Visit to Tasmanian Hemp House built by Rodney Gregg

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.

View from the approach to Roger's house

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.

Close -up of unrendered wall

Unrendered "truth" wall in the garage

Fine chop of the hemp

Once the walls had been placed they used more magnesium board as a ceiling lining, leaving the bottoms of the timber I-beams exposed in the main living area, as a decorative feature. A light hempcrete mix was then placed between the roof beams, the sarking installed and the Colorbond decking style roofing material was placed on top. 

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.  

Main living area

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.

Lots of windows facing north and the views

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.