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This guide will help you narrow down your options for adding insulation to your DIY garden room project. We’ve put together a list of the best insulation for garden rooms, by floor, walls, and roof, with U-value ranges. Read on and see how they compare.
If you’re working with a prefab wooden garden room kit, adding insulation can be a warranty-voiding modification if you’re deviating from the standard product specification. Just bear that in mind before you start.
Garden Room Floor Insulation Materials Compared
Here are three choices for insulating your floor:
EcoQuilt multifoil
EcoQuilt is a good choice when you need good insulation without raising the floor height. It gives a U-value of around 0.18 to 0.30 W/m²K, which is strong for a thin insulation layer.
You can lay it over the base frame or under tongue-and-groove boards. It suits tight cavities and small builds, or you could pair it with PIR boards for an even lower U-value.
PIR insulation boards
PIR boards fit between floor joists and give a low U-value of 0.15 to 0.25W/m²K. The boards are rigid, so the floor stays solid under heavy loads. You can also add a thin multifoil layer on top for extra insulation if needed.
Mineral wool slabs
Mineral wool slabs sit between joists and add both warmth and sound insulation. A typical floor with mineral wool gives a U-value around 0.22 to 0.30 W/m²K. This material is also fire-resistant, so it adds a safety benefit alongside the thermal and acoustic boost.
Wall Garden Room Insulation Materials
Here’s what you can use to insulate your walls:
EPS insulation boards
This one is perfect if you want a simple insulation layer that you can fit in an afternoon. EPS stands for expanded polystyrene, a rigid foam board you fit between wall studs to keep heat in.
The boards are light, and you don’t need special gear to fit them. Once the boards are fitted, you add your cladding on both sides, and the wall closes up.
Most wall builds with EPS achieve a U-value of 0.28-0.32 W/m²K at 50 to 75 mm, which is decent for the price.
Exterior T&G cladding
The tongue and groove timber on the outside gives your walls a strong, stable finish. It sits over the insulation and helps keep the whole wall airtight. While it doesn’t add much to the U-value, it protects the insulation and supports the structure.
Interior T&G cladding
On the inside, matching tongue and groove lining gives an even and clean finish. It also helps hold the insulation in place and prevents gaps where heat could escape. This makes the insulation more effective and gives the room a tidy, solid feel.
Note: You can fit both exterior and interior T&G yourself with basic carpentry. If you prefer a flawless finish, a professional can help. Learn more about tongue and groove cladding below:
[What Is Tongue and Groove Cladding]
Roof Insulation Materials Compared for Garden Rooms
Three insulation options to keep your roof warm:
EcoQuilt multifoil
EcoQuilt multifoil is a versatile material that can also be used in roofs. It’s often added under rafters to boost insulation without lowering your ceiling height too much. In a typical roof setup, it gives a U-value of around 0.18 to 0.25 W/m²K. This helps keep the room warmer and reduces heat loss.
You can staple or tape the layers between the rafters to create a continuous thermal barrier. It can be used on its own for a basic roof build, or you can layer it with rigid boards like OSB or PIR for a stronger, lower-U-value roof. Layering it like this helps seal gaps and improve overall insulation.
OSB roofing boards
OSB, or oriented strand board, is a type of engineered timber made from layers of wood strands pressed together. It’s used as a structural base under your roof covering.
By itself, OSB has a little effect on thermal performance, but it gives a solid surface for your insulation and the final roof layer. You can fix multifoil, PIR, or mineral wool on top of it, while the boards hold everything in place. This is worth considering, especially if you’re adding a membrane like EPDM on top.
EDPM rubber roof
EPDM is a single-piece rubber membrane that sits on top of your roof to keep water out. It doesn’t contribute much to the U-value, but it keeps the insulation dry. But its flexibility handles slight movements in the roof while keeping the membrane watertight. This makes a difference, as even a small amount of moisture can lessen the insulation performance.
You can lay EPDM over OSB or timber boards, and it adheres with adhesive or a mechanical fix.
Using Multiple Insulation Layers in Insulated Garden Rooms
Many insulated garden rooms use more than one type of material in the same build-up. Floors can have a multifoil layer with timber boards on top. Meanwhile, walls take rigid boards between studs with timber cladding on both faces. Roofs often mix multifoil and OSB for strength and warmth.
If you’d rather skip the work, our BillyOh Dojo E insulated building already comes with a complete setup, combining multiple insulation materials together. It gives you a ready-made garden room prefab kit with insulation built into the design.
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