Domakihub How to Insulate a Loft and Cut Your Energy Bills
A practical step-by-step guide to loft insulation for homes, rentals, and hotels in Greece.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
A poorly insulated loft is one of the biggest sources of heat loss in any building — and in Greece, where summer cooling costs can be just as punishing as winter heating bills, proper loft insulation pays for itself quickly. The video above walks through the process visually; this article gives you the ordered steps, material choices, and answers to the questions Greek homeowners and property managers most often ask. Whether you own a villa in the Peloponnese, a rental apartment in Athens, or a boutique hotel on an island, the same principles apply.
Why Loft Insulation Matters in the Greek Climate
Up to 25 percent of a building's heat can escape through an uninsulated roof space. In Greece this cuts both ways: in winter, warm air rises and leaks out through the loft floor; in summer, a sun-baked roof deck radiates intense heat downward into living spaces, driving up air-conditioning demand. Insulating the loft creates a thermal buffer that reduces both effects.
For short-term rental properties and hotels the business case is straightforward — lower energy bills directly improve net operating income, and guests notice and review the comfort of rooms on upper floors. EU energy-performance regulations are also tightening, and a well-insulated loft boosts a building's EPC rating.
Choosing the Right Insulation Material
The two most common choices for a cold loft (where the insulation sits on the loft floor rather than at rafter level) are mineral wool rolls (glass or rock wool) and rigid foam boards. Mineral wool is the most widely available, easiest to handle for a DIY project, and performs well across the temperature range Greece experiences. Rock wool also adds acoustic damping and is fire-resistant.
Rigid PIR or EPS foam boards give higher thermal resistance per centimetre, making them useful where headroom or joist depth is limited. For a warm loft conversion — where the habitable room is inside the roof — the insulation goes between and below the rafters, and rigid boards or spray foam become the more practical option. In either case, aim for a finished U-value of 0.16 W/m²K or better, which is the standard referenced by Greek building regulations (KENAK).
How to Insulate a Loft: 5 Steps
- 1
Inspect and prepare the loft space
Before touching any insulation, check the loft for damp patches, roof leaks, and existing insulation that may need removing or topping up. Repair any leaks first — insulation traps moisture and will degrade rapidly if laid over a damp surface. Locate and mark the position of any recessed light fittings below the loft floor; these need fire-rated covers placed over them before insulation is laid, because covering them directly can cause overheating.
- 2
Measure and order materials
Measure the loft floor area in square metres and calculate the number of rolls or boards needed, adding about 10 percent for offcuts and overlaps. For a cold loft the standard approach is a two-layer system: a first layer of mineral wool fitted between the joists (typically 100 mm deep in older Greek buildings) and a second layer of 170–200 mm laid at right angles on top, giving a total depth of around 270–300 mm. This cross-layered approach eliminates thermal bridging through the joists.
- 3
Lay the first layer between the joists
Starting from the eaves and working toward the centre of the loft, unroll the mineral wool and press it gently between the joists. Do not compress the material — its thermal performance depends on the air trapped within the fibres. Butt pieces tightly together and cut around obstructions with a sharp knife. Wear a dust mask, safety glasses, and long sleeves; mineral fibres irritate skin and airways. Keep the eaves clear to maintain ventilation into the roof space, which prevents condensation.
- 4
Lay the second layer across the joists
Roll out the second, thicker layer of mineral wool at 90 degrees to the joists, covering the joist tops as well as the gaps. This perpendicular orientation is critical — it eliminates the cold bridge that would otherwise run along every joist. Stagger the joints of the second layer so they do not align with the joints of the first. Once both layers are in place, do not compress or walk on them; lay loft boards on timber bearers raised above the insulation if you need to access the space for storage or to reach water tanks.
- 5
Insulate the loft hatch and any pipes or tanks
The loft hatch is a frequent weak point. Fit a hinged insulated hatch cover on top of the existing hatch — mineral wool stapled to a rigid board works well — and add a draught-proof seal around the frame. Any water pipes or tanks sitting in the cold loft (above the insulation level) must be lagged separately with pipe insulation and tank jackets, because they are now exposed to colder air than before. Check and top up lagging on these before closing up the loft.
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FAQ
- How thick should loft insulation be in Greece?
- Current best practice, aligned with the EU's EPBD targets and Greece's KENAK standard, is a total depth of around 270–300 mm of mineral wool, achieved with a 100 mm first layer between the joists and a 170–200 mm second layer on top. Older properties often have 50–100 mm, which is well below modern standards and worth upgrading.
- Can I insulate a loft myself, or do I need a contractor?
- A cold loft with accessible joists is one of the more manageable DIY jobs in home improvement — no specialist tools are needed and the materials are sold in standard rolls at building merchants across Greece. A warm loft conversion (insulating at rafter level) is more complex and usually benefits from a professional, especially if airtightness membranes and vapour control layers need to be installed correctly to avoid condensation risk inside the roof structure.
- Will loft insulation help keep the building cool in summer as well as warm in winter?
- Yes, though the effect in summer is moderate rather than dramatic. By slowing the rate at which heat conducted through the roof deck enters the living space, insulation reduces peak afternoon temperatures on upper floors and cuts the load on air-conditioning systems. For maximum summer performance, combine insulation with ventilation in the roof space and, where possible, a reflective sarking membrane under the roof tiles, which bounces radiant heat back before it can conduct through.