Retrofit Airtightness for Social Housing & Existing Buildings
The Retrofit Airtightness Opportunity
The UK has 29 million homes, the majority of which are draughty, energy-inefficient and expensive to heat. Airtightness improvement is one of the most cost-effective measures available to housing providers — reducing heat loss, improving EPC ratings, eliminating draughts, and reducing the risk of condensation and mould.
Until recently, retrofitting airtightness meant extensive, disruptive works — stripping plaster, battening walls, and installing sheet membranes before re-plastering. Passive Purple Retrofit changes this: it can be applied directly over existing substrates (brick, blockwork, plaster, concrete) from the inside, with no need to strip or alter the existing fabric.
Why It Matters — By the Numbers
How It Works — Retrofit Application
Step 1: Substrate Assessment
Existing walls and floors are assessed for contamination, loose material and significant cracks. Minor cracks (up to 5mm) are sealed with Passive Purple Brush; larger structural defects are repaired first.
Step 2: Brush Application at Details
Passive Purple Brush is applied first at all critical junctions: floor–wall, ceiling–wall, window reveals, pipe and cable penetrations, and any cracks. Fibres in the formulation bridge small gaps.
Step 3: Full-Surface Application
Passive Purple Retrofit is spray or roller applied across the full wall and ceiling surface to achieve the specified dry film thickness. The product creates a continuous airtight and vapour control layer.
Step 4: Overcoat and Finish
Once cured (typically 4–6 hours), Passive Purple can be plastered, rendered, skimmed or painted over — with no impact on the airtight layer below.
Recommended Products for Retrofit
| Product | Use | Notes |
|---|---|---|
| Passive Purple Retrofit (Spray) | Full-surface spray or roller application over existing substrates | Passivhaus certified; suitable for brick, block, plaster, concrete |
| Passive Purple Retrofit (Brush) | Junctions, penetrations and difficult-to-spray areas | Fibre-reinforced; bridges cracks up to 5mm |
| Passive Purple Brush | Critical junction detailing before spray application | Use with Passive Purple Internal for comprehensive VCL + airtight layer |
| IM Passivhaus Sealant | Large gap filling and interface sealing | Flexible; suitable for joints up to 20mm |
Suitable for Social Housing Programmes
- Whole-house retrofit to EPC C or above (Warm Homes Plan / ECO4 schemes)
- EnerPHit deep retrofit programmes
- PAS 2030/2035 retrofit schemes (works as part of a coordinated strategy)
- Void improvement works between tenancies
- Damp and mould remediation strategies (airtightness + MVHR)
- Tower block and flat over-cladding programmes
- Solid wall insulation (internal or external) programmes where airtightness is required
Applicable Standards
- PAS 2030:2023 & PAS 2035:2023 — Retrofit co-ordinator programmes
- EnerPHit — Passivhaus standard for retrofitted buildings (≤1.0 ACH or ≤0.6 ACH depending on method)
- UK Building Regulations Part L — Existing dwellings notifiable extension/change of use
- SAP / RdSAP — Airtightness improvement feeds directly into SAP calculation and EPC rating
Case Studies
See how Passive Purple has been used on real retrofit projects:
Talk to Us About Your Retrofit Programme
Whether you're a housing association, local authority, retrofit coordinator or main contractor, our team can support your programme with technical advice, training, coverage estimates and approved installer referrals.
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