Types of insulation for garden rooms

There are currently many different types of insulation widely available on the market today. In this article I will aim to give an explanation of the pros and cons of the market leading types of insulation and their potential applications and performance in garden rooms.

Building insulation falls into three main categories. These are woollen, solid foam and reflective foil.

Woollen insulation works by trapping air within the wool fibres and therefore slowing the movement of air out of the building, thus maintaining the internal temperature for longer. It can be made from either fibreglass (usually now made from recycled glass bottles) or rock mineral wool (often made from slag waste from the steel industry).

The advantages of woollen insulation are that it is relatively low cost, lightweight, non-combustible and has good acoustic absorption properties. It is often used in roofing and cavity applications in garden rooms and is usually the most cost effective type of insulation on the market, providing that the space being filled is large enough to take the required amount of insulation. An example of glass wool being used in one of our buildings is below left.

Solid foam insulation comes in five varieties, although extruded polyethylene (XPE) is rarely used in garden rooms, except perhaps underneath timber flooring to prevent noise.

The four other types are expanded polystyrene (EPS), extruded polystyrene (XPS) , phenolic foam and polyurethane/polyisocyanurate (PUR/PIR).

EPS is the least thermally insulating of these foams, and is the stuff that polystyrene coffee cups are made from. It is relatively low cost and is often used in flooring applications in garden rooms and other types of construction.

XPS is the next best foam for its thermal properties, and it is very rigid so mainly gets used where compressive strength is required (flooring applications in particular). Phenolic foam is also used for similar purposes, but has lower levels of thermal conductivity (i.e. better insulating).

PUR and PIR are one of the most widely used insulation in construction today, as they are per inch of thickness the best thermal insulator of the five types of solid foam. It tends to have foil facing to both sides in order to reflect heat and to prevent the breakdown of the foam, which reduces thermal performance of the insulation over the long term. This foam is used in many applications in garden rooms, such as cavity wall insulation and pitched roofs. The common brand names are Celotex, Xtratherm and Kingspan, however manufacturers do make more than one type of solid foam board. We use a lot of PUR and PIR in our buildings, one picture of which is below middle.

The final type of insulation being covered is foil insulation. There are two broad types of foil insulation available, multi-foils and foil faced bubble wrap.

Foil faced bubble wrap is exactly what it sounds like, and is most commonly used for applications such as heat reflective mats that go behind radiators. Some manufacturers of garden rooms use this foil as their main source of insulation, although it isn’t widely used towards the top end of the market.

Multi-foil insulation is a relatively new entrant to the market. It works by reflecting radiant heat back into the building as air flows across it. This means that one side of it must be next to an air cavity in order for it to function properly. There has been controversy surrounding multi-foils on occasion.

As it works be deflecting and reflecting air and heat, its effectiveness changes dependent upon the application and other environmental factors. This means that it can be hard to accurately predict the exact u value that will result when it is fitted in a garden room or other building. Tests have been conducted more extensively over recent years however. The foil used within the roof of our Prestige range for instance (Triso super 10) has in tests performed equivalent to 210mm of glass wool in roofing applications. A photo of some multifoil being used in a wall application in one of our garden rooms is below right.

All of our garden rooms are insulated, with different ranges containing different combinations of types and thicknesses of insulation. Please take a look at our garden room specifications or phone for specific and individually tailored advice.

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