Garden Office Guide: Insulation


Insulation is one of the key concerns of garden office buyers, we all know it’s important but can get baffled by all the options. This section won’t tell you which insulation is best but will hopefully make the topic a little clearer.

As warm as a house

Many garden office companies claim that their garden offices are better insulated than modern houses. The Building Regulations set out target u-values for the insulation of the floor, walls and roof and garden office suppliers have these targets in mind when designing their garden offices and many have even managed to exceed them!

U-values are the unit of measurement used to measure thermal performance, it’s not just the u-value of the insulation that is used but the values of all the materials used in the floor, walls and roof makeup, these details are entered into special software and the u-value of the garden offices floor, walls and roof is calculated the lower the u-value the better performing the floor, wall or roof. We conducted a survey of garden office u-values on The Garden Room Guide and its worth taking a look at it, it is encouraging to see how well insulated garden rooms are.

Insulation is not only good in winter

Everybody thinks that insulation is all about keeping warm in winter but forget that it also helps keep you cool in summer – warm air wants to travel to cooler areas so if it’s hot outside the warm air will want to travel to the cooler air inside your garden office, a well insulated garden office will minimise this transition so your garden office will be a cool and comfortable on a hot summers day.

Types of insulation used in garden offices

There is a wide choice of insulation that can be used in garden office construction, garden office suppliers make their choice based on performance, cost factors, ease of installation, wall thickness and environmental benefits, let’s look at the options:

Reflective Foils

These work in a different way to mineral wool and rigid insulations in that they reduce radiant heat transfer. Reflective foils come in two types – foil faced bubble wrap and multi layered foils which are made up of sheets or foil and polyethylene foam. For reflective foils to work efficiently one or both the faces should face an unventilated air space. These foils are light weight and create a thin wall structure.

Rigid Insulation

Rigid insulation is regularly used in garden office construction as it has high u-values but is relatively thin meaning relatively thin walls are created. Rigid insulation comes in several types the most basic being extruded polystyrene known as XPS and expanded polystyrene known as EPS; polyurethane insulation known as PUR and polyisocyanurate known as PIR are better performing than XPS and EPS and are usually faced with foil to add reflective insulation properties, the performance of the insulation can be hampered if this foil facing is damaged.

When comparing SIP’s it’s important to ask what the insulation is, some cheaper panels will have XSP or EPS insulation but SIP’s filled with PUR or PIR insulation, although more expensive  will be better performing.

Mineral Wool

Mineral wool comes in two types glass mineral wool and rock wool, glass mineral wool is made from recycled glass, sand and limestone and spun to form strands which are bonded together to form a mat, rock wool is made from the recycled waste of blast furnaces. Walls insulated with mineral wool are often thicker than those insulated with rigid insulation as a deeper thickness is needed to achieve the same u-value.

Recycled Plastic Bottles

Insulation can be made from recycled plastic bottles, it is a cleaner and less itchy material than mineral wool and good for the environment, like mineral wool this type of insulation is packed between the studwork frame.

Sheep’s Wool

Obviously a natural product, sheep’s fleeces are used to create a mat which can be fitted between the studwork frame. At the end of its useful life sheep’s wool insulation can be fully recycled.

Hemp Insulation

Hemp is a durable fibre cultivated from cannabis plants it is mixed with polyester to create matting which can be fitted in-between the studwork frame.

Cold Spots

Cold spots or thermal bridging to give it its proper name are areas on the building where there’s no insulation, in timber frames this can occur where the timbers in the frame are – this is particularly common in the corners of the garden offices, if there’s no insulation in these places the heat inside the garden office can escape. Some suppliers overcome this problem by putting a layer of rigid insulation on the outside of the timber framework this creates an insulative sheathing around the garden office. Overcoming problems with cold spots is one of the main advantages of SIP’s which create a tight envelope of insulation with no framework to bridge it.

Whichever insulation type you choose the important message you should consider is that you need to buy a well insulated garden office, lesser insulated garden offices maybe cheaper in the first instance but they will cost you and the environment more to run in the long term.

In the next section of the Garden Office Guide we look at roofs.

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