Property Development Costs and Timescales: Does Your Appraisal Still Stack Up?

A property-development appraisal is not something we should prepare before buying a site and then forget about.

Costs change. Programmes slip. Building Control fees, professional costs and finance charges can increase. The property may also take longer to sell than anticipated.

A development that appeared profitable at the beginning can look very different six or twelve months later. That does not necessarily mean we made the wrong decision. It means the appraisal needs to remain a working document throughout the development.

Yesterday's build costs are not today's build costs

One of the most dangerous mistakes is taking the construction cost from a previous development and simply inserting it into a new appraisal.

The last project may have been similar in size, but that does not mean it will cost the same. The design may be different. Ground conditions, access, specification, drainage, services and planning requirements may all have changed. Labour and material prices may also have moved significantly.

Following Covid, the speed and scale of material-cost increases were, frankly, breathtaking. Timber, steel, insulation and many other products increased sharply. Availability became unpredictable, quotations expired quickly and costs that had appeared reasonable only months earlier were no longer achievable.

Those increases destroyed the assumptions behind many development appraisals.

Developers who relied on historic costs without checking the current market could find that a large proportion of their anticipated profit had disappeared before construction was properly underway.

Before buying, we need to establish what the proposed development is likely to cost now—not what a different development cost several years ago.

Do not make the figures fit the deal

It is easy to become enthusiastic about a potential development and start making the appraisal fit the opportunity.

We may use the highest comparable sale price, assume an uncomplicated planning process, choose the lowest initial building estimate and allow very little for delays.

The result can be an appraisal that looks attractive but has no room for the realities of property development.

Before committing to a purchase, I want to understand:

• What can the finished development realistically achieve?
• How reliable are the comparable sales?
• What work has been included in the construction estimate?
• Which costs have been excluded?
• How current are the construction figures?
• How long might planning, construction and the eventual sale take?
• What happens to the profit if costs increase or the programme slips?

A deal should still make commercial sense when the figures are challenged.

“I can do it more cheaply” needs testing

Developers often believe they will be able to complete the work more cheaply than the next buyer. Sometimes they can.

They may have reliable trades, good supplier relationships, relevant experience or the time and ability to manage parts of the project themselves.

But we should not kid ourselves.

If the appraisal only works because we assume that we can build substantially more cheaply than everyone else, we need evidence to support that assumption.

Ask yourself:

• Which costs will genuinely be lower?
• Have those savings been confirmed?
• What work will you personally undertake or manage?
• How much time will that require?
• What happens if your preferred trades are unavailable?
• Who will coordinate the programme and correct defective work?
• What happens if the saving is not achieved?

Managing trades directly or undertaking more of the work ourselves may reduce costs. It may also involve considerable time, hassle, stress and responsibility.

There is nothing wrong with accepting that challenge if the reward justifies it. But the appraisal needs to answer an honest question:

A projected saving is not a saving until the work has been completed properly for that amount.

Compare construction quotations properly

The lowest building quotation is not necessarily the lowest cost of completing the development.

One contractor may include scaffolding, skips, temporary services, drainage connections, external works and certification. Another may exclude them.

Unless the contractors are pricing the same drawings, specification and scope of work, it is difficult to make a meaningful comparison.

We need to identify:

• What is included?
• What is excluded?
• Who is supplying the materials?
• Who is responsible for temporary works and site facilities?
• Are external works and service connections included?
• What professional inspections, warranties and certificates are required?
• How will variations be agreed and valued?

A quotation of £300,000 with £30,000 of missing work is not really a £300,000 quotation.

Whether we appoint a main contractor, manage individual trades or use a hybrid arrangement, we need to compare the likely total cost of reaching a completed, compliant and saleable development.

Building Control costs may need reviewing

Changes to the way local authorities can charge for Building Control services come into force mainly from 6 November 2026.

The changes allow councils to recover the full cost of a wider range of Building Control functions and activities. That does not mean every development will face the same increase. Charges will depend on the local authority, the project and the services required.

The practical lesson is simple: do not rely on an old Building Control allowance taken from a previous development or an outdated schedule of fees.

Obtain a current quotation for the specific project and establish what it includes. We should also understand whether additional inspections, amendments or other services could generate further charges.

Building Control may represent a relatively small proportion of the total development cost, but several underestimated items together can materially reduce the profit.

Allow for a realistic contingency

A contingency is not an optional amount we include only when the deal can afford it.

Property development involves unknowns. Existing buildings can hide structural problems, asbestos, damp, defective drainage and inadequate services. Development land can present difficult ground conditions, contamination or unexpected foundation requirements.

The level of contingency should reflect the information available and the risks involved.

A project with detailed surveys, completed design information and firm contractor prices may justify a different allowance from a site being appraised before planning or intrusive investigation.

The less we know, the more dangerous it is to use an unrealistically small contingency.

Construction output is slowing—but understand what that means

The Office for National Statistics reported that private new-housing construction output fell by 3.2% during the three months to August 2026. It also fell by 1.9% in August itself.

That tells us that less private new-housing construction work was being carried out during that period. It does not automatically prove that every property will take longer to sell or that every development market is weak.

Property markets are local. The demand for a well-designed family house in one location may be completely different from the demand for city-centre apartments somewhere else.

There is not simply a good market or a bad market. There is the market we are operating in, and we need to understand what that particular market means for our development.

Reduced construction activity might create less competition in some locations. In others, it may reflect weaker developer confidence or more difficult viability.

We should not make assumptions. We should investigate the local evidence.

Other developers are doing the same calculation

When bidding for a property or development site, remember that the other interested developers are usually carrying out a similar appraisal.

They are considering the purchase price, construction costs, planning risks, finance and eventual sale value.

If another developer offers more, it does not automatically mean that they understand the opportunity better than you do. They may have different costs, a different strategy or a more optimistic view of the risk.

They may also simply be offering too much.

It can be frustrating to lose a development opportunity, particularly after spending time assessing it. But losing a site because somebody else has paid more than your appraisal supports can be a good result.

There will always be another opportunity.

The objective is not to win every deal. It is to buy the right development at the right price.

Property development profit is often made—or lost—at the point of purchase.

What does a delay really cost?

Developers often focus on construction costs while underestimating the cost of time.

If a project takes three or six months longer than expected, the additional cost may include:

• Development-finance interest
• Lender monitoring or extension fees
• Council tax or business rates
• Insurance
• Utilities
• Security
• Site management
• Professional fees
• Marketing and estate-agency costs
• The opportunity cost of having capital tied up

The project may still be profitable, but the return on the money invested can be significantly reduced.

Every appraisal should therefore include a realistic programme and an allowance for possible delay.

I would also want to see what happens if the development takes three months longer than expected—and then what happens if it takes six months longer.

Stress-test the completed value

The gross development value is often the most influential figure in an appraisal.

A relatively small reduction in the eventual selling price can remove a large proportion of the anticipated profit.

If a development is expected to sell for £500,000, what happens if it achieves £475,000? What if incentives, legal contributions or further work are required to secure the sale?

We should base the appraisal on relevant completed sales rather than optimistic asking prices.

Comparable evidence should be examined carefully. Is the property genuinely comparable in terms of size, location, condition, parking, outdoor space and specification? When did it sell? Has the local market changed since then?

If the development only works when we use the very highest possible sale price, it may not have sufficient margin for the risks involved.

Keep updating the appraisal

The appraisal should be reviewed at important points throughout the development:

• Before making an offer
• Before exchanging contracts
• After obtaining planning permission
• When detailed construction quotations are received
• Before starting work
• When significant variations arise
• When the sales strategy is agreed
• As the project approaches completion

Updating the appraisal does not change what has already been spent. It helps us understand the current position and make better decisions about what happens next.

We might decide that additional expenditure will improve the finished value. We might reduce part of the specification, renegotiate a quotation or change the timing of the sale.

Those decisions should be based on the commercial effect on the whole project—not simply on whether one individual item appears expensive.

Does the development still stack up?

A good appraisal should not tell us what we want to hear. It should help us decide whether the potential return justifies the money, time and risk involved.

Before committing to a development, I would want to test:

• A realistic purchase price
• Current professional and statutory fees
• Current construction costs rather than figures from a previous project
• Properly compared contractor quotations
• A suitable contingency
• A realistic construction programme
• The full cost of development finance
• A possible delay in completion or sale
• A reduction in the expected selling price
• The amount of profit remaining after those changes
• Whether the return justifies the time, stress and responsibility involved

Sometimes the revised figures will confirm that the development remains a good opportunity.

Sometimes they will show that the purchase price needs renegotiating.

Occasionally, the best commercial decision will be to walk away—and allow somebody else to discover that they paid too much.

How I can help

My one-to-one property-development mentoring is based around the actual opportunities and projects you are considering.

We can examine the purchase price, planning position, construction costs, programme, professional team, finance and expected selling value together.

I will not make the decision for you, and my mentoring does not replace advice from appropriately qualified professionals. My role is to bring practical development experience to the discussion, challenge assumptions and help identify the questions that need answering before you become financially committed.

A spreadsheet can show that a development makes a profit.

The real value comes from knowing whether the figures entered into it are realistic.