Your home is a 1930s semi-detached house in Harrogate, built with solid brick walls (225mm) and a timber ground floor over a ventilated void. The loft has some insulation but only around 100mm — below current standards, with gaps at the eaves. The property is heated by a gas combi boiler installed in 2018. Total floor area is approximately 120 m².
The main issues you have raised are high energy bills, cold rooms during winter — particularly the ground floor and north-facing bedrooms — and draughts from the original windows and front door. There is no mechanical ventilation; the building relies on natural infiltration through gaps in the fabric, which contributes to the heat loss.
The priority for this phase is the thermal envelope: internal wall insulation, window and door replacement, and loft top-up. As the envelope tightens, mechanical ventilation with heat recovery (MVHR) is needed to maintain air quality and manage condensation risk. These four measures are interdependent and must be sequenced correctly — this Build Pack sets out that sequence.
Floor plans recorded at survey, alongside annotated versions showing the proposed measure positions.
These measures are sequenced to work together. Windows and doors are installed first so that the IWI system can be dressed around the frames correctly, bringing them within the insulation layer. The loft top-up completes the envelope. MVHR follows once airtightness is confirmed.
Four measures recommended for this property. Click each card for the full specification and installer detail.
Why this property: The existing windows are original sash-style, either single glazed or early double glazed with degraded seals. They are a major source of heat loss and draughts. Installing before IWI is the correct construction sequence: the insulation is then dressed around the outer frame, bringing the window into the insulation layer and avoiding a cold bridge at the reveal.
Minimum whole-window U-value of 1.4 W/m²K. Triple glazing recommended for north-facing elevations. All frames to achieve at least Window Energy Rating Band B. Product selection confirmed by appointed installer to these performance standards.
FENSA or CERTASS registered installer required for all glazing replacement. This is a legal requirement for replacing windows in England and Wales. The installer will issue a certificate of compliance on completion.
Why this property: At 225mm solid brick, these walls have a U-value of approximately 2.1 W/m²K — well above the 0.3 W/m²K target for a well-insulated home. There is no cavity to fill. IWI is the only viable route for this wall construction.
Minimum U-value of 0.30 W/m²K post-installation. BBA-certified system required. All penetrations sealed to maintain airtightness. Junctions designed to avoid thermal bridging. We specify either the IWI Pro mineral wool system (Partnership — specifiable; render finish only) or the K Systems M mineral wool system (BBA-certified, A1-rated, suitable for any building height). System selection confirmed at specification stage.
Installer must hold relevant accreditation for externally insulated render systems and carry appropriate liability insurance. System manufacturer approval and training certification required.
Why this property: The existing 100mm is significantly below the 300mm recommended minimum. The loft is accessible and the top-up is straightforward. Eaves require sealing to prevent cold air infiltration into the loft space.
Minimum total depth of 300mm. We specify Knauf Earthwool Loft Roll 44 (glass mineral wool, 0.044 W/mK, Euroclass A1, BS EN 13162 certified, ECOSE® Technology). Second layer laid perpendicular to joists to eliminate thermal bridging. Eaves vents maintained where required for roof ventilation.
Installer must be registered with the relevant accreditation schemes. Our vetted specialist installers carry appropriate insurance and references for this type of work.
Why this property: Once IWI and windows are installed, natural ventilation through gaps will be greatly reduced. Without controlled ventilation, air quality deteriorates and condensation risk increases. MVHR is the correct response to a well-sealed envelope and must be sized and designed after the airtightness re-test is complete.
System designed by independent MVHR specialist before installer is appointed. Minimum 85% heat recovery efficiency. Units specified from: Zehnder, Paul, or Brink. Ductwork: Lindab. Semi-rigid or rigid duct throughout; no flexible duct run longer than 1.5m.
BPEC-accredited installer required. The MVHR system design must be produced by an independent specialist before the installer is appointed. This is not the installer’s responsibility to design.
Indicative durations based on similar projects. Works can be phased to suit your schedule and budget.
Projections are based on current energy tariffs and SAP/RdSAP modelling. Actual savings depend on occupancy and how the heating is used.
These items need further investigation before specifications and quotations are finalised. None block you from moving forward — we will work through them together.
The IWI cost estimate is based on an approximate wall area. A surveyor will measure the property precisely before quotations are issued. Gables, bay windows, and any existing attached structures will affect the final area.
Action: Furbnow to arrange at surveyIWI on a semi-detached house in England does not typically require planning permission under permitted development, but the local authority should be consulted. Conservation area status and any Article 4 directions need to be confirmed for this address.
Action: Furbnow to check with North Yorkshire Council prior to specificationNo airtightness test result is available for this property. A baseline test before works begin is recommended to confirm the current infiltration rate and inform MVHR sizing. A re-test after windows and IWI are complete is required before MVHR is designed.
Action: Furbnow to arrange baseline blower door testAccess hatch size and any obstructions (tanks, pipework, stored items) need confirming at survey. If the hatch needs enlarging, this will be noted in the quotation.
Action: Confirmed at surveyTechnical designs and specialist reports will be added here as the project progresses. No documents have been produced yet — this is a post-survey outline.