What sound insulation does a loft party wall need?

Part E requires separating walls between dwellings to achieve a minimum of 45dB Rw airborne sound insulation. In a loft conversion, the party wall must be upgraded from the underside of the roof covering to the top of the new ceiling, using fire-rated and acoustic-rated boarding with sealed edges.

How many layers of plasterboard do I need on the party wall?

For 60-minute fire resistance (Part B requirement for loft conversions), you typically need 2 layers of 15mm fire-rated plasterboard (such as Fireline) on each side of the party wall. Joints must be staggered between layers. For 30-minute rating, 1 layer of 15mm fire board may suffice.

What is acoustic sealant and where does it go?

Acoustic sealant is a flexible, non-setting mastic applied to all perimeter joints where the party wall boarding meets the floor, ceiling and external walls. It fills gaps that would allow sound to pass through (flanking transmission). It must remain permanently flexible — standard decorator's caulk is not adequate.

Do I need a Party Wall Agreement for a loft conversion?

If the party wall is being cut into, loaded onto (steel beam bearing), or if work is within 3-6 metres of the neighbour's foundations, you need a Party Wall Notice under the Party Wall Act 1996. This must be served at least 2 months before work starts. If the neighbour dissents, surveyors must be appointed.

Should the party wall extend above the ceiling?

Yes. The party wall separating construction must extend from the underside of the roof covering (tiles/slates) down to the ceiling of the room below, without gaps. Any gaps between the party wall and the roof must be fire-stopped. This prevents fire and sound from passing through the roof void.

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Loft Party Wall Calculator — Part E Sound & Fire Boarding

Calculate fire-rated boarding, acoustic insulation and sealant quantities for loft conversion party walls to meet Part E (45dB Rw) and Part B requirements.

Wall Length

Length of party wall in loft

Wall Height

Floor to underside of roof

Existing Wall Type

Price Per m² (optional)

Material and labour per m²

Fire Upgrade Needed

Part B fire-rated boarding

Sound Upgrade Needed

Part E acoustic insulation

How We Calculate This

This calculator determines the boarding and materials needed to upgrade a loft party wall for fire and sound compliance.

The formula

Wall Area = Length × Height

Fire Board Sheets = ceil(Area / 2.88) × Layers

Acoustic Sealant = Perimeter × 2 sides

Part E & B requirements

Part E: 45dB Rw airborne sound insulation
Part B: 60-minute fire resistance (loft rooms)
Fire board: 2 × 15mm for 60 minutes
Acoustic: Mineral wool + resilient bar option

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.