How to Specify


A guide to specifying Terra Lana Insulation

Terra Lana insulation is formulated in such a way that each product can often be used in more than one location ie the R3.6 140mm wall product can be used in the ceiling.  This guide is to help you better understand the product formulation and to assist you as the designer/specifier to ensure the best thermal performance of the building.

Terra Lana insulation is made from wool and polyester that both have a fibre diameter of around 30-35 microns.  Fibreglass is around 6 microns and can achieve more small air pockets between the fibres and subsequently a higher theoretical thermal rating (R-Value).  All insulation products are tested in bone dry laboratories at elevated temperatures.  Keeping in mind these are theoretical tests, so once moisture in the building, durability of product and installation quality are considered, Terra Lana often becomes the product of choice.


Truss Ceilings generally have a large cavity space for insulation.  Terra Lana truss ceiling insulation is formulated to achieve high loft with low density which in effect gives the highest R-Values for the lowest possible cost.


The limited cavity depth of skillion or flat ceilings creates challenges when high R-Values are desired. 

Terra Lana skillion ceiling insulation is formulated with higher fibre density to achieve high R-Values within the limited cavity space.  Truss insulation products can be specified in skillion roof applications when lower R-Values are acceptable or where there is a large rafter cavity space.

One of the challenges with skillion and flat ceilings is the rafters carry a higher thermal conductivity than the insulation, creating a thermal bridge. Terra Lana has developed a skillion roof batten insulation system that not only reduces the thermal bridging (adding thermal performance), but adds an additional layer of risk mitigation that might otherwise be compromised by services or poor installation when using a single layer.

Based on NZS4642:2016 insulation must maintain a 25mm gap between the top of the insulation and the roof underlay.  There are systems available where you can remove the 25mm gap by using proprietary roofing underlays – see or similar products.


The second option to reduce thermal loss through external walls is to design an insulated service cavity on the internal side of the external wall.  All services are run through this cavity which ensures the external wall insulation has minimal obstructions.  Other benefits of this insulated service cavity are an additional layer of insulation to increase overall R-Value for the external wall assembly and to mitigate thermal bridging through the studs by covering them with this layer.  Designing the service cavity battens to run horizontal to the vertical studs will usually give the best performance.

Terra Lana has multiple insulation options for the external wall insulation depending on the depth of the stud wall, as well as an R1.2, 45mm option for the service cavity insulation.

When both thermal and acoustic performance is required within the external walls, consider our Chatterblock range of products that have been acoustically tested with Marshall Day Acoustics.


External wall insulation is determined by the thickness of the studs.  This limits the R-Value that can be achieved in these cavities.  Terra Lana external wall insulation is formulated with a high density and with anti-slumping in mind.  We strike the same performance issue with standard design with large areas thermal bridging between the layers of insulation, whether through the stud or nog.  Often multiple studs are used at window and door jambs which create further thermal loss to the envelope.

There is one simple option to help mitigate thermal bridging through the nogs and that is to design them to be fixed on edge to the external side of the cavity.  This reduces the size of the nog/dwang framing required, allowing the back of the insulation to be notched out at each nog and still ensures structural fixing for the external cladding if required.


Most internal walls are designed with 90mm walls due to their non-structural requirements.  Terra Lana has many acoustic options to help reduce sound transmission from one room to another.  Chatterblock ECO is 60mm thick to avoid wiring and pipe obstructions from services.  The reduced thickness is made up for in the density of the product, which is friction fit and self-supporting.  Chatterblock ECO is more cost-effective, easier to cut and the highest performing acoustically of all our tested products.  Chatterblock ECO should be the first choice when acoustic performance is desired above all else.


When considering insulation options for the mid-floor, there are generally two things to consider: acoustic and thermal requirements.

Due to the mid-floor not forming part of the thermal envelope there are no requirements for thermal insulation, however there may be situations where thermal loss is wanting to be kept to a minimum between floors of a building.  Consider specifying Chatterblock ECO when only acoustic performance is required due to its rigid self-supporting structure and its high acoustic rating.  Chatterblock ECO is limited to R1.4, so when higher thermal ratings are desired, consider Chatterblock+.  Chatterblock+ still has excellent acoustic properties, however cost a little more to manufacture so should only be specified when required the thermal component.

Mid floors can often have joist centres that do not match our standard widths, however, do not be concerned as we can manufacture to a specific width on request at no extra charge*.

*Please note that a minimum of 50m2 is required when manufacturing widths outside our standard product options.


Terra Lana underfloor has been formulated to have a semi-rigid polyester base.  This creates a ‘wind-wash layer’ to prevent wind under the building reducing the performance of the insulation.  It also creates a layer that can be stapled into to hold the insulation in place when being installed from the underside.  Generally, Terra Lana underfloor insulation is installed from the underside and is considered a retrofit product.  If wanting to install in a new build situation from the top site considerations will need to be made to ensure the correct width is made and the product will be held in place using strapping or similar.

If the underfloor structure is being lined underneath the floor joists with ply or another similar substrate, our ceiling or wall products can be specified due to not requiring the ‘wind wash’ layer.

The same methodology should be taken for soffit areas that require underfloor insulation for the floor above.  Due to the insulation being enclosed a standard wall or ceiling product should be used that best fits the R-Value required and cavity space available.