Have you ever noticed ‘Unknown Wall Type’ listed on your Energy Performance Certificate (EPC) and wondered what it means? This seemingly small detail can drag down your EPC rating and misrepresent your property’s true energy efficiency.
In this guide, we’ll explain:
The meaning of ‘EPC unknown wall type’
Why it appears on EPCs
How it affects your rating
Steps to correct it and improve your EPC score
What Does ‘EPC Unknown Wall Type’ Mean?
‘Unknown Wall Type’ on an EPC means that the assessor was unable to visually verify or identify the construction type of your external walls during the survey.
When this happens, the EPC software defaults to a conservative (often worst-case) assumption about the wall’s insulation performance, which directly impacts the property’s rating.
➡️ Need help correcting an EPC with ‘Unknown Wall Type’? Contact EPCrate for expert assessments.
Common Causes of ‘Unknown Wall Type’ on EPCs
1. Lack of Visible Access
If external walls are:
Fully plastered over inside and
Covered with cladding or render outside
the assessor may be unable to visually determine whether they are solid walls, cavity walls, timber-framed, or other types.
2. No Documentation Available
If the property owner cannot provide:
Architectural plans
Construction drawings
Cavity wall insulation certificates
the assessor has no evidence to input a specific wall type and must select ‘Unknown’.
3. Non-Standard or Mixed Wall Constructions
Older properties, extensions, or conversions often have:
A mix of solid and cavity walls
Custom wall constructions (e.g., timber frame with brick infill)
If the EPC software does not have a matching wall type, the assessor may default to ‘Unknown’.
4. Inaccessible Areas
For walls in loft extensions or side returns where inspection is impractical, the wall type may remain unverified.
How ‘Unknown Wall Type’ Impacts Your EPC Rating
When a wall type is marked as ‘Unknown’, the EPC software applies default U-values that assume poor insulation performance.
| Scenario | U-Value Assumed (W/m²K) | EPC Rating Impact |
|---|---|---|
| Verified insulated cavity wall | ~0.30 W/m²K | Positive Impact |
| Solid wall with verified insulation | ~0.50 W/m²K | Neutral-Positive |
| Unknown wall type (defaulted) | 2.10 W/m²K | Severe Downgrade |
🔴 Result: Your EPC rating could drop from Band C to D or E simply due to the unknown wall default, even if the actual wall is well-insulated.
➡️ Discover how EPC defaults silently harm your rating.
How to Fix ‘Unknown Wall Type’ Entries on EPCs
1. Provide Documentation Evidence
If you have:
Original construction drawings
Cavity wall insulation certificates
Building Control completion reports
these can be used to verify the wall type and update the EPC accordingly.
2. Photographic Evidence
In some cases, clear photographs of exposed wall cross-sections (e.g., from refurbishments or during minor repairs) can help assessors determine wall type.
3. Invasive Inspection (Optional)
Where permissible, small inspection holes may be made to identify wall structure, especially in concealed cavity wall areas. However, this is generally a last resort.
4. Commission a Corrective EPC Survey
If the original assessor was unable to identify wall types, commissioning a new assessment with a specialist EPC provider like EPCrate ensures:
Detailed investigations to minimise defaults
Accurate wall type input based on evidence
➡️ Book a corrective EPC survey with EPCrate.
Long-Term Implications of Leaving Wall Types as ‘Unknown’
Decreased property valuation due to lower EPC band
Rental restrictions if the rating falls below legal compliance (e.g., Band E)
Loss of eligibility for green grants, retrofit funding, and favourable mortgage rates
Market disadvantage compared to similar properties with documented wall types
Why EPCrate?
At EPCrate, we specialise in:
Investigating ‘Unknown Wall Types’ and reducing EPC defaults
Supporting property owners with documentation preparation
Ensuring your EPC reflects the true efficiency of your property’s construction
➡️ See our transparent EPC pricing
➡️ Explore all EPC assessment services
Conclusion: Don’t Let ‘Unknown Wall Type’ Penalise Your EPC Score
An ‘Unknown Wall Type’ entry in your EPC is not just a technicality—it can significantly lower your rating and affect your property’s market appeal. By providing the right documentation and working with experienced assessors, you can ensure your home’s construction is accurately represented.
For properties in London, EPCrate offers expert EPC correction surveys to fix unknown entries and maximise your rating.
