Insulated external doors: replace only when repair is not enough | Homecode

What is known — and what is not

When this improvement may fit

• Repair and draught-proofing have been compared with replacement. Evidence needed: Condition report and options appraisal. [10]
• The complete door set can meet thermal, weather, security, impact, escape and accessibility needs. Evidence needed: Product and installation specification. [10]
• Appearance and permissions fit the building and street context. Evidence needed: Planning/heritage/freeholder decision. [10][12][11]

When it may not fit

• A repairable historic door makes an important contribution to the building. Decision: Prefer skilled repair and reversible draught-proofing unless heritage advice supports replacement. [10][12]
• The proposal treats the slab alone while the frame, threshold, seals or water path remain defective. Decision: Do not assume an insulated core solves the whole opening. [10]
• Active damp, water ingress, condensation, mould, decay or a fabric defect has not been diagnosed and resolved. Decision: Do not cover the symptom with insulation. Repair the cause, verify drying and then reassess the measure. [10]
• The post-retrofit ventilation and moisture strategy is unknown, or the work would block an airbrick, trickle vent, eaves route, sub-floor path, flue or other designed opening. Decision: Pause for a ventilation and moisture assessment; a warmer or tighter element is not a reason to remove required airflow. [10][3]
• The work would disturb unknown material in a home or part refurbished before 2000, or suspect board, coating, lagging, loose fill, tile or adhesive is present. Decision: Do not disturb it. The asbestos survey scope must match the planned work before drilling, cutting, lifting, stripping or removal. [10][8]
• The proposal affects listed fabric, a protected elevation, a conservation-area character feature, a leasehold/common part or another owner's structure without the required advice or consent. Decision: This is a consent and compatibility stop, not proof the measure can never work. Obtain written decisions before specifying the installation. [10][12][11]

Assessment before spending

• Diagnosis first: Identify whether discomfort comes from perimeter leakage, letterbox/keyhole, warped joinery, threshold, glazing, water ingress or conductive heat loss. [10]
• Can the existing door and frame be repaired and draught-proofed? [10]
• Is the door part of a required escape, fire or security strategy? [10]
• Will the threshold remain safe and accessible? [10]
• Are trickle vents, combustion air or undercuts involved? [10][3]
• Does the opening, lintel or surrounding wall need repair? [10]
• What planning, listed-building or lease consent applies? [10][12][11]
• What are the property and refurbishment dates, and does the planned work area have asbestos information appropriate to the intrusive scope? [10][8]
• Are there active leaks, damp, mould, salts, rot, corrosion or defective rainwater details, and has the source been diagnosed rather than labelled from appearance? [10]
• Which background, extract, sub-floor, roof-space or combustion ventilation paths could the measure change? [10][3]
• Is the home listed, in a conservation or other designated area, leasehold, or subject to freeholder, lender, insurer or planning restrictions? [10][12][11]
• What does the current EPC actually record, and has the construction changed since that assessment? [10][1]
• Door/frame condition and repair appraisal [10]
• Product thermal and safety specification [10]
• Threshold and escape assessment [10]
• Planning/freeholder decision [10][11]
• Competent-person or building-control certificate [10][13]
• Decision output: Require a written suitable / suitable with conditions / not suitable decision, with reasons, excluded areas and dependencies. [10]
• Likely mechanism: An insulated core and well-fitted seals reduce heat transfer and uncontrolled leakage through a complete external door set. [10]
• Reduced draught and cold-surface discomfort [10]
• Lower heat loss through the opening [10]
• Improved weather seals when the whole opening is correctly installed [10]
• Uncertainty: The opening area is limited and results depend on fit, exposure, frame, threshold, glazing, letterbox and occupant use. [10]
• Not guaranteed: No bill saving, EPC change, comfort result, payback, mortgage acceptance, sale price or rent increase is guaranteed. [10][1][4]

Safe observations only

• Operate the door normally and photograph gaps, seals, threshold and rain staining. Boundary: Stop if glass, frame or heavy leaf is loose. [10]
• Check whether the door is listed, leasehold, fire-rated or escape-critical. Boundary: Do not remove labels, closers or seals. [10][12]
• Ask for repair and replacement quotes on the same diagnosed defects. Boundary: Do not compare only headline product ratings. [10]

Stop conditions and professional route

• Do not DIY remove or install a whole external door and frame. [10]
• Do not reduce escape width, threshold accessibility, fire performance or designed ventilation. [10][3]
• Do not discard a repairable historic door without heritage advice. [10][12]
• Do not treat insulation as a cure for an undiagnosed damp or mould symptom. [10]
• Do not block or reduce designed ventilation, drainage, flues, airbricks or fire-stopping. [10][3]
• Do not drill, cut, lift or strip unknown pre-2000 fabric without asbestos information that covers the exact work. [10][8]
• Do not rely on a product brochure, an EPC recommendation or a grant offer as a property-specific suitability survey. [10][1]
• Next assessor: A competent door/window surveyor or conservation joiner for historic doors; structural or fire-door expertise where applicable. [10][12]
• Installer: An installer registered for the exact work under an authorised Competent Person Scheme, or a competent installer working through building control. [10][5][13]
• Current Competent Person Scheme registration covering replacement external doors [10][5]
• Conservation joinery experience for historic fabric [10][12]
• Fire-door competence where the door has a fire function [10]
• For government-funded work, verify current TrustMark registration and PAS 2030 certification for the exact measure, with PAS 2035 roles where the scheme requires them. [10][5][7]
• For privately funded work, verify relevant experience, insurance, references, product-system authorisation, written scope, exclusions, guarantees and a complaints route; TrustMark is a quality option, not a universal legal licence. [10][5][7]
• Replacement external doors are controlled fittings; choose the competent-person or building-control route before work [10][13]
• Check planning, Article 4, conservation and listed-building consent [10][12][11]
• Obtain freeholder/management approval for flats and leaseholds [10]
• Survey, design and moisture/ventilation assumptions [10][3]
• Building control or competent-person evidence where applicable [10][13]
• Product and system specification, photographs of concealed details and commissioning checks [10]
• Guarantee, maintenance instructions, invoice and complaint route [10]

EPC, grant and property evidence

• Relationship: An EPC may identify an inefficient door, but it cannot assess repairability, historic significance, frame defects, weathering, security, escape or threshold access. [1]
• Limit: An EPC recommendation is modelled decision support, not a condition survey, moisture design, quotation or assurance that this measure fits the property. [1]
• Post work: Keep installation evidence and consider an updated EPC where a current certificate or letting decision needs to reflect completed work. [1]
• ECO4 was current and scheduled to run to 31 December 2026 as reviewed on 2026-08-13, but household eligibility, measure packaging, contributions and delivery remain case-specific. Treat this page as measure guidance, not an ECO4 approval; recheck Ofgem and the obligated supplier before relying on the route. [5]
• Condition and sale: Keep the compliance certificate, product specification and consent. Removing historic fabric or lacking replacement certification can create conveyancing questions; no value uplift is assumed. [10][12][11]
• Letting: Landlords/freeholders should control replacement, security, escape, fire and accessibility, and give tenants keys and operating instructions. Tenants should not replace a fixed external door without written permission. [10][4][11]
• Pre-work survey and photographs [10]
• Permissions, notices and building-control route [10][11]
• Design, quotation, variations and installer credentials [10][7]
• Concealed-work photographs, completion records and guarantee [10]
• Maintenance and any post-work moisture or ventilation checks [10][3]
• Value statement: Treat any market effect as property-specific and evidence-dependent; this page makes no claim that the measure increases value or rent. [10]
• Is replacement always better than draught-proofing? No. A sound door may perform well after repair and seals, and historic doors should usually be retained where possible. [10][12]
• Can I replace the external door myself? The live safety row is Red for whole door-and-frame replacement. Use a competent installer and the correct Building Regulations route. [10][13]
• Does an insulated slab guarantee a warm doorway? No. Frame fit, seals, threshold, glazing, letterbox, exposure and installation determine the whole opening. [10]