Marrickville Award Wining Hemp Extension

Hemp walls with second story clad in timber

Location:
Marrickville, Sydney, NSW

Type of Build:
Two story extension to single story semi detached house

Owner:
Holly Askins and Simon Rumble

Designer:
Tracy Graham
Connected Design
www.connecteddesign.com.au
0405 431 119

Builder:
Nick Sowden
Sowden Building Solutions
http://www.sowdenbuildingsolutions.com.au
0433 323 513

Unrendered wall finished with Waterglass

Size: 
195sqm block
Property 130sqm - First Floor addition 35sqm

Cost:
$450,000
Includes : New extension and addition; new front fence; replacement of slate roof at front; new metal deck roof to old part of roof; insulation for existing roof and subfloor; subfloor ventilation; asbestos removal; new side access gate; solar hot water; kitchen appliances and paint to whole house

Date of construction:
July 2015 – November 2015

Purpose of Build:
Main Brief was to improve the connection to the garden at the rear of the property whilst respond to northern solar access. Provide an additional bedroom, study and small bathroom with a second storey addition. Replace existing bathroom and laundry down stairs. Create a new open plan Kitchen and Dining area. The existing footprint was retained and the space rearranged creating a separate living space much needed for a growing family.

Choice of Material:
Hempcrete was suggested by the builder for its low embodied energy, high thermal performance and breathability. it was easy to see it had so many positives in particular a monolithic wall system, instead of a multi layered wall system, thus fewer building materials and relatively easy construction method.

Climate:
Zone 5, Warm Temperate

Local Council:
Marrickville Council

Obtaining Approval:
Approval was tricky as the builidng had to comply with Acoustic controls (due to aircraft noise). There was a lot of discussion between designer, builder, hemp supplier and acoustic engineer to show how the building would not only meet but exceeded the acoustic requirements. The DA was slowed initially negotiations took place with a neighbour over a shared chimney. Holly and Simon also had to compromise and use an alternative wall system on the boundary between the semi detached buildings as the hempcrete wall did not have testing for the required fire rating.

Construction:
Built by Sowden Building Solutions. (Building Designer, Tracy Graham volunteered 1 day to help with the hempcrete walls)

Footings:
Concrete strip footings

Floor:
Ground floor level – new area insulated burnished concrete slab
First floor level -  timber framed floor, with tongue and groove Australian beach hardwood flooring over
 
Frame:
70mm timber stud frame

Walls:
The Australian Hemp masonry company supplied hemp hurd and binder. 200mm thick walls with frame in the middle. Lime render by heritage renderer with lime wash paint externally. Silicate paints internally.  Hempcrete walls exposed internally finished with Waterglass. Second storey hempcrete wall finished externally with timber cladding.

Hemp walls finished with lime render and lime paint

Windows:
Rylock aluminium double glazed with laminate glass to comply with acoustic requirements

Ceiling:
Magnesium oxide board for ceiling. Rafters were filled with a lighter mix of hempcrete - no sand.

Roof:
Metal deck roofing on 190mm timber rafters and timber battens with 60mm foil backed fibre glass.

Heating:
Bayonet allowed for gas heating in new dining room, which has not been used much.

Cooling:
Ceiling fans, including Big Ass fan in Dining room

Wall construction:
The builder, Nick Sowden, learned to build with hemp by attending a course with Australian Hemp Masonry and also plenty of reading - particularly The
Hempcrete Book by Alex Sparrow and William Stanwix.  The team was only four strong, one person mixing for the entire duration, one labourer placing the hempcrete and the builder and a carpenter placing and working the formwork when needed. Tracy Graham the building designer worked on the first day of hemp walling as well!   Two 120L hired screed mixers were used.

Formwork:
Construction ply 

Section Diagram:

Technical issues:
Over stacker door; plumbing; day cracks. Finish on concrete floor
Salt leaching through render from old brick wall which was rendered over (with hemp wall built on top) which required remedial works to suck the salts out of the brickwork and re-render.  This was done using a product called "cocoon" from Westox.
 
Advice/Recommendations:
Plan every detail of where anything may need to hang in future, including awnings, privacy screens, power points and even a speaker. 

Photo: Lena Barridge - Corner Studio

Awards:
Winner Marrickville Council Medal 

Sustainable Building Award 2016

Commendation Chris Reardon Memorial Aware for Residential Sustainable Buildings
2016 National Building Designers Australia Awards
 
Contact:
Holly Askins
Owner
0415 334 386

Tracy Graham
Connected Design
www.connecteddesign.com.au
0405 431 119

Nick Sowden
Sowden Building Solutions
http://www.sowdenbuildingsolutions.com.au/
0433 323 513