A subtle hint of a loft extension...: modern Houses by The Market Design & Build

Beginner's guide to converting your loft into a room

Johannes van Graan Johannes van Graan
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In most cases, people who require more space opt for an extension into the garden; this can be a great way to increase kitchen space, add a home office, or enjoy a beautiful dining room that the occupants have always dreamed about.

However, in other instances, people tend to go up by using vertical space – yes we are indeed referring to a loft conversion, which is something that almost all houses can benefit from with a bit of basic planning. 

Have you ever thought about turning that roof area into a usable room? Will it be possible with your relevant house and structure?

Only one way to find out: read on…

1. Is your loft suitable for conversion?

A subtle hint of a loft extension...: modern Houses by The Market Design & Build
The Market Design & Build

A subtle hint of a loft extension…

The Market Design & Build

Apart from obvious obstacles, such as a water tank or chimney stack, the features that will determine whether your roof space is suitable for a loft conversion are: 

Head height: Take a measurement from the bottom of the ridge timber to the top of the ceiling joist; the usable part of the roof should be greater than 2.2 m.

Pitch angle: The higher the pitch angle, the higher the central head height is likely to be. If dormers are used or the roof is redesigned, then the floor area can be increased.

2. Costs: A room in roof conversion

South Crown Street Bedroom: modern Bedroom by Brown + Brown Architects
Brown + Brown Architects

South Crown Street Bedroom

Brown + Brown Architects

How much that conversion will shake your budget will depend on your roof structure, the existing available space and whether any alterations need to be made to the floor below to accommodate the staircase.

However, a basic ‘room in roof’ loft conversion is the cheapest and could start around £15,000. This will usually involve: 

• The reinforcement of the floor.

• Some skylights.

• Added insulation.

• A staircase to the loft. 

• Electrics, lighting and heating.

• Fire safety measures to comply with Building Regulations, such as fire doors and smoke alarms.

3. Costs: A dormer loft extension

Exterior with bay and dormer windows: classic Houses by The Wood Window Alliance
The Wood Window Alliance

Exterior with bay and dormer windows

The Wood Window Alliance

The second option which does not involve dramatic changes to the roof is to opt for the aforementioned features and then add dormer windows. This can increase the usable floor space and head height, which gives you more options when it comes to placement of the stairs. This will cost upwards of £20,000. 

However, the average dormer loft conversion with a double bedroom and en suite can work out to about £35,000–£45,000.

4. Costs: Changing the roof structure

Structural glass linkway : classic Houses by Ion Glass
Ion Glass

Structural glass linkway

Ion Glass

As this option involves the removal and rebuilding of the existing roof, it is the most expensive. It also requires planning permission approval, meaning your local planning permission application cost must be added on.

Another additional expense will be the extra design work that may be required, seeing as this is a more complicated option than a simple room-in-roof or dormer loft conversion. This type of work is likely to cost upwards of £40,000.

5. Converting a loft with a low head height

rustic Bathroom by von Mann Architektur GmbH
von Mann Architektur GmbH

Badezimmer im Dachgeschoss

von Mann Architektur GmbH

If your initial roof space inspection reveals a head height of less than 2.2 m, there are two available (if not costly) solutions. 

Solution 1: Raise the roof, which would involve removing part of the (or the whole) existing roof to rebuild it and give it the required height and structure. This is structurally possible, but the major problems are the high cost and getting planning permission approval. 

Solution 2: Lower the ceiling in the room below, which will require all the existing ceilings in question to be removed, causing a bit of a mess. For this option, a plate will need to be bolted to the wall, using shield anchors or raw bolts, for the new floor joists to hang from.

6. New ceiling joists

Les Prevosts Farm:  Corridor & hallway by CCD Architects
CCD Architects

Les Prevosts Farm

CCD Architects

Chances are slim that the existing ceiling joists are likely to be strong enough to support a conversion floor, which means additional new joists will be required to comply with Building Regulations.

These new joists span between load-bearing walls and are normally raised slightly above the existing ceiling plasterwork by using spacers below the joist ends. This spacing must be sufficient to prevent any new floor joist deflection from touching the ceiling plaster below. 

If head height is limited, then thicker joists, more closely spaced, can be specified.

7. Cold roof loft insulation

Subtle hint of what is below...: minimalistic Houses by The Market Design & Build
The Market Design & Build

Subtle hint of what is below…

The Market Design & Build

Although the building inspector will specify what is required, the roof structure can be insulated in one of two main ways: cold roof- or warm roof insulation.

Cold roof insulation is the most straightforward option, which involves filling the space between the rafters with 70 mm-thick slab foam insulation. This ensures that there is 50 mm spacing between the roofing felt and the insulation (for ventilation via the roof and soffit vents).

In addition, 30 mm slab insulation is attached to the inside of the rafters, resulting in 100 mm of insulation. The rafter thickness is often less than 120 mm, so a batten may be required along each rafter to allow the 50 mm spacing and the 70 mm insulation. 

The roof section requires 300 mm of mineral wool insulation, or 15 0mm of slab foam insulation. Seasoned DIYers can undertake this project themselves; however, we suggest a professional on site to ensure all required steps (and safety procedures) are taken.

8. Warm roof loft insulation

Country Children's Bedroom:   by Casa Più Arredamenti
Casa Più Arredamenti

Country Children's Bedroom

Casa Più Arredamenti

The warm roof method uses 100 mm insulation over the rafters and includes a covering capping, followed by the tile battens and tiles. It is required that the roof coverings be stripped off for this option. It could be used with a dormer, especially if it has a flat roof.

Continuity of insulation between walls and roof is required to avoid any cold bridging. The dormer walls can be insulated with 100 mm between the studwork, while the internal partition walls use a 100 mm quilt that will provide sound insulation. 

Plasterboard is attached to one side of the wall before the quilt is inserted, followed by plasterboard on the other side. Insulation is also placed between floor joists, which is typically 100 mm fibre or something similar.

9. A staircase to your loft extension

modern Corridor, hallway & stairs by PictHouse

The ideal location for your staircase landing is in line with the roof ridge, as this will make the best use of the available height above the staircase. 

The minimum height requirement above the pitch line is 2 m, although this could be reduced to 1.9 m in the centre, and 1.8 m to the side of the stairs. 

The Building Regulations specify that the maximum number of steps in a straight line is 16. This is not normally a problem, as only 13 steps are usually required for a typical installation. 

When it comes to step size, the maximum step rise is 220 mm, whereas the step depth will be a minimum of 220 mm. Any winders must have a minimum of 50 mm at the narrowest point. The width of steps is unregulated, but in practice the winders are likely to limit the reduction in width.

For balustrades, the minimum height is 900 mm above the pitch line, and any spindles must have a separation distance that a 100 mm sphere cannot pass through.

10. Window options: Roof lights

Of course natural light will need to seep into that converted loft. And for that we look at two options: roof lights and dormer windows. 

Using roof lights that follow the pitch line of the roof is the most sought-after option. This type is fitted by removing the tiles and battens where the roof light will be fitted. The rafters are cut to make way for the roof light after suitably reinforcing the remaining rafters.

This type of windows is the most economic and more likely to be allowed without planning permission, under your Permitted Development (PD) rights.

11. Window options: Dormer windows

Guildford House: modern Houses by C7 architects
C7 architects

Guildford House

C7 architects

Not only do dormer windows add natural light, but they also bring space to a loft extension; they can be placed at the ends or the sides. They are particularly effective where the pitch angle is high, as the useful floor area can be increased. 

Dormers and other similar conversions are normally installed by opening up the roof, and cutting the required specified timbers to size on site. Some loft conversion companies will make the dormers off site in their workshop and lift into place. This process allows quick installation, as well as quick weatherproofing.

Dormers can have gabled or hip roofs, and with careful design can enhance a roof line. In practice, a mixture of the available types can result in the maximum amount of light and space, as well as a fire exit.

12. Fire safety for your loft conversion

Loft Conversions :   by POWER 2 BUILD LTD
POWER 2 BUILD LTD

Loft Conversions

POWER 2 BUILD LTD

Certain safeguards need to be in place to reduce the risk of fire: 

• All habitable rooms in the upper storeys served by a single staircase should have an escape window with a penetrable area of at least 0.33 m², a minimum 450 mm high x 450 mm wide, and not more than 1.1 m above the floor level. 

• For loft conversions to existing two-storey houses, stricter provisions apply, due to the greater risk associated with escape via high-level windows. These require a new 30-minute fire-resistant floor to the loft conversion. In addition, they also need a protected 30-minute fire-resistant stair enclosure discharging to its own final exit, with fire doors to all rooms (except bathrooms). The fire doors do not need to be self-closing. 

• At least one mains-operated smoke alarm with battery backup must be installed in the circulation space of each storey. All alarms are to be interconnected.

In the spirit of safety first, let’s take a look at: The homify guide to safely demolish walls.

Is a loft conversion in your plans? Tell us more, below...
Whitton Drive:  Terrace house by GK Architects Ltd

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