A dormer bungalow is a single storey house with rooms in the roof lit by dormer windows. Many were built that way and many started as plain bungalows and gained an upstairs later. They are attractive to extend because the plot is usually generous and the roof volume is already partly used, and awkward to extend because the existing upstairs was often built to a lower standard than anything you would build today.
What you are starting from
The rooms in the roof of an older dormer bungalow commonly have limited head height, sloping ceilings that eat the usable floor, a staircase that was fitted where it would go rather than where it should be, and very little insulation in the sloping parts. None of that is a reason not to extend, but it does mean the honest scope is often upgrade plus extend rather than extend alone, and a quote that ignores the existing upstairs is quoting half the job.
Extending out against extending up
A dormer bungalow usually sits on a wider plot than a terrace, so a single storey rear extension is frequently the simplest way to gain living space and needs no work to the roof at all. Extending up means enlarging the dormers or replacing the roof form entirely, which gives bedrooms rather than living space. Deciding which kind of room you are short of is the decision that should drive the design.
A bungalow dormer extension: enlarging the dormers you already have
Replacing several small dormers with one larger one, or running a full width dormer across the rear, is a common and effective upgrade because it converts sloped ceiling into vertical wall. It is a structural job: the existing openings were trimmed for the dormers that are there, and a bigger hole needs the load carried differently. It also changes the appearance considerably, so check the planning position before assuming a like for like replacement is permitted.
What modern dormer bungalow designs UK owners choose tend to do
Current designs lean towards fewer and larger openings, flat roofed rear boxes with large glazed faces, standing seam metal or dark cladding to the cheeks, and rooflights on the front slope where a dormer would be refused. Inside, the trend is to take the ceiling up into the ridge over the main space rather than flat ceiling it at the collar. All of that is more glazing and more insulation than the original house had, which is where the cost sits.
Questions people ask about dormer bungalow
What is the difference between a dormer bungalow and a chalet bungalow?
In ordinary British usage they describe the same thing: a bungalow with habitable rooms in the roof. Chalet tends to be used where the upstairs was part of the original design and the roof is steeper.
Is dormer bungalow extension cost lower going up or out?
Out is usually simpler per square metre because it does not disturb the roof, the staircase or the escape route. Up makes sense when the plot is constrained or when what you need is bedrooms rather than living space.
Do I need approval to enlarge an existing dormer?
Building regulations approval yes, because it is structural work to a habitable room. Planning depends on size and position against the permitted development limits, and a significantly larger dormer often needs an application.
Why is the upstairs of my dormer bungalow so cold?
Sloping ceilings in older conversions frequently have thin insulation between shallow rafters and little else, and the dormer cheeks are often worse. Upgrading them means losing some internal space to a thicker build up, which is the trade nobody enjoys.