While this system will work well, two issues arise from installing in this way. The first is that heat escapes through the exposed ceiling joists because wood is a poor insulator (ie there is an incomplete thermal envelope of insulation across the roof space). Secondly the spacing between joists tend to be inconsistent in older homes meaning pre-cut product does not necessarily fit and requires a lot of cutting and fitting. The net result of these two issues is that a higher grade of material needs to be used to achieve the same level of overall performance as a blanket system. On the plus side leaving the ceiling joists exposed makes walking across the ceiling and accessing wiring and services a lot easier. There is also no gap between the product and the ceiling meaning less chance of heat loss if the insulation is disturbed.

Blanket format

Installing insulation in blanket format is the more modern method. It creates a very complete thermal envelope in the ceiling as the insulation is rolled out over the top of the ceiling joists essentially ‘blanketing’ the whole ceiling. The insulation comes in roll form rather than pre-cut segment. With the blanket system it is very important that the cavity under the blanket is filled in before the blanket is laid. If you are starting with no insulation we recommend installing a lighter layer between your joists first (thus filling the cavity) and then laying another blanket layer completely over the top. The cavity left by just installing a blanket over the top of the joists can easily be compromised resulting in significant heat loss.

Whilst more insulation material is used to insulate the ceiling, the grade of material can be dropped to achieve the same level of performance as segment insulation. The major disadvantage of blanket insulation is that it can become hazardous to walk across the ceiling as the joists are no longer visible. Secondly because the insulation sits on top of the joists, and not hard against the ceiling (ie Gib or plasterboard) there is a pocket of air trapped between the insulation and the ceiling. If this pocket is compromised, for example when one portion is moved, then thermal performance drops. What this means in real terms is that it becomes more important that insulation is fixed up by tradesmen or others working in the ceiling space when they have finished.

There are two material types we install into ceilings; polyester and fiberglass:

Polyester

100% polyester insulation is becoming more and more popular as an alternative choice to fiberglass. It is manufactured to the same performance levels as other types of insulation but has a number of distinct advantages.

Advantages

• Completely safe to handle and live around — no respiratory or protective clothing required in handling.
• Non itchy — the dust or fibers are not small enough to enter your pores to create irritation.
• No dust capable of entering your respiratory system is created by the product.
• Environmentally friendly being made from at least 45% recycled plastic.
• Strong durable product which can handle being moved at a later date or walked on.
• Fibers are not small enough to enter and be distributed by attic ventilation systems.
• Odorless and neutral.
• No formaldehyde used in its’ manufacture.
• Long life material (50 year + durability rating).
• Can be stapled into place to ensure it will not move.
• Will not absorb moisture.

Disadvantages

• It is more expensive than fiberglass.
• It has to be thicker in volume than fiberglass to achieve the same thermal performance which can restrict its’ use in some areas.
• Handling of the material during installation is more difficult as the bales are quite large

We install polyester material manufactured by Autex industries in Avondale, Auckland, under the brand name of Cocoon or Greenstuf. View the Greenstuf brochure here.

Fibreglass

Fiberglass is very much the traditional mainstay of insulation in NZ. It is a very common product both here and around the world used in both new and older homes. The product is manufactured from glass and usually contains around 30% recycled glass. The following is some advantages and disadvantages of fiberglass.

Advantages

• An economical option
• Achieves a higher thermal performance level by thickness than other materials meaning it can often be fitted into tighter spots than other products.
• Is easy to work with when installing as it can easily be cut and manipulated around fixtures in the ceiling such as downlights, fans etc.
• Bales can be tightly wrapped and compressed making them easier to move into the attic space.

• The fibers are small enough to create irritation of the skin and respiratory system.
• Protective clothing and light respiratory equipment (ie a dust mask) must be used when handling.
• The bonding agents in many fiberglass products contain formaldehyde.
• More recent products are made of bio-soluble glass which will dissolve in your system if inhaled.
• Has an odor for the first few months of its life (although this is not usually noticeable in the home).
• Can tend to become damaged if moved or walked on too many times.

When we visit your home we will happily show you samples of the products.

Downlights

At The Insulation Warehouse we will install insulation over the top of down lights that are rated appropriately.  There are many imported products on the market that suggest they can have insulation laid over them but to ensure there is no risk of causing a fire we will only install this way if your electrician specifically signs off on their Certificate of Compliance that “the down lights installed in this property are suitable to have insulation laid over the top of them”.