Adding a dormer to an existing loft conversion

There are two reasons why people may want to do this: 

  • People buy a house with an existing roofline conversion and decide they want to upgrade the loft accommodation. They might do this to make the space larger, brighter and, perhaps change the interior usage.  
  • Secondly, the loft conversion is planned in two stages to spread the cost. Or because the demand for accommodation at that time is satisfied with a simpler roofline conversion. 

What is a dormer loft conversion? 

A dormer is a box-like structure with vertical walls which come out from the roof slope. They can vary in size and style. In addition, dormers are commonly used to increase the usable space in a loft and to create window openings in the roof.  

Do you need planning permission to add dormers to an existing loft conversion? 

The same planning deliberations will apply to the upgrade just like if you were to start from scratch. If your loft conversion was built under permitted development, you shouldn’t assume that the dormer you’re adding will be as well. So, some points that may make you need planning permission are: 

  • How far the dormer windows project from the roof 
  • Whether the property is listed or in a conservation area.  
  • How much structural change is made to the appearance and height of the existing roof.  
  • The overall size of the loft conversion, the upgrade could make the conversion larger than the original design.  
  • Your neighbours are affected by your dormer. Either by being over shadowed or over looked.  
  • The dormer exceeds 40 square meters on a terraced house or 50 square meters on a semi-detached or detached house.  

Although, not all dormer conversions require planning permission. Your builder or architect will be able to advise you on whether your plans fall within permitted development rights.  

Advantages of adding a dormer –  

Dormer loft conversions are one of the most popular options when it comes to loft conversions. So, here are some advantages of adding them:  

  • They are suitable for almost every type and style of house. 
  • Dormers increase the head height and usable floor space.  
  • You can use any type of window to match the property. You aren’t confined to Velux windows or roof lights.  
  • Could add a small Juliet balcony 

How much would it cost?  

Finally, if you already have an existing loft conversion and you want to add a dormer, you should expect to pay upwards of £5000. However, this all depends on the size, style, and other factors when it comes to a dormer.  

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