Bungalows are the best value in Norfolk housing and the most under-used. A bungalow gives you a large footprint, a generous plot, and a roof void sitting above it doing nothing. Converting that void is usually cheaper per square metre than extending outwards and it consumes no garden at all.

Whether it is a straightforward job or a substantial structural project comes down to one question, and it is worth understanding before you ring anybody: is the roof cut, or is it trussed.

Cut roofs and trussed roofs, explained

A cut roof is built on site. A carpenter cuts individual rafters, fits purlins — horizontal beams that support the rafters partway up their length — and lays ceiling joists across the top of the walls. The purlins are usually propped off internal walls by struts. Look up into a cut roof and you generally see a clear central space with timbers around the edges. Most bungalows built before the middle of the twentieth century have one.

A trussed rafter roof is made in a factory. Each truss is a single engineered frame — rafters, ceiling tie and a set of diagonal internal members called webs — pressed together with nail plates and delivered ready to lift into place. Look up into a trussed roof and you see a forest of diagonal timbers filling the void completely. Trussed rafters became the standard way to build a roof in Britain from roughly the 1960s onwards, and the great majority of bungalows built since then have them.

The difference is not cosmetic. In a trussed roof every member is doing structural work. The webs are not partitions and the ceiling tie is not a floor joist — it is a tension member holding the feet of the rafters together. Cut a web out and the truss starts to deform. Cut several and the roof spreads.

That is why the answer to "can we just take those bits out" is no.

How to tell which you have

Put your head through the hatch with a torch.

  • Diagonal timbers crossing the middle of the void, all the same size, joined with toothed metal plates: trussed.
  • Larger timbers around the perimeter, a horizontal beam running the length of the roof partway up the slope, and a reasonably clear middle: cut.
  • Slender timbers, closely spaced, all the same section throughout the roof: trussed.
  • Chunky, varied, sometimes with a ridge board and struts down to internal walls: cut.

Age is a good guide but not proof. Extensions, re-roofing and post-fire reconstruction all confuse the picture, and some bungalows have one type over the original house and another over a later wing.

If you have a cut roof

You are in the easier position. The usual approach is to insert steel beams to pick up the roof load and to carry a new floor, remove the struts and any redundant timbers, and strengthen or replace the ceiling joists to floor standard. The purlins may be retained and supported, or replaced by steel.

It is still an engineered job — a structural engineer sizes the steels and designs the connections and the padstones they bear onto — but it is done from inside, the roof covering stays on, and the house stays weathertight for most of the work.

The design freedom is greater too. A cut roof can be opened up, given a vaulted ceiling, and worked with rather than around.

If you have a trussed roof

You have three routes, and the right one is a cost and disruption judgement rather than a technical one.

Route 1: replace the roof with attic trusses

Attic trusses are the same factory-made product, designed differently. Instead of webs filling the void, the truss is shaped to leave a clear rectangular room inside it, with the floor forming the bottom chord of the truss and the room's side walls and sloping ceiling formed by the truss members themselves. They are engineered to carry the floor loading of habitable accommodation as well as the roof.

For a bungalow this is very often the best answer, and clients are frequently surprised by that, because it sounds drastic. The logic is straightforward: the existing trusses cannot stay, so the roof is coming off anyway. Once it is off, a set of attic trusses delivered as a kit is quick to erect, gives a fully engineered floor and roof in one operation, and produces a better room than a patched-together alternative.

What you need to know about it:

  • The room dimensions are fixed by the truss design. The width of the room and the ceiling height are determined by the span of the bungalow and the roof pitch. If the pitch is shallow, the design may need the ridge raising to produce a usable room, which is a planning matter.
  • There is a lead time. Trusses are made to order, and the design has to be finalised and signed off before manufacture.
  • The roof comes off. That means craneage, temporary weather protection, and a period during which the house is not habitable or is very unpleasant to live in. Plan around it.
  • The existing walls have to take it. A structural engineer will check the wall plate, the walls beneath and the foundations. Bungalow foundations are sometimes shallower than expected.

Route 2: design a new cut roof

Rather than ordering attic trusses, the new roof is designed and cut on site with steel or engineered timber beams. This costs more in labour but gives complete freedom over the room shape — asymmetric plans, a raised section, a vaulted area, dormers exactly where you want them. On an interesting plot or an unusual bungalow it is often worth the difference.

Route 3: modify the existing trusses

It can be done. A structural engineer designs a system of beams — usually steel — that takes the roof loads before any truss member is cut, the beams go in, and only then are the webs removed, truss by truss. It avoids taking the roof off, and it keeps the house habitable.

It is not the cheap option people expect. Getting steel into a loft through a hatch is difficult, the design is bespoke, and the resulting room is usually compromised by the beams. We suggest it where the roof covering is new, where the disruption of a roof-off is genuinely intolerable, or where the site makes craneage impossible.

Getting light and volume in

Once the structure is resolved, the roof form decides the room.

Rooflights are the least intrusive and the cheapest. On a bungalow they are often all you need on the front slope, and they are the option least likely to cause a planning problem.

Flat-roofed box dormers give the most floor area with full head height, which is why builders like them and why so many are built. They are also the least attractive option and, on a bungalow front elevation in a village street, the most likely to be refused. On a rear slope, out of public view, and designed with proper proportions and cheeks that are set in from the eaves and the ridge, they can be perfectly good.

Pitched-roof dormers — gabled, hipped or with a small pitched roof of their own — cost more, give less internal space, and look considerably better. On a visible elevation this is the version that gets consented.

Gable-end glazing is the underused option. If the bungalow has a gable, a large window in it lights the new floor with no dormer at all.

Raising the ridge transforms a shallow-pitched bungalow but changes the height of the building, which is a significant planning consideration, particularly in a street of consistently low roofs.

Whether any of this is permitted development or requires an application depends on the property, the designations that apply, and any conditions attached to the original permission. Those rules have changed and continue to change, so we do not publish figures here. It has to be checked against the specific bungalow, and it is the first thing we check.

The two things that decide the plan

Where the stairs go. This is the real constraint in a bungalow, more than the roof. Bungalows rarely have a hall with enough length for a staircase, so the stairs usually take space from a bedroom or a hall extension. The stair position determines where the landing lands upstairs, which determines the room layout, which determines where the dormers go. Design it from the stairs outwards.

Fire and escape. Adding a habitable storey changes the building regulations position significantly — protected escape routes, fire doors, alarm systems, and stair construction. This, rather than planning, is where bungalow conversions most often need rethinking. It is resolved at technical design, and it is worth having in mind from the start because it affects the plan.

A worked example

Our loft conversion at Strumpshaw combined new accommodation in the roof with a single-storey extension, which is a common and effective pairing: the roof provides the bedrooms, the extension provides the living space, and neither has to do the whole job. More on how we handle these projects is on our loft conversions and house extensions pages.

Find out what you have

The first useful step is somebody looking into the roof void and telling you honestly which category you are in, because it changes the budget by a large margin. Our free initial consultation is on site, and includes exactly that assessment along with a view on the planning position and the realistic options.

Call the Norwich studio on +44 (0) 1508 830 310 or email info@archidite.com.