The great thing about barn conversions is the way that old agricultural buildings lend themselves to bright, open plan, modern living spaces whilst retaining their rural character.
Windows play a key part in this transformation and help to form a comfortable and modern family home. But, when it comes to barn conversion windows, they’re far more than just a decorative choice; they influence the planning design, structural integrity, energy efficiency and fire safety of the building.
This makes them a focal point for building control, so the earlier you start thinking about them, the better.
Introducing light into a barn conversion
Barns offer opportunities to place windows in places you wouldn’t normally think of. A skylight above a staircase can turn what would otherwise be a dark place into a bright, uplifting feature.
High-level slit windows can bring light into a bathroom without compromising privacy. Even small rooflight windows positioned over circulation spaces can change the atmosphere dramatically.
Because barns tend to have tall rooflines and wide spaces, these types of windows often work brilliantly to make livable spaces.
Choosing between rooflights and dormers
Most barns have large roof structures, and many barn conversion layouts don’t have traditional first-floor windows. This means that you’ll usually need new openings to bring light into loft rooms or mezzanine floors.
The two main options are rooflights and dormers, and each brings its own character and set of challenges.
A rooflight is usually the easiest to construct as it can be fitted neatly between the existing rafters. It shouldn’t need major structural alterations, so it's usually cost effective, and in many cases can be done without any planning implications.
While they let daylight flood in without drawing too much attention to themselves, the downside is that rooflights don’t create any additional headroom. This is where dormers have the advantage.
Dormers add headroom and usable floor space, make rooms feel bigger and often improve the layout. However, dormers usually require more structural work, and have planning implications.
Because barns were never meant to have domestic-looking dormers, planners may push back unless you can show that the design complements the agricultural character.
Using architectural glazing to your advantage
A distinctive feature of barn conversions is the use of glass to create openness without disturbing too much of the historic fabric. Architectural glazing such as floor-to-ceiling windows and double-height picture windows can make a barn feel completely different, whilst still preserving the 'olde worlde' feeling.
Floor-to-ceiling glazing is especially effective where old barn doors once sat. Many designs retain the shape of the original opening but fill it with modern aluminium or timber-aluminium composite systems.
The look is stunning, particularly on south facing elevations with landscape views. However, it does come with implications for overheating, thermal performance and structural design. In most cases, this level of glazing struggles to pass overheating assessments, which can influence the choice of glass, ventilation and even shading.
The benefits of bespoke windows
When it comes to barns, no two structural openings are the same. Walls may lean, timber frames may not be perfectly square, and historic stonework can be irregular. Bespoke windows then become necessary which neatly deal with the original shape of the openings.
Bespoke windows offer the potential to echo the barn’s original structure by following the lines of structural members, and replicating the proportions of the building’s agricultural past.
Many barn conversions use a blend of bespoke glazing and standard units. The bespoke elements become the architectural highlights, while the standard windows help keep barn conversion costs under control.
Building regulations and barn windows
Windows in barn conversions must comply with the building regulations, which must be understood early in the design and planning stages.
Escape windows fall under Part B (Fire Safety) and apply to any habitable room where a protected stair route isn’t available. This is surprisingly common in barn conversions where staircases are often features, and positioned in habitable places such as lounges and kitchens.
Escape windows must have openings of at least 0.33 square metres and meet minimum dimensions of 450mm high and 450mm wide, with the bottom of the window no higher than 1100mm from the finished floor. For loft rooms in particular, this can influence the type, size and position of windows and rooflights may become unsuitable.
Ventilation is covered by Part F and every habitable room needs purge ventilation, which usually means an openable area equal to at least one-twentieth of the floor space. Background ventilation is also required and unless this is provided by an mechanical ventilation heat recovery system (MVHR), trickle vents providing at least 5000mm² of free area are often incorporated into the window.
Thermal performance comes under Part L, and U values of 1.6 W/m²K or better are typically required. Most modern double-glazed units with low-E coatings and argon filling achieve this without too much difficulty, but for large glazed units which form a large proportion of the external wall, lower U values may be required to meet the overall energy efficiency requirements and pass the SAP assessment.
Security falls under Part Q for new homes and barn conversions that form a new dwelling will need to have PAS 24-rated doors and windows. However, depending on the extent of conversion, some barn conversions may not technically need to comply (check with your building designer).
Accessible windows – especially those on flat roofs – should still meet modern security expectations. Laminated glass, multipoint locking and robust frames all help to provide an acceptable level of security.
It’s worth remembering that building regulations approval is required for any new window opening, even if it’s simply swapping roof tiles for a rooflight. Depending on the level of conversion, the barn may be classed as a new dwelling, so full compliance with the regs is required with a particular focus on structure, fire safety, energy performance and ventilation.
Part O - Overheating
In most barn conversions, there will also be a requirement to comply with Part O of the building regulations because you’re creating a new dwelling.
Barns often feature large areas of south-facing glazing, especially where old barn doors are replaced with feature windows. Without proper analysis, these can turn into an overheating risk.
Part O looks at window size, orientation, ventilation strategy, shading and the type of glass. With larger south facing glazing brise-soleil, overhangs or solar control glazing may become an essential part of the design. Sorting this out early in the design process prevents last-minute redesigns, and protects the approved planning design from unexpected changes.
Planning considerations for your barn conversion windows
Planning is surprisingly nuanced when it comes to barn conversion windows. Rooflights sometimes fall under permitted development as long as they don’t project more than 150mm above the roof plane.
Dormers are more controlled, partly due to their visual impact. They also have volume limits depending on the building type, and side-facing dormer windows often need to be obscure glazed and fixed shut below 1.7 metres, to protect neighbours' privacy.
If the barn sits within a conservation area or an area of outstanding beauty, expect more design scrutiny. Conservation-style roof windows that sit flush with the roof tiles and use a central glazing bar are often preferred.
There may also be restrictions on the extent of glazing to limit light pollution and avoid negative impacts to the landscape. Listed barns require listed building consent, and every new window must be justified carefully.
Class Q conversions come with their own rules, and the fundamental principle is that the existing structure is being converted rather than replaced. New windows must hang off the existing frame, and the extent of alterations becomes limited. What’s possible is often down to local planning policies, so be prepared to compromise.
FAQs
Can I add completely new window openings in the barn walls?
Yes, but planning authorities tend to prefer using existing openings where possible. New openings must be justified carefully and designed to respect the barn’s character and structural integrity.
Are modern aluminium windows better than timber for barn conversions?
Actually, both work well, but aluminium tends to suit modern, minimalist glazing, while timber windows blend more naturally with traditional barns. The choice really depends on the look you want to achieve.
Can I install floor-to-ceiling glazing without overheating the room?
Yes, but a Part O assessment may require shading, solar-control glass or changes to the glazing ratio to prevent overheating.
Are bespoke windows worth the extra cost?
In barns, often yes. They allow you to follow irregular openings and retain historic character in a way “off the shelf” windows can’t.
Not getting the lighting right in your barn conversion is a common error. Find out what other barn conversion mistakes architects warn against, and while windows may provide you with natural light, be sure to take time to choose your barn conversion lighting ideas as well.
