Altering the roof structure & Floor Joists

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 encroach on the space available in the loft void.
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.

Loft Conversion Stairs

Stairs are invariably tricky to design on loft conversion projects, as space for them is tight. Narrow winding flights are acceptable, but may prove impractical, because it’s difficult to get furniture up them.
Purpose-built staircases are around 10 times the cost of standard (off-the-shelf) designs, so bear this in mind when you’re planning your loft conversion.
If you do need a purpose-built loft conversion staircase, it pays to have the design approved by your Building Control officer before you actually commission them. Ask your joiner or builder to send Building Control a copy of the design.
As part of the fire safety upgrade for your loft (see below) your stairways should lead to a hall and an external door. If you have an open-plan arrangement where the stairs rise from a room, it is likely you’ll have to alter it, fitting a new partition wall or choice of escape routes.

Fitting Windows & Gaining Natural Light

You don’t need to make a lot of structural alterations to accommodate rooflight or skylight windows in your new loft conversion, which makes them relatively easy to fit. Typically the rafters on either side of the rooflight are doubled-up and trimmed across the top of the opening.
A popular alternative is to fit dormer windows, which are structures in themselves, as they have walls and a roof as well as the window itself.
At the rear of many homes dormer windows can fall into the permitted development quota and so may not require planning permission. At the front of the house, however, they will require planning permission, which is why you often see rooflights or skylights instead.
Dormer windows may be essential to maximise the headroom in the loft and provide useable space, but will need to be supported at the apex point (ridge). A ridge beam is installed beneath the apex before the dormer roof joists can themselves be fixed in place and the roof weathered.
It is at this stage, when the dormer windows are being constructed, that your loft conversion will be exposed to the elements, so you’ll need good temporary sheeting to protect against the weather.

Upgrading Loft Fire Safety

Loft conversions on bungalows have little effect on the fire safety of your home, beyond making sure that the new windows are large enough to escape out of. But in a house where two storeys become three, there are implications.
The new floor will need at least 30 minutes of fire-protection, which could mean re-plastering the ceilings below it and the loft room will have to be separated by a fire door, either at the top or bottom of the new stairs. You’ll also need one escape-sized window per room – some skylight windows are made specifically with this in mind.
Door self-closing devices are no longer required in homes. They’ve proven to be a risk to children’s safety because they can trap tiny fingers. Instead, existing doors on the stairway (ground and first floor) should be replaced with fire-resistant doors or upgraded – and this should be indicated on your loft conversion drawings for Building Control.
As part of the electrical installation, mains-powered smoke alarms should be installed on each floor of your home and these should be interlinked so that they all sound when one is activated. Most have a re-chargeable battery as a back-up that allows the supply to be extended from a lighting circuit if need be.

Loft Storage Ideas

When you convert your loft you are, of course, going to lose storage space. Make the most of what you have by using the eaves behind the ashlaring – fit access hatches and have roll-out storage bins made to fit. And if you insulate down the rafter line to the eaves you’ll create a warm store for your belongings.
Built-in wardrobes are also a great feature in loft bedrooms, where standard units won’t fit – and are among the most innovative loft storage conversion ideas.