Finding Comparable Evidence for GDV: Sources and Methodology

Comparable evidence is the foundation of every gross development value assessment. When a RICS valuer determines the GDV of your proposed development, they are not expressing a personal opinion about what the completed units might be worth. They are analysing evidence of what similar properties have actually sold for in the relevant market and applying professional adjustments to account for differences between those properties and your proposed scheme. The stronger your comparable evidence, the more confidently the valuer can support your projected GDV figure. Weak or insufficient evidence forces the valuer to be conservative, which results in a lower GDV and a smaller development finance facility.

The importance of comparable evidence cannot be overstated. In our experience arranging development finance across the UK, the single most common reason for GDV down-valuations is insufficient comparable evidence rather than genuinely overpriced expectations. Developers who spend time before the valuation researching and compiling comprehensive evidence packs consistently achieve valuations closer to their expectations than those who rely on the valuer to conduct their own research. The valuer is working to tight timescales and may not have the same local knowledge or access to information that the developer has accumulated during the planning and pre-development phase.

Comparable evidence also serves a broader purpose in the development process. It validates your pricing assumptions before you commit to a site purchase, informs your marketing strategy for the completed units, and provides data for the development appraisal that underpins your finance application. Developers who treat comparable research as an ongoing intelligence exercise rather than a one-off task for the valuation are better positioned to make informed decisions at every stage of the project.

The Land Registry is the primary source of achieved sales price data in England and Wales. The Price Paid Data dataset is publicly available and records every residential property transaction, including the address, price, date, property type, and whether it was a new-build sale. The data is updated monthly with a lag of approximately 6-8 weeks from the date of completion. For development finance purposes, you should search for all sales within a reasonable radius of your site, typically one mile for urban areas and three miles for rural areas, filtering for property types comparable to your proposed units. New-build sales are particularly relevant because they provide direct evidence of what buyers have paid for newly constructed homes in the area.

Rightmove, Zoopla, and OnTheMarket provide current asking price data and, through their sold price tools, historical transaction records sourced from the Land Registry. These platforms also show current market listings, which indicate the pricing level at which similar properties are currently being marketed. While asking prices are not the same as achieved prices and must be treated with caution, they provide useful context about current market conditions and developer pricing strategies. We recommend recording both the asking price and the eventual sold price for comparable properties to understand the typical negotiation discount in the area, which for new-builds is typically 0-5%.

For new-build specific evidence, developer sales offices and show homes are invaluable sources. If there are other new-build developments in the area, visit them to understand the pricing, specification, and sales pace. Most developers will share price lists and brochures, and some will discuss sales rates informally. This intelligence is extremely valuable for supporting your GDV assumptions and for briefing the RICS valuer. If a competing developer is achieving £425 per square foot for three-bedroom detached houses and your specification is comparable, this is strong evidence to support a similar pricing level for your scheme.

Estate agent opinions provide qualitative support for your quantitative comparable evidence. Approach three to four local agents who are active in the residential sales market and ask them to provide written opinions on the expected selling prices of your proposed units. These should be formal letters on headed paper, not casual emails, and they should reference specific comparable sales or current market activity that supports their opinion. Agent letters are most persuasive when they come from firms that have actually sold new-build properties in the immediate area, as they can speak from direct experience of buyer behaviour and demand levels.

Specialist property data providers such as BCIS, Hometrack, and LonRes offer more granular data than the free public sources. BCIS provides construction cost benchmarking that can support the cost side of your appraisal, while Hometrack offers local market analytics including price trends, demand indicators, and area demographics that help contextualise your GDV assumptions. LonRes is particularly valuable for London and prime South East schemes, offering comprehensive transaction data for high-value properties. Access to these platforms typically requires a subscription, but your broker or valuer may have access and can provide relevant data for your scheme.

Planning portals and local authority records provide evidence of other development schemes in the pipeline, which can both support and challenge your GDV assumptions. If multiple developers are bringing similar schemes to market in the same area, this validates demand but may also indicate potential oversupply risk. The valuer will consider the competitive supply pipeline when assessing your GDV, so being aware of it and addressing it proactively in your evidence pack demonstrates market awareness. For guidance on how comparable evidence feeds into your overall development appraisal, see our guide on how to calculate GDV.

Raw comparable data must be adjusted to account for differences between the comparable properties and your proposed units. The RICS framework requires adjustments for factors including location, size, age and condition, specification, plot attributes such as gardens and parking, aspect and views, and market movement since the date of the comparable transaction. Each adjustment should be quantified and justified, not simply stated. For example, rather than saying your units will achieve a premium for a superior specification, quantify the premium by reference to evidence of what specification improvements typically add in the local market.

Size adjustment is usually the most significant factor. The standard approach is to convert comparable sales to a price per square foot or per square metre and apply this rate to the floor area of your proposed units. If comparable three-bedroom houses are selling at an average of £375 per square foot and your proposed houses are 1,100 square feet, the indicated value is £412,500 per unit. However, this assumes a linear relationship between size and price, which is not always accurate. Larger properties often achieve a lower per-square-foot rate than smaller ones because there is a diminishing return to additional space. For schemes with a mix of unit sizes, separate comparable analyses for each unit type will produce more accurate results.

Market movement adjustment is essential when comparable evidence is more than three months old. If comparable sales achieved six months ago are used unadjusted, they may understate current values in a rising market or overstate them in a falling market. The Land Registry House Price Index provides monthly data on price movements by region and property type that can be used to time-adjust comparable evidence. For example, if a comparable sold for £380,000 nine months ago and the local market has risen by 4% since then, the time-adjusted comparable is £395,200. Document each adjustment clearly so the valuer can follow and verify your methodology.

The format and presentation of your comparable evidence pack can significantly influence the quality of the valuation outcome. We recommend presenting the evidence in a structured document that includes a summary schedule of all comparable sales with key details such as address, price, date, size, and property type, followed by individual property sheets for the most relevant comparables with photographs, floor plans where available, and your adjustment analysis. Include a map showing the location of each comparable relative to your site to give the valuer spatial context.

Organise the evidence by relevance, with the most directly comparable properties presented first. A three-bedroom new-build house sold 200 metres from your site three months ago is far more relevant than a five-bedroom period property sold two miles away a year ago. Highlight the comparables that are most supportive of your pricing and explain why you consider them appropriate. Where comparables support a higher figure than your assumed GDV, note this as it gives the valuer comfort that your pricing is conservative rather than optimistic.

Include evidence that challenges your pricing as well as evidence that supports it. If there are comparable sales that suggest lower values, acknowledge them and explain why you believe they are less relevant, whether because of inferior location, smaller size, lower specification, or distressed sale circumstances. A balanced evidence pack that addresses both supportive and potentially contradictory data is more credible and more useful to the valuer than one that cherry-picks only the highest comparables. For additional guidance on preparing for the valuation process, see our guide on RICS Red Book valuations.

Some locations and property types present challenges for comparable evidence, particularly in rural areas, regeneration zones, and for unusual property types where few transactions take place. When direct comparables are limited, you need to adopt a wider evidence strategy. Start by expanding the geographic search radius from one mile to three or five miles, accepting that more distant comparables require larger location adjustments. Look for transactions of similar properties in comparable towns or villages at similar distances from the nearest city or transport hub.

Agent letters become even more important when transaction evidence is thin. If the quantitative data is limited, qualitative evidence from experienced local agents who can speak to buyer demand, pricing levels, and market dynamics carries more weight. Agents who have sold new-build properties in the wider area, even if not in the immediate vicinity, can provide valuable perspective on the premium that new-build commands and the demographic of buyers likely to purchase your units. Three consistent agent opinions supporting a £400,000 unit price are meaningful evidence even if Land Registry data for the specific postcode is sparse.

For schemes in emerging markets where there is genuinely no comparable evidence of new-build sales, you may need to build the evidence case from secondary indicators: second-hand sales adjusted for a new-build premium, planning approvals for other development schemes that indicate developer confidence in the area, local authority housing need assessments that demonstrate demand, and infrastructure investments such as new transport links or schools that will support future values. While this is a harder case to make, it is not impossible, and we have successfully supported GDV assessments in emerging markets throughout the UK. Submit your scheme through our deal room and our team will advise on the evidence strategy for your specific location.

Comparable evidence is not a one-off exercise conducted before the valuation and then forgotten. Market conditions change throughout the development process, and maintaining an ongoing evidence base serves multiple purposes. During the construction phase, monitoring comparable sales helps you track whether the market is moving in line with your assumptions or whether adjustments to your marketing strategy may be needed. If comparable prices are rising, you may be able to increase your asking prices and improve the profit margin. If prices are falling, early awareness gives you time to adjust the strategy, whether by bringing forward sales, adjusting the specification to reduce costs, or engaging with the lender about facility restructuring.

For schemes with sales periods extending beyond practical completion, up-to-date comparable evidence supports your agent's pricing recommendations and helps you make informed decisions about offers. A developer who can demonstrate that comparable sales support an asking price of £475,000 is in a stronger negotiating position than one who simply insists the price is right without evidence. Similarly, if you need to justify a price reduction to accelerate sales and exit the development finance facility, evidence of comparable price movements provides the lender with comfort that you are responding rationally to market conditions rather than panic-selling at below value.

We recommend setting up automated property alerts on Rightmove, Zoopla, and the Land Registry to receive notifications of new sales data in your target area. Review this data monthly and maintain a running schedule of comparable transactions. This ongoing intelligence feeds into your marketing strategy, informs your negotiations with buyers, and provides evidence for any valuation discussions with the lender during the development or sales period. For detailed support in managing your development through to successful sales, contact our team through the deal room.