Reducing External Noise

 Aircraft Noise

It’s not always possible to build in a quiet area so there are a number of techniques for reducing noise that you can use in your new home.

Here is a quick review of the options:

  • Minimising  windows facing the noise. OK  as long as the noise source isn’t on the North side otherwise you loose the effect of sunlight in the house.
  • Screen walls. These reflect sound. If you are going for this approach at the front of the house put some thought into the design of the wall. A plain wall just looks ugly.
  • Buffer zones. I’ve previously talked about Buffer Zones in relation to heating and cooling but they can work well in keeping some rooms quieter.
  • Soft landscaping. Absorbs sound, rather than paving which reflects sound. If possible a landscaped bund (low embankment) can be effective.
  • Roofing material.  Tiles will absorb more noise than a colorbond roof.
  • Acoustic Plasterboard. It’s possible, on special order, to get a range of Plaster boards including ones with a denser core that help to reduce sound transmission. A second layer of plasterboard at a different thickness to the original can help.
  • Ceiling  and wall insulation. Ordinary heat insulation batts will absorb noise but for the best performance it is better to use ƒspecialist acoustic insulation.
  • Glazing. Thicker glass will help but double glazing with a larger air will give better performance. The use of  laminated glass can also improve performance.
  • Curtains Heavy curtains can be effective, when they are closed.
  • Solid Doors. Better performance than the standard lightweight doors.
  • Windows and door seals. Need to be  properly fitted, and maintained.
  • ƒRefrigerated Air Conditioning.  Unlike evaporative cooling this doesn’t rely on open windows.
  • Sound absorbing materials Although acoustic tiles, carpets, underlays don’t stop noise getting in they will absorb it better than hard surfaces like tiles or wood floors.

To get effective performance  will require a range of the above options rather than a single ‘Magic Bullet’.

When you are considering these options its also worth bearing in mind that most of these improvements will also improve the thermal performance of your new house.

 

For more posts about plans see the Design Category.

To save money on Heating and Cooling see Insulation

 

Slab Insulation

I have previously posted about the relatively small heat loss from a slab on ground
But what if you have got in slab heating, or just want to minimise heat loss/gain from your house?

Before Construction

This sketch shows the placement of the insulation, if you can arrange for the builder to install it before construction.

The way this is installed is the insulation foam is installed inside the slab formwork.

A 40mm foam board with an R value of 1.0 will typically reduce the heat loss from the slab by 50%.

If you have a small builder or are having a custom home built this should be possible……some project builders however will probably be unwilling to do this installation.

After Construction

If you want to insulate after construction this detail is as effective as the previous method.

It works by using the soil as insulation.

Although soil is not a great insulator by stopping the heat escaping upwards 1m of  soil will provide a R value around 1.

 

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For Posts about Green Building see Sustainability

 

Insulation – Heat loss Suspended Timber Floor

I have previously posted about the Heat Loss from a Slab Floor so how does that compare with a suspended timber, or particle board, floor?

Well its not as bad as you might think because the the space under the floor acts as a Buffer Zone between the room and the external temperature. (Unless you have got a pole house or a Queenslander.)

The main considerations are:

    1. The amount of external wall compared with the area of the floor, ‘ Perimeter to Area Ratio’ (PAR).
    2. The height of the floor above the ground (the calculations below are based on this height being 0.5m or less)
    3. The amount of ventilation expressed as m2/ m length of perimeter wall.

Heat loss Calculations

Perimeter to Area Ratio.

For a 10m x 10m house the PAR = 40/100 = 0.25

For a 20m x 5m house the PAR = 50/100 = 0.5

Ventilation

Low ventilation = 0.0015m2/ m length of perimeter wall

High ventilation = 0.003m2/ m length of perimeter wall.

The  table below provides some values of ‘U’ for the floor .

PAR

.2

3

.4

.5

6

7

8

.9

‘U’ low ventilation

0.4

0.51

0.59

0.66

0.72

0.77

0.82

0.86

‘U’ high ventilation

0.42

0.53

0.62

0.7

0.76

0.81

0.86

0.9

So for a typical single storey house of 20m x 10m

The PAR = 60 / 200 = 0.3

From the table ‘U’ is 0.51 -0.53 depending on ventilation

The heat loss from the slab = Area x ‘U’

= 200 x (0.51 -0.53)

= 102 -106 watts/degree C

The heat loss for this floor is 4 – 8% higher than the same sized slab on ground. The suspended floor will however have a lower thermal mass.

 

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For Posts about Green Buildings see Sustainability

 

Insulation – Heat Loss Slab On Ground

Why is there less fuss about insulation under a concrete raft slab than ceilings and walls?…………well here are a few interesting facts:

  1. A thick layer of earth provides a reasonable amount of insulation.
  2. The soil contributes to the thermal mass of the structure which helps smooth out any temperature variations.
  3. The temperature of the ground below the surface varies much less than the air temperature. For Victoria a ground temperature range in the order of 13 degrees in winter to 22 degrees in summer is typical.

As a consequence the main heat loss from the slab is only from the edges of the slab rather than from the middle.

Heat Loss Calculation

When estimating the heat loss a key factor is the ‘ Perimeter to Area Ratio’ (PAR). Examples are:

For a 10m x 10m slab the PAR = 40/100  = 0.25

For a 20m x 5m slab the PAR   = 50/100  = 0.5

The  table below provides some values of ‘U’ for the total structure for various values of the ‘PAR’ .

PAR

.2

.3

.4

.5

.6

.7

.8

.9

‘U’

.37

.49

.6

.7

.78

.86

.93

.99

So for a typical single storey house of 20m x 10m

The PAR = 60 / 200 = 0.3

From the table ‘U’ is  0.49

The Heat loss from the slab  =   Area x ‘U’   =   200 x 0.49   =   98 watts/degree C

The ‘U’ value for this standard slab is similar to an Insulated  Brick Veneer  Wall.

A Waffle Pod Slab will have a slightly better insulation value but have a lower thermal mass.

If you want to install slab edge insulation see Insulating Your Slab.

 

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For Posts about Green Building see Sustainability

 

Green Roof

How would you like to be mowing the roof of this house?

This is a ‘Green Roof’ something which is quite common in many Northern Hemisphere Countries but not so common in Australia.

They can work well in keeping a house warm with around 2-300mm of soil providing good insulation.

I’m not sure how well they would work in Australia on conventional houses.

  • You would probably need to water the roof in summer to minimise any bushfire risk.

Other issues would be:

  • Upgrading roof trusses for the much heavier loads from all that soil.
  • Finding the right native species to plant so you wouldn’t have to mow!

 

For more Unusual Houses and Fails go to What the………………….?

For Posts about Green Building see Sustainability

 

Insulation Basics – Brick Veneer Walls

This post will help you understand how much heat you lose through walls. A previous post has explained ‘R’ and ‘U’ values

When considering insulation a typical brick veneer wall would be:

Element

R value

Outside surface air layer

0.03

110mm brick

0.08

25mm cavity

0.12

R1.5 Insulation

1.5

Plasterboard 10mm

0.06

Inside surface air layer

0.12

Total R value

1.91

U value = 1/R

0.51

The heat losses or gains for 150 sq m (fairly typical external wall area) of this type of brick veneer wall at 15 degrees above, or below, outside temperature will be:

Area x ‘U’ x temperature difference = watts per hour

150m2 x 0.51 x15degrees = 1178watts per hour

Heating/Cooling Requirement = 1.17kw/hour

To change the U value calculation simply change the value of the element or add an element in.

Example 1 Changing the Insulation to R 2.0

New Total R = 2.41

New U = 0.41

Reduced Heating/Cooling requirement to 0.92kw/hr

Example 2 Adding a reflective building wrap to example 1 (increases cavity R by 0.18

New Total R = 2.59

New U = 0.39

Reduced Heating/Cooling Requirement to 0.87kw/hr

Remember this isn’t the total heating requirement as heat is also lost through windows, ceilings floors and ventilation.

 

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For Posts about Green Building see Sustainability

Insulation Basics – Ventilation

A significant factor in the comfort of you house is the Ventilation Rate. No one likes cold drafts in winter., and a burst of hot air in summer can be equally unwelcoming.

So how do you calculate heat losses due to Ventilation?

Well it starts by deciding how many air changes per hour (ac/hr) you have. How often is the air in the areas you want to heat, or cool, replaced.

Its hard to measure the actual changes without specialist equipment however here are some typical values:

  • Old weatherboard property – More than 2ac/hr
  • Typical new house – Around 1 ac/hr
  • Well draft sealed house – 0.5ac/hr

To calculate the ventilation heat loss the following formula is used:

Qv = 0.36 x V x N

Qv – Ventilation heat loss in in W/degree C
V – Volume in cubic m of space being heated or cooled
N – Number of air changes per hour

So for a typical house with a floor area of 250m2 with 2.3m ceilings:

Qv = 0.36 x (250 x 2.3) x 1 = 207W/degrees C

To keep this house at 20 degrees with an outside temperature of 10 degrees would need 207 x 10 watts = 2.07kw/hour…… just for ventilation losses

Good draft proofing will reduce the heating required to 1.04kw/hour. (You would be saving $1 every five hours, more on colder nights)

WARNING
If you have got a flue less heater (such as portable gas heaters, kerosene heaters or bio ethanol heaters) you will need some ventilation to keep a safe level of oxygen in the room.

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For Posts about Green Building see Sustainability

 

Double Glazing or Smaller Windows?

I’ve posted on Double Glazing but that not the only way to save heat loss through windows so I thought I would do a numerical comparison of the various options for glazing treatment of windows.

In a bedroom of our current house the South facing windows were approximately 4m square (We are in Australia so these windows don’t get any sun).The  basis of my calculations is a difference of 15oC between internal and external temperature.

The equation used to calculate heat loss is:

Heat Loss  =  Area  x  Temperature Difference   x   ‘U’

for

‘U’ single glazing = 7*

‘U’ double glazing = 3*

‘U’ brick veneer = 0.51

* ‘U’ value includes effect of frame.

Option 1 Do Nothing

Heat loss through glass  =  4 x 15 x 7  =  420watts  =  0.42kw/hour

Remember this heat loss is for one room only.

Option 2 Reduce window by 40% to 2.4 m

Heat loss through glass  =  2.4 x 15 x 7  =  252watts  =  .25kw/hour

Heat loss through brick   =  1.6 x 15 x .51  =  12 watts  = 0.012kw/hour

Total heat loss  =  0.25kw/hr  +  0.012kw/hr  =   0.262kw/hour

With our builder this was a no cost option that has reduced the heat loss by 38%.

Option 3 Double Glazing

Heat loss through glass = 4 x 15 x 3 = 180watts = 0.18kW/hour

This is a heat loss reduction of 57% but at a significant cost.

Option 4 Reduce Window by 40% and Double Glazing

Heat loss through glass = 2.4 x 15 x 3 = 108watts = 0.108kW/hour

Heat loss through replacement brick wall = 1.6 x 15 x .51 = 12 watts = 0.012kW/hour

Total  =   0.108kW/hour  +  0.012kW/hour  =  0.12kW/hour

This final option has reduced the heat loss by over 70% and will be around 30% cheaper than double glazing the original large windows.

I hope this has given you some food for thought!

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For Posts about Green Building see Sustainability