Loft Conversions: Plastering, Drylining and Finishing

Understanding Loft Conversion Plastering Requirements

Loft conversions represent one of the most cost-effective ways to add living space to your home, but the plastering and drylining work requires significantly more expertise than standard room plastering. Unlike ground-floor rooms with straight walls and easy access, loft spaces present unique challenges that demand careful planning.

Building Regulations Part L mandates that all loft conversions meet current thermal efficiency standards. This means you’ll need substantial insulation between rafters (typically 270mm of mineral wool or equivalent) before any plasterboard goes up. The government’s Building Regulations Approved Document L sets these standards, and failure to comply will result in your building control officer rejecting the work.

Most loft conversions also require fire-rated plasterboard — usually 12.5mm Gyproc FireLine or British Gypsum Fireline board — to provide 30 minutes’ fire resistance between the conversion and the floor below. This isn’t optional; it’s a legal requirement under Part B of the Building Regulations.

Drylining vs Wet Plastering in Loft Conversions

You have two main options for finishing loft walls and ceilings: drylining (plasterboard with taped joints) or drylining followed by a skim coat. The choice affects both cost and timeline, and most professional plasterers recommend the latter for habitable loft spaces.

For a standard 25m² loft bedroom conversion, most homeowners opt for the middle option: drylining with a 2mm skim coat using British Gypsum Thistle Board Finish. This provides a smooth, paint-ready surface that hides any minor imperfections in the boarding while keeping costs reasonable.

If you’re planning an en-suite bathroom in your loft conversion, you’ll need moisture-resistant plasterboard in wet areas. Our guide to bathroom plastering and which plaster to use in wet areas covers this in detail.

Step-by-Step: The Loft Conversion Plastering Process

Professional loft conversion plastering follows a strict sequence. Rushing any stage or working out of order will compromise the final result and potentially fail building control inspection.

Stage 1: Insulation and Vapour Control (Days 1-2)

Before any plasterboard goes up, your loft needs proper insulation. This typically involves:

• Between-rafter insulation: 100-150mm rigid PIR boards (Celotex, Kingspan, or Recticel) or mineral wool batts friction-fitted between rafters
• Under-rafter insulation: Additional 50-100mm PIR boards on battens to achieve total U-value of 0.16 W/m²K or better
• Vapour control layer (VCL): Continuous polythene sheeting (minimum 250 micron) on the warm side of insulation to prevent interstitial condensation
• Service routing: Electrical cables and any plumbing installed before boarding begins

The Kingspan technical team recommends overlapping VCL joints by at least 150mm and sealing with waterproof tape. Any penetrations for downlights or pipes must be carefully sealed to maintain the vapour barrier’s integrity.

Stage 2: First Fix Drylining (Days 3-5)

Once insulation is signed off by building control, drylining begins. This involves:

• Ceiling boarding first: 12.5mm plasterboard fixed to ceiling joists at 400mm centres using 38mm drywall screws
• Wall boarding: Plasterboard fixed to stud walls or battened masonry walls, working from top to bottom
• Eaves details: Careful cutting and fitting around the eaves junction where roof meets floor
• Window reveals: Velux or dormer window reveals squared and boarded with returns

Experienced plasterers fix boards with screws at 150mm centres around perimeters and 230mm centres in the field. Screws should sit just below the surface (about 1mm) without breaking the paper face. Over-driven screws create weak points that will crack through the skim coat.

Stage 3: Jointing and Taping (Days 6-7)

Before skim plastering can begin, all board joints need taping and filling. This creates a stable base and prevents cracks appearing at joints. The process involves:

• First coat: Gyproc Easi-Fill 60 or similar joint compound applied along all tapered edges with a 150mm taping knife
• Tape embedding: Paper joint tape pressed into wet compound, smoothed flat with no bubbles or wrinkles
• Second coat: Wider application (200-250mm) of joint compound feathered out beyond the tape edges
• Screw spotting: All screw heads filled flush with joint compound
• Internal angles: Metal corner bead on all external angles; paper tape on internal angles
• Drying time: Minimum 24 hours between coats; 48 hours before skim coating

Some plasterers skip the taping stage when they’re skim coating, but this is poor practice. Proper taping prevents movement cracks and provides a much more stable substrate for the finishing plaster.

Stage 4: Skim Coating (Days 8-10)

This is where professional skill really matters. Loft conversions present awkward angles and tight working conditions that make skimming challenging. A typical 25m² loft conversion requires:

The skim coat goes on in two passes. The first coat (about 2mm thick) is applied fairly rapidly and left to firm up for 20-40 minutes. Once it’s firm but not dry, the second pass tightens the surface, removes trowel marks, and creates a smooth, level finish. Our step-by-step guide to skim coating walls explains the detailed technique.

Board Finish vs Multi-Finish: For loft conversions, most plasterers use Thistle Board Finish rather than Multi-Finish because it’s specifically formulated for low-suction backgrounds like plasterboard. Board Finish remains workable slightly longer, which is crucial when working in tight loft spaces where you can’t move as quickly. We’ve covered the differences in detail in our comparison of Multi-Finish and Board Finish plasters.

Stage 5: Drying and Curing (Days 11-17)

This is the stage that homeowners always underestimate. Skim plaster needs proper drying time before any decoration or furniture installation:

• Days 1-3: Plaster changes from dark to light pink as it sets chemically. Keep windows closed and heating off to prevent too-rapid drying
• Days 4-7: Surface fully light pink. Introduce gentle heating (15-18°C) and ventilation to draw moisture out
• Days 8-14: Plaster continues drying internally. Surface should feel dry to touch but may still show moisture meter readings above 10%
• Day 14+: Fully cured and ready for mist coating. Moisture content should be below 2% on a moisture meter

In well-ventilated loft conversions with adequate heating, 7-10 days is usually sufficient for painting. In winter or poorly ventilated spaces, allow 14-21 days. Rushing this stage leads to paint blistering, damp patches, and potential mould growth behind finishes.

Loft Conversion Plastering Costs in 2026

Pricing varies significantly based on loft size, access difficulty, and finish quality. Here’s what you can expect to pay in Kent and the South East for professional plastering work:

These prices include drylining, taping, and skim coating but exclude the initial insulation and structural carpentry work. If your loft conversion includes dormer windows, expect to add 15-20% to the plastering costs due to the additional complexity of window reveals and wall returns.

For a detailed breakdown of how plasterers calculate their rates, see our comprehensive guide to room plastering costs in the UK.

Common Loft Conversion Plastering Challenges

Loft conversions present unique technical challenges that don’t arise in standard room plastering. Professional plasterers need to anticipate and solve these issues during the planning stage.

Low Eaves and Restricted Headroom

Most loft conversions have areas where the ceiling height drops below 2.3m at the eaves. Creating smooth transitions between vertical walls and sloping ceilings requires:

• Gradual curves: Using flexible metal corner beads or building up layers of plaster to create smooth transitions rather than sharp angles
• Stud positioning: Studs at eaves junctions need careful positioning to provide solid fixing points without creating bulges
• Boarding technique: Small, manageable board sections (600mm x 900mm) work better than full sheets in tight eaves spaces

Awkward Access and Material Handling

Getting materials into a loft conversion typically means navigating narrow staircases or ladders. This affects both cost and timeline:

• Sheet goods: 2400mm plasterboards often need cutting to 1800mm or 1200mm sections to fit up staircases
• Material storage: Limited space means multiple material deliveries rather than bulk drops, adding 5-10% to material costs
• Waste removal: Plaster bags, offcuts, and waste need bagging and carrying down — factor an extra half-day for cleanup on typical conversions

Thermal Movement and Cracking

Loft spaces experience greater temperature fluctuations than lower floors, especially at the roof junction. This thermal movement causes cracking if not properly detailed:

• Expansion gaps: Leave 3-5mm gaps between plasterboard sheets and top plates to allow for movement
• Scrim tape: Use fibreglass mesh tape (scrim) at all angles and junctions for added crack resistance
• Flexible sealants: Use decorators’ flexible acrylic caulk at ceiling-to-wall junctions rather than plaster, which will crack with seasonal movement

Fire Safety and Building Regulations Compliance

This is non-negotiable. Every loft conversion creating a habitable room must meet Building Regulations Part B (Fire Safety). The plastering specification directly affects compliance.

Key requirements include:

• 30-minute fire resistance: The floor/ceiling between the loft and the floor below must provide 30 minutes’ fire protection. This typically requires 12.5mm Gyproc FireLine plasterboard on the underside of joists, or 15mm Soundbloc with additional fire protection
• Protected escape route: The stairwell from loft to ground floor usually needs upgrading with fire-rated plasterboard and fire doors
• Smoke alarms: Interlinked smoke and heat alarms are mandatory. Recessing alarm bases into plasterboard ceilings needs careful detailing to maintain fire ratings
• Building control inspection: Most authorities inspect at first fix (before plasterboard) and at completion. Any non-compliant work gets rejected

The Local Government Association’s guidance on fire safety provides detailed technical requirements that your plasterer and builder must follow. Don’t cut corners here — the insurance implications of non-compliant fire protection are severe.

Soundproofing Considerations

A poorly soundproofed loft conversion quickly becomes unusable, especially if converting to a bedroom above a living room or kitchen. The plastering specification significantly affects acoustic performance.

Acoustic plasterboard options:

• British Gypsum SoundBloc: 15mm high-density board providing 10-12dB additional sound reduction compared to standard plasterboard (about £18-£22 per sheet at Travis Perkins or Jewson)
• Knauf Acoustic Plus: 12.5mm board with similar acoustic performance to 15mm SoundBloc but lighter for ceiling applications (£16-£20 per sheet)
• Gyproc QuietPanel: Premium option incorporating viscoelastic layers for up to 15dB improvement (£28-£35 per sheet)

For optimal soundproofing, combine acoustic plasterboard with acoustic mineral wool between joists (Rockwool RWA45 or Knauf Earthwool) rather than standard loft insulation. This adds £150-£300 to material costs but dramatically improves sound transmission performance.

Preparing Loft Plasterwork for Decoration

Once your loft conversion plastering is complete and fully dried, proper preparation ensures a professional decorating finish. This final stage is often rushed, leading to disappointing results.

Essential preparation steps:

• Mist coat application: Dilute white vinyl matt emulsion 20-30% with clean water and apply as first coat. This seals the porous plaster and provides a stable base for topcoats
• Allow 24 hours drying: Don’t rush the mist coat. It needs to fully dry before topcoats go on
• Light sanding: Very gentle sanding with 240-grit paper removes any raised nibs or slight imperfections
• Two topcoats minimum: Apply two full-strength coats of your chosen finish paint, allowing proper drying between coats

Many homeowners choose feature walls or accent colours in loft conversions to maximise the feeling of space. Our guide to painting and decorating your home covers colour choices and application techniques in detail.

DIY vs Professional Loft Conversion Plastering

We’re often asked whether competent DIYers can tackle loft conversion plastering themselves. The honest answer: it’s possible but rarely advisable unless you have prior plastering experience.

When DIY might work:

• You’ve successfully plastered multiple rooms before
• The loft conversion is simple (single rectangular room, no en-suite, standard ceiling height throughout)
• You’re prepared for a 3-4 week timeline including drying time
• Building control is satisfied with your competence and will pass the work

When you need a professional:

• The conversion includes dormer windows or complex rooflines
• Fire-rated plasterboard is required (professional installation is necessary for certification)
• En-suite bathroom included (moisture-resistant boarding and tanking required)
• You need the work completed quickly to meet a moving deadline
• The loft has restricted access or very low eaves (professional handling saves material wastage)

Professional plastering for a typical 25m² loft conversion costs £1,700-£2,550 including materials. DIY might save £1,000-£1,500 in labour but typically takes 2-3 times longer and risks building control rejection if standards aren’t met. For most homeowners, professional installation offers better value when you factor in time, stress, and guaranteed results.

Maintaining Your Loft Conversion Plasterwork

Properly finished loft conversion plasterwork should last 20+ years with minimal maintenance. However, a few issues commonly arise in the first 1-2 years:

Hairline cracks at joints: Small cracks (under 1mm) appearing at ceiling-to-wall junctions or along board joints are normal settlement. Fill with flexible decorators’ caulk and repaint. If cracks exceed 2mm or reappear after filling, this indicates structural movement and needs professional assessment.

Nail or screw pops: Occasionally fasteners work loose as timber dries, creating small bumps in the plasterwork. Tap any protruding fixings back flush, apply joint compound, sand smooth when dry, and touch up paint.

Condensation staining: Brown or yellow staining on ceilings usually indicates condensation issues rather than plaster defects. Check loft ventilation is adequate and consider installing trickle vents in windows. The problem lies with inadequate ventilation, not the plastering.

For more detailed guidance on addressing plaster defects, our article on repairing cracked plaster walls covers diagnosis and fixing techniques.

Frequently Asked Questions

How much does it cost to plaster a loft conversion in 2026?

Professional loft conversion plastering costs £1,200-£3,500 depending on size and complexity. A typical 25m² single-bedroom conversion costs £1,700-£2,550 including materials. This covers drylining with 12.5mm plasterboard, taping and jointing, and a 2mm skim coat finish. Add £300-£600 if the conversion includes an en-suite bathroom requiring moisture-resistant boarding and tanking. Dormer window conversions cost 15-20% more than simple Velux conversions due to additional wall returns and reveals. Prices are higher in London and the South East (typically 20-30% above national averages) and lower in the North and Midlands.

How long does loft conversion plastering take?

Expect 2-3 weeks from starting drylining to being ready for decoration. The actual plastering work takes 7-10 days (3-4 days drylining, 1-2 days jointing, 1-2 days skim coating, 3-5 days drying). A competent two-person team can dryline a 25m² loft in 3 days, complete jointing in 1.5 days, and skim coat in 1-1.5 days. The drying phase can’t be rushed — skim plaster needs 7-10 days minimum before painting, longer in winter or poorly ventilated spaces. Factor in building control inspections which may require work to be exposed for longer before boarding or skimming proceeds.

What type of plasterboard should I use for a loft conversion?

Use 12.5mm tapered-edge plasterboard as standard, upgraded to specific performance boards where needed. For the ceiling (floor of loft), most building control officers require 12.5mm Gyproc FireLine or similar fire-rated board to provide 30 minutes’ fire resistance. For walls and loft ceilings, British Gypsum SoundBloc (15mm) provides excellent acoustic performance for bedrooms, though standard 12.5mm plasterboard is acceptable for storage conversions. En-suite bathrooms need moisture-resistant board (Gyproc Moisture Resistant or Knauf Aquapanel) in wet zones. Always choose tapered-edge rather than square-edge boards as the tapered edges make jointing far easier and create better finished surfaces.

Do I need fire-rated plasterboard for my loft conversion?

Yes, Building Regulations Part B requires 30 minutes’ fire resistance between your loft conversion and the floor below. This is legally mandatory for any loft conversion creating a habitable room (bedroom, home office, living space). You achieve this by fixing 12.5mm Gyproc FireLine or Knauf Fireboard to the underside of the ceiling joists below the loft. Some plasterers use 15mm British Gypsum SoundBloc which also provides adequate fire resistance when properly installed. The fire-rated boarding protects the escape route (stairwell) and gives occupants time to evacuate in case of fire. Building control will inspect this specifically and won’t sign off work without compliant fire protection. Don’t use standard plasterboard for this critical element — the few pounds saved aren’t worth the safety risk or insurance implications.

Can I plasterboard a loft conversion myself?

Drylining is more DIY-friendly than skim plastering, but loft conversions present challenges that make professional installation advisable. Competent DIYers can handle straight walls and flat ceilings, but loft conversions involve awkward angles, restricted working space, heavy sheets in confined areas, and critical details like eaves junctions and window reveals. Fire-rated installations need professional certification for building control approval. If you do DIY, use a plasterboard lift for ceilings (hire from HSS or Jewson for £35-£50 per day), cut sheets to manageable sizes before carrying upstairs, and allow double the time you think it’ll take. Most homeowners find the £850-£1,200 professional drylining cost worthwhile given the physical difficulty and importance of getting building control sign-off first time.

How soon can I paint new plaster in a loft conversion?

Wait minimum 7-10 days after skim plastering before applying any paint or wallpaper. Skim plaster contains substantial moisture that must evaporate before decoration. Painting too soon traps moisture, causing bubbling, flaking, and potential mould growth. The plaster surface will turn from dark pink to pale pink as it dries, but internal moisture content remains high for another week. Use a moisture meter to check — readings should be below 2% before decorating. In winter or poorly ventilated lofts, allow 14-21 days. Speed drying with gentle heating (15-18°C) and ventilation, but never use direct heat from fan heaters or dehumidifiers in the first 48 hours as rapid surface drying causes cracking. When ready to paint, apply a mist coat (20-30% diluted emulsion) first to seal the porous surface.