Thatch Roofing in Rain and Snow

Thatch Roofing in Rain and Snow


Thatch roofing has been used on every inhabited continent and in nearly every country.  Thatching traditions have been developed over centuries to handle everything from humidity, drought, rain, to snow and to use the available resources to meet many other unique local demands.  This article will address the specialized ways that thatch stays dry in rain and snow.

Cottage with thatched roof.
Classic English cottage with a thatch roof.  While thatch is a beautiful roofing material it is also very durable in wind, rain and snow, lasting up to 70 years.

Many Northern European countries such as Ireland, the United Kingdom, Sweden, Denmark and Germany, where thatch traditions are well established, receive plenty of rain.  On the west coast of Scotland, Glencoe and surrounding villages can receive up to 70 inches of precipitation annually.

Naturally waterproof, water reed, a type of thatch, is actually hollow and the cellular structure is so tightly overlapped that water can’t get inside.  Bundled together, as it would be on a thatch roof, water can’t penetrate beyond 1 maybe 2 inches.  In fact water reed has such high amounts of silica (the same substance used in waterproof silicon caulk and solar panels) that researchers are exploring ways to use it to replace synthetic silicon in batteries.

Mushroom house in Charlevoix
This is the mushroom house of Charlevoix Michigan renovated by Michael Seitz and thatched by Colin McGhee. If you look at the detail in the upper left image corner you'll see that all the thatch is pointing downward to easily shed rain water and melting snow.

Water reeds are naturally water repellent and direct water from the ridge to the eaves, according to William Cahill, a US based thatcher.  As with all types of roofing, a waterproof membrane is installed beneath the reeds and provides an additional layer of protection.  Thatch roofs installed over open framing tend to breathe better, and what little of the surface thatch that does get wet, will dry out faster.

Thatchers often harvest their own thatch.  Water reed is very abundant in the US.  William Cahill cuts 40 acres of water reed every year in New Jersey.  “It’s a very invasive weed", he said.  Japan is known for it's heavy rainy season, which is referred to as both baiu and tsuyu.  Japanese thatching traditions have been in use for over five thousand years and it is well documented that prior to modern times thatch was by far the most common roofing material in Japan.  

Felice Beato, a famous foreign photographer from the the late 1800s, noted on a visit to Japan that most buildings were roofed with thatch, from the temples down to the peasant's cottages.  He went on to remark that tile and wood shingles were occasionally used, but by far the greater proportion of all buildings were thatched (Felice Beato's Japan: Places, by Allen Hockley).  

Today, Japan's thatching industry is represented by one of the world's largest thatching organizations.  So needless to say, Japanese thatchers living in a place known for it's rain, know how to keep a home, or any other building, dry with thatch.

The ridge is one of the most important parts of a thatch roof for shedding water.  There are a variety of ways to finish the ridge.  In the UK and Ireland, each thatcher has their own signature way of finishing the ridge.  The details below illustrate a few methods.

Ridge thatch detail
There are a variety of ways to finish a thatch ridge.

Today's coastal storms can pose a serious threat to roofs.  According to Virginia based thatcher Colin McGhee, thatch roofs offer wind and storm protection better than any other type of roofing.  Thatch is attached directly to the rafters, essentially becoming part of the structure.  

Is thatch suitable for snowy climates?  This question is of special interest for us since many of our clients are looking for a mountain architecture style home.  Part of the lure for having a mountain home is experiencing the winter wonderland that snowy winters bring.

Ogimachi Gassho style thatched homes
Snow covered thatch gassho style homes in Ogimachi the largest village of Shirakawa-go Japan.  Note that the thatch is steep and thick, which is ideal for snowy climates. Photo Credit Karen Hamasaki by permission.

To cope with snow, thatch roofs are steeply pitched.  Thatch is suitable for snowy climates if the roof pitch is at least 12/12 (45 degrees).  A roof with this pitch or greater has more aesthetic appeal anyway, in our opinion.

Historical villages such as Shirakawa-gō and Gokayama in Japan receive heavy snow in winter and their gassho style houses are known for their thatch roofs.  The gassho houses of Kirakawa-go and Gokayama have pitches up to 20 / 12. At this pitch cross ties take the place of columns and the attics become multiple levels.  With the attics freed of columns they were put to more useful purposes such as silk production and dwelling space.  

When the roofs are rethatched, the community works together to complete it in one day.  They start the day early, the old roof is pulled off, and the thatch is separated into good and bad.  The good thatch is reused, other thatch is mixed with new thatch for use at the roof top, and the bad thatch is thrown out.  The ridge is made of five or more layers.  The day ends late with the completion of the new roof, which is followed by a big dinner.

Thatched country cottage and gardens
Thatched cottage with country garden in Cockington, England. This part of the country is made green by rains from the Celtic Sea.

In rain and snow, there are many thatch roof traditions the world over, uniquely suited for each type of climate.  Are you considering thatch for your next roof? Feel free to leave a comment below.  If you enjoyed this post, check out our other posts about thatch.

Hendricks Architecture, architects in Sandpoint, Idaho.  We've designed everything from small mountain cabins and storybook houses, to mountain lodges and estates.

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