Maclean Hemp Understorey Extension

Location:
Maclean, mid north coast NSW

Type of Build:
Understory extension to relocated weatherboard Federation Cottage

Owner:
Eshana Bragg and Peter Cuming

Designer:
Eshana Bragg prepared DA Application

Builder:
Corey Thomson
Xylosinuous Building and Design

Size:
Gross addition 94m2

Cost:
TBA

Date of construction:
August 2013 – flooring yet to be completed

Purpose of Build:
Multi purpose space, providing an office and workshop space for Sustainable Futures Australia, music studio, bathroom, laundry and woofer accommodation

Choice of Material:
Eshana looked at various methods of how to infill around the existing steel frame of the house. She wanted the material to have good thermal qualities.  She looked at using Hebel, but had some difficulty determining how to the Hebel would be detailed around the steel frame. Eshana saw Klara Marosszeky from the Australian Hemp Masonry Company at a stall at the Sustainable Housing Expo at Mullumbimby. Once she held a block of the hemp masonry she knew she had found her building material.   At the time she commenced building hemp masonry was a relatively new building material but she was willing to take a risk to use a sustainable material.

Climate:
Zone 2 - Warm humid summer, mild winter

Local Council:
Clarence Valley Council

Obtaining Approval:
Eshana spoke to the senior building surveyor at Clarence Valley Council before lodgement and also got the building surveyor’s input on the DA (Development Application). Council officers look at the property before the DA was lodged and were very cooperative and interested. The DA was approved in 10 days. AHMC provided an Alternative Solution report to be submitted with the CC Application (Construction Certificate).
 

Walls left unrendered under balcony

Construction:
The hemp walls were constructed over two workshops. The remainder of construction was carried out by Corey Thomson. A professional renderer was contracted to do the more visible parts of the render and Eshana, Peter and their interns carried out the remainder of the rendering.

Footings:
Concrete slab on ground

Floor:
Not yet completed but will be polished concrete

Frame:
Existing steel frame, with some of the frame altered to allow space for triple sliding doors in the extension. Between the steel frame a recycled hardwood timber frame was constructed to provide support for the hemp walls.

Walls:
AHMC binder and Ecofibre horse bedding hemp were used to construct 300mm thick hemp walls. The builder wanted 300mm thick walls to provide sufficient thickness between the timber frame and the outside of the hemp wall. The timber frame is centrally located and the hemp walls also cover the steel frame. The hemp walls are rendered externally. Eshana and Peter engaged a professional renderer to render the walls that are visible from the front of the house and the renderer used a first coat of the AHMC  hemp render and did a second coat of sand lime render over the top. The remainder of the walls were rendered by Eshana, Peter and their interns, who used a single coat of sand/lime render. They experimented with oxides to colour the render but finally chose to go with the colour naturally provided by the sand. Internally and externally around the entrance, under the protection of a large veranda, the walls have been left unrended. On the inside of these walls render has been used to create skirting and decorative window reveals.

 

Windows:
A mix of windows were used. Recycled timber windows, similar in style to the windows used in the upstairs part of the house, were used at the front of the extension. Taking inspiration from a historical cottage in Maclean built in the mid 1800s by a German settler, these windows were set toward the outside of the walls to provide deep reveals on the inside. Beautiful rendered decorative arches were put over the top of these windows. In the open plan workshop and office space high quality single glazed, using Viridian comfort glass, aluminium framed triple sliding doors from Yamba Glass were used, as well as large square tilt windows and louver windows.

Ceiling:
High ceilings of Gyprock Fyrcheck were installed on a treated pine frame, insulated from vibrational sound by rubber inserts usually used in solar panel installation. Ceiling cavity contains Greenstuff polyester bulk insulation with a double lay of insulation above the music studio. This was installed by Ian Brophy Builders. Eshana and peter report excellent sound insulation between the storeys of the house. Steel beams left exposed provide a sculptural element in the open plan workshop area, cotrasting with the high set ceilings painted bright white. Plywood together with acoustic insulation (to be installed)

Roof:
NA 

Heating:
Small fan heater. The extension does not need much heating.

Cooling:
Not needed, in summer the extension has remained at 23 degrees when it has been 37 degrees outside.

Niches in walls

Attractive window reveals

Wall construction:
The builder Corey Thomson had experience in rammed earth, but this was his first hemp build. The hemp walls were built on a row of concrete besser blocks at the bottom, with a moisture barrier under the besser blocks. Two workshops were conducted to construct the hemp walls. Klara Marosszeky and an assistant were paid to teach the workshops. Eshana and Peter paid for Corey Thomson and his build team to attend and the workshop participants each paid $300. The first two day workshop was attended by 10 people, mostly from the building industry and 15 people attended the second workshop two weeks later, with the builders and owners continuing an extra day to complete all the hemp walls.  The hemp walls were all done in the 5 days of workshops and the workshops used a 250L diesel pan mixer owned by the AHMC.  The initial render around the doors and windows did not work well and a professional renderer was engaged to remove and redo this render and it now has crisp edges.  The professional renderer also rendered over the besser block creating a render skirting.

Formwork:
Plywood formwork with attached horizontal timber walers, that the builder had from rammed earth construction. The formwork was secured with threaded metal rod, from one side of the formwork to the other. The holes in the hemp walls from  the rods were plugged later.

Section:
 

Technical issues:

• Some areas of hemp wall were insufficiently tamped by workshop participants and the walls were crumbly, particularly in the difficult to reach area under the steel beams.  After a few weeks Eshana removed the crumbly section around a hole that had been left, dampened the area with a spray bottle of water and packed the area with new hemp masonry mix and covered the repair with a small piece of formwork screwed to the wall.
• When by mistake a conduit was pushed out of alignment, the material was very forgiving and easy repair. Heat was needed to bend the conduit back into place and the hemp walls could easily withstand the heat of the blowtorch necessary to repair the conduit.
• While the walls were left unrendered a Kookaburra pecked at a soft spot creating a hold in the wall for their nest. The hole created by the Kookaburras almost went all the way through the wall.  Once discovered the Kookaburra hole was easily patched up with more mix.
• High quality rendering is a professional job and for Eshana this was a costly mistake when she had to get the work done again.
• Eshana is still assessing the pros and cons of using a breathable wall in a damp environment.

Advice/Recommendations:
Go for it. Hemp building is a great community building activity. It can be done with an extended family, neighbours or a community and anyone can participate from kids to the elderly (Eshana’s dad at 80 was able to help out as much as other crew).
If you host a workshop, make sure that you keep the participants well fed, to keep them happy and avoid them flagging at the end of the day. For workshops also be well prepared, if you want any different shapes in the hemp have the formwork done prior to the workshop.
Hemp building is still a bit experimental and if working with an inexperienced crew this can lead to mistakes that have to be fixed and more expense. But it's worth it!

Contact:
Eshana Bragg
eshana@sustainablefutures.com.au

Corey Thomson
Xylosinuous Building and Design
0419 715 820
Xylosinuous.com.au