The short answer
Budget £35,000 to £60,000 for a loft conversion in Rugby in 2026. A rear dormer on a three bedroom semi, giving one double bedroom and a small en suite, is the most common job in the town and lands near the middle of that range. A rooflight conversion with no change to the roof shape can be done for less. A mansard, where the roof is largely rebuilt, sits at the top and is the one most likely to need planning permission.
On top of the build, hold £1,500 to £3,000 for drawings, structural calculations, building control and, if a neighbouring wall is involved, a party wall surveyor. If you need a planning application, the householder fee in England is £548 and rises to £575 on 8 December 2026.
The two numbers you will find online, and why they disagree
Search for the cost of a loft conversion and you will be given two figures that are thousands apart for what looks like the same job. The HomeOwners Alliance puts a dormer conversion at £50,000 and a hip to gable at £60,000. MyJobQuote puts the same dormer at £35,000 to £50,000 on a thirty square metre project.
Neither is wrong. They are describing different scopes. One assumes a finished, decorated room with an en suite. The other assumes a shell that is watertight, structurally signed off and plastered, with the bathroom and the flooring still to come. That single difference is worth more than fifteen thousand pounds, and it is the reason two local builders can look like they are a fortune apart when they are actually quoting the same work.
| Conversion type | MyJobQuote, 30m² | HomeOwners Alliance | What you are buying |
|---|---|---|---|
| Rooflight, often called a Velux conversion | £15,000 to £20,000 | £27,500 | Nothing is added to the roof shape. You gain a room, not extra head height. |
| Rear dormer | £35,000 to £50,000 | £50,000 | A box built out from the rear slope. The usual way to get a double bedroom and an en suite into a Rugby semi. |
| Hip to gable, usually with a rear dormer | £45,000 to £60,000 | £60,000 | The sloping side of the roof is built up square. Common on end terraces and detached houses on the town's post war estates. |
| Mansard | £45,000 to £60,000 | £65,000 | The roof is largely rebuilt. Most space, most disruption, and planning permission is far more likely. |
Sources: MyJobQuote and HomeOwners Alliance 2026 cost guides, listed in full at the end of this page. These are national figures, not Belmax quotations. Belmax prices every loft against the roof it is standing under.
What that works out at per square metre
Per square metre is the fairest way to compare two quotations for different sized lofts. The HomeOwners Alliance gives a range of £1,250 to £2,500 per square metre. MyJobQuote gives £1,200 to £1,800. A £50,000 dormer over thirty square metres is £1,667 per square metre, which sits comfortably inside both.
One warning about that figure. Small lofts always look expensive per square metre, because the steel, the staircase and the building control fees do not shrink when the floor does. A twenty square metre conversion is not badly priced simply because the rate is higher. Compare the total against what the room gives you, not against the rate alone.
The costs that sit outside the build price
These are the items most often left out of a headline figure. Ask directly whether each one is in or out before you compare two quotations.
- Architect or designer drawings, around £400 for basic plans and up to £1,500 for a detailed set
- Structural engineer calculations for the new floor and any steel
- Building control application and inspections, through Warwick Building Control for Rugby Borough
- A staircase, £1,500 to £2,500 for a standard flight, £5,000 and upwards if it is bespoke
- A party wall award if you share a wall, from £800 to £1,000 for a single agreed surveyor
- Planning application fee, £548, only if the work falls outside permitted development
- The en suite, which adds several thousand and is the single most common exclusion
- Plastering, decoration and flooring, frequently priced separately
Do you need planning permission in Rugby Borough?
Most likely not. Loft conversions are usually permitted development, which means the work is allowed without an application, provided it stays inside a set of limits. The limits that matter are:
- No more than 40 cubic metres of additional roof space on a terraced house, or 50 cubic metres on a semi detached or detached house
- Nothing higher than the highest part of the existing roof
- No extension beyond the plane of the existing roof slope on the elevation that fronts a highway
- Materials similar in appearance to the existing house
- Side facing windows obscure glazed, and non opening below 1.7 metres above the floor
- The enlargement set back at least 20 centimetres from the original eaves where practicable
The exception that catches people out is designated land. If the property sits in a conservation area, these rights do not apply and a full application is needed. Rugby Borough Council points homeowners to the Planning Portal for the rules and holds the local conservation area mapping itself, so check both before you assume.
If you want certainty rather than an assumption, apply for a lawful development certificate. It costs half the householder fee, £274 at current rates, and it gives you a document to hand a buyer's solicitor in ten years' time.
Is it worth it on a Rugby house?
This is the part most cost guides avoid, because the honest answer is not always yes.
The average house price in Rugby was around £276,000 in June 2026, according to the Office for National Statistics. A £50,000 dormer conversion is therefore roughly eighteen per cent of the entire value of the average house in the town. That is a serious sum to place on one improvement.
Two things follow from it. If your house is already near the ceiling for its street, adding a fourth bedroom will not necessarily return what it cost, and you should treat the money as buying you space rather than value. If your house is a family home you intend to stay in for another decade, the comparison is not against your house price at all. It is against the cost of moving to the next house up, including stamp duty, agent fees and the move itself, which on a £276,000 to £350,000 step is frequently more than the conversion.
Belmax will tell you which of those two situations you are in before quoting. It is a shorter conversation than most people expect.
How long it takes
Six to eight weeks on site is the normal range. A rooflight conversion can be four to six weeks. A mansard runs to eight or ten. The stage that surprises homeowners is not the build, it is everything before it: measured drawings, structural calculations, the building control submission and, where a party wall is involved, the notice period. Start that four to six weeks before you want scaffolding up.
Frequently asked questions
Usually not. Most loft conversions are permitted development, which means the work is already allowed without an application. The volume allowance is 40 cubic metres of additional roof space for a terraced house and 50 cubic metres for a semi detached or detached house, and the new roof must not sit higher than the existing ridge or extend beyond the roof slope on the elevation that fronts a highway. Permitted development rights do not apply on designated land such as a conservation area, so check the Rugby Borough Council mapping before assuming.
Building regulations approval is separate from planning and it is required for every loft conversion, without exception. Rugby Borough Council's building control function is delivered by Warwick Building Control, which also covers Warwick District. Fees vary with the size of the job and are quoted on application, so ask your builder whether the figure in your quotation includes them or excludes them.
Six to eight weeks on site is the usual range for a standard conversion. A rooflight conversion can be four to six weeks and a mansard eight to ten. Design, structural calculations and approvals happen before that and are the part homeowners most often underestimate.
The honest answer is that it depends on what the house is worth now. The average Rugby house sold for around £276,000 in June 2026, so a £50,000 dormer conversion is roughly eighteen per cent of the whole property value. On a house near the top of its street's range, that is a lot of money to place. On a family home you intend to stay in, the extra bedroom and bathroom is usually the cheaper move compared with buying the next house up.
Almost always because they are quoting different scopes. Structural steel, the staircase, the en suite, plastering, decoration, flooring, building control fees and the party wall surveyor can each be inside one quotation and outside the other. Ask both builders to price the same written list before comparing the totals.
Sources used on this page
- HomeOwners Alliance, Loft conversion costs and how to reduce them, 2026 figures by conversion type, house type and cost per square metre
- MyJobQuote, Loft conversion cost guide, 2026 ranges for a 30m² project, durations, drawings, staircase and party wall costs
- Planning Portal, Loft conversion planning permission, the permitted development limits quoted above
- Planning fees in England, the £548 householder fee effective 1 April 2026 and the increase to £575 on 8 December 2026
- Office for National Statistics, Housing prices in Rugby, average price of £276,000 in June 2026
- Rugby Borough Council, Do I need planning permission?, local guidance and the borough's building control arrangement with Warwick Building Control
National cost guides are used deliberately on this page so the figures can be checked. Where Belmax quotes its own recent Warwickshire projects, the page will say so explicitly.