Dormer Attic Conversion Cost Ireland 2026 | Rear, L-Shaped, Full-Width

Introduction

A dormer conversion is the most popular attic upgrade in Ireland for one simple reason: most Irish homes do not have enough head height for a proper room without one.

A standard Irish roof has a pitch of about 30-35 degrees. At the ridge, you might have 2.3-2.5m of height. But the 2.4m rule — which requires at least 2.4m of ceiling height over 50% of the floor area for a habitable room — means most standard attics fail the test before a contractor even arrives.

A dormer changes that. By extending the roof outward and upward at the rear, it creates a full-height box room at the back of the attic where you could not stand before.

Dormer attic conversion cost Ireland in 2026 ranges from EUR28,000 for a basic rear dormer on a terraced house to EUR65,000+ for a full-width dormer with en-suite on a larger detached home. This guide gives you the specific prices, the three dormer types explained clearly and the planning rules you need to know before signing anything.

Dormer Attic Conversion Cost Ireland — Quick Answer

Most Irish homeowners pay between EUR28,000 and EUR60,000 for a dormer attic conversion in 2026.

Dormer type	Typical cost (no en-suite)	With en-suite
Rear box dormer (standard)	EUR28,000-EUR45,000	EUR38,000-EUR58,000
L-shaped dormer	EUR38,000-EUR55,000	EUR48,000-EUR68,000
Full-width rear dormer	EUR42,000-EUR60,000	EUR52,000-EUR72,000
Hip-to-gable + rear dormer	EUR45,000-EUR65,000	EUR55,000-EUR78,000

These are national average figures for April 2026. Dublin adds 12-15%. All figures include materials, labour, structural steel (if needed), insulation, windows, staircase, electrics, plastering and VAT at 13.5%. Decoration is not included.

Use our free attic conversion cost calculator for a figure based on your house type and county.

What Is a Dormer and What Does It Actually Do?

A dormer is a structure that projects vertically from the sloping surface of a roof. It adds a vertical wall and a flat or low-pitched roof at the rear of the attic.

The main benefit is headroom. Without a dormer, the floor area where you can stand upright is limited to the ridge area. A dormer pushes the roof outward and up at the back, creating a full-height zone that runs across the width of the extension.

The secondary benefit is floor space. A rear dormer typically adds 4-12 m2 of genuinely usable floor area at the back of the attic, depending on how wide and deep it runs.

What a dormer does NOT do — despite what many homeowners expect — is dramatically increase the total internal floor area of the attic. It increases headroom in the dormer zone and adds some floor area at the rear. The sloped sections of the attic on each side remain unchanged.

As one experienced Dublin attic specialist put it: the greatest benefit of a dormer is achieved when the roof is low. If you already have 2.4m+ of head height across most of the attic, a dormer adds relatively little practical benefit compared to a Velux-only conversion.

Three Types of Dormer — Which One Suits Your Home?

Rear box dormer
The most common type in Ireland. A flat-roofed box structure is built at the rear of the roof. It spans part or all of the rear elevation. The standard depth is 1.5-2.5m. Most rear dormers on standard semi-Ds and terraced houses fall under exempted development and do not need planning permission.

Best for: terraced houses, semi-Ds, any home with low head height at the rear.

L-shaped dormer
An L-shaped dormer combines a rear dormer with a smaller side dormer in an L-configuration. This is common on end-of-terrace or semi-detached homes where the side elevation has room. The L-shape creates a larger overall room and allows for a more practical staircase position.

Best for: end-of-terrace and semi-D homes where the side is accessible.

Full-width rear dormer
A full-width dormer spans the entire rear width of the roof. It creates the maximum floor area and head height. However, full-width dormers were restricted by many councils — including Dublin City Council — in the past decade. Where they were once commonly approved, they are now subject to more scrutiny and in some areas require planning permission where a standard dormer would not.

Best for: detached homes with full rear access. Check with your local authority before designing.

Cost by Dormer Type

Here is a closer look at what drives the cost difference between dormer types.

Rear box dormer: EUR28,000-EUR45,000
The standard specification. A timber-framed box structure is built at the rear, clad in slate, tiles or zinc. Flat or slightly sloped felt or EPDM roof. Two windows. This is the most cost-effective option and the most commonly built in Ireland.

The main variables:

• Width of the dormer (narrower = cheaper)
• Roof material — zinc cladding costs more than slate or felt
• Whether truss removal and steel beams are needed (adds EUR5,000-EUR12,000)

L-shaped dormer: EUR38,000-EUR55,000
The extra cost over a rear box dormer comes from the additional structure on the side, more complex corner junction waterproofing and typically a larger window count.

Full-width rear dormer: EUR42,000-EUR60,000
Full width means the dormer runs the full span of the rear elevation. More structural work, more material, more waterproofing detailing. Also more likely to need planning permission in urban areas.

Cost by House Type

Terraced house
Terraced houses — particularly pre-1980 Victorian and Edwardian terraces — often have cut roofs with good existing head height. A rear dormer on a terraced house adds headroom at the back and can cost EUR28,000-EUR40,000 for a basic rear dormer without en-suite.

Post-1980 terraced houses in estates are almost all truss roofs. Add EUR5,000-EUR10,000 for steel work.

Semi-detached house
The standard spec for a Dublin or Cork semi-D is a rear box dormer with no en-suite, costing EUR30,000-EUR45,000 at the national average. With an en-suite, expect EUR40,000-EUR58,000. This is the most-built dormer specification in Ireland and the best price-to-value combination.

Detached house
Larger roof, more structural complexity, more options. A rear dormer on a detached home costs EUR38,000-EUR55,000 for a basic dormer, EUR50,000-EUR68,000 with en-suite. A full hip-to-gable with dormer on a large detached home reaches EUR55,000-EUR78,000.

Full Cost Breakdown — What Are You Paying For?

Here is a line-by-line breakdown for a standard rear box dormer on a 3-bed semi-D:

Item	Typical cost
Structural survey and engineer cert	EUR600-EUR1,200
Truss removal and RSJ steel beams	EUR5,000-EUR12,000
Floor strengthening and OSB decking	EUR2,000-EUR4,000
Dormer structure (timber frame, flat roof, cladding)	EUR8,000-EUR16,000
Dormer waterproofing (EPDM or zinc)	Included above
2 Velux or dormer windows (fitted)	EUR2,000-EUR4,500
Rafter insulation and floor insulation	EUR2,000-EUR4,500
New staircase (code-compliant)	EUR3,500-EUR7,500
Plasterboard and plastering	EUR2,500-EUR4,500
Electrics (lighting, sockets, smoke alarm)	EUR1,000-EUR2,000
Fire door to landing	EUR350-EUR650
Basic paint finish	EUR800-EUR2,000
Total without en-suite	EUR27,750-EUR58,850
En-suite bathroom	EUR8,000-EUR15,000
Total with en-suite	EUR35,750-EUR73,850

The truss removal and dormer structure are the two biggest line items. Always ask your contractor to quote these separately.

Does a Dormer Always Give You More Headroom?

Not as much as most people expect.

A rear box dormer raises the roof at the back of the attic. But a standard rear dormer does not increase the ceiling height, and it rarely increases the floor space significantly. What it does is create a full-height zone at the back — typically 2.4-2.6m — while the front of the attic stays at the original pitch.

This matters for how you design the room. The full-height zone at the back is where you put the main use area. The lower-pitched sections toward the front are where you use the eaves for storage, fitted wardrobes or low furniture.

If you need full head height across the entire attic, you need either a full-width dormer or a hip-to-gable conversion. A standard rear box dormer gives full height in the rear section only.

Does a Dormer Need Planning Permission in Ireland?

According to planningcheck.ie, based on the Planning and Development Regulations (SI 600/2001, last reviewed March 2026):

Usually exempt from planning permission:

• Rear dormers that do not exceed 40m2 total attic floor area
• Dormers that sit at least 1m from the roof edge on each side
• Dormers not visible from a public road
• Dormers not in an Architectural Conservation Area

Planning permission required:

• Any dormer or window visible from the front or a public road
• Dormers in ACAs where external appearance is materially altered
• Full-width rear dormers in many urban areas
• Any change that raises the ridge height

The planning application fee is EUR65. Professional drawings typically cost EUR800-EUR2,000. A newspaper notice costs EUR80-EUR150. A planning consultant, if needed, adds EUR500-EUR1,500.

Even when planning permission is not needed, a commencement notice must be submitted before work starts. An assigned engineer or architect must certify the finished work. Without these, the conversion has no legal status.

How Long Does a Dormer Conversion Take?

Stage	Typical time
Getting three quotes	1-2 weeks
Booking a contractor	2-6 weeks (peak season up to 10 weeks)
Planning application (if needed)	8-12 weeks minimum
Structural work (steel, floor)	3-7 days
Dormer construction	5-12 days
Insulation, boarding, plastering	5-10 days
Electrics, staircase, fire door	3-6 days
Total build time on site	5-9 weeks
Total from first call to done	8-16 weeks

Booking in autumn or winter (October to February) cuts wait times and may reduce pricing by 5-10% on some jobs.

Regional Price Differences

Region	Rear dormer (no en-suite)	With en-suite
Dublin	EUR32,000-EUR50,000	EUR42,000-EUR64,000
Cork city	EUR30,000-EUR46,000	EUR40,000-EUR60,000
Galway / Limerick	EUR28,000-EUR42,000	EUR38,000-EUR56,000
Rural areas	EUR25,000-EUR38,000	EUR35,000-EUR52,000

Dublin prices run 12-15% above the national average. Cork city is 7-10% above. Rural areas are broadly at or below the national average, though remote locations may carry contractor travel premiums.

What Does a Dormer Add to Property Value?

A well-built dormer conversion adds meaningful value in Ireland.

The SCSI estimates attic conversions deliver 12-15% return on property value in Dublin. A properly certified dormer — with commencement notice and certificate of compliance — is documented as a habitable or semi-habitable room that any buyer can verify. Without the paperwork, the value is recognised but not bankable during a sale.

Chartered Building Surveyor Val O'Brien of the SCSI made a key point in the Irish Times: converting a loft tends to represent better value than moving, once you factor in stamp duty and moving costs. For a typical Dublin semi-D, stamp duty on the next house up costs EUR12,000-EUR20,000 alone. A dormer conversion at EUR40,000-EUR50,000 gives you an extra room, a better BER rating and property value uplift — for less than the cost of moving.

How to Choose a Contractor for Dormer Work

Dormer construction involves structural engineering, waterproofing, carpentry and electrics. Not every builder who has done a few attic conversions is qualified to manage all of these properly.

Look for:

• CIF membership (cif.ie) or CIRI registration (ciri.ie)
• Specific experience in dormer construction — not just standard Velux conversions
• A clear process for commencement notice and engineer certification
• A workmanship warranty of at least 10 years
• Recent reviews mentioning dormer projects specifically

Ask at every quote visit: "Can I see photos of a recent dormer you have built?" If they cannot produce any, ask why.

Frequently Asked Questions

How much does a dormer attic conversion cost in Ireland in 2026?

Most Irish homeowners pay EUR28,000-EUR60,000 for a dormer conversion. A standard rear box dormer on a semi-D with no en-suite costs EUR28,000-EUR45,000. With an en-suite, budget EUR38,000-EUR58,000. Dublin runs 12-15% above these figures.

Does a dormer conversion need planning permission in Ireland?

Usually no, for a standard rear dormer on a semi-D or terraced house. Exemption conditions include maximum area of 40m2, no visibility from the road and not in an ACA. Front dormers, full-width dormers and dormers in conservation areas usually require planning permission. A commencement notice is always required.

Does a dormer give me more headroom?

It creates a full-height zone at the rear of the attic — typically 2.4-2.6m. It does not raise the height across the entire attic. If you need full height throughout, you need a full-width dormer or a hip-to-gable conversion.

What is the difference between a rear dormer and an L-shaped dormer?

A rear dormer extends from the back of the roof only. An L-shaped dormer extends from both the rear and one side, creating a larger room and more options for staircase positioning. L-shaped costs EUR8,000-EUR15,000 more than a standard rear dormer.

How long does a dormer conversion take?

5-9 weeks on site. From first call to completion, allow 8-16 weeks, including getting quotes and booking. Add 8-12 weeks if planning permission is required.

Can I claim SEAI grants for a dormer conversion?

Not for the structural work. But combining a dormer with attic insulation qualifies for SEAI grants of EUR1,200-EUR2,500 depending on house type, updated February 2026. Apply at seai.ie before work starts.

Conclusion

A dormer conversion is the right choice for most Irish homes that lack enough head height for a Velux-only room. It solves the headroom problem at the back of the attic, adds usable floor space and gives the finished room a full-height feel that a Velux-only conversion cannot match.

The most common mistakes are expecting more headroom gain than a dormer actually delivers, not checking planning exemption conditions before starting design, and not confirming whether the house has a truss or cut roof before accepting any quote.

Get three written quotes, confirm the structural spec, check your planning status and make sure commencement notice and engineer cert are included in every quote.

Use the free calculator to estimate your dormer conversion cost by house type and county.

Internal links: Attic conversion cost Ireland · Attic conversion cost Dublin · Attic conversion cost calculator · SEAI roof insulation grant · Small attic conversion cost

Outbound links

• SCSI
• planningcheck.ie
• BCMS commencement notice
• CIF
• SEAI grants

Prices reflect April 2026 contractor rates. Always get three written quotes from CIF or CIRI registered contractors.