There are a number of insulation products with reflective surfaces now available but how do they work?
Why do the instructions tell you to put the more reflective surface on the underside rather that the top?
Here is some information to help you understand what’s happening.
All surfaces have different levels of ability to reflect heat with black and matt finishes being very poor and shiny metal surfaces being very good. Most reflective surfaces are also poor emitters of heat. This characteristic is called emissivity (normally written as ‘e’).
An example is clean aluminium foil has an ‘e’ value of around 0.03. This is much less than common building materials such as:
bricks ‘e’ = 0.9 ; or
Building membrane ‘e’ = 0.5
Low emissivity finishes are generally considered to have an ‘e’ value of less than 0.05.
As dust can increase emissivity by 0.25 Aluminium foil is only considered to be low emissivity on vertical surfaces or the underside of a inclined or horizontal surface such as a roof or ceiling, where it will remain clean.
The emissivity acts with the surface layer of air on the building material to give an overall R value for the surface.
The following table shows how the ‘R’ values increase with a Reflective (low emissivity) surface compared with a high emissivity surface.
Sloping 45 degrees
You will see that low emissivity insulation such as aluminium ceiling insulation has better performance (Higher R values) when the the Hotter air is above the insulation than the reverse.
This means that in summer it resists heat during the day but allows the house to cool more quickly at night. In winter, however the performance in keeping the heat in the house will not be as good.
I frequently see comments like “Ceiling insulation is next to worthless in summer.”
I have even heard people say “With a hot roof space it will be overwhelmed.” and “After the sun has gone off it stops the house cooling down.”
Here is the truth:
All insulation works by slowing the rate of heat transfer. If the roof space is hot some heat will pass through to the room below. The insulation will slow the rate that the room heats up from the roof space.
Ceiling insulation isn’t enough to keep the room cool by itself. The room will still get hotter if heat is leaking in through poorly insulated walls and windows.
Ceiling insulation, by slowing the heat gain from the roof space, will reduce the cost of mechanical cooling.
In a well insulated conventional ceiling minimal residual heat remains in the plasterboard and ceiling insulation. The heat in the room is just hot air. The best way to remove the hot air is to open the windows when the air temperature outside is less than inside, or run the air conditioning.
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.
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.