Owner Building a Strawbale House
in the Bega Valley,
NSW,
Australia.



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Design Criteria

Style

  • Single pitch roofs.
  • Modular – in standard sized blocks to reduce construction complexity.
  • Cathedral ceiling in living space. Standard ceiling in all other spaces.
  • Second and third bedrooms to be built in a free-standing unit, preferably between house and workshop. Undercover access from house if possible.
  • Workshop and studio in similar style as house and located within curtilage.
  • Feeling of permanence, assume we live in it for 30+ years, assume we live in it until no longer capable of looking after ourseves (hence accessibility guidelines, etc.).
  • Solar passive. Least heating required in winter.
  • Natural summer cooling (breezeway / cooling chimney / etc.). Vents at top of living area cathedral ceiling.
  • Owner-buildable (simplification of processes in general).
  • Reduce ledges where dust can collect.

Bubble Diagram

  • Master bedroom with rising sun (east facing glazing).
  • Toilet for main house accessible by guests without going through private areas (master bedroom).
  • Open plan kitchen/lounge/dining.
  • Study (computers) open to lounge/dining/kitchen, and close to master bedroom.
  • Undercover attached parking (prefereence to attached parking rather than attached second & third bedrooms, based on % usage).
  • Loung/dining/kitchen view to north, north-east and north-west.
  • Outdoor eating/cooking area.

Accessibility

Preference for design meeting accessibility guidelines.

  • No stairs or steps. Space for ramps where external landscape requires level changes between buildings.
  • Hallways: minimum 1000mm wide, prefer 1200mm wide
  • Doorways: minimum 800mm, prefer 1000mm.
  • Kitchen: 1550mm between opposite opening cabinets in kitchen.
  • Carport for two cars
    Carpark A: 3800mm w x 6000mm d x 2500mm h
    Carpark B: 2400mm w x 6000mm d x 2500mm h.
  • Place cupboards in hallways such that they can be removed later if circulation space required.
  • No lip on shower recess. Toilet not in small enclosed space with inward opening door.

Space Requirements

Room

Minimum Dimensions

m2

Kitchen

4 x 5

20

Eating

3 x 4

12

Living

4 x 6

24

Bedroom

3.5 x 4

14

WIR

2.5 x 2.5

6.25

Bathroom

2 x 3

6

Study

3 x 3.5

10.5

Cupboards

3 x 1

3

Laundry

2 x 3

6

Storeroom/Pantry

1 x 2

2

Total


103.75

  • Outdoor covered area required (including sink & bench) – min 5m x 5m.
  • Storeroom required for longer term storage of produce – cool and dark.
  • External access to bathroom. Bathroom to contain toilet, bath and shower.
  • Workshop space approx 10m x 20m with some enclosed (approx 75%) and some open bays (approx 25%) - flexible space requirement, but enclosed shed space is required.
  • Studio space prefer around 6m x 10m, minimum 5m x 5m. Washing sink required. Flexible space requirement, could be merged with shed.

Heating and Ventilation

Solar orientation

  • North facade 65% glass to wall area
  • East, West & South facades 15% glass to wall area
  • Eaves to provide total summer shade to north windows.
  • All windows to have glazing mounted towards exterior of walls to minimise weather exposure of bales.

Auxillary heating

  • Wood combustion stove, centrally located, radiant heat.

Ventilation

  • Cross ventilation of all rooms.
  • Southern windows to have openings close to floor level.
  • Living space to have ventilation at highest point, possibly undereaves on N/W & N/E ends.
  • Ceiling sweep fans in living area (and possibly the bedroom?).

Wind Directions

Afternoon winds, particularly in summer, are generally from the east. In winter a significant portion of afternoon winds are from the south west. Morning winds, particularly during winter, are from the south west. Generally, afternoon winds are twice as strong as morning winds, with August to February being the windiest months.

Construction materials

  • Strawbale walls.
  • Render – TBD (concrete external ? Concrete or mud or lime internal ?)
  • Raft concrete slab, polished for interior floor finish (what sealant and concrete finish ?)
  • Metal frame and roofing – Colourbond – light coloured.
  • Double-glazed windows?
  • Low or no outgassing materials, no chipboard, few plastics, low glues, natural paints (Porters ?).
  • No termite (or other) pesticides (ie: use termi-mesh or granitguard).

Construction methods

One-piece raft slab. Plinth seperate to allow easy screed & polishing of slab (compared to laying plinth as integral structural member ?). Plinth to keep bales above grade by about 250mm. Moisture barrier above plinth, probably including termite shield (externally visbile ant-cap, internally bitumenised aluminium).

Dyna-bolt frame to slab. Easier construction method.

Assume dig in services, install slab, put up frame, attach roofing, then infill with straw-bale, render and internal fit-out.

Run services in roof cavity as much as possible (reduces floor penetrations and gives shortest hot-water runs for roof mounted solar hot water).

Insulation


R value

Description

Roof

3

Foil backet blanket under roofing iron. Batts (plus services) in cavity. Strawboard for interior roofing finish (eg: ortech easywall).

Walls

n/a

Strawbales

Slab edge

1

50mm polystyrene Foam?

Power

  • Run through roof and down walls to reduce slab penetrations. Unsure on best method to get down through/beside bale walls.
  • Limited to single phase power (approx 70 amps for entire property?).

Water

  • Tanks for roof collection – one below house for collection pumped up to one above house for gravity feed.
  • Tank for creek water. Potentially use creek water for toilet flushing and other non-potable requirement (double-piping ? Selection valve ?). Creek water to be used for garden watering (and firefighting?).
  • Need access for tankers to deliver water during dry periods.
  • Solar hot water heater to be mounted on roof of living area of house.
  • Tank sizes :
    1. Creek tank – 76000L. Located above house with approx 30m head. Used for garden watering, stock, & other non-potable requirements. 22,000L reserved for firefighting.
    2. Capture tank – 49000L. Located below house within house paddock. Used to collect rain water from roofs. Sized to handle a storm event of 200mm within 24 hours. Seperate downpipe feeds required for main house, workshop and B2&3/Studio to handle storm event.
    3. Main potable tank – 129000L. Located above house with approx 30m head.
  • Pipes for water to be run through roof cavity to reduce floor penetrations. Lagged to prevent freezing ? Assumed to be copper inside the house ? Assumed to be poly-pipe outside house, except for above ground metal pipes (fire-proof).

Sewerage

  • Onsite wet composting system – Aqua Clarus or A & A Worms.
  • Assume sewer pipes to be PVC. Should under & in-slab pipes be copper for longevity ?

Structured cabling

  • Cat5E (or maybe cat6) structured cabling throughout for phone and data outlets.
  • Requires a patch-panel places somewhere, plus network switch. Potentially seperate to this are two computer servers (requiring power and air circulation, and probably sound baffling, and not near sleeping/living areas).
  • Fibre optic data cable between buildings.

Bushfire protection

Asset Protection Zone (APZ) to be located entirely within lot 1. Lot 1 is designated as low bushfire risk.

Lot 1 is Group 3 vegetation classification (pasture with some remanent trees – predominantly eucalyptus). The adjoining lots on both sides contain sections of Group 1 vegetation in gullies with the remainder pasture. The closest section of Group 1 vegetation is approximately 70 m from the nearest edge of the proposed building site - *** Need to check this. If it is more than 100m then no building requirement applies. If Group 2 vege (eg. Woodland) is the closest bit then Medium bushfire building requirements may apply.

Group 1: Upslope APZ = 20m (Inner - IPZ) + 10m (Outer - OPZ) – > 5 deg slope
Downslope APZ = 50m (IPZ) + 10m (OPZ) – 10 to 15 deg slope

Group 3: 20m APZ in alldirections.

Roads: Minimum 6m wide (4m plus 1 m each side cleared). Require either passing bays every 200m or 8m wide for two way access.

Distances are measured in the horizontal plane.

Woodpiles or stacked flammable materials not to be located in IPZ (includes hay & stock feed).

Water supply for fire fighting – Minimum of 22,000 litres if sprinkler system installed. Tankers need to be able to park within 20m of the water tanks, prefer within 10m downslope.

Outdoors

  • Pergolas on north facing windows, with grape vines (or deciduous vine of some sort) ?
  • Wood fired pizza oven out near north/west corner of house.
  • Vegetable patch north of house on flatish land.
  • Will build mobile chook pen, dog run, glass house, shade house.

Issues

Issues with the current (25/11/03) U shaped design are:

  • Is there enough natural light into the bathroom? Try not to make the window too big.
  • No space allocated for wiring closet or computer racks.
  • Location of secondary heating (wood stove) in walkway may create a burn hazard if people trip. Alternative location against kitchen bench would reduce heating to bedroom and study.
  • Shading of east windows required??
  • Location of washing line, gas bottles and bins?
  • Double glazing to all windows is very expensive.

Notes from Discussion with BVSC

Met with Coucil Building Inspector on 9th December to get guidance on requirements for DA.

  • There is a seperate application form for Onsite Sewerage Management (OSM). Have now picked up a copy.
  • Need to use 10 year storm event data to size water storage, gutters, pipes, etc. Note that the development control plan for OSM states that the 90th percentile rainfall data should be used.
  • Zincalume tanks can be specified as they are not considered a “reflective” material. No requirement for colourbond.
  • Sewerage absorbtion trenches must be on the flattest possible ground, so cannot be placed on the slopes to the east or west of the house as originally intended.
  • Windows should meet N3 specifications for wind loading.
  • Soil class will be in the range 10 to 15 (class M). Decomposed granite.
  • Driveway needs to be considered and covered in the DA. Because of the slope sediment and erosion control is of major concern to the Council.
  • Bushfire controls discussed were mainly on the right track. Need to specify bronze mesh flyscreens and ensure that cement sheeting (or equivalent) is used to fill in the sections where the roof lines overlap so that no ember traps are created.