–16½ inch long lengths to make each nail. The next step is to heat one end of the rod red hot. This hot tip is drawn out with a hammer on an anvil to a sharp point. The other end is bent in a vise into a crook. This is accomplished by making a bend first 1 inch from the end and then again at 2½ inches from the other end. See diagram. A good assortment of nails in finished lengths from 7–14 inches long is needed.
Per square of roof (10ft x 10ft), I estimate 35–40 yealms are needed. This is calculated for a 12 inch coat of reed. Also 15–20 thatch nails and 10–20 sways per square. These numbers are just a rough estimate.
Framing for a Thatch Roof
There are some general considerations for roof framing if the structure is to be thatched. The pitch of the roof, eaves treatment, and the use of battens are all critical components that need to be planned for. A steep pitch of 13/12–18/12 (47º–60º) is necessary for a thatch roof. This is a steeper pitch than is common on most buildings.(1)
(1) see The Thatchers Craft pg. 220
By increasing the pitch of the roof, water runs off faster and has less time to soak in. This organic roofing material also has an increased life span with a steeper pitch.
Battens are small boards fastened to rafters running perpendicular. Experience has taught me that battens too small and/or spaced too far apart are frustrating and time-consuming when it comes to thatching. In my opinion, 1½x3 inch battens spaced about 4 inches apart and screwed down to the rafters work the best (see drawing #1). I have also used 1×3 inch for battens but they tend to split with the large ¼ inch thatch nails. It can also be difficult to find a rafter or batten with the thatch nail underneath 4–5 inches of reed. Thus a closer spacing on battens makes a nailing surface more readily found for each thatch nail. The first batten is placed 5 inches from the edge of the barge board, to tie down the bottle course. The top batten at the ridge should stop 2 inches from the ridge.
Another important framing detail is how you finish the gable end and eaves. A barge board is firmly attached with screws 1½ inches above the roof plane, see drawing #3. These raised boards on the roof edges enable the first bunches, called bottles, to be tied down under tension with a sway in the bottle at the tie. This sway, or dip, at the point where the thatch is tied down follows all the way up the roof.
It is important to note the angle of thatch from tie down to tips on the base end. This should slope down and away from the tie or sway. This keeps the water quickly dripping off the tips with no ability to drain back into the house. Not enough sway exposes too much of the length of the reed to the weather. Too much sway getting too close to level can cause water to sit or even run back into the house.
In the fall of 2022, work was ready to commence on rethatching a home that previously had rye straw for thatch. These pictures document this project. Khoke Livingston, Nathan Miller, and I worked on the roof, and Steven Wilson and sometimes other men worked on the ground crew. We worked together for about 18 days to remove the old roof one section at a time and replace it with new thatch.
Thatch and thatching has been an active part of my life. I grew up in a house thatched with water reed, and I continue to use this distinct roofing material and learn more as I go. The details in this thatch article come from my experience with thatch which is admittedly limited in scope. My grandfather taught me to thatch and Khoke, my brother Nathan and I have worked together on many houses. I am still learning how to do it better. The book, The Thatchers Craft, has also been a valuable resource.
Anyone with moderate hand skills could learn to thatch. My grandfather originally learned from reading how to in The Thatchers Craft and then applying trial and error. This craft takes time and effort and will require commitment. My advice would be to start on a small outbuilding and learn and develop from there.
Water reed is in my opinion the most suitable material for thatch. Many eastern states have the introduced species from Europe (phragmites communis) now growing wild. In some states it is considered invasive and you may need a permit to grow it. South Dakota and probably other northern states have a native species of phragmites that is considered superior to the European variety. A little scouting might yield a location where it grows near you.
Thatching Terms
The word thatch is both a noun and a verb.
Thatch n. is the water reed or straw material applied in this roofing method. In this case phragmites.
Thatch v. is the action of applying this material to the roof.
Bottle: A small bunch used on eaves and gables, 28–32 inches long, 4–4½ inches in diameter at the tie.
Barge or Brow Course: The first course of reed after the bottles on eaves. This course sets the thickness of the finished thatch.
Course: One layer of thatch layed horizontally across the roof.
Dolly: A bundle of reed wrapped with string to make a long roll that is used to build up the ridge, prior to capping.
Spotting: To tamp a bundle of thatch on a flat board to even up the ends.
Spot Board: The board used to stamp thatch on prior to laying it on the roof. It needs to be at least 14 inches square.
Sway: Small straight sway willows 6–12 feet in length that are used to secure thatch to the roof. Also used to describe the dip in the course where it is tied or nailed down. See drawing #4.
Thatch Nails: ¼ inch diameter steel rod, 7–14 inches long, specially made nails; pointed on one end with crook on the other. The crook fits over the sway and is nailed down tightly into a batten or rafter to hold each course in place.
Tilting Fillet: a special board that runs the length of the barge board giving it strength. It is rectangular in the cross section.
Yealm: A bundle of water reed or straw tied 12 inches from lower end. Yealms are 36–48 inches long and about 6 inches in diameter at the tie.
Leggett: A tool with grooves in a wooden piece attached to a handle used for tapping the ends of water reed up into a neat position.
Thatching Needle: ? inch diameter steel needle about 36 inches long with an eye in one end. Used for stitching down a sway to the batten underneath as an alternative method to nailing down the sway. Also can be used for the bottle course and capping.
Probe: A ¼ inch diameter steel spike with a handle used to push through thatch to find the batten or rafter covered with thatch to know where to drive the thatching nail.
Things Not to Do When Thatching
• Do not use rye or wheat straw thatch. It is easy and convenient to grow but since you cannot remove 100% of the grain it will attract birds and rodents which then tear up the thatch. In my opinion the problems with grain straw outweigh the benefits.
• Do not sway down the thatch too tightly so that the tip of the thatch to the sway is close to level. See drawing #4.
• Do not use bottles and yealms of the same length. Bottles should be 10-12 inches shorter. You don’t want to have a step in the tops of the thatch created from building up the eave thickness.
• Do not use 1×2 inch battens or 1 inch rafters. This makes it very frustrating to find a place to drive a thatch nail in. Having 1½x3 inch battens and 2 inch rafters are best.
