Imagine insuring your home for £150,000 when rebuilding it would actually cost £200,000. A storm causes £20,000 of damage. Instead of getting the full amount, your insurer applies the average clause and pays you £15,000 — leaving you £5,000 short. That gap is underinsurance, and it is far more common than most people realise. With UK property insurance payouts hitting a record £6.1 billion in 2025, getting your sum insured right has never mattered more for your own pocket.
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This article is general information only and does not constitute professional advice. For your specific situation, consult a qualified professional.
The average combined buildings and contents policy cost £375 a year in early 2026, according to the ABI Premium Tracker. But a cheap premium is worthless if the sum insured is too low. The difference between market value and rebuild cost catches thousands of homeowners out every year, and the gap is widening as construction inflation and new building regulations push rebuild costs higher. Here’s what you actually need to know.
What rebuild costs actually include — and what they cost
The single most common mistake is treating the sum insured as a rough guess. Insurers expect it to reflect the full reinstatement cost, which goes far beyond bricks and mortar. The table below breaks down the components using a realistic example from the Landlord Association.
→ Scroll right to see all columns
| Component | Amount | Notes |
|---|---|---|
| Base rebuild estimate | £240,000 | Two-storey semi with extended kitchen and HMO upgrades |
| Professional fees (10%) | £24,000 | Architects, engineers, surveyors, planning fees |
| Debris removal and site clearance (7%) | £16,800 | Demolition, waste disposal, site prep |
| Outbuildings, boundaries, hardstanding | £9,200 | Walls, fences, gates, drives, paths |
| Total declared value | £290,000 | Before any Day One uplift |
If that same property had been insured for £220,000 to save on premiums, it would be roughly 24% underinsured at inception. The average clause would then reduce every claim by nearly a quarter. What I tend to notice is that landlords and homeowners focus on the base rebuild figure and forget the extras — then wonder why a claim falls short.
The BCIS residential rebuild index put average rebuild costs at roughly £1,700 per square metre in 2026, with a broad range of £1,500 to £2,500 depending on location and construction. For non-standard homes — thatched roofs, listed status, timber frame — a professional reinstatement valuation is worth the cost. Many insurers will require one from 2026 onwards for certain property types, as scrutiny of rebuild values intensifies.
Three costly mistakes that leave you underinsured
Using purchase price or mortgage valuation as the sum insured
Market value includes land, location and demand — none of which matter to an insurer when you need to rebuild. In London, market value can be double the rebuild cost. In other areas, the reverse is true. The only figure that matters is what it would cost to reconstruct the property to current standards, including compliance upgrades such as fire doors or emergency lighting in Houses in Multiple Occupation (HMOs). A real estate lawyer can help clarify property-specific legal requirements that affect rebuild specifications, but the valuation itself needs a surveyor or a recognised calculator.
Omitting professional fees, debris removal and VAT
Architects, structural engineers, planning permission, site clearance and VAT (if you are not VAT-registered) typically add 15–20% to the raw rebuild figure. Policies vary in how they handle these — some include them within the buildings sum insured, others provide separate limits. Either way, the total allowance must be sufficient. A landlord who insures a £240,000 rebuild for £240,000 but forgets the £40,000 of fees and clearance is already 14% underinsured before a single brick is laid.
Not updating sums insured after renovations or upgrades
Extensions, loft conversions, kitchen refits and HMO compliance work all increase rebuild cost. If you do not update your policy, the gap widens silently. The same applies to outbuildings, boundary walls and hard landscaping — many policies require these to be included, and they are easy to overlook. A quick walk around your property once a year, comparing what is there now against what your policy says, catches most of these before they become a problem at claim time.
- Obtain a professional rebuild assessment or use a recognised BCIS-based calculator
- Include professional fees and debris removal according to your policy structure
- Include VAT if you are not VAT-registered
- Review sums insured after any extension, loft conversion or compliance upgrade
- Use Day One reinstatement with an appropriate uplift (typically 25–35%)
- Set loss of rent cover to match actual rent and consider 18–24 month durations for complex risks
- Maintain a detailed property schedule listing declared values, contents limits and special features
- Ask your insurer about waiver of average options and understand any conditions attached
How to get your sum insured right — and keep it right
Calculate the rebuild cost, not the market value
The industry benchmark is the BCIS House Rebuilding Cost Index, which the ABI and RICS both use in their free online calculators. You enter your property type, size, location and construction method, and it gives a per-square-metre rate. For a typical three-bedroom semi of around 100 square metres, that works out to roughly £170,000 at the 2026 average of £1,700 per square metre. For anything non-standard — thatch, listed status, timber frame, unusual roof pitch — pay for a professional reinstatement valuation from a surveyor. It typically costs a few hundred pounds and removes the guesswork entirely.
Set contents cover room by room
Contents sum insured should equal the cost of replacing everything you own on a new-for-old basis. Walk through each room and total furniture, electronics, appliances, clothing, kitchenware and soft furnishings. Most people underestimate by thousands. Watch the single-article limit — typically £1,500 to £2,000 — above which items such as engagement rings, watches, laptops and bikes must be specified individually or they will not be paid in full. If you rent, you only need contents cover; the landlord insures the building.
Use Day One reinstatement and declaration-linked policies
Day One reinstatement policies require you to declare the current rebuild value, and the insurer applies an automatic uplift — often between 15% and 50% — to account for inflation between the policy start date and any future claim. Accurate initial valuation remains essential because index linking cannot correct an inaccurate starting figure. For portfolio landlords, declaration-linked policies require annual declarations of property values, with adjustments at year-end. Both features help, but neither replaces getting the base figure right in the first place.
What changes in 2026 that affects your sum insured
From July 2026, Flood Re’s annual levy on insurers increases to £160 million and its statutory loss limit rises to £250 million. The Build Back Better programme — which provides up to £10,000 of flood resilience measures as part of repairs — is now offered by over 70% of the residential market. Flood Performance Certificates, similar to Energy Performance Certificates, are being introduced to assess property flood resilience and enable premium discounts. Separately, insurers are expected to scrutinise rebuild values more closely, request documented justification, and decline risks with underestimated valuations. If your sum insured has not been reviewed in the last two years, 2026 is the year to do it. A FireAngel smoke alarm and a X-Sense Wi-Fi water leak detector are simple additions that can reduce risk and may help with insurer confidence, but the core protection comes from a correct sum insured.
Frequently asked questions about sum insured and underinsurance
What is the difference between rebuild cost and market value? ▾
How does the average clause work in practice? ▾
Do I need a professional valuation for a standard home? ▾
What happens if I am underinsured and do not claim? ▾
Does underinsurance affect loss of rent cover? ▾
Can I get a waiver of average on my policy? ▾
Getting your sums insured right in 2026 and beyond
The direction of travel is clear: from 2026, insurers will demand documented justification for rebuild values, decline risks with outdated figures, and enforce proportionate settlement clauses consistently. Combined with rising claims costs — the average household claim hit £6,340 in early 2026 — the financial penalty for underinsurance is growing. A correct sum insured is not about paying more; it is about making sure the cover you already pay for actually works when you need it. If you are a landlord, the same logic applies to loss of rent periods and contents cover for furnished lets. One afternoon spent checking your sums insured against current rebuild costs could save you thousands.
Remember: this article is general information only. For advice on your specific situation, speak to a qualified professional.
If this was useful, you might also want to read Flooding in the UK: Is Your Property Insurance Adequate Protection?.
Sources and Further Reading
Hidden property insurance clauses UK homeowners need to know about — A closer look at policy terms that can catch you out, including average clauses and other conditions.
Navigating property insurance policy limits in the UK — Practical guidance on understanding policy limits and avoiding coverage gaps.
NetRent Insurance Services (2025). Sums Insured & Rebuild Costs: Ending Underinsurance for Good in 2026. 🔗
Browne Jacobson (2026). UK property insurance in 2026: Five trends reshaping risk, pricing and coverage. 🔗
MyInsuranceExpert (2026). Buildings and contents home insurance UK 2026. 🔗
Landlord Association (2026). Underinsurance and the Average Clause – Avoiding Reduced Payouts. 🔗
