Dormer window or roof extension?
A dormer and a roof extension both add upstairs space, but they differ greatly in cost, impact and permit complexity.
If you need more space upstairs, start by deciding whether better attic usability is enough or whether you need a full extra floor.
That choice determines budget, design and planning.
Choose a dormer when
A dormer is ideal when the attic already has enough floor area but lacks headroom or daylight.
It is faster, less invasive and often cheaper than a full roof extension.
Choose a roof extension when
A roof extension is better when you need multiple full-height rooms or a complete extra level.
It is more complex and usually needs a permit and structural checks.
Compare total value
A dormer can be the smartest investment for one room.
A roof extension can transform the home when the structure and permit situation support it.
Summary
A dormer improves an attic; a roof extension changes the whole capacity of the home.
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