Insulation is Key to a Cool Garden Room
Published: 28 June 2024
Reading Time: 4 minutes 54 seconds
We recently spoke with a prospective garden room buyer who posed an important question: "Is a garden room comfortable to use on a hot day, or is it like a conservatory that becomes too hot to use comfortably?" This concern is shared by many who have experienced spending time in a conservatory on a summer's day and worry that garden rooms might suffer from the same problems of being unbearably hot in summer and freezing cold in winter.
However, garden rooms and conservatories are very different buildings. Conservatories are typically timber, metal, or uPVC frameworks filled with glass or polycarbonate, while garden rooms are multi-layer structures that utilise the same materials and construction techniques used in modern timber frame housebuilding.
There are several different approaches used for the core structure of a garden room, including traditional timber frames, structural insulated panels (SIPs), and light gauge steel frames. One thing they all have in common is that they incorporate insulation into the floor, walls, and roof structures.
Most people understand that insulation plays a key role in keeping a garden room warm in winter. Less understood is the role insulation plays in keeping a garden room cool on the hotter days of the year.
How Insulation Keeps a Garden Room Cool
Insulation is crucial for maintaining a comfortable temperature inside a garden room during the summer. It acts as a barrier to heat transfer, slowing down the movement of heat from the outside to the inside of the building. This is achieved through several mechanisms:
- Thermal Resistance: Insulation materials resist the flow of heat due to their low thermal conductivity. This means less heat is able to pass through the insulated layers, keeping the interior cooler.
- Reflecting Radiant Heat: Certain insulation materials, such as reflective foils, can reflect radiant heat from the sun away from the building. This is particularly effective in the roof, where a large amount of heat is absorbed.
- Preventing Heat Conduction: Materials like fibreglass and foam boards trap air within their structure. Air is a poor conductor of heat, so trapping it within the insulation reduces heat conduction into the garden room.
- Reducing Convection: Insulation also minimises heat transfer through convection by creating a tightly sealed envelope around the garden room. This prevents warm outside air from entering and cool indoor air from escaping.
Different Insulations Used in Garden Room Design
Various types of insulation are used in garden room construction, each with its unique properties, benefits, and drawbacks:
Foil-faced PIR boards like Celotex
Type: Polyisocyanurate (PIR) rigid foam.
Benefits: High thermal resistance, lightweight, and easy to install. Reflects radiant heat, adding to its effectiveness.
Drawbacks: More expensive than other insulation types. The foil facing can be delicate and may require careful handling during installation to prevent damage.
Rockwool Insulation
Type: Mineral wool.
Benefits: Excellent fire resistance, soundproofing, and thermal insulation. Durable and resistant to water damage.
Drawbacks: Heavier than other insulation types, which can complicate installation. Can cause skin irritation if not handled properly, requiring protective gear during installation.
Sheep's Wool Insulation
Type: Natural fibre.
Benefits: Eco-friendly, excellent moisture management, and high thermal performance. Sustainable and renewable resource.
Drawbacks: More expensive than synthetic alternatives. May require treatment to prevent pests and can have a distinctive smell that some find unpleasant.
Wood Fibre Insulation
Type: Compressed wood fibres.
Benefits: Good thermal and acoustic insulation properties. Breathable, helping to regulate humidity levels within the garden room.
Drawbacks: Heavier and bulkier than other insulation types, potentially complicating installation. Can be more expensive and may require protection from moisture during installation.
Fibreglass Insulation
Type: Glass fibres.
Benefits: Cost-effective, widely available, and provides good thermal performance. Non-combustible and resistant to moisture.
Drawbacks: Can cause skin and respiratory irritation if not handled properly. Requires proper protective equipment during installation. Lower thermal performance compared to some modern insulation types.
Structural Insulated Panels (SIPs) also use different types of insulation materials, including:
Expanded Polystyrene (EPS)
Type: Rigid foam.
Benefits: Lightweight, cost-effective, and provides good thermal insulation.
Drawbacks: Lower thermal resistance compared to PUR and PIR. Can be flammable if not treated properly.
Extruded Polystyrene (XPS)
Type: Rigid foam.
Benefits: Higher density and better moisture resistance compared to EPS. Offers improved thermal performance.
Drawbacks: More expensive than EPS. Still not as thermally efficient as PUR and PIR.
Polyurethane (PUR)
Type: Rigid foam.
Benefits: Excellent thermal resistance and higher R-value per inch compared to EPS and XPS.
Drawbacks: Can be more expensive and may emit toxic fumes if burned. The production process has a higher environmental impact.
Polyisocyanurate (PIR)
Type: Rigid foam.
Benefits: Higher thermal performance than PUR, with excellent fire resistance and lower smoke production.
Drawbacks: Among the most expensive insulation options. Can be less effective in very cold temperatures compared to its performance in moderate climates.
It Can Be Difficult to Compare Garden Room Insulation
Comparing the insulation of garden rooms can be challenging due to the different materials used by various companies. For example, you cannot simply say that Company A’s 150mm of fibreglass insulation is better than Company B’s 50mm of foil-faced PIR because of the thickness. The 50mm of foil-faced PIR might outperform the 150mm of another insulation material.
Furthermore, not all specifications that say Structural Insulated Panels (SIPs) are the same. Company A's EPS SIP will not perform as well as Company B's PIR filled SIP. Not all companies make it clear what the insulation type is, so it is crucial to ask when comparing your options. PUR and PIR filled SIPs offer greater thermal performance than their EPS and XPS counterparts.
When Comparing Garden Rooms, Ask About the U-values
U-values are the standard measure of thermal performance in a building. Most garden room designers aim to meet or exceed the U-value targets set out in Building Regulations for new build houses. Higher specification garden rooms often surpass these targets, making them more highly insulated than a newly built house.
It’s not just the insulation layer that contributes to the U-value; the multi-layer structure of garden rooms means each layer adds to the overall thermal performance of the floor, wall, and roof.
An experienced garden room designer should be able to provide the U-value numbers for their floor, wall, and roof structures without hesitation. When comparing U-values, the lower the figure, the better the thermal performance.
Double Glazing and Opening Windows Play Their Part
In addition to insulation, double glazing and the strategic placement of opening windows contribute significantly to maintaining a comfortable temperature in a garden room. Double glazing reduces heat transfer, while opening windows allow for ventilation, enabling hot air to escape and cool air to enter, enhancing the overall cooling effect provided by the insulation. Some garden room companies also utilise triple glazing, which offers even better thermal performance, further improving the energy efficiency and comfort of the garden room.
By including the benefits and drawbacks of each type of insulation, your article will provide a balanced and thorough overview, helping readers make more informed decisions about their garden room insulation options.