When and How to Get a House Extension or Loft Conversion Quote

Perhaps you're considering a 4m × 3m rear extension, a loft conversion or a complete home renovation. It's natural to want a builder's quotation before spending money on drawings or planning applications. However, this is where many homeowners become frustrated. Some builders will give a rough figure with very little explanation, while others will simply refuse to provide a quotation until they have seen your drawings. This is because a builder's quotation is only as accurate as the information they are given. The more detailed your design and specification, the more reliable the quotation will be. That doesn't mean builders don't want to help—it simply means there are too many unknowns at this early stage. For example:

• What level of specification are you expecting?
• What type of foundations will be required?
• Will structural steel be needed?
• How many rooflights are included?
• What type of windows and doors are you choosing?
• Is underfloor heating included?

Without drawings and a clear specification, any quotation is likely to be a rough estimate rather than a reliable construction price.

Stage 1 – Know Your Budget Before You Design

Before speaking to architects or builders, it's important to understand whether your ideas are financially realistic. Having an early cost estimate can save both time and money, helping you avoid designing a project that is beyond your budget. For example, you may discover that:

• A single-storey extension fits comfortably within your budget.
• A two-storey extension offers better value for money.
• A loft conversion provides all the additional space you need.
• Moving house may actually be the more economical option.

Understanding your likely construction budget first allows you to make better decisions before committing to design fees. BuildCostHub's free calculators are designed to provide an independent cost estimate, giving you a realistic starting point before beginning the design process. Try our free project calculators: https://www.buildcosthub.com/#project-types

Stage 2 – Develop Your Design with Confidence

Once you've established a realistic budget, the next step is developing your design. Depending on your project, you may work with:

• An architect
• An architectural technician
• A residential designer During this stage you may also need:
• A measured building survey
• A topographical survey
• A planning consultant (where required)
• A structural engineer (particularly if removing load-bearing walls or creating large structural openings) As your design develops, your budget can also be refined, allowing adjustments to be made before construction begins.

Stage 3 – Planning Permission (If Required)

Not every extension or loft conversion requires planning permission. Some projects can be completed under Permitted Development, while others require a formal planning application. If planning permission is required, there is often a waiting period while your application is being considered. Rather than waiting passively, this is an ideal opportunity to prepare for the next stage of your project.

Stage 4 – Obtain Builder Quotations

Once your drawings are sufficiently developed—and ideally after planning approval has been granted where required—you should approach at least three builders for quotations. At this stage, builders have enough information to prepare much more accurate and detailed prices. Provide each builder with the same information, including:

• Architectural drawings
• Structural drawings (if available)
• Specifications
• Planning drawings
• Any additional project information Using the same information for every builder allows you to compare quotations fairly and make a more informed decision.

Don't simply choose the lowest price. A well-detailed quotation that clearly explains what is included often provides much better value than the cheapest figure.

What's Next?

Once you've received your quotations, the next challenge is understanding what is actually included. A lower price doesn't always represent better value, and the cheapest quotation can sometimes become the most expensive if important items have been omitted. In our next guide, How to Compare Builder Quotes Like a Quantity Surveyor, we'll explain:

• How to compare builder quotations fairly
• What Provisional Sums (PS) and Prime Cost (PC) items really mean
• Common items that are often excluded
• The warning signs to look out for before accepting a quote

Coming soon: BuildCostHub's AI Quote Review will allow you to upload a builder's quotation and receive an independent review, helping you identify missing items, pricing anomalies and potential risks before signing a contract.