House extension in Czechia 2026: cost per m², junction and permits

In 2026 a turnkey extension to a family house in the Czech Republic (přístavba) costs roughly CZK 40,000–55,000 per m² excluding VAT on the market; ours start from CZK 42,000/m². A 20 m² room therefore costs about CZK 0.8–1.1 million and a 40 m² kitchen-diner CZK 1.6–2.2 million. Per m², an extension costs more than a new house: the small volume carries the full cost of site set-up, foundations and, above all, the junction with the existing house — and the junction decides whether the extension will crack within a few years.

Below you will find the types of extension, cost by size, the items involved in connecting to the house, the general permit procedure and the whole build step by step.

Types of extension and what they suit

Type	Typical use	What to consider
Single-storey extension	bedroom, kitchen-diner, study, ground-floor bedroom for older relatives	simplest structure; roof junction with the facade
Two-storey extension	several rooms, a new staircase	higher demands on foundations and on joining two floors
Upward extension (nástavba, extra storey)	loft conversion, new floor	a structural engineer must assess the existing walls and foundations
Attached garage	garage, workshop, storage	different use; fire separation from the house
Timber-frame extension	light extension, fast build	lower weight, suits weaker ground too

The extension does not have to copy the material of the house. Clay block or aircrete suits traditional masonry houses, insulated concrete formwork works where speed and a monolithic structure matter, and timber frame where low weight and a short build time are important. What matters is the right junction, not the same material. The differences are summarised in timber-frame or masonry house.

Extension cost by size

Extension area	Market price (CZK 40–55k/m²)	Our price (from CZK 42k/m²)
15 m² (room, study)	CZK 600 – 825k	from CZK 630k
20 m² (room with bathroom)	CZK 0.8 – 1.1 m	from CZK 840k
30 m² (living area)	CZK 1.2 – 1.65 m	from CZK 1.26 m
40 m² (kitchen-diner)	CZK 1.6 – 2.2 m	from CZK 1.68 m

Prices exclude VAT and are for a turnkey extension, based on our 2026 construction price list. For comparison, a new turnkey house costs CZK 35,000–45,000/m² on the market. An extension costs more because transport, site set-up, design and service connections are spread over a small area, and the junction with the old house is manual work that a new build does not have.

With an older house, keep a contingency. For houses over 50 years old the price list recommends 15–20% for hidden defects such as missing damp-proofing, aluminium wiring or a damaged roof structure. For a 30 m² extension costing CZK 1.2 million that is CZK 180,000–240,000.

Connecting the extension to the house: items that must be in the budget

Ask whether the junction is included in the extension price or charged separately. According to the price list, the individual tasks cost:

Task	Price
New opening in a load-bearing wall incl. lintel (excl. structural report)	CZK 8,000 – 15,000 each
Demolishing a load-bearing wall (incl. temporary support, excl. structural design)	CZK 900 – 1,800/m²
Bricking up an old window or door incl. plaster	CZK 1,300 – 2,000/m²
Removing an old door frame	CZK 700 – 1,200 each
Core drilling for services, ø 100–160 mm	CZK 900 – 1,800 each
Flashings — roof junction, gutters, downpipes	CZK 450 – 900/lin. m
Demolishing an old lean-to incl. removal	CZK 800 – 2,000/m³
3 m³ skip (Prague)	CZK 4,500 – 7,000

Budget example: a 25 m² kitchen on a 1970s house

A single-storey turnkey extension of 25 m²: 25 × CZK 40,000–55,000 = CZK 1.0–1.375 million. If the junction is not included, add a new opening in the load-bearing wall (CZK 8,000–15,000), bricking up a 2 m² original window (CZK 2,600–4,000) and two rubble skips (CZK 9,000–14,000). The house is over 50 years old, so a 15–20% contingency adds another CZK 150,000–275,000. In total roughly CZK 1.17–1.68 million excluding VAT, plus design and the structural engineer's report.

Technical rules for the junction

• Movement joint (dilatace). A new structure settles differently from a house that has stood for decades. The extension is therefore separated from the house by a movement joint filled with compressible insulation and sealed. Bonding the masonry rigidly without a structural design is the most common cause of cracks.
• Foundations. New foundations go next to the old ones, down to frost-free depth. The old foundations must not be undermined — if they are shallower, the structural engineer decides how to proceed. More on foundations in the foundation slab.
• Damp-proofing. The extension's damp-proof membrane must continue the house membrane or be reliably terminated at the joint. Otherwise water gets into the junction and you get a damp seam.
• Roof. The roof of the extension is joined to the house facade with abutment flashings. Valleys and places where water runs towards the wall are the riskiest.
• Insulation. The insulation of the extension and the house must meet, otherwise a thermal bridge forms and mould appears at the junction.
• Floor level. Match the extension floor to the house so there is no step or threshold.
• Services and heating. Check whether the existing heat source and main circuit breaker can cope with the extra rooms.

Extending an old house

If you do not know what foundations the house has or what the walls are made of, start with a survey. A trial pit next to the existing foundations shows their depth and condition, and a moisture survey of the masonry shows whether the house needs remedial work before anything is added to it. A structural engineer will assess whether the walls can take a new opening or an extra storey.

A common and sensible approach is to combine the extension with a renovation: new services, insulation and windows done at the same time, with one set of scaffolding and one site set-up. Process and prices are covered in renovating an old house.

Permission for an extension

An extension is a change to a completed building (změna dokončené stavby). It changes the footprint, the volume and often the structure of the house, so it usually cannot be done without a design and dealing with the local building authority (stavební úřad). Which procedure applies to your extension depends on its size, use, position on the plot and on the municipality's zoning documents. Always check this with your building authority in advance, ideally together with your architect or designer.

In general, expect to deal with:

• design documentation by an authorised designer and an assessment by a structural engineer,
• distances from plot boundaries and neighbouring buildings, and possibly the neighbours' consent,
• statements from utility owners if the extension affects their networks,
• a fire safety solution, especially for an attached garage,
• completion and occupancy as instructed by the building authority.

You can order the permitting from us together with the construction. Do not start building without confirmation from the authority — retrospective approval is usually more complicated and more expensive than the proper one.

Building an extension step by step

1. Brief and rough budget — area × CZK 40,000–55,000/m² plus contingency.
2. Measured survey and investigations — trial pit at the foundations, wall moisture, roof condition.
3. Design and structural engineering — layout, junction, movement joint, opening into the house.
4. Check and permission at the building authority.
5. Itemised budget and contract at a fixed price.
6. Foundations next to the existing ones, with insulation and service ducts.
7. Shell — walls, floor or roof structure, roof joined to the house.
8. Windows, doors, services and connection to the house networks.
9. Interior works — plaster, floors, tiling, painting, insulation and facade.
10. Breaking through into the house — we leave the dusty work until last, so you can live in the house throughout.

Building a 20–40 m² extension usually takes 2–4 months. Add the time needed for design and permission.

Common mistakes

• Rigid connection without a movement joint. After the first winter the plaster and tiles at the junction crack.
• Undermined old foundations. This can damage the existing house.
• A roof junction "sealed with silicone". Water gets in and the damp only shows up inside.
• No structural report for the new opening in a load-bearing wall.
• A budget without the junction and contingency. Old houses almost always reveal hidden defects.
• Building without checking with the authority. Retrospective procedures cost time and money.

Checklist

• Do you know which permit procedure your extension needs?
• Does the design solve the movement joint, foundations and roof junction?
• Has a structural engineer assessed the new opening in the load-bearing wall?
• Is the junction with the house included in the extension price, or separate?
• Can the existing heat source and electrics handle the extension?
• Do you have a 15–20% contingency if the house is over 50 years old?
• Is it agreed when the opening into the house will be made and how the interior will be protected?

Planning a garage instead of a living-space extension? Costs and process are in building a garage.

Frequently asked questions

How much does a house extension cost per m²? A turnkey extension costs CZK 40,000–55,000 per m² excluding VAT on the market; ours start from CZK 42,000/m².

How much does a 20 m² extension cost? About CZK 0.8–1.1 million excluding VAT, turnkey; ours from CZK 840,000.

Why does an extension cost more per m² than a new house? Fixed costs for site set-up, design and service connections are spread over a small area, and the junction with the old house is extra work.

Does an extension need planning permission? An extension is a change to a completed building. Which procedure applies depends on its size, use and position — always check with the building authority in advance.

How is an extension connected to the house? Usually via a movement joint, on its own foundations to frost-free depth, with continuous damp-proofing and insulation, and with a flashed roof junction.

We build extensions in Prague and the Central Bohemian Region, including design and the junction with the existing house. In the calculator choose "New build → Extension" to see an indicative price straight away; we will prepare a site visit and an itemised budget free of charge.