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Before you begin on your loft conversion it is worth finding out exactly what it will involve and how it will affect the design of your home.
Here are some things you need to consider when weighing up whether a loft conversion is the right way to add more space to your property.
Clearly it will add weight to your house and, although it may only be a modest increase, you’ll need to make sure that the structure of the building can take it. You’ll need to expose the foundations and check them, together with any beams or lintels that will be asked to carry more weight.
Get your designer to illustrate clearly how much headroom you’ll have in your loft once it’s converted – people are often disappointed by how much space they have to actually stand up in and on plans this isn’t always clear. Don’t forget you’ll have to accommodate a staircase leading up into the loft – to make the best use of space the new staircase should rise above the old one and not from within an existing bedroom. There’s not much point in converting the loft space if it means losing an entire room on the first floor. Without the roof space for water tanks and plumbing, the heating and hot water system may have to be replaced with a sealed system. It’s better to have an unvented hot water cylinder than a combination boiler, but it will take up a cupboard-size room and you’ll need to find somewhere to put it.
Loft conversions always need approval under Building Regulations (irrespective of whether they need planning permission) so it pays to adopt the full plans application approach and have a detailed scheme approved before you find a builder. Having an approved design will take much of the risk out of the work and also mean the builder has a chance to give you a fixed quotation, rather than a vague estimate. If your house is semidetached or terraced don’t forget to notify your neighbour of your proposals, which will usually fall under the Party Wall Act 1996. Your Building Control officer will inspect the work at various stages and on a final inspection should issue you with a completion certificate – don’t settle any final accounts until you’ve received the certificate.
Most roofs are constructed with internal support struts in the loft, propping up the rafters and purlins (horizontal roof beams) in traditional cut and pitched roofs, and making up the web of braces in modern trussed rafter roofs. All these have to be removed to make way for the new room and replaced with new supports that don’t impose on the space. There are many ways of altering roof structures for loft conversions, but they all have one common element –the ceiling joists will almost certainly be inadequate as floor joists. This means that new floor joists are fitted alongside them, slightly raised above the ceiling plasterboard to avoid contact with it. These joists (often 200mm or 225mm in depth) will rise above the tops of the current ceiling joists to form the floor structure. Depending on their span they will bear either directly on to the existing wall plates of external and internal load-bearing walls, or on to newly installed beams.
In smaller lofts, it is often the case that the floor joists themselves will be used to support the sloping rafters. This is possible by constructing a dwarf timber stud wall 1m to 1.5m high, known as an ashlering, between the two. With the supporting ashlering in place, the internal struts and braces can now safely be removed.
You don’t need to make a lot of structural alterations to accommodate skylight windows, which makes them relatively easy to fit. Typically the rafters on either side of the skylight are doubled-up and trimmed across the top of the opening. Dormer windows, on the other hand, are structures in themselves, as they have walls and a roof as well as the window itself.
With standards being increased, loft conversions have become awkward to insulate. The sloping ceiling will need insulation cut and fitted between the rafters, and on top of them. As the plasterboard will have to be fixed to the rafters through the bottom layer of insulation, you will want this insulation to be as thin as possible. So, you should use some high performance insulation (typically a foam board) for all of these areas.