Green Oversite



New Subdivision Design

Good solar access for housing is the first and most fundamental requirement for passive solar, energy efficient design. (Solar access requires access to the sun's rays on the north face of the building and the roof at all times of the year and especially during winter. This allows the house to be designed in such a way as to get winter sun into the house through the northern windows (in southern hemisphere temperate climate zones - through the southern windows in the Northern hemisphere), which can lessen the amount of heating required from fossil fuel sources, and also allows the placement solar hot water panels and photo voltaic panels for the generation of electricity.)

For houses to have solar access it is often taken to mean that the house should be facing north. However even with the best subdivision design only 50% of blocks are going to be able to face north. However with the judicious use of covenants on adjoining lot building, tree locations and heights, building regulation governing the size of blocks, and in particular their width, and in-block building envelopes, then blocks of all orientations should also be able to be guaranteed solar access on the north side of houses built on the block.Note1.

Blocks which face east or west should be able to get solar access to the north side of the house if they have sufficient width and the neighbouring property has appropriate height covenants. For example if a standard house width is 10 metres then in order to get solar access into the north side of an east or west facing house during winter the block width would have to be at least 15.5 metres, and the neighbouring house on the north side would need to have a single storey height restriction (to top of gutter - or ridge for gable) of approximately 3 metres at the neighbouring fence line and a maximum roof slope of 29 degrees (the sun angle in Melbourne at the winter solstice)Note 2. Tree height restrictions would also be required in the front section of the north side neighbouring block. The block itself should have an allowable building envelop so that the house is built on the south side of the block, leaving open the north side. (The figures indicated will change for cross sloped blocks so they would need to be calculated individually for different sloped blocks and also a different location to Melbourne.)

Where the blocks do face north or south they need to have sufficient width to allow enough solar access (say a minimum of 20 metres, preferably more, when at least 3.5 metres of that frontage will usually be taken up by the connected garage or side driveway and/or the house is larger).

There would need to be regulation to restrict the location double storey construction relative to the building envelop of the house block to the south. Double story construction can be allowed on north or south facing blocks, provided they are not so close to the rear house as to block the rear house solar access. So would need at least 11 metres from the back of the double storey part of the house to the rear of the house on the adjoining block. East west blocks could be partially double storey but again the rule the double section proportion of the house to the north would need to be at least 11 metres from the northern wall of the house of the block to the south (but as this block would have a building envelope restriction of 5.5 metres from the northern boundary the double storey section of the house to the north only needs to be 5.5 metres from its southern boundary.

Where the blocks face south there would need to be tree height restrictions in the rear yards of the blocks adjoining to the rear.

Other angled blocks can also get solar access provided they are sufficiently wide to allow angling of the house to open up the living area windows to the North.

With good design and appropriate covenants the only blocks that should be problematic for solar access would be those on a south (and SW & SE) facing slopes.

So if this is possible then the question needs to be asked why isn't it done? I suggest the following reasons:

  • Current energy ratings means houses do not need solar access to achieve the mandatory rating - so there is little demand from the public and from housing designers;
  • It would impose restraints on the subdivider meaning they may not be able to squeeze that additional lot or two out of a new estate. Developers/subdividers would therefore believe that there would be less profit so they would oppose it;
  • Subdividers seem to think that people don't like having restraints on what they can build on their land (though it doesn't seem to stop subdivider from putting covenants for minimum housing size on their estates and a whole lot of other things - my comments on this in the Additional Thoughts on Subdivisions section on this page);
  • With a solar access requirements subdivision lots may need to be wider, that is, have a longer street frontage. Streets are expensive to build so narrow frontages (and long blocks) are cheapest for the subdivider to construct. For solar access blocks there may be additional costs to the subdivider (again leading them to oppose this change); and
  • Most potential home builders don’t necessarily know what it means for a site to have solar access and the benefits to them and even if they are interested in passive solar don’t know what to look for or think that the current rules are just the way it is for medium density construction.

From this I conclude that subdividers will not subdivide for solar access voluntarily so therefore the only way to implement it is to regulate/legislate these changes to make them mandatory.

Additional Thoughts on Subdivisons

In addition to these requirements certain covenants that are common at present should be disallowed. From my experience a large number of new subdivisions put covenants on the construction type that they allow on the new blocks limiting the construction to brick or brick veneer. This construction has high embodied energy - with brick being manufactured by firing clay at a high temperature. These types of covenants should be banned, allowing lower energy construction methods to be used, such as timber, (insulated) mud brick, AAC (Hebel) block or sheet, timbercrete, hempcrete, cement board (insulated), structural insulated panels (SIPs) or even straw bale. Also some subdivisions have minimum house size restrictions on the blocks (e.g. minimum house size of 190sqm). Again this should be banned. Small is beautiful and always more energy efficient (given the same construction techniques) and if people want a smaller house with more surrounding land I can’t see why they should be restricted in this. If anything a maximum housing size could be imposed. (I visited a subdivision established by VicUrban (in May 09), the land development company owned by the Victorian State Government. I was disappointed to learn that they had exactly the same type of covenants in place. As a Government owned organisation I don't see how they can justify this. Leaving alone the solar and energy efficiency arguments having these covenants is encouraging a form of social exclusion. The larger house size requirement means higher building cost and therefore poorer people may not be able to afford to live in that estate. (If house size is reduced from 190 to 140 sqm there would be, say, a $40K to $75K (Aus) decrease in housing costs - very significant.) Government should not be participating in this and should be actively encouraging full social mixing. The Government could at least partially solve the housing affordability problem if they firstly forbid VicUrban from setting these minimum house sizes and then outlaw it in the rest of the industry.)

Within each subdivision there should be a range of block sizes to cater for different budgets, to try to eliminate potential “ghettos”. A certain percentage of higher density one and two bedroom flat or unit construction should be required.

"Third pipe" systems should be considered to supply second grade water, probably runoff, for the flushing of toilets and watering of gardens, although this may not be required if the house have there own collection and reuse system(s).

Needless to say public transport considerations should be incorporated into the subdivision design. Developers should pay an additional “headworks” type fee so that the cost of provision of additional public transport does not completely fall on to the tax payer. Bicycle and walking paths are of course integrated into the new subdivision design. Where a new shopping centre is to be constructed the new centre should be required to contain a reasonably large area of office space so that people who live in the new subdivisions will have the option of office work close to where they live. Encouragement for employers to establish there may need to be considered (e.g. tax breaks).

Also in conjunction with this there needs to be solar access legislation that will guarantee the existing levels of solar access for all existing houses. So putting on a double storey extension or growing large trees which would deprive the neighbouring house of solar at least to its roof (and probably its northern wall) would be outlawed. Without this then passive solar renovations or placement of solar hot water or even photo voltaic panels could be thwarted.

Note 1. The only exception to this would be blocks located on the Southern side of a hill.

Note 2. Figures used in this article are typical of what would be required in Melbourne Australia (latitude 37 degrees South). Other latitudes would have different requirements.

Energy Efficient House Design

Green Planet Home Page

Top of Page
| Site Information | (C) |