Conversion Options

Rear Dormer Conversion with French doors and two UPVC Windows

Choosing what type of conversion you want is a decision that should not be taken lightly. This extension will affect your property and yourselves for as long as you live there.

That’s why when it comes to choosing which conversion you want, we at Marble Construction can help you.

When designing a conversion there are two main things to consider

  1. The size of the conversion,
  2. How it will look on your house.

Conversions need to be built to balance the room space inside with the aspiration for maintaining or enhancing the property’s external appearance.

When it comes to conversion options there are two basic designs to choose from.

Roof-Space Only Conversions

Out of the two, this is the cheaper and simpler option to build. If your attic already has a fair amount of room then this may be the option for you. Sometimes all that is required is the installation of roof windows into the roof slope and flooring.

As Marble Construction would not have to perform major surgery on your roof for this type of conversion there should be no potential planning problems. However, although this conversion is cheap, it is not suitable for many properties. You need to have a decent-size to start with, otherwise you will have to choose the second option.

Dormer Conversions

Dormers are the most popular type of conversions because nearly everyone can have one built. In many cases is is too small to do a roof-space only conversion so a dormer is the only option.

The great thing about dormers is that they can add a huge amount of space. If you don’t have much space and you’re thinking about converting it to a bedroom this may be the best choice for you.

A dormer is simply a window that projects from a sloping roof, meaning that a dormer can be installed practically anywhere. If you have a very shallow roof then installing a dormer can provide the much needed headroom and light.

If you feel that a dormer conversion is best for you, then you now need to decide what type of dormer to have. In many cases not all dormer-types would be suitable for your roof and during the quotation process we will advise you on the best option to go for. However, if you wish to get an idea before the quotation then here are details of the common types of dormer conversions.

Box dormers

Box dormers look like large flat-roofed boxes on the top of your roof. They are one of the most popular designs of all the dormers because they significantly increase the amount of usable space inside. An added bonus is that they are quick to install and pretty cheap to build.

It is a shame, however, that they are also the clumsiest looking design of all the dormers and it is hard to get planning permission for one visible from a street view. This why they are usually built at the rear of the property where they are not easily spotted. However if a neighbour or similar property on your road has One on the front, it is hard for planning permission to veto one on yours.

When choosing a box dormer you have a couple of options for its position on your roof. They can either be built straight up from the main wall of your house, or they could be built slightly set back up the roof, the latter of which is more common. The dormer itself is typically constructed of timber framework, clad with tiles, all of which is of course designed to blend in with the roof of your house as much as possible.

The construction of a box dormer requires us first to remove a section of the existing roof tiles where the box dormer will fit in. We then construct the timber framework for the side walls and then the roof is built. Here again you have two options to choose from: a pitched roof, or a flat roof. After that, the window frames can be added and then the entire framework covered with plywood and extra suitable cladding.

Unlike roof-space only conversions, dormers add a significant load to the house and so before construction can begin a decision will have to be made as to how to get that entire load spread evenly around the house.

Full-width dormers

Similar to box dormers, the difference here is that the dormer extends the full width of the roof. As the side walls are connected it is common to use the same material on the dormer that was used for the side wall in order that it blends in.

These dormers maximise space inside even more than the box dormer. However, as they are generally larger, this means that it can look out-of-place externally. The full-width dormers are most suited to terraced houses due to the maximising of space, which is often an issue with this type of house.


One of the more individual styles of dormers, the mansard is a roof with a combination of a very steep lower slope and a very flat upper part. They are basically extremely large dormers which, as you can imagine, create a lot of space.

The great thing is that they look good on the outside as well, so essentially both conditions have been fulfilled: they increase the space dramatically, and they look good. The mansard is so big that it requires the complete rebuilding of at least one roof slope. However, unfortunately, as with the roof-space only conversions, things that seem too good to be true are often only appropriate for certain houses. Although the mansard can be built on most house-types it generally looks very out-of-place on houses lacking in height. Mansards only really suit buildings with three or more storeys (or a building with two large storeys).

Mansards are usually built full width. The sides of the extension are built from the existing party walls in brick, similar to that of the full-width dormer conversions. However, they have to be constructed this time to match the slope of the steep pitched front roof. The front roof pitch is typically sloped at a rather steep 60° to 70° angle.

Traditional small dormers

Introducing one of the smallest dormers available, the small traditional dormer is perhaps one of the most common. These dormers have the opposite attributes of box dormers. Whereas box dormers give you lots of room but lack visual appeal, traditional small dormers look excellent but unfortunately don’t give you much room.

If you are trying to make your house look more attractive but do not need too much extra space then this is the perfect dormer for you. Unfortunately they are not as cheap as you may think and this can prove to be a rather expensive option if you want simply to add visual interest to your house.

If, however, you are looking for a conversion at the front of your property you are left with only two options: rooflights or small dormers. The front of your house is highly sensitive from a planning perspective so if you want to build something at the front then a couple of traditional small dormers could do the trick.

Dormer Styles

Now you know what types of dormers there are to choose from you may need to start thinking about the style of your dormer. Again, like dormers, you may find that some of these styles are not appropriate for your house.


One of the most common style types, the pitched roof dormers are built to the classic ˄ shape. The small size of the roof means that ceiling joists can sometimes be removed within the dormer, creating a nice looking ceiling up to the apex.


Very similar to the gabled style but this time with a laid-back hipped front roof slope, this type of style is common on hipped roofs when the styles mesh together.


The flat style of roof is by far the easiest to construct; there is no tricky valley detailing as it is simply built flat across the dormer. You can have it clad in lead, zinc, copper or modern felt. This last option is better avoided as it looks cheap and has a very short lifespan. Although the roofs are flat they are, however, generally inclined at a small angle to let rainwater disperse off the roof.

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