Garden office insulation options

Garden offices are insulated like houses

The majority of garden offices on the market today, are built using the same materials and techniques as modern housebuilding. They use the same insulating materials and aim for the same performance targets.

Garden offices don't need to comply with Building Regulations unless they contain sleeping accommodation or are more than 30sqm in size. Many garden office companies, however, use the targets for insulation set out in the Building Regulations as a guide for their buildings. Some companies try to exceed the Building Regulation targets.

Comparing garden office insulation levels

When buying a garden office it is a good idea to compare several designs and purchase the best-insulated building you can afford. Reading a suppliers specification sheet can be useful when doing this.

Insulation performance is measured by its u-value, this is the rate at which heat passes through the material. Garden offices are made up of several layers of material, not just the insulation, and each element of the construction has its own u-value. These are combined to create the overall u-value of the section, i.e. wall, floor or roof.

Most suppliers will have worked out the u-value of their structure, and many will publish this on their specification sheet. Allowing you to compare the performance of one supplier against another. When comparing note that the lower the u-value figure, the better performing the section.

Thick insulated walls are not always better than thinner ones

As we mentioned in the previous section the way to compare the insulation values of a garden office is to examine the u-value of the floor, walls and roof. Some specifications quote the thickness of the insulation they use, implying that their 150mm insulation is better than another suppliers 50mm. This is not a reliable way to compare how well the insulation will perform.

So many different types of insulation are used in garden office construction from natural materials like sheep's wool to foil backed rigid insulation's, and they require different thicknesses to achieve the same u-value / performance level. For instance, 150mm of a fibreglass might be needed to accomplish the same u-value as 50mm of a rigid, foil backed board like Celotex.

Bear this in mind when comparing specifications and use the u-value method as your comparison tool. If a company does not mention the u-value of their structure on their specification, don't be afraid to ask them what it is, a good company should know.

Make sure the floor, walls and roof are insulated

This may seem an obvious statement, after all, we have mentioned that garden offices are built like houses, but some log cabin style garden offices don't feature insulation in all these sections because their construction doesn't have room to accommodate it.

Many log cabin garden offices don't have insulation in the walls. This is because this style of this building is built using interlocking timbers which form both the exterior and interior wall/finish. Thus leaving no void for insulation.

The argument is that wood is a good insulator in itself. This is indeed true, but its not as good a multi-layer wall construction that includes a good level of insulation.

The design of the structure will influence the type of insulation used.

Timber frame garden offices have voids in the framework which can be filled with insulation. While with structural insulated panels (SIP's) the insulation is an integral part of the panels.

Many suppliers use house quality SIP's while other suppliers create their own build-ups using rigid insulations such as Celotex.

There is an argument that SIP's built garden offices are better insulated than traditional timber frame designs. With timber frames the insulation is packed between the framework this means that in the areas where there is wood there is no insulation which creates areas known as cold spots.

With SIP's there isn't the timber, so the insulation is continuous creating an envelope of insulation around the building, and no cold spots!

Many types of insulation are used in garden office construction.

There are lots of different insulation materials used in garden office design, and a supplier will make their choice based on cost, installation speed, performance and environmental credentials.

In a sense, all insulation is eco-friendly because it minimises the amount of energy needed to heat or cool the building. However, some insulation's are more eco-friendly in their production.

Rigid insulation boards - are the most used insulation used in garden office construction. This is because it achieves 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 insulation and expanded polystyrene known as EPS insulation. Polyurethane insulation known as PUR and polyisocyanurate known as PIR are better performing than the XPS and EPS variants 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, so you don't want to see any dents and tears in the foil during construction.

Rigid insulation is a key component of a SIP

When comparing SIP’s built garden offices, 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 - although once popular, mineral wool is not often used in garden office construction. It has been superseded by the rigid insulation boards described above. Mineral wood 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.

Reflective foils - Not commonly used in garden office design these days. Reflective foils work in a different way to mineral wool, and rigid insulation's 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 polyethene foam.

For reflective foils to work efficiently, one or both the faces should face an unventilated airspace. These foils are lightweight and create a thin wall structure.

Sheep's wool insulation - a few companies who design eco garden offices choose sheep's wool insulation. The fleeces are washed and made into mats which sit within the timber framework. There are a number of UK manufacturers of sheep's wool insulation, so it does not have too many miles to travel.

Recycled plastic bottle insulation - only offered by a few companies. The insulation mats are made from our plastic drinks bottles. The fibres are spun into mats which can be fitted between the framework.

Hemp insulation - only offered by a few companies who are eco-design conscious. Hemp is a plant which is easy to grow and absorbs CO2 as it grows. It is then harvested and made into mats which can be used as insulation.

A well insulated will cost more now but save you money in the long run

The best-insulated garden offices also tend to be the most expensive, and there are lots of more desirable features of a garden office to spend your money on! But, actually, the better insulated the building, the less it will cost to run in the long run, because it will require less energy to heat and cool the building.