A work conference in Tasmania provided me with the
opportunity to visit Roger Bodley’s hemp house on the north coast
of Tasmania near Wynyard. Unfortunately Roger could not be there as he was
attending the 3
rd International Hemp Building Symposium in
Switzerland. However his builder, Rodney Gregg, kindly showed me around and gave
up hours of his time to speak to me about hemp building, giving me renewed hope
and confidence in our build after our recent problems.
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View from the approach to Roger's house |
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Roger's house showing the ocean view |
Roger’s house is built on a steep site with uninterrupted
ocean views of Bass Strait. Hemp has been used extensively in the walls, floor
and ceiling. For the floor a magnesium board was attached to the underside of
the floor joists, the area between the joists filled a light hempcrete mix and
the beautiful Blackwood timber floor boards attached over the top. The magnesium board is vapour permeable,
enabling this characteristic of the hempcrete to be retained. The walls of
Roger’s house were, at about 350mm, almost twice as thick as in my build. They
also did not have noggins to contend with, they are unnecessary in a hemp
house as the hempcrete once dried will provide the necessary resistance to
lateral forces (my Council would not accept this).
Rodney and I compared our hemp building work methods,
although he was working on a much larger scale that I am. In parts the walls of
Roger’s house are two storey’s high. Rodney had his own scaffolding and put
this up around the house, then formed up the full height of the external walls
using Formboard with external stiffening timbers that Rodney usually uses for
casting suspended concrete slabs. He
then formed up and poured 600mm rises on the inside. The chop of hemp he was
using from the UK was much finer than the hemp I am using from Ecofibre, and
finer than the hemp I used at Klara Marosszeky’s workshop (in which was a chop finer
than the Ecofibre hemp). They had some issues in working out how to mix up a
sufficiently large volume of hempcrete mix and ultimately used a concrete truck
to mix the hempcrete. This is not a solution Rodney would use again as they had
to make the mix wetter than they would have liked to enable it to tumble in the
mixer and not just get stuck to the sides. They put in and tamped a 200mm thick
layer of hemp at a time. Despite their layers being much thicker than mine, I
am doing layers of about 50mm, in an unrendered section of wall in the garage
the tamping looked even and you could not see definite lines between the
layers. I suspect that this may have to do with the finer chop of the hemp
allowing thicker layers to be placed and tamped. I was reassured that Roger’s
finished wall did not look different to mine, except for the size of the hemp.
Rodney showed me the binder and render they used, all of
which was imported from Europe – the binder was the UK Tradical binder, it was
a very fine almost slippery lime based powder, it did not look like it had any
sand in it and did use any added sand like the AHMC binder I am using. For the
renders he used one type of render, done in three coats by a professional
renderer on the inside and three coats each with a different product on the
outside. The internal render was a very fine lime based powder and each coat was
quite thin. The external render was much thicker and Roger had wanted a
textured finish on the outside, so one of the external coats looked like it had
little polythene beads in it, that created this finish. I can not recall the
product used but it was imported from Europe. The need for a special external
render on Roger’s house may have come from the absence of eaves and the driving
rain and wind that would come straight off Bass Straight in bad weather.
Thankfully I was there on a beautiful day.
|
Detail of external textured render and curves around windows |
The day was sunny with cloudy patches and a gentle breeze,
but the inside of the house was warm but not stuffy. It had a soft comforting
feel that is hard to describe. The large rooms were not echoey but at the same
time sound was not overly dulled. I could not tell whether this feeling came
from the hemp walls themselves or the gentle curves in the corners of the walls
and the ceiling, but it was very pleasant nonetheless.
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Main living area |
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Upstairs bedroom with view |
I was also impressed by the use of timber in the house, the
beautiful timber stairs showing the natural edge of the log, as well as the
custom made Blackwood timber doors and door jambs. The timber work in Roger’s
house has inspired me to make my own door jambs – I just have to source some
nice timber. Roger’s house also used Aluminium framed windows. I was very happy
to see this as I am also using Aluminium framed windows, whereas most other
hemp houses I have seen in books and on the Internet use timber framed windows.
The finishing detail on Roger’s windows was a little different to the approach
I will take as his walls are thicker than mine, but I was pleased to see that
the Aluminium framed windows did not look out of place.
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Lots of windows facing north and the views |
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Curve of the house matched the curve of the slope |
I asked Rodney lots of questions about construction detail
and how different materials could be used in conjunction with hemp walls.
Rodney generously and patiently answered all my questions and i think I will
have a better house because of it. Roger’s house does not use any skirting
boards and I will do likewise. I had been worried about my internal door jambs
detail and how to joint the plywood I had intended to use for my internal wall
linings with the renders hemp walls. Both matters were solved by switching the
internal wall lining to rendered Magnesium board, so I could (try to) replicate
the lovely rounded corners in Roger’s house and bring the render up to the edge
of my door jams.
Rodney also introduced me to renderers mesh and recommended
that I place it in the render at any stress point, such as above the corners of
doors and windows, to prevent the render cracking. I could also use it over the
sections where my hemp wall had cracked to prevent any movement in the render.
Rodney also provided me with a method to rectify the sections of wall that had
pulled away from the stud using a large round plastic anchor disk, normally
used from attaching polystyrene, and a long decking screw. I will definitely
obtain the necessary materials and try this out. He also shared with me his
neat method where extra keying in was required. It involved the attachment of a
piece of timber shaped like a wedge with the tip cut off. This could then be
attached to a stud or lintel and the hempcrete would key into the narrower end
of the wedge, with the wider end holding the mix in. We also discussed parapet
wall detailing and flashing – he cut a 25mm slit into the hemp wall, slipped
the top of the roof over flashing into the slit, then sealed the slip with some
silicon and rendered over it all.
I am indebted to Roger for opening his house to
me and Rodney for his time and sharing his experiences. It is this kind of sharing
of knowledge that will support the growth of a hemp construction industry in
Australia.
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After watching Landline i was impressed with all aspects of hemp. I have a video somewhere, think i recorded it off TV at some stage of a car that was built of hemp in the 40-50s i think. Is there any houses around the Hobart area built from hemp. I have a vacant block at Sorell that would be good for a hemp home (STCA) but no funds unfortunatly to have it done and probably getting on a bit to do it. Must say that hemp is the future and hopefully it gets rid of a lot of plastics. Ian.
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