6,000+ lofts.
Every layer explained.

A good insulation plan starts by identifying the construction, the current thermal layer, moisture condition, ventilation route, access, services and how the space will be used. A cold unused loft, a room-in-roof, a flat roof and a suspended timber floor all need different build-ups. Green Dragon surveys the whole system before recommending a material or thickness.

• Construction and age
• Existing insulation depth and condition
• Leaks, staining or mould
• Eaves and roof ventilation
• Wiring, lights, tanks and pipes
• Future storage or conversion plans

In a cold-loft build-up, insulation follows the ceiling line rather than the roof slope. Flexible mineral wool is commonly fitted between joists, then cross-laid above to reduce gaps and thermal bridges. Around 270 mm is a widely used guide for suitable mineral-wool installations, but the finished design must also protect eaves ventilation, downlights, cables, tanks, pipes and the loft hatch. Storage needs a correctly raised deck so the insulation is not compressed.

• Continuous coverage at edges
• Eaves airflow kept open
• No wet or contaminated material
• Services remain safe and accessible
• Hatch is insulated and draught controlled

Rafter-level insulation is used for roof rooms, conversions and some warm-roof upgrades. The build-up may place insulation between, below or above rafters. PIR, mineral wool and hybrid systems can all be suitable, but only when the complete roof is checked for U-value, condensation risk, ventilation strategy, fire performance and continuous sealing at eaves, ridges, dormers and party walls. Never assume a generic air gap or board thickness suits every roof.

• Rafter depth and condition
• Roof underlay type
• Ventilated or unventilated design
• Vapour-control and airtightness layer
• Cold bridges at timber and junctions
• Current Welsh Building Regulations

A warm flat roof normally places insulation above the structural deck; a cold flat roof places it between or below joists and needs a carefully designed ventilation route; an inverted roof places moisture-resistant insulation above the waterproofing. The waterproof layer, vapour control, falls, outlets, upstands and edge details all influence the specification. Condensation analysis and the roofing manufacturer’s system details should control the final build-up.

• Roof type and deck
• Waterproofing condition
• Falls and drainage
• Vapour-control position
• Upstands and edge continuity
• Manufacturer-approved system

A room-in-roof may combine sloping rafters, a short flat ceiling, dormer cheeks, dwarf walls, floor voids and inaccessible eaves. Each surface needs the right material and all surfaces must connect into one continuous thermal, airtight and moisture-safe envelope. Common failures include uninsulated dwarf-wall doors, gaps behind plasterboard, cold bridges at rafters and open eaves cupboards.

• All six sides of the heated room
• Hidden eaves and dwarf walls
• Dormer roof and cheeks
• Access panels and doors
• Ventilation behind the thermal line
• Fire and escape requirements

Suspended timber floors can be insulated from below where access allows, or from above when floorboards are lifted. Flexible mineral wool or an appropriate rigid/semi-rigid product is supported between joists with a continuous fit at edges and around services. Draught paths at the perimeter may be sealed carefully, but subfloor air bricks and cross-ventilation must remain open. Damp, rot, leaks and timber condition are checked before covering anything.

• Suspended floor confirmed
• Joists dry and sound
• Air bricks unobstructed
• Support mesh or system secure
• No gaps at perimeter and services
• Pipes protected from freezing

Semi-rigid stone or glass mineral-wool slabs are often friction-fitted between timber studs; rigid boards and continuous external layers can also be used in designed systems. The build-up must coordinate sheathing, breather membrane, drained cavity, internal vapour control and airtightness, services and linings. An additional continuous layer can reduce thermal bridging through the studs. Product choice depends on thermal, acoustic, fire and moisture requirements.

• Stud centres and cavity depth
• Tight fit without compression
• Continuous layer at junctions
• Breather membrane and cavity
• Warm-side vapour strategy
• Fire-stopping and service penetrations

Raised boarding creates a defined storage platform above the insulation. The fixed 200 mm supports shown in Green Dragon’s system are secured to the ceiling joists in a planned grid, then suitable structural loft boards are fixed above. Layout depends on joist direction, spacing, services, access and the board manufacturer’s fixing pattern. This is storage flooring, not automatically a habitable-room floor, and the existing structure must be suitable for the intended load.

• Joist direction, spacing and condition
• Support grid and board specification
• Cables and pipes kept accessible
• Insulation remains uncompressed
• Ventilation routes stay open
• Storage load explained

Removal can be appropriate when insulation is water-damaged, heavily contaminated by pests, mixed with building debris, badly compressed, incorrectly installed or blocking investigation. The ceiling, junctions, wiring, timbers and ventilation become visible for inspection. Minor dust is not automatically a reason to remove otherwise dry and effective insulation; the survey should justify the disruption and disposal cost.

• Reason for removal documented
• Potential asbestos excluded
• Safe access and containment
• Waste route and disposal
• Timbers and ceiling inspected
• Cause of wetting fixed first

Glass mineral wool is available as rolls and slabs in different thermal and acoustic grades. It is widely used between and over ceiling joists because it is light, adaptable and can form a non-combustible thermal layer when the selected product has the appropriate classification. Performance depends on declared lambda, installed thickness, coverage and avoiding compression, wind-washing and wetting. Always check the exact product datasheet.

• Correct product and declared lambda
• Two-layer cross-laid coverage
• No compression under storage
• Protective handling and dust control
• Dry installation
• Edges and hatches complete

Stone wool is made from mineral fibres and supplied in rolls, batts and semi-rigid slabs. Depending on the exact product, it can combine thermal resistance with non-combustibility, sound absorption and dimensional stability. It is useful between timber studs and joists, around irregular details and in systems where fire or acoustic performance matters. Thickness and product grade must match the certified application.

• Product certified for the application
• Correct width and friction fit
• No slumping or gaps
• Fire-stopping remains continuous
• Vapour and wind layers coordinated

Polyisocyanurate, or PIR, is a rigid foam board commonly faced with foil. Many products declare thermal conductivity around 0.021–0.022 W/mK, so a thinner layer can achieve useful resistance compared with many flexible products. Poor cutting leaves bypass gaps, and foil facings alone do not automatically create a complete vapour-control layer: continuity, taped joints, perimeter seals and the full construction matter. Fire classification and permitted application vary by product.

• Exact certified product
• Board thickness from calculation
• Tight cuts and sealed joints
• Layer continuity across rafters/studs
• Fire and lining requirements
• Condensation-risk design

Phenolic foam boards can offer low declared thermal conductivity and are used where build-up depth is restricted. They are not interchangeable with every PIR or polystyrene product: facings, reaction-to-fire classification, moisture behaviour, compressive strength and approved applications differ. Use the selected manufacturer’s current datasheet and system details rather than a generic thickness rule.

• Current product certification
• Approved application
• Joint and perimeter detailing
• Compatible tapes and membranes
• Fire performance
• Moisture exposure

Expanded polystyrene (EPS) and extruded polystyrene (XPS) have different structures, strengths and moisture characteristics. Product grade matters: some are intended for floors and load-bearing applications, others for walls, roofs or inverted-roof systems. They must be protected and installed within a certified build-up, with fire, moisture, compressive load and thermal bridging considered.

• EPS or XPS correctly identified
• Required compressive strength
• Water exposure
• Fire-protective layers
• Compatible waterproofing
• Edge and joint design

Cellulose is commonly made from treated recycled paper and installed as loose fill or dense-pack material by a specialist system. Other blown fibres include mineral or glass products. The installer must control density, design depth, settlement allowance, fire treatment, wind-washing and containment at eaves and openings. It is not suitable for every loft, especially where strong air movement, water entry or frequent access is expected.

• Certified blowing system
• Installed density and depth
• Eaves containment
• Services and downlights
• Settlement allowance
• Dry substrate

Wood-fibre boards and flexible batts, hemp products and sheep-wool insulation can support moisture-buffering and low-embodied-carbon designs. Each behaves differently. A vapour-open build-up still needs controlled airtightness and a moisture strategy; it is not permission for uncontrolled draughts. Confirm fire treatment, pest resistance, lambda, density, durability and the manufacturer’s approved application.

• Compatible breathable build-up
• Declared thermal performance
• Fire and pest treatment
• Moisture exposure
• Airtight layer
• Manufacturer installation guide

Polyester insulation is commonly made partly from recycled plastic fibres and supplied as rolls or batts. It can be pleasant to handle and resilient to minor movement, but products vary widely. Verify the declared lambda, reaction to fire, acoustic performance, maximum service temperature and certified applications. It still needs a dry, continuous installation with the correct ventilation and vapour strategy.

• Certified application
• Declared lambda
• Reaction to fire
• Fit and support
• Exposure to heat sources
• Moisture strategy

YBS describes SuperQuilt as a 19-layer reflective insulation around 40 mm thick for roof, wall and floor applications. Reflective layers depend on the air spaces and installation arrangement used in the tested calculation. When designed and sealed correctly it can contribute to vapour and airtightness control, but it is often combined with PIR or mineral wool in hybrid build-ups. The final U-value and condensation assessment must use the manufacturer’s exact system.

• Correct SuperQuilt product
• Specified air spaces
• Tight laps and approved tape
• Sealed perimeter and penetrations
• Hybrid insulation where required
• U-value and condensation calculation

Spray polyurethane foam applied to the underside of an existing roof changes how the roof behaves and may hide the condition of timbers and roof coverings. RICS advises homeowners to understand potential effects on surveys, valuation and lender decisions. Before installation or removal, obtain independent building-survey and mortgage advice, identify the foam type and system, and collect the specification, installer competence evidence, warranty and moisture-risk assessment. Do not accept pressure selling or an automatic removal claim.

• Independent survey
• Lender and insurer position
• Open- or closed-cell foam
• Roof timber visibility and condition
• Design and condensation evidence
• Documents and warranty

U-value is the rate of heat transfer through a complete building element, expressed in W/m²K. A lower result means less heat flow. It is not the rating of one insulation product: the calculation includes plasterboard, timber, membranes, cavities, insulation, finishes and repeating bridges. For alterations, the target and practical specification depend on current Welsh Building Regulations, the existing structure and what is technically feasible.

• Whole build-up defined
• Repeating timber bridges included
• Declared product lambda
• Real installed thickness
• Junctions assessed
• Current regulatory route confirmed

Lambda, written λ and measured in W/mK, is a product’s declared thermal conductivity; lower values indicate less conduction through the material. R-value, measured in m²K/W, is the thermal resistance of a layer and is calculated from thickness divided by lambda. U-value is the inverse-style whole-element measure after all layers and bridges are considered. Compare certified declared values, not marketing names alone.

• Units match
• Declared rather than guessed lambda
• Thickness converted to metres
• Bridging not ignored
• Whole-element U-value calculated

Thermal bridging occurs where a more conductive material or a gap interrupts the insulation layer. Repeating bridges include rafters and studs; junction bridges occur at eaves, party walls, dormers, hatches and wall-to-roof connections. Bridging lowers the real U-value and can create cold surfaces where condensation forms. Cross-layers, accurately cut infill, insulated linings and continuous perimeter detailing help reduce it.

• Rafters and joists
• Eaves and wall plates
• Hatches and doors
• Dormer cheeks
• Party-wall junctions
• Service penetrations

Airtightness limits uncontrolled air leakage through cracks, gaps and service penetrations. Ventilation deliberately removes moisture and pollutants through designed routes such as extract fans, trickle vents and roof-space ventilation. Good retrofit improves airtightness while checking the ventilation strategy. Blocking eaves vents or sealing a roof void without calculation can create condensation; leaving uncontrolled gaps can waste heat and carry moisture into cold layers.

• Bathroom and kitchen extract
• Ceiling penetrations
• Loft-hatch seals
• Eaves/ridge ventilation
• Indoor moisture sources
• Post-work ventilation provision

A vapour-control layer, usually placed toward the warm side, limits water-vapour diffusion and often contributes to airtightness. A breather membrane on the colder outer side can allow vapour to escape while resisting wind-driven water, depending on the certified product. Neither term guarantees performance on its own. Laps, penetrations, junctions and compatibility with the roof design are critical, and a condensation-risk assessment may be needed.

• Layer position
• Sd/vapour resistance
• Continuous seals
• Penetration detailing
• Outer membrane type
• Condensation analysis

Condensation forms when moisture-laden air reaches a surface below its dew point. Adding ceiling-level insulation makes the roof void colder, so existing moisture and ventilation problems can become more visible. Causes can include blocked eaves, bathroom fans discharging into the loft, open penetrations, missing vapour control, water leaks and patchy insulation. Mould is a symptom, not the complete diagnosis; the source must be corrected before new insulation is installed.

• Roof leaks and staining
• Extract ducts vent outside
• Eaves and ridge airflow
• Ceiling air leakage
• Tank overflow and plumbing
• Timber moisture condition

In many cold pitched roofs, outdoor air enters at the eaves and may leave through opposite eaves, high-level vents or a ridge route. Insulation at the wall plate must remain continuous while an unobstructed path is preserved above it, often using eaves trays or retainers where suitable. The required provision depends on roof geometry, underlay type and existing ventilation design; adding random vents without diagnosis can also be wrong.

• Soffit/eaves openings
• Underlay type
• Insulation not blocking path
• Cross-flow or high-level route
• Eaves trays correctly placed
• No wind-washing of insulation

The loft hatch should have insulation compatible with the surrounding ceiling layer and a continuous draught seal at the frame. A ladder installation may require enlarging and trimming the opening; structural work must be designed correctly and should never involve cutting trusses without specialist approval. Handholds, landing space, headroom, lighting and the route onto raised boarding all affect safe use.

• Hatch insulation
• Compression seal
• Opening structure
• Ladder rating and angle
• Safe landing zone
• Lighting and clear access

Cold-loft insulation reduces heat escaping from the rooms below, which can lower winter temperatures around tanks and pipework. Tanks should be insulated at the sides and top as appropriate, while the area directly beneath may need a deliberate strategy so some warmth can reach it. Pipes need suitable continuous insulation, including bends and valves, without concealing leaks or unsafe fittings. Plumbing alterations require the appropriate competent trade.

• Tank lid and jacket
• Pipe insulation at bends
• Overflow and leaks
• Access to valves
• No unsafe heat source
• Local freezing exposure

Insulation changes heat dissipation around electrical equipment. Electrical Safety First says downlights must not contact or be covered by insulation unless specifically designed and rated for it. Cable capacity can also be affected when surrounded by insulation, and junctions must remain accessible where required. We identify visible services and use product-approved protective details; questionable or altered wiring is referred to a registered electrician.

• Downlight insulation-contact rating
• Drivers and transformers
• Cable routes and loading
• Accessible junction boxes
• Signs of overheating
• Electrician referral where needed

Buildings built or refurbished before 2000 may contain asbestos-containing materials. In lofts these can include insulation board, pipe lagging, textured coatings, cement products and debris from earlier work. Appearance alone cannot reliably confirm asbestos. Suspect material should not be drilled, swept, vacuumed or removed until assessed; higher-risk work requires appropriately licensed contractors.

• Building age and refurbishment history
• Unknown boards and lagging
• Existing asbestos survey
• No disturbance or dry sweeping
• Independent sampling where required
• Licensed contractor for higher-risk work

Active leaks, failed flashings, cracked tiles, overflowing gutters, plumbing leaks and long-term condensation can all wet insulation and timber. Wet insulation loses performance and can hide decay. The cause must be fixed and the structure allowed to dry; damaged timber may need assessment by a competent building professional. New insulation should not be used to conceal staining, mould or soft wood.

• Active water entry
• Staining pattern
• Timber moisture and firmness
• Roof covering and flashings
• Plumbing and tank overflow
• Drying before reinstatement

Flexible insulation depends partly on trapped air, so compression reduces its effective thickness and resistance. Patchy coverage and gaps allow heat to bypass the layer. Air moving through or across loose fibres at exposed eaves can also reduce performance. A survey records depth, condition and continuity rather than judging one easy-to-reach spot.

• Depth across the whole loft
• Boards or boxes compressing rolls
• Gaps at joists and edges
• Wind at eaves
• Disturbance by trades or pests
• Cross-layer continuity

Rodents, birds and other pests can disturb insulation, damage cables and leave biological contamination. The animal or entry route should be handled by the appropriate pest-control or wildlife professional before insulation work. Heavily contaminated areas may require controlled removal, suitable respiratory and hygiene measures, waste handling and disinfection. Minor disturbance does not always justify full-loft removal; the extent should be surveyed.

• Species or contamination identified
• Entry points controlled lawfully
• Electrical damage checked
• Removal boundary defined
• PPE and waste route
• Dry clean substrate before reinstatement

A useful survey records property type, loft access, roof construction, dimensions, existing insulation, ventilation, visible moisture, timbers, party-wall and eaves details, tanks, pipes, electrics, hatches and the intended use. We then explain what can stay, what must change, the proposed material and thickness, important exclusions, access needs and how the job will be finished.

• Photos and measurements
• Existing material identified
• Ventilation and moisture findings
• Services and access
• Proposed build-up
• Clear scope and exclusions

Two similar-looking houses can need different work. The price depends on measured area, access and headroom, existing material, waste removal, chosen product and thickness, eaves and hatch detailing, electrical or plumbing constraints, boarding and travel. Green Dragon provides a free survey and a written scope so the price is tied to the actual job rather than a misleading headline rate.

• Measured area
• Access and protection
• Removal/disposal
• Material and thickness
• Detailing and services
• Boarding or ladder options

Green Dragon serves Cardiff, the Vale of Glamorgan, Bridgend, Rhondda Cynon Taf, Newport, Swansea and surrounding South Wales areas. Coverage can vary with job size and schedule, so the quickest answer is to send the full postcode with a short description of the property and work required.

• Full postcode
• Property type
• Service needed
• Access or parking notes
• Preferred timing

Duration depends on area, access, preparation, material, removal, services and detailing. The 200 mm fixed raised-boarding system shown on this site is often installed in one to two days after survey, but complex lofts can take longer. Before work, remove valuables and fragile items from the loft where safe, clear the access route and tell us about alarms, pets, parking or vulnerable occupants. Do not enter an unsafe loft to prepare it.

• Confirmed start and duration
• Clear access route
• Valuables removed safely
• Dust protection agreed
• Parking and waste route
• Utilities or trade coordination

Energy-efficiency work in Wales may need to satisfy current Building Regulations, including Approved Document L guidance, and other parts covering structure, fire, ventilation and electrical safety can also apply. Targets and notification routes depend on the work and building. Product datasheets, U-value calculations and condensation analysis support the specification, but Building Control or a competent designer should confirm unusual or conversion work.

• Work type and regulatory route
• Current Welsh guidance
• U-value calculation
• Condensation risk
• Structure and fire
• Manufacturer certification

Use only the defined boarded storage area and respect the advised load. Do not place boxes directly on insulation, block eaves, cover electrical equipment or alter the roof build-up without checking. Inspect from the safe access zone after severe weather and periodically for leaks, pests or disturbed material. Keep the work description and product information with the house records for future owners and trades.

• Store only on the platform
• Keep vents and access clear
• Do not cover services
• Watch for new water or mould
• Retain product/job records
• Ask before later alterations