loft conversion

Loft Conversion Vs Extension

Which is better, a loft conversion or an extension? 

The answer to that will ultimately depend on the property being converted/extended as some properties will automatically lend themselves to one or the other. 

Extensions will usually be built on the land around the existing house, most often in the back garden; if the back garden is tiny or if an extension has already been built in the garden, it might be better to convert the loft. 

Conversely, some properties may have lots of land around them and a relatively small roof to convert, which would lend them more to being extended. 

If a client has sufficient budget and space around the property, the best option is to do both at the same time! 

Pros and Cons 

Here is a list of items which apply to both loft conversions and extensions with comparisons. 

Getting approval 

Both loft conversions and extensions can be completed under what is known as 'permitted development', whereby you don't need to make a planning application to the local authority as long as you meet certain criteria. 

For an extension, this means limiting the extension at the rear of the property and single storey only. The extension cannot take up more than 50% of the empty land around the property, which includes previous extensions if they have been made since 1948. 

A loft conversion under permitted development can only have roof lights at the front of the house, but dormers at the back. Dormers, hip-to-gable or mansard conversions which affect the shape of the front or sides of the roof require planning permission, as do balconies. 


Every project is different, but on balance, the design of a loft conversion is probably trickier because there are more constraints on space and where things like windows and stairs can go. There are, however, fewer things to design in a loft conversion. 

An extension will usually need not just walls and windows but: 

  • Drainage 
  • Foundations 
  • A Roof 
  • Steel beams to support new entrances in the existing property 


The construction pros and cons will vary drastically depending on the size and complexity of a project. 

A simple loft conversion will be cheaper and quicker to build than a large extension and vice versa. 

Loft conversions will usually require scaffolding to at least one elevation of the property and may need the whole house to be completely covered for a sufficiently large project.  

Mansard and hip-to-gable loft conversions require the removal of a lot of the existing roof, replacing the old timber rafters with new ones which provide more space inside. Timber has become very expensive over the last five years and has increased in price more than any other product in construction. 

An extension will also require timber for the roof in most cases, but flat roofs will be much cheaper and simpler to build than a dormer or mansard roof on a house. 

Extensions may still need scaffolding if they are two storeys in height, but they will also need foundations, which can be quite substantial if the ground is poor or contains lots of clay. 

An extension will often connect to the existing property through a new opening in a wall which will need to be supported by a steel beam in most cases. 

If you are not sure whether your house would suit an extension or a loft conversion more, give us a call and we can help you, as we have a great deal of experience with both! 


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