Many people worry about the possibility of structural damage to their or their neighbour’s property as a result of an extension or loft conversion. This article will look at what problems can occur both during the build, and once the works have been completed, and how to prevent these problems from occurring.
Why Are Structural Alterations Necessary When a Loft is Converted?
An original loft structure is not designed to support a room but is only designed for light storage, to separate the roof from the floor below, and to accommodate the roof outline.
There are a variety of possible loft conversions depending on your type of property. Check out our visuals and pricing guide here. Depending on what type of loft conversion you are looking to have, some or all of the below may apply.
Steel beams sit on padstones, – cubes of concrete made to a specific size -, which sit on the external walls of a house. A typical external wall has two leaves of brickwork, and sometimes a cavity, depending on when the property was built. The steel beams and padstones sit on the inner brick leaf, thereby avoiding damage to the neighbouring property’s internal finish, or if it is a detached property, the external finish.
Ceiling and Floor Joists
The joists forming the floor of the loft are replaced with thicker floor joists. Steel beams are installed to pick up the weight of these new floor joists, typically taking the weight of the dwarf wall too (the dwarf wall is a wall approximately 1000mm in height around the edge of the loft room which has openings for storage in the remaining roof space).
The rafters, which are the roof timbers that meet each other at the highest point of the roof, known as the ridge, need insulation between and over them. Due to the additional weight placed on these rafters, and the increased thickness of the insulation, it is highly likely that replacement of these rafters will be necessary.
Hip to Gable Conversion
The roof of end of terrace, semi-detached, and detached houses usually have a hipped section of roof at the detached side of the property. This hip can be converted into a gable by building a new wall off the external wall and installing new rafters so that the roof has more usable floor space and head height. A hip to gable conversion is usually combined with a dormer conversion.
If the loft conversion features a dormer, a ‘ridge’ beam, which is installed around ceiling level, is required. This ridge beam bears the weight of the dormer roof structure.
What Structural Damage Can Occur From a Loft Conversion?
Not all structural works mentioned above are needed for every conversion, it all depends on the existing structure and the type of loft conversion. To comply with building regulations, the structural alterations need to be proved as sufficient, and this is done by building in accordance with the structural engineer’s design.
It is important that the floor joists and rafters can withstand the additional stress caused by the loft conversion. If they aren’t strong enough, over time they will begin to bend, and in the worst cases collapse.
Hand tools should be used when cutting holes in party walls to install steel beams and great care should be taken to prevent cracks from forming in either your or your neighbour’s property.
Steel beams evenly spread the weight placed upon them over a certain area. If the steel beam isn’t strong enough, it can bend slightly, causing cracking to the finishes and potentially the brickwork of the property. If too much load is placed on a wall from a steel beam, the wall could suffer structural damage and could collapse. To prevent this from occurring, the structural engineer must specify which steel beams are suitable and their exact positioning. The builders must then build exactly to this design.
What Structural Works Are Involved in an Extension?
Extensions are usually built where the ground conditions are soil, clay or similar. The walls of a new extension are too heavy to be placed directly onto ground conditions such as these and they would sink and move, therefore a foundation of some type is required.
In order to create an open plan space, steel beams replace the section of wall that forms the external wall of a house or an internal load bearing wall. The openings above these need to be permanently supported, usually by one or two horizontal beams which sit on padstones laid on brick piers.
What Structural Damage Can Occur From an Extension?
Similar to loft conversions above, to comply with building regulations, extensions are built in line with the structural engineer’s design.
If the foundations are of the wrong size, position or are mixed incorrectly, they will move over time. This will cause the walls of an extension to move, resulting in large cracks in the walls, roof distortion and the risk of collapse. The Party Wall Act 1996 applies when digging foundations within three metres of a neighbour’s property. The neighbour’s property should be safeguarded from excavation works by use of the correct tools, complying with building regulations, building in accordance with the design, and the use of experienced builders.
Steel beams used as part of the structural opening must be strong enough to bear the load of everything above them, and usually the weight of the extension roof too. If the steel beam is the wrong size, it will bend, causing structural movement and large cracks in your and your neighbour’s walls. Steel beams may be too heavy to sit directly on brick piers; therefore, cracking can occur to the brick piers as they are forced downwards, and movement of the whole house above can occur. If the brick piers are of inadequate size or strength, horizontal beams may be used to form part of a goal post system which involves vertical steel beams that sit on pad foundations.
It is clear that there are risks to the structure of your and your neighbour’s property when loft or other extension works take place. The likelihood of these risks occurring is very low, but you need to be prepared for them in a worst case scenario.
Make sure your builders have the necessary insurance (public liability, employers’ liability, contractors’ all risk and warranties/guarantees) and that your home or contents insurance covers you during the building works.
With the use of a design and build team, the stress of dealing with multiple parties such as the structural engineer, architect, builder and manager is removed. In short, make sure the people you choose are capable, fully insured and know what they are doing!