This is of the most unusual projects that Turfonline has ever been involved with. Read more about this turf roof project.
Why turf a windmill?
When Alan Chapman and his partner Christine fell in love with a partly refurbished windmill in Oxfordshire they had no idea of the amount of work facing them. I suspect though, that neither of them would change a single thing about it.
This beautiful building was first constructed in 1709. It started life as a working windmill. Presumably grinding corn from local farms. The mill was built into a huge mound of earth to help level and support the foundations.
Alan and Christine’s refurbishments involved excavating the mound to enlarge the basement and build more living accommodation. To avoid changing the appearance of the windmill too much, they decided to top the new extension with a turf roof.
Benefits of a turf roof
Any living roof has a myriad of benefits other than just the way it makes the building look. Turf needs a minimum of 15cm of growing medium. And the 15cm of growing medium on a turf roof is a very good insulator.
A turf roof is also great at absorbing rainfall. In the case of this project, the basement building is below ground level and has been carefully engineered to protect it against damp. The turf roof helps with that by soaking up around 80% of the rain that falls on it. That helps keep excess water away from the foundations of the building beneath.
A thick layer of growing medium also helps to protect a building against noise. Although, having visited the windmill project when it was in progress, I doubt that road noise will ever be a problem. It’s in a very peaceful spot, miles from anywhere.
Environmental benefits of a turf roof
A turf roof has all of the environmental benefits of a grass lawn. Apart from natural drainage, it filters pollution from the air, converts carbon dioxide to oxygen and cools the area in summer.
For a truly biodiverse roof, using wildflower turf will support more wildlife. But of course, it looks very different to a turf roof or even a sedum roof.
Creating the turf roof
Alan and Christine designed their whole building to be able to support a turf roof. First of all, it needed to cope with the sheer weight of 20cm of growing medium, rain, snow, and a man with a mower.
Then it needed an edge. In this case, there is an upstand to keep the growing medium and the turf on the roof and protect it against drying out.
Of course, drainage is important too. With the best will in the world, no amount of soil can hold onto every millimetre of rain that falls on it. Alan designed in some drainage outlets so that the turf roof will not become waterlogged.
The other extreme of English weather of course is drought. This turf roof has an irrigation system built into it too.
For maintenance – the roof is flat and has a nice broad staircase leading up to it. So it’s easy to carry a lawnmower onto the turf roof. Trimming the edges of the lawn is something that needed careful consideration too. Alan likes nice clean lines but he’s very conscious that sharp edging tools and expensive waterproofing are not a happy combination. He’s been very careful to set the level of the lawn in such a way as the edges will be trimmed when the mower runs over them.
Laying turf on the roof
Turf was laid in the same way as it would be at ground level. New growing medium was added to the roof 6 months before turfing. As it was freshly installed and not at all compacted, the soil preparation was simple.
Weeds were killed off using a systemic weedkiller. The growing medium was lightly disturbed to create a level surface. Alan and his team used a small garden tiller and just tickled the surface with no risk to the waterproofing. A quick rake over and then the turf was laid in the usual way.
The new turf was watered using the built-in irrigation system.
What does the finished turf roof look like?
In a word. Spectacular.
Just as Alan and Christine had hoped, the turf roof helps to blend the new part of the building with the old part and with the landscape beyond.
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