With the right tools and a bit of preparation, installing insulation is a job many DIYers can handle. Especially in lofts, floors, and internal walls. This short guide will help you understand:
- What tools and materials you need
- Key safety precautions to follow
- Step-by-step basics for floors, walls, and roofs
- How different insulation materials (rolls vs. boards) affect the installation process
Let’s walk through each application.
Floor Insulation: Keeping heat from escaping downwards
When it comes to installing insulation under floors the approach varies based on whether you’re dealing with a suspended timber floor or a solid ground floor.
For suspended timber floors, mineral wool rolls are often the go-to. These are cut slightly wider than the joist space and gently friction-fit between joists, and it’s best to staple support netting or membrane underneath to stop sagging. If you’re using rigid PIR or phenolic boards instead, you’ll need precise measurements, ensuring all gaps are sealed with expanding foam or tape to prevent thermal bridging.
On solid floors, rigid boards like PIR or EPS are laid directly over the concrete slab and under screed or final flooring. These boards must sit flat and snug, so the subfloor must be level and clean before installation.
Tools & Tips: You’ll need a utility knife or insulation saw (especially for boards), gloves, knee pads, and measuring tape. Always check for moisture under existing floors before laying insulation as trapped moisture can lead to rot or mould.
Safety note: Watch out for wiring or pipework beneath older floors. Always isolate electricity before lifting boards.
Wall Insulation: From internal retrofits to cavity upgrades
Installing insulation in walls depends on whether the structure has cavity walls, solid masonry, or internal partitions.
Cavity walls in newer buildings can often be filled with blown-in mineral wool, foam, or polystyrene beads. This is a professional job, but knowing the material used is useful if you're topping up or patching.
Insulation on solid walls can be applied internally or externally. Internally, insulated plasterboards (often backed with PIR) can be dot-and-dabbed to the wall or mechanically fixed. Boards must be cut accurately, and joints sealed to minimise heat loss. Alternatively, mineral wool batts between timber studwork provide a breathable option, ideal for older buildings where moisture movement matters.
Tools & Tips: Use a straightedge and knife for cutting plasterboards, adhesive or fixings for boards, and always tape seams. When using mineral wool slabs, wear long sleeves and a dust mask as fibres can irritate skin and lungs.
Safety note: Before drilling or fixing anything to internal walls, check for pipes and electrical cables.
Roof & Loft Insulation: Thermal Performance Starts at the Top
Installing insulation in your roof or loft is one of the most cost-effective ways to boost energy efficiency.
For pitched roofs, mineral wool rolls can be laid between rafters for a simple, cost-effective solution. A second layer across the rafters adds further thermal protection. In converted lofts or where space is tight, foil-backed PIR boards work well between rafters. Boards must be cut tightly and sealed to avoid gaps.
Flat roofs usually require a warm roof method, with rigid insulation (PIR, XPS, or rockfibre) laid above the roof deck and below waterproofing layers. This helps avoid condensation and maximises thermal efficiency.
In unconverted lofts, laying mineral wool rolls between and over ceiling joists is straightforward and affordable. Rolls should be laid in two layers, first between the joists, then a second layer crosswise over the top. Avoid compressing the insulation, and don’t block any ventilation.
Tools & Tips: Use a sturdy board to kneel on joists, a measuring tape, utility knife or handsaw, and PPE. Keep eaves vents clear to allow airflow and reduce condensation risk.
Safety note: Only install loft insulation in dry, well-ventilated conditions. Avoid working alone if you're in an attic space.
Final Thoughts
While the installation basics for insulation are manageable, every home and every insulation material differ. Whether you’re rolling out loft insulation or fitting rigid boards to a wall, always plan your materials and cuts in advance, prioritise safety, and take your time. If in doubt, especially when dealing with external walls or flat roofs, consider a professional assessment.