Best Floor Insulation Board for Garden Studios: 2025 Expert Review
DR Joinery
Expert Joiner & Timber Frame Specialist
A garden studio without proper floor insulation is essentially just a posh shed. In York, where the damp cold seeps up from the ground, the difference between a usable home office and a freezer box often lies in what is hidden beneath the floorboards.
Many homeowners make the mistake of using unsuitable materials or insufficient thickness, only to realise their error when the first frost hits. Structural timber floors need rigid insulation that won't sag, whilst solid bases require high compressive strength.
In this review, I've selected three insulation products tailored for different garden room scenarios: a handy 50mm board for standard joists, a high-density XPS option for underfloor heating, and a serious 75mm board for maximum thermal efficiency.
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Specs vs. The Real World
The Spec: "Foil Tape Not Required"
"Some DIY guides suggest simply wedging boards in tightly creates a seal."
This is false. Without aluminium foil tape over the joints, air will travel through the gaps (thermal bypass), significantly reducing efficiency. Always tape your joints.
The Spec: "U-Values Claims"
"Manufacturers claim specific thermal conductivity ratings (like 0.022 W/mK)."
These figures are accurate for the board itself, but if installed poorly with gaps or cold bridges (timber studs touching both sides), the overall performance drops drastically. The installation quality matters as much as the board.
My Top 3 Recommendations
Three options to cover different needs and budgets
PIR Insulation Board 1200 x 450 x 50 mm; 47.2 x 17.7 x 2 in, One Panel Covers 0.54m² (5.81 ft²), Rigid Thermal Panel with Aluminum Foil on Both Sides for Walls, Roofs, Floors and Sheds
NOVECRAFTO
This is your standard 50mm PIR board, sized conveniently for handling. At 50mm, it provides a baseline of insulation suitable for spring/summer use or storage sheds. The narrower width (450mm) is handy for fitting between standard joist centres without excessive cutting.
The Good
- Cost-effective for smaller projects or patching
- Lightweight and easier to handle in confined spaces
- Foil backing reflects radiant heat effectively
The Bad
- 50mm is the bare minimum for a home office in winter
- Small board size means more joints to tape
Installer Tip:
When cutting this PIR board, use a fine-toothed saw or a sharp insulation knife. Always cut slightly oversize (2-3mm) to ensure a friction fit between your timber floor joists, then seal the perimeter with expanding foam for an airtight finish.
Priced at £14.95 at the time of writing
Check Price on AmazonEkoBoard 10mm XPS Boards Floor Underlay Thermal Insulation Underfloor Heating (1200 x 600mm)(10 Pack), Blue)
EkoBoard
Whilst PIR boards sit between joists, these XPS boards are designed to sit *on top*. They are incredibly dense and waterproof, making them the perfect substrate for laying electric underfloor heating mats or engineered wood flooring. They stop reliability issues with cold bridging through the subfloor.
The Good
- High compressive strength (won't squash under furniture)
- Waterproof structure ideal for potential damp areas
- Maximises efficiency of underfloor heating systems
The Bad
- At 10mm, it provides less total thermal resistance than thick PIR
- More expensive per square metre than standard foam
Installer Tip:
If you are installing a 'floating floor' in your garden studio, lay these boards perpendicular to your finish floor direction. Tape all seams to create a vapour barrier, preventing ground moisture from warping your final floor finish.
Priced at £64.89 at the time of writing
Check Price on AmazonKingspan Thermawall Multi Purpose Insulation Boards 450mm x 1200mm x 75mm Floor Wall Roof & Underfloor (1)
LOWENERGIE
When customers in York ask for a 'proper warm' garden office, I reach for 70mm or 75mm boards. This Kingspan product offers significantly higher thermal resistance than the 50mm standard. It solves the problem of heat loss in deep winter, keeping your workspace comfortable in January.
The Good
- Superior thermal performance for year-round use
- Genuine Kingspan rigidity and quality
- Low emissivity foil faces maximise heat retention
The Bad
- Requires deep floor joists (minimum 95mm or 4x2 timber)
- Reduces headroom if you have to raise the floor level
Installer Tip:
Because these boards are 75mm thick, ensure your floor joists are verified as at least 95mm (4 inches) deep. You need an air gap of roughly 20mm above the insulation (if ventilated) or ensure tight contact if fully filling, though leaving a service void for cables is always good practice.
Priced at £25.99 at the time of writing
Check Price on AmazonFrequently Asked Questions
What is the best thickness for garden office floor insulation?
PIR vs XPS: Which is better for floors?
Do I need a vapour barrier with insulation boards?
Can I install floor insulation myself?
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