I have previously carried out a worked example of the insulation of a Brick Veneer Wall, so as a comparison here is double brick wall.
I have also shown (in brackets) the effect of using a hebel block in place of one of the brick ‘leaves’:
Element
R value
Outside surface air layer
0.03
110mm brick
0.08
25mm cavity
0.12
110mm brick (*or 125mm Hebel Block)
0.08 (*0.81)
Plasterboard 10mm
0.08
Inside surface air layer
0.12
Total R value
0.51(*1.24)
U value = 1/R
1.96 (*0.81)
The heat losses or gains for 150 sq m (fairly typical external wall area) of this type of double brick wall at 15 degrees above, or below, outside temperature will be:
Area x ‘U’ x temperature difference = watts per hour
150m2 x 1.96 x 15degrees = 4410watts per hour
Heating/Cooling Requirement = 4.41kw/hour
Using Hebel for one of the leaves will improve the heat loss as follows:
150m2 x 0.81 x15degrees = 1822watts per hour
Heating/Cooling Requirement = 1.82kw/hour
Still not as good as the 1.17 kw/hour of the typical brick veneer construction
Don’t forget heat is also lost through windows, ceilings floors and ventilation.
Condensation, a minor inconvenience, or a major problem?
A little condensation on windows is easily dealt with, . . . . . . but heavy condensation in poorly ventilated corners can lead to mould damaging your walls, ceilings, or even your clothes.
Why does Condensation Occur
Condensation in a building occurs when warm air, containing water vapour, comes into contact with a cold surface.
As the air cools it can’t hold as much water vapour so the excess changes into liquid water which is deposited on the cold surface.
The water usually appears as surface condensation as water droplets or water film on cold surfaces, typically windows.
Condensation occurring on cold walls and ceilings is a major issue as it is when mold problems start. Of particular risk are wardrobes on an external wall as there is a cold surface and a lack of ventilation.
Sources of Water
Here are five main sources of water vapour in the home
People –A typical adult will lose around 0.8L/day of water, half from skin evaporation, and half from breathing.
Bathrooms –Not just the obvious showers and baths, its also those drying towels and bathrobes
Kitchen – Kettles, Pans, dishwasher, and the microwave will add water vapour
Un-Flued Combustion – Portable Gas Heaters, Gas Hobs, Bio Ethanol Heaters, even Candles, all emit water vapour into the room as they burn.
Laundry – Unvented Tumble driers, Airing Clothes.
Evaporative Cooling – Because it is mainly used in summer less of a problem, but can be an issue on cold nights.
Preventing Condensation Damage
Action to prevent condensation damage involves looking at both insulation and ventilation.
Insulation. Additional insulation in walls or ceiling will keep those surfaces warmer which will reduce the risk of condensation damage in most rooms .
Ventilation In bathrooms and kitchens the more moisture laden air means that insulation by itself will not be enough. The moist air needs to be effectively extracted to prevent condensation being an issue. (Although I have previously posted about Heat Loss due to Ventilation some ventilation is needed throughout the house)
Role of Double Glazing
Double glazing is often suggested as an answer to condensation however this is not really the case. As the windows are now less cold there is less surface condensation on the windows, so it looks like the issue has gone away. The problem is that without removing the moisture laden air the risk of condensation on walls and ceilings is increased.
See this link to find out why I prefer a separate Extraction fan in the Bathroom: 3 in 1 Bathroom Heaters
To keep moisture out of the insulation materials see this link: Vapour Barriers
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 specialist 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.
Refrigerated 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.
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.
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:
The amount of external wall compared with the area of the floor, ‘ Perimeter to Area Ratio’ (PAR).
The height of the floor above the ground (the calculations below are based on this height being 0.5m or less)
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.
Why is there less fuss about insulation under a concrete raft slab than ceilings and walls?…………well here are a few interesting facts:
A thick layer of earth provides a reasonable amount of insulation.
The soil contributes to the thermal mass of the structure which helps smooth out any temperature variations.
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
