New Mews (2/2)
New Mews (1/2) recap: This is a typical Perth suburban block measuring approximately 190m long by 110m deep. In the past it would have had perhaps sixteen single-storey houses. Now it has 22 but some other plots have been subdivided to allow up to eight houses on land previously occupied by two. Such subdivisions have vehicle access via a shared driveway and little open space apart from the construction setback.
This New Mews proposal redevelops the entire block to provide sixty dwellings in the same space previously occupied by twenty. This is possible by eliminating the gap between detached dwellings – i.e. by making them terraced or row houses and by adopting a row house typology – that of the Japanese machiya. Further land savings are possible by treating the single access road as a car park where the greatest efficiency of area results from parking as many cars as possible along both sides of it. The dwelling width is 6m and, although each house is now a single dwelling and not a main house + service house, there is still a street or “public” frontage and a “mews” frontage for servicing and vehicle access. To do this on the street side would cause too much disruption to traffic and would require the removal of what roadside trees remain.
Before I get on to my proposal, here’s some notes on the other stuff.
Suburban blocks of which this is typical, have a sewer line down the middle and roughly along the back fenceline. This proposal will therefore have it down the middle of the mews. Each dwelling has a separate, straight line to it, and all bathrooms, laundries and kitchens connect to it from directly above.
Ground floor: Concrete slab; Party walls: AAC (autoclaved aerated concrete) or cavity brick party walls; Floor joists: steel sections at regular intervals; Upper floors, 4.6m span AAC slabs; Roof joists: steel sections at regular intervals; Roofing: Sheet metal w/valley gutter.
I envision some kind of shared bin facility at each end of the block. However, the Australian norm however is for individual bins. In the proposals that are to follow, I imagine many owners would opt for some sort of service yard on the mews side adjacent to the space for car parking.
- Courtyard drainage
Courtyards can have individual soakpits, perhaps linked with a sub-grade gravel-filled overflow channel leading to a larger soakpit in the front yard. This channel would pass beneath the slab. Fortunately, Perth has sandy soil.
- Roof drainage
The roof shouldn’t add to the drainage load of the courtyards so rainwater needs to be led to downpipes at the house ends. My first thought was two asymmetrical monopitch roofs draining to a valley gutter along the line of the courtyards, and emptying into end downpipes. This gutter would overflow into the courtyards in case of gutter or drainpipe blockage. This centrally-draining monopitch arrangement has the construction advantage of horizontal parapet flashings/cappings of fixed dimensions not requiring custom fitting.
So then, let’s take this system for a drive and see what it can do! I’ll go SMLXL as that’s most likely how these houses will change over time.
The TYPE A is the smallest possible configuration, with the household entrance from the mews side and the “back” garden on the street side.
The TYPE B is the same footprint with a second storey. One floor panel is removed to accommodate the stair. The household entrance remains on the mews side but now the living area fronts the garden on the street side. A second TYPE A or TYPE B could be built on the remaining site for some arbitrary household composition or tenure.
The TYPE C is the spatial equivalent of the three-bedroom house with two living areas, one family bathroom and one bedroom with en-suite. Many variations are possible. One would be a TYPE B with the extra bays added on both levels and the upper level street-side bathroom relocated to the end of the house. Or the upper level could stay the same for the time being. Or the upper middle space could be left as a terrace. Or the lower middle space could be left open to make a single large ground floor “alfresco” area. In all these examples I’m showing only generic windows in generic positions in all walls where windows are possible. All bathrooms are naturally lit and ventilated. All habitable rooms have cross ventilation.
Variants have more possibilities for upper and/or lower terraces, double length modules, double-height modules, and various combinations thereof.
Type D has a large outdoor area, an informal entrance on the street side and an additional office/guest room at the driveway end. The dining area is double-height to preserve cross ventilation to the bedroom above.
These final three variations on Type E all follow the same spatial rules and occupy maximum buildable area. Type E1 has four bedrooms, five bathrooms, two living areas and secure parking.
Type E2 has three bedrooms, two bathrooms and three living areas, although it could easily have four or five bedrooms and three bathrooms.
Type E3 has three bedrooms, two and a half bathrooms and two living areas.
I didn’t make any stupid decisions but was curious how much space was being used for circulation.
|GROSS INT. AREA|
|CIRC’N % OF G.I.A.|
( % )
Efficiency becomes progressively lower as the houses become longer because the decision to have windows on both sides of all habitable rooms means additional space is needed to pass by the courtyards to access those habitable rooms and, in the larger houses, to pass by the rooms themselves.
This is the nature of the problem. If you want more windows you need more external wall, especially if there are to be windows on opposite sides of the room.
This additional area is most apparent on the living level as the larger bedroom levels can be split into two, each having relatively efficient layouts. The challenges are
- to place kitchens, stairs, storage and as much other functionality as possible along the circulation space and
- to use the remaining circulation space to make the living areas appear larger but without reducing their functionality and/or versatility.
The % of circulation space in this new mews proposal is high because the dwelling width is six metres and rooms are on only one side of the corridor.
So just how much more efficient are double-loaded over single-loaded corridors?
These layouts are from the Property Supplement post. Without knowing actual scales or areas, I can still calculate the circulation space as a percentage of the GIA.
- The lowest is No. 5 with 14.8% as it’s a central circulation spine accessing rooms on both sides.
- The highest is No.2 with 21.5% because in one place it has three parallel corridors.
- All except No.2 use the living/dining area as a corridor.
- Nos.1 and 3 traverse the length of the living/dining area rather than its width, severely reducing the amount of useable space.
- Nos.2 and 6 are decent, suggesting 16% is reasonable for a double-loaded corridor in houses whose area I estimate as approx 200 sq.m.
If my average circulation space is 25% then I need to test the difference a double-loaded arrangement for a 200 sq.m dwelling would make, even if it increases the width by 40% and is counter to one of my initial premises. Type F is a 193 sq.m single-storey double-fronted mews house with 15.4% circulation. In addition to providing daylight and enhanced ventilation, all site area not built-on is fully useable amenity space. This can’t be said for detached houses.
Type F2 comes in at 16.00%. It would have been 13.75% because the GIA is seven square metres less but I added some circulation space to make the entrances to the end bedrooms, laundry and guest bathroom less direct. It’s better. I also added a kitchen island counter dead centre. Some things are better left as they are.
Comparing the length of external wall of F2 with a conventional house of equivalent area on the same site shows F2 has 89 metres of external wall, excluding party walls, while the conventional dwelling has 68. This is no surprise as the proposal is premised on more windows and windows need walls. It becomes a question of relative ventilation rates and the view from those windows.
The conventional dwelling is more compact but only four of its habitable rooms have a direct connection to open space. The other spaces look onto the fence. None have windows on opposing walls or the cross ventilation that resuts.
To end, I’ll just repeat that earlier sentence about the advantages of this proposed configuration, whether single- or double-sided. In addition to providing daylight and enhanced ventilation, all site area not built-on is fully useable amenity space. This can’t be said for detached houses. Having said that, exactly how much cross ventilation will actually occur for various wind directions and speeds is a matter for energy modelling. Type D will be best.
Because these houses can be constructed incrementally, a streetscape varied in shape, setback and materials will occur anyway. There’s not much point of a render such as this next with its unified materials, components and colours.