The Challenge of Insulating Older Homes
Victorian and Edwardian properties are typically built with solid brick walls (no cavity), suspended timber ground floors, and single-skin slate or clay tile roofs. They were designed to breathe — to allow moisture to pass through the building fabric and evaporate.
Insulating them incorrectly can trap moisture, leading to interstitial condensation, timber decay, and mould growth. The key principle in retrofitting older homes is to use breathable (vapour-open) materials and to understand how moisture moves through the building.
Roof and Loft Insulation
The roof is the easiest and most cost-effective place to add insulation in an older home.
Cold roof (insulation at ceiling level) If the loft is unused, insulation is laid between and over the ceiling joists. The current recommended depth is 270mm of mineral wool. This leaves the loft cold and ventilated.
Warm roof (insulation at rafter level) If the loft is converted or used for storage, insulation is placed between and below the rafters. For Victorian properties with narrow rafters, rigid insulation boards are often used to maintain adequate depth without reducing headroom too much.
Materials: Mineral wool (glass or rock) is the standard. Rigid PIR boards (Kingspan, Celotex) offer higher performance per mm. Natural materials such as wood fibre are increasingly preferred for older properties.
External Wall Insulation vs. Internal Wall Insulation
Solid brick Victorian walls have a U-value of around 2.0–2.1 W/m²K, compared with a modern new build at approximately 0.18 W/m²K. Improving this significantly requires insulating the walls.
External Wall Insulation (EWI)
Insulation boards are fixed to the outside of the building, then rendered or clad.
Pros:
- Does not reduce internal floor area
- Protects the masonry from weather
- Can improve the external appearance of rendered properties
Cons:
- Changes the external appearance (may not be acceptable in Conservation Areas)
- Expensive (£150–£250+ per square metre installed)
- Affects window reveals, door openings, and eaves details
Internal Wall Insulation (IWI)
Insulation is fixed to the internal face of external walls.
Pros:
- Preserves external appearance
- Can be done room by room
- Lower cost than EWI (£60–£120+ per square metre)
Cons:
- Reduces internal floor area (even 50mm insulation reduces room width by 50mm per wall)
- Must be carefully specified to avoid interstitial condensation
- Skirting, architrave, electrics, and radiators must all be removed and refixed
For Victorian solid-wall properties, wood fibre board or calcium silicate boards are preferred over PIR (foil-backed) insulation because they allow moisture to move through the wall. PIR boards can trap moisture if the vapour control layer is not perfectly executed.
Ground Floor Insulation
Victorian suspended timber floors sit above a ventilated void. Insulation is typically installed from below (if there is access under the floor) or from above (lifting floorboards).
- Below-floor: Mineral wool or rigid insulation held between joists
- From above: Rigid insulation laid between joists before relaying boards
Sealing draughtproofing at the joist ends where they sit in the wall is also important.
Note: Do not seal the underfloor ventilation bricks. The void must remain ventilated to remove moisture from the soil and prevent timber decay.
Window and Door Draught Proofing
Before investing in wall insulation, draught-proofing windows and doors provides a significant improvement in thermal comfort at low cost.
- Original sash windows can be draught-proofed with brush or compression seals
- Sash window secondary glazing preserves the character of the window while dramatically improving thermal performance and acoustic insulation
Double-glazed replacement sash windows are available in timber or uPVC — but their use in Conservation Areas requires planning permission (or approval from the local planning authority).
Whole-House Planning
The most effective insulation retrofits are planned as a whole-house exercise, not as isolated improvements. A domestic energy assessor or retrofit coordinator can produce a report identifying the optimal sequence of measures, taking account of:
- The existing building fabric and construction
- Current EPC rating and target rating
- Budget available
- Occupant priorities
RCB Design & Build
RCB incorporates insulation upgrades into refurbishment projects, advising on appropriate materials and specifications for older properties. We coordinate with retrofit assessors, architects, and specialist subcontractors to ensure improvements are correctly detailed and sequenced within the wider programme.