Category: Design

Height Above Ground


For the typical modern house with slab on ground base there are two minimum heights above ground level that need to be considered:

  • Next to the building.
  • Distance of 1m away.

The reason for these minimums is to keep water out of the building, including the structure and foundations.

Next To The House

Floor level above external finished surfaces must be a minimum of:

  • 50 mm above impermeable (covered paved or concreted areas) that slope away from the building
  • 100 mm above the finished ground level in low rainfall intensity areas ( 5 minute intensity of less than 125mm/hour for a recurrence interval of 20 years -see: Rainfall Intensity to check your site), or sandy well-drained areas
  • 150 mm in any other case.

Distance of 1m

The external finished surface surrounding the slab must be sloped away from the building, for the first 1m by a minimum  of the following:

  • 25 mm in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving)
  • 50 mm  in any other case.

Normally in clay soils I would allow another 15-20mm to allow for any ‘Soil Heave’. (See:Building on Clay Soils)

Overall

To meet the Building Code the range of total heights above ground will vary between 75mm and 200mm depending on circumstances. If you want a smaller step between inside and outside (for reasons such as Better Accessible Design) you will need to talk with your House Designer about a detail which meets the intent of the Building Code (Keeps water out of the house).

 

Rainfall Intensity

When most people think about rainfall they think about the amount of rainfall . . . . . . . . . but it’s just as important to understand how hard it can rain, the  ‘Rainfall Intensity’.

The ‘Rainfall Intensity’ is important when thinking about things like; Roof Gutters, Down Pipes, Stormwater Pipes , Tank Overflows, and even how high your house is above ground level.

Photo courtesy of www.mirror.co.uk

Recurrence Interval

When talking about heavy rainfall you will frequently hear talk on the news about things like a ‘1 in a 100 year storm’. What that means is that a statistical calculation indicates that a storm of that strength is only expected to occur once in any 100 year period, the ‘Recurrence Interval’.

There are two rainfall intensities that the building codes normally consider. They are based on the peak 5 minutes during a storm for vaious ‘Recurrence Intervals’.

Intervals can be from: 1 in 20 years to: 1 in 100 years (See this link for more information: Roof Choices)

Intensity Calculation

Statistical intensities have been calculated for all locations in Australia and are available at the Bureau of Meteorology (BOM) Website.

Search for ‘Intensity Frequency Duration (IFD)’

To Use the IFD

  1. Enter “your town name ”  “coordinates”  into Google and write down the coordinates
  2. Click on the Create An IFD button
  3. Enter the coordinates into the Decimal Coordinate box
  4. Enter the town name in the Location Name box
  5. Tick that you accept the Conditions of Use
  6. Press the Submit button
  7. Click on the Table tab
  8. The following is the top line of the table for Werribee in Victoria.
Duration

1EY

1 year

50%

2 years

20%

5 years

10%

10 years

5%

20 years

2%

50 years

1%

100 years
5 mins

44.9

60.1

83.4

99.7

121

153

179

The units are mm of rain in 5 mins (Multiply by 12 to get an hourly flow rate)

Low Rainfall Intensity

Parts of the Plumbing and Building Codes refer to areas of “Low Rainfall Intensity”.

A location  of “Low Rainfall Intensity” means the 5 minute rainfall intensity for an average recurrence interval of 20 years is not more than 125 mm/hour.

 

For more on rainwater plumbing see Drainage

Rainwater includes more on rainwater collection

 

 

 

 

Kitchen Drawer Fail

Have you ever wondered why kitchens with all the unit along a wall are so popular with builders?. . . . . and island units?

Why are drawers without a large handle common?

Well it stops mistakes like this happening!

I would have thought most kitchen installers would have made this mistake once, but only once!

One thing to think about though if planning a kitchen space with corners is the storage volume in those corners is very hard to access.

The picture is from Furafuwa.com 

For more Fails and unusual houses go to What the………….?

 

Plumbing Acronyms

There are a lot of acronyms used on plumbing drawings so here are a few definitions:

AG – Agricultural (Drains)
B – Basin
Bth – Bath
BT – Boundary Trap
DP – Down Pipe
FW – Floor Waste
HWS – Hot Water Service
IC – Inspection Chamber
IS – Inspection Shaft (also IO -Inspection Opening)
ORG – Overflow Relief Gully
PRV – Pressure Reducing Valve
RRJ – Rubber Ring Joints
RWH – Rain Water Head
SHR – Shower
ST – Stop Tap
SW – Storm Water Pipe (or SWD – Storm Water Drain)
SWJ – Solvent Welded Joints
TR – Laundry Trough
VC – Vitrified Clay
VP – Vent Pipe (sometimes UVP – Upstream Vent Pipe)
WC – Water Closet (Toilet)
S –  Kitchen Sink
SV – Stop Valve

If you have seen an acronym you don’t understand, then let me know, and I will try to give you an answer.

See Jargon for more posts

 

Underground Garage

Basement, or underground garages are becoming more popular.

Its one way of getting a bigger house on a smaller inner suburban block.

Before you make a decision to go for this solution its worth thinking about the cost, and the risk.

Cost

They aren’t a cheap solution for a few reasons:

  • There is a lot of additional excavation with all excavated soil needing to be removed. Expect to pay over$100/cubic m
  • Supporting adjacent properties during excavation. You are probably going to be excavating below the foundation level of your neighbours, so its not just digging a big hole. Specialised techniques to do this safely will add to the cost
  • Not only are the basement floor and walls going to be strong they are going to have to be waterproof.
  • As the garage floor is probably going to be below the Storm Water Drains you will need a  pumping to keep the garage dry.

Risk

The drainage company I work for has had to pump out several flooded basement garages over the past few years. The reasons for this are:

  • Even in Melbourne a heavy storm can easily result in over 25mm/hour.
  • For a driveway like the one in the photo above with a total area of around 100 m2 that means about 2500/hour litres flowing into the garage.
  • With that sort of rain you might also get water coming off the street, or the garden.
  • If the pump blocks, or there is a power cut  the water can quickly build up.

Haven’t got room for a ramp? . . . Check out a different idea at this link: Spot the Garage!

 

Have you ever had problems with an underground garage?

 

 

Floor Space Ratio, or Plot Ratio

When you are buying a new house block it’s important you understand how much of the block you can build on!

One way in which NSW councils prevent Over development is by prescribing a ‘Floor Space Ration’ (FSR). The same principle applies in WA but is called ‘Plot Ratio’.

The FSR of buildings on a site is the ratio of  ‘Gross Floor Area’ to Total Site Area.

Gross Floor Area is defined as – The sum of the internal floor area of each floor of a building  measured at a height of 1.4 m above the floor.

It includes  habitable rooms in a basement or an attic.

It excludes:

  • Stairs
  • Voids above a floor in 2 storey properties.
  • Non habitable storage including basement areas
  • Vehicular access and car parking
  • Terraces / Balconies with outer walls less than 1.4 metres high, and

To calculate, you multiply the site area by the FSR ratio.

For example

For a 800sqm site and a FSR of 0.5:1

Maximum Floor Space = 800 x 0.5 =  400sqm.

See Restrictions for  more posts  about what you can do on your land

 

 

Overlooking – Avoiding ‘Direct Lines of Sight’

When considering Overlooking you need to avoid having a ‘Direct Line of Sight’ into:

  • A  Habitable Room window. (The following link explains what a habitable room is: Habitable Room )
  • A Secluded Private Space – Area primarily intended for outdoor recreation activities screened for at least 90% of its perimeter by a wall, fence or other barrier that is at least 1·5m high.

 

Window Location

Windows are not considered to be overlooked if:

  • One of the rooms in considered ‘Non- Habitable’ ; or
  • There is a minimum offset of 1·5m from the edge of one window to the edge of the other; or
  • The sill height of the ‘Overlooking’ window is at least 1·7m above floor level.

 

Obscured Window View

Another solution is to obscure the “Direct line of Sight’ by:

  • Installing frosted glass or other obscured glazing in any part of the window below 1·7m above floor level. (Any window opening, when open, should not provide a direct line of sight) ; or
  • Obscure with a permanent, fixed screen that has no more than 25% of its area open. An example of this type of screen is pictured below.

 

Screening Raised Open Spaces

A raised open space is considered to not Overlook a ‘Habitable Room’, or ‘Secluded Open Space’, if the ‘Direct Line of Sight is obscured by a permanent and fixed screen which has no more than 25% of its area open.

 

Non – Complying Designs

It may be possible to obtain consent for a non-complying design following a report to the council,  although this will be difficult and is unlikely to endear you to your neighbour . . . . . Not Recommended!

 

Also see the post: Direct Line of Sight

Overlooking – Direct Line of Sight

An important issue when building a new house is Overlooking . . . . . . you won’t want to be overlooked by your neighbours . . . . . . and you need to avoid overlooking them, otherwise they will have grounds to object to your new house!

The Regulations refer to a ‘Direct Line of Sight’ which has a particular meaning . This is based on:

  • The view below a horizontal line 1.7m (a typical eye line) above the floor
  • A horizontal view of 45 degrees either side of straight in front of the view.
  •  A horizontal distance of 9m

This is further is illustrated below:

View from a Habitable Room

The regulations are concerned with the view from a  ‘Habitable Room’ such as a living room, but not a ‘Non Habitable Room’ like a corridor. (see the following link to find out which are Habitable, and Non-Habitable rooms. See this link: Habitable Room )

Vertical Line of Site

Horizontal Line of Sight

 

View from a Raised Open Area

A Raised Open Space is an area of more than 2m2  above normal ground level and can include: Balconies, Patios,  Decks,  Terraces, or a landing.

Vertical Line of Site

Horizontal Line of Sight

Exclusion

There is no ‘Direct Line of Sight’ if . . . . . The floor level of the room or the raised open space is less than 800mm above ground level at the boundary, and there is a visual barrier at least 1·8m high at the boundary.

 

This link will explain: How To Avoid Overlooking

 

 

Habitable Rooms

What is a Habitable Room?

You see the phase in several planning and building documents with regard to things like Ceiling Height (see Room Height) and  Overlooking.

Well according to the Building Code of Australia (BCA)

A Habitable Room is ” A room used for normal domestic activities”

Habitable Rooms Include: 

  • Living / Lounge / Family rooms
  • Bedrooms
  • Television Room/Home Theater
  • Kitchen
  • Dining Room
  • Sewing Room/Study
  • Music Room
  • Playroom/Family Room
  • Sunroom

Habitable Room Normally Excludes:

  • Bathrooms / Ensuites / Toilets
  • Laundry/Clothes Drying Room
  • Pantry
  • Walk-in Wardrobe
  • Corridor/Hallway/Lobby
  • and “Other spaces of a specialised nature occupied neither frequently nor for extended periods.”

 

Also see  Overlooking

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