What we know, what we estimate, and what we don’t.

How an assessment is produced

1. You upload a photograph of your house. A vision model reads visible characteristics — house form, wall material, roof form, windows, any existing extension — and locates where an extension would sit in the photo.
2. An image-editing model repaints only that region to show a concept extension. The rest of the photo is masked so your house is preserved.
3. You describe the house and what you want from it: type, rough measurements, objectives, budget, and a planning checklist where “I don’t know” is always allowed.
4. A deterministic model — ordinary, inspectable rules, not AI — selects extension types that suit your house and priorities, sizes them, prices them, screens them against the planning conditions, and compares them. The same inputs always give the same output.

The numbers in your assessment come from step 4, not from an AI model. That is deliberate: costs and planning conditions should be reproducible and explainable, not generated.

Observed, inferred, unknown

Every assessment separates three kinds of statement:

• Observed — read from your photo or stated by you. “Walls appear to be painted render.” “You estimated the garden at 14m deep.”
• Inferred — a reasonable conclusion from what was observed. “As a terraced house, any extension is likely to sit against a party wall.”
• Unknown — what nobody has measured or checked. “Actual site dimensions have not been surveyed.”

Where something is unknown, we lower confidence rather than substitute a guess. Where a typical value has to be used to size a concept (a house width, for example), the assessment says so.

Dimensions

Concept dimensions are derived from the measurements you provide and from typical proportions for each extension type. A single-storey rear extension, for example, is sized where possible to stay within the 40m² exempted-development limit and to leave at least 25m² of rear garden. We do not measure anything from your photograph — a photo cannot give reliable dimensions. All dimensions are indicative concept dimensions to be verified on site.

Cost methodology

Construction is priced per square metre of gross floor area using ranges commonly cited for Irish domestic extensions in 2025–26. They are not derived from tender prices for your site and we do not claim a published source for any single figure. Base construction rates (including VAT at 13.5%, before adjustment):

Adjustments: Dublin +10%; areas outside the main cities −7%; standard specification −8%, high specification +15%; projects under 15m² +15% because fixed costs don’t shrink with floor area.

On top of construction, the total project budget adds:

• Design and planning drawings: 7–12% of construction, including VAT at 23%.
• Structural engineer, measured survey, and planning costs (statutory fee and notices; or confirmation of exempt status).
• Building Control (BCAR) assigned certifier where the extension is over 40m².
• Allowances for feature glazing, external works and making good, and — where your objectives include them — a kitchen and a bathroom.
• Contingency of 10–15%.

Three scenarios are shown: lower, typical and higher complexity. All figures are rounded to the nearest €1,000; finer precision would be false. Excluded: furniture and appliances outside the kitchen allowance, works to the rest of the house, abnormal ground conditions, rerouting a public sewer, and inflation. Only priced drawings and competitive tenders produce a real cost.

Planning screening

Each option is screened against the conditions for extensions to the rear of a house in Class 1, Part 1, Schedule 2 of the Planning and Development Regulations 2001 (as amended), as we understand them in October 2026. Where we have the information, we test: total floor area including earlier extensions (40m²); upper-floor area (12m² for terraced and semi-detached houses, 20m² for detached); a 2m separation from boundaries for upper floors; and at least 25m² of private open space remaining to the rear. We treat side extensions, the side element of wraparounds and dormers as generally outside these exemptions. A protected structure, an Architectural Conservation Area or a condition removing exempted-development rights all point to a planning application.

The result is a likely route (potentially exempt, application likely, or unclear), a confidence level and a list of issues to verify. We never give high confidence to an exemption, because the regulations contain conditions — window separation distances, wall and roof heights — that cannot be checked from a photograph. Regulations change; proposals to revise the exempted-development limits have been discussed in recent years, so confirm the current position. Read the planning guide.

How we use AI

• Image generation: an image-editing model (FLUX Fill Pro, run via Replicate) repaints a masked region of your photo to show a concept. Images can contain errors and are illustrative only.
• Photo reading: a vision language model describes the visible house and suggests where an extension would sit. Its observations are labelled as such and can be wrong.
• Not AI: option selection, dimensions, costs, planning screening, comparison and recommendation are rule-based and reproducible.

Your photos and data

• Your photo is stored so we can render concepts and show them back to you. Generated images are stored at unguessable addresses.
• Your project is reachable by anyone who has its link. Share it only with people you trust.
• You can delete your photo and every generated image at any time from your project page. A minimal record of any payment is kept for accounting.
• Analytics are cookieless and never include your photo, its address, your email or anything you type.
• Full details: privacy policy.

Refunds

If a package does not deliver what it describes, reply to your receipt email and we will fix it or refund you in full. Upgrades are charged the difference against what you have already paid. A refunded order removes the features it paid for.

Professional limitations

• Visualisations are conceptual images generated from your photo. They are not architectural drawings.
• Dimensions are indicative and have not been surveyed. Verify on site.
• Cost estimates are indicative ranges, not quotations, and carry no guarantee.
• Planning screening is not planning or legal advice and does not guarantee that any route applies or that permission will be granted.
• No structural assessment has been carried out.
• No measured survey has been carried out.
• Local and site-specific conditions can materially change the outcome.
• Professional advice is required before design is finalised and before any construction.

ExtensionVision is preparation for professional advice, not a substitute for it. Before you commit, engage a registered architect or architectural technologist, and a structural engineer where structure is affected. We have no commercial relationship with any professional or builder.