Spray foam insulation is a liquid polyurethane foam that installers apply using a spray gun in the area they want to insulate. The foam then sets, forming an insulating layer. As it's a liquid, installers can apply it quickly. They can also apply it in tricky areas that may be more complicated and time consuming than if you were to use solid insulation materials.
Spray foam can be used to insulate the:
roof
walls
floors
There are two main types of spray foam insulation, closed-cell and open-cell.
Closed-cell foam
Closed-cell polyurethane foam is one of the most effective insulation materials commonly used in homes. It sets solidly and contains lots of gas pockets that can slow the escaping heat from a space. It can also help support the structure of the insulation area.
Its main drawback is that it's not vapour permeable. That means that any moisture in the surrounding air or other building materials can't travel through the closed-cell foam insulation and escape.
Open-cell spray foam insulation
This type of spray foam is the more vapour permeable, which is generally a good thing. It's also lighter and more flexible, but it is a less effective insulator. This means you'll need to use a thicker layer than closed-cell foam to get the same insulating effect.
How is spray foam used?
Foam can be used in various parts of the home:
Roofs: if a home has a pitched roof with an uninsulated loft, foam is sometimes sprayed onto the underside of the sloping roof. This is one alternative to laying mineral wall insulation at joist level (or what you might call the horizontal 'floor' of the loft).
Walls: foam is sometimes sprayed into empty cavity walls, usually in situations where standard cavity wall insulation isn't considered suitable.
Floors: foam can be sprayed to the underside of a suspended timber floor, often using a robot to access the underfloor space. This is a less disruptive alternative to lifting the floorboards and fitting insulation material from above.
