A void fill is a type of design that is used in the manufacturing process of building products such as joinery, doors and partitions.

Void filling is when you fill an area with insulation. Void filling keeps your home insulated and helps conserve heating and cooling costs.

The purpose of void filling in construction is to provide structural strength, general overall stability and sound-proofing where it would otherwise be unachievable or impractical. More specifically, we can differentiate between an idealistic “ideal” void fill and the one most commonly presented in practice:

An ideal void fill:

A) Has no thermal effect on surrounding structures (i.e., does not absorb or store heat [does not add or remove heat from the structure]

B) Provides the same degree of sound insulation as the product surface (i.e., has no effect on noise heard by occupants)

C) Allows relative movement between structures to accommodate differential movements

D) Provides the least cost/weight-efficient structure that fulfills (A)-(C).


The ideal void fill does not exist because there are factors that will inherently change under different conditions. These include: building orientation, internal and external loads, soil conditions, etc. However, you can achieve a level of performance through good design practices which ensures sufficient insulation is achieved within the given constraints. This could mean adding additional insulation or taking corrective measures where it is lacking. For example, using drywall for interior wall insulation or extra insulation under the exterior of a window or door.

There are several elements within construction design that are important to consider when trying to determine which void fill is right for your project. This includes insulation R-value, flame spread, moisture resistance, etc.


R-Value: The insulating value of a material expressed as an R-value per unit thickness. It measures the effectiveness of insulation to resist heat flow and is used to compare different types of material for thermal resistance. For example, knowing the R-value will tell you how much heat loss or gain occurs in an area over time, thus allowing you to make informed decisions about what products you need for your specific needs.

Ruby Rich