ARCHITECTS FROM LONDON Building Tender
for House Extensions & Renovations
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RIBA Chartered
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London · Vienna · Rome
Featured in The Times
Panel at Grand Designs Live
Building Tender intro
Building Tender for House Extensions & Renovations
Once your design is developed and the technical information is ready, the next question is usually a very practical one:
How much is this actually going to cost to build?
That is where the building tender process begins.
Rather than sending a few drawings to different builders and asking for a price, a properly prepared tender gives contractors a clear and consistent set of information to quote against.
The goal is simple: every builder should be pricing the same project.
At Tholos, we help prepare the project for tender, approach suitable contractors and review the quotations you receive so you can understand not only which price is lowest, but what each builder has actually included.
Building Tender explained
What Is a Building Tender?
A building tender is the process of inviting contractors to submit a quotation for your construction project.
For a house extension or substantial renovation, builders should ideally receive enough information to understand the work properly before they calculate their price.
That can include:
- technical drawings
- structural information
- specifications
- key construction details
- the scope of work
- relevant approvals and project information
The more clearly the project is defined, the less each contractor has to assume.
That makes their quotations considerably more useful.
Building Tender
Why Not Just Ask Three Builders for a Quote?
You can.
The problem comes when each builder is interpreting the project differently.
One might include decorating.
Another might assume you are supplying the kitchen.
One might include scaffolding and waste removal while another lists them as extras.
A third might base their price on a structural assumption that turns out to be completely wrong.
On paper you now have three quotations.
In reality, you may have three different versions of the project.
A structured tender process helps reduce those differences and gives the builders a common basis for pricing.
Get the Design Ready Before Tendering
The quality of the tender depends heavily on the information you give the contractors.
If large parts of the project are still unresolved, the price will contain assumptions.
Before going to tender, it is usually sensible to have the main technical information developed, including areas such as:
- construction details
- structural design
- significant material choices
- insulation and building fabric
- windows and doors
- drainage where relevant
Not every light fitting or paint colour needs to be selected before tender.
But the decisions capable of materially changing the construction price should ideally be understood.
Structural Design Before Builder Quotes
Structural work can make a significant difference to the cost of an extension.
Steel beams, columns, foundations and major openings are difficult for a contractor to price accurately if they have not yet been designed.
Without structural information, builders may:
- make their own assumptions
- include provisional allowances
- exclude certain work
- add substantial contingency
That makes quotations harder to compare and can lead to additional costs later.
Resolving the main structural work before tender gives everyone a much clearer starting point.
Building Tender
Choosing Builders to Invite to Tender
A good tender is not simply about sending the project to as many builders as possible.
The contractors invited should be appropriate for the type and scale of work.
A company that specialises in new-build developments may not necessarily be the right choice for a domestic extension.
Likewise, the cheapest small contractor may not have the resources for a complex renovation involving multiple trades and structural alterations.
When considering builders, we look at factors such as:
- relevant project experience
- size and complexity of previous work
- references
- accreditations where appropriate
- insurance
- availability
- professionalism and communication
You want enough competition to compare the market without creating an unnecessarily large tender exercise.
Building Tender
Giving Every Builder the Same Information
This sounds obvious, but it matters.
If Builder A receives one set of drawings and Builder B receives additional structural information three days later, their prices are no longer based on exactly the same information.
Tender documents should therefore be issued consistently.
If an important clarification arises while builders are preparing their quotations, it should normally be shared with everyone taking part.
That helps keep the process fair and makes the final comparison much more meaningful.
Building Tender
What Should Builders Include in Their Quote?
The exact breakdown depends on the project, but the quotation should be detailed enough to understand where the money is going.
For an extension or renovation, this might cover areas such as:
- site setup and preliminary costs
- demolition and enabling work
- foundations and groundworks
- structure and steelwork
- walls and roofing
- windows and doors
- plumbing and electrics
- plastering and finishes
- waste removal
- external works
A single figure at the bottom of a page tells you very little.
If something later turns out not to have been included, it becomes difficult to establish whether it was genuinely omitted or simply assumed to be part of the overall price.
Building Tender
Comparing Building Quotations
The lowest tender is not automatically the best tender.
The first step is checking whether the contractors have actually priced the same scope.
Imagine receiving these prices:
Builder A: £92,000
Builder B: £99,000
Builder C: £105,000
At first glance, Builder A appears considerably cheaper.
But perhaps their quotation excludes flooring, decoration and part of the external works.
Once those items are included, the difference may become very small.
This is why tender comparison needs to look beyond the headline number.
A single figure at the bottom of a page tells you very little.
If something later turns out not to have been included, it becomes difficult to establish whether it was genuinely omitted or simply assumed to be part of the overall price.
What We Look for When Comparing Tenders
When reviewing builder quotations, we want to understand where differences come from.
That may mean comparing:
- exclusions
- allowances
- provisional sums
- material specifications
- labour assumptions
- VAT
- programme and duration
- payment arrangements
Large differences between prices often deserve investigation.
Sometimes one contractor has simply found a more efficient way to approach the project.
Sometimes something important has been missed.
Understanding which is which is far more useful than simply selecting the middle quote.
Provisional Sums and Allowances
You will often see provisional sums within building quotations.
These are allowances for work where the final cost cannot yet be confirmed.
They are not necessarily a problem.
Sometimes there is genuinely not enough information available to provide a fixed price.
However, a quotation containing a large number of provisional sums gives you less cost certainty.
If one builder allows £2,000 for an item and another allows £6,000, the cheaper overall tender can quickly become the more expensive project once the actual cost is known.
Provisional sums therefore need to be understood rather than ignored.
Be Careful With Missing Items
One of the easiest ways for an apparently cheap quotation to increase during construction is through exclusions.
These can sometimes be obvious.
Others are buried in the wording.
Typical questions might include:
- Who supplies the sanitaryware?
- Is decorating included?
- Is waste removal included?
- Are Building Control fees excluded?
- Who supplies flooring?
- Is landscaping included?
- Are utility alterations included?
There is nothing inherently wrong with a builder excluding something.
The important thing is that you know about it before comparing the price with someone who has included it.
Builder Questions During Tender
A contractor asking questions during the tender process is not necessarily a bad sign.
In fact, sensible questions can indicate that they are looking carefully at the information.
A builder may identify something that needs clarification or spot an area where several construction approaches are possible.
Those questions should be answered before the tender is finalised where possible.
If the response materially affects the project, the same information should normally be made available to the other tendering contractors.
Should You Negotiate the Builder's Price?
Sometimes there is room for discussion after tenders are returned.
But negotiation should not simply mean demanding that the preferred builder matches the cheapest number.
There may be legitimate reasons why their price is higher.
Instead, it can be useful to understand whether particular parts of the project are driving the cost and whether alternatives are available.
This might involve:
- changing a material specification
- simplifying a construction detail
- removing non-essential work
- changing the timing of certain items
The objective should be to reduce cost intelligently rather than remove necessary work from the quotation without understanding the consequence.
Building Tender
What If All the Tenders Are Over Budget?
It happens.
A tender can be the point where the design meets the real construction market.
If all suitable builders are pricing the project above the available budget, simply asking them to reduce their prices is unlikely to solve the underlying problem.
Instead, the project may need to be reviewed.
That could mean looking at:
- the overall scope
- expensive design elements
- material choices
- structural complexity
- items that could be completed later
Because the project is already properly documented, those changes can be considered deliberately rather than making rushed compromises once construction has started.
Building Tender
Tendering Can Give You Better Cost Certainty
No building project comes with absolute cost certainty.
Existing properties in particular can reveal unexpected conditions once work begins.
But a properly prepared tender significantly improves your starting position.
It helps establish:
- what the builder is pricing
- what has been excluded
- where allowances have been made
- how different quotations compare
- what the agreed contract value is based on
That creates a much stronger foundation for the construction stage.
Building Tender
From Tender to Appointing Your Builder
Once the tenders have been reviewed, you can identify the contractor you want to appoint.
Price matters, but it should sit alongside other considerations.
You are also choosing the company that will potentially spend months working inside or around your home.
Relevant experience, communication, organisation and confidence in the contractor all matter.
Before work begins, the scope, price and key responsibilities should then be recorded within an appropriate building contract.
A handshake and a quotation are not a substitute for a properly documented agreement.
Building Tender
A Better Route From Design to Construction
Tendering works best when it is treated as part of the wider project rather than an isolated hunt for a builder.
The sequence should ideally be:
- Develop the design.
- Resolve the relevant planning route.
- Prepare the technical and structural information.
- Define what builders are being asked to price.
- Invite suitable contractors to tender.
- Compare the quotations properly.
- Select the preferred builder.
- Put the appropriate building contract in place.
Each stage gives the next one better information.
That means fewer assumptions and a much clearer transition from architecture to construction.
Client experience
"
Lorem ipsum dolor sit amet, consectetur adipiscing elit. We had a vision for our home but no idea how to realise it. Tholos Interiors took complete ownership of the project — every detail was considered, every decision explained. The result exceeded everything we had imagined.
– Lawrence Ipsum, Homeowner · London –
Frequently Asked Questions
How many builders should I invite to tender?
For many domestic projects, a small shortlist of suitable builders provides enough competition without making the process unnecessarily complicated. Quality and suitability are more important than approaching a very large number of contractors.
Do I need technical drawings before getting builder quotes?
You can obtain early estimates without them, but detailed quotations are much more reliable once the project has been technically developed.
Should I choose the cheapest builder?
Not automatically. You need to compare what each quotation includes, the contractor’s experience, references, programme and overall suitability for the project.
Why are builder quotes sometimes so different?
Different scopes, exclusions, specifications, allowances and interpretations of the drawings can all create substantial price differences.
Do I need a building contract after accepting a quotation?
Different scopes, exclusions, specifications, allowances and interpretations of the drawings can all create substantial price differences.
Can Tholos help compare builder quotations?
Yes. Tholos can help prepare the project for tender, approach appropriate contractors and review their returns so you can compare the actual scope and price rather than relying only on the headline figure.
Ready to Take Your Project to Builders?
Once the design, structural work and technical information are ready, Tholos can help turn that information into a clear tender package and take it to suitable contractors.
We can help you find builders with relevant experience, review their quotations and understand exactly what you are getting before you make your final decision.
Disclaimer:
This article is part of a series created by our dynamic marketing team for informational purposes only. While we strive to review all content thoroughly, occasional oversights may occur, even after publication. Therefore, we cannot accept liability for any interpretations or use of the information provided. For the most up-to-date information or to report any discrepancies, please contact us at hello@tholos-architects.com.
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