Hip to Gable Loft Conversions

What a hipped roof is, and why it wastes the loft

The hip slopes the roof inwards from three or four sides, so the loft tapers away to nothing at the end.

A gabled roof has two slopes and two vertical triangular walls at the ends. A hipped roof slopes on the ends as well, so instead of a flat brick triangle you get a third and fourth plane of tiles running back from the eaves up to the ridge. It is the standard roof on speculative housing built between about 1920 and 1939, and it is why so much of Colchester’s suburban stock looks the way it does.

Structurally the hip is elegant. Diagonal hip rafters run from each corner of the wall plate up to the end of the ridge, jack rafters cut into them, and the whole corner triangulates itself. It is stiff, it sheds water well, and it needs no gable wall.

Inside, it is a problem. Head height in a roof is a function of how far you are from the eaves, and the hip pulls the roof surface inwards on the end elevation as well as the front and back. The zone with two metres or more above the floor is not a rectangle, it is a lozenge, and the hip shortens that lozenge at one end by roughly the same distance as the height of the roof above the eaves. On a house with a seven metre span and a forty five degree pitch, the hip is eating about three and a half metres off the length of the usable room.

That is not a corner you can lose gracefully. It is the end of the room, and it takes the bed wall with it.

Why this is the defining conversion for the interwar semi

Everything else about that house type is already right. The hip is the only thing in the way.

A typical 1930s Colchester semi has a traditional cut roof with rafters, purlins and struts, a pitch somewhere between forty and forty five degrees, and a ridge height that gives around 2.4 metres above the ceiling joists. The timber is usually sound, the loft is usually dry, and the head height is usually there.

It also has a landing with enough length to take a staircase over the existing one, a flank wall that can generally carry more load, and a rear elevation that is not the principal elevation, which is the elevation that matters most for permitted development.

What it does not have is width at height. The hip removes it, and no amount of clever internal planning gets it back. You can convert a hipped loft without touching the hip, and people do, but what you end up with is a room that is generous at one end and a crawl space at the other, with the wardrobe wall missing and nowhere sensible for the stairs to arrive.

Square the hip off and the room becomes rectangular. Add a dormer to the rear slope and it becomes a double bedroom with an en suite and a proper landing at the top of the stairs. That combination is the reason this conversion is so common on that house type, and it is why the two are usually priced together rather than separately.

What removes permitted development, and what a conservation area does

A roof extension in a conservation area is not permitted development at all. That is the single biggest constraint on this job.

Permitted development for roof additions does not exist for flats and maisonettes. On a listed building it is not removed either, but listed building consent applies as a separate and additional requirement, and on a historic roof that is generally the harder of the two to satisfy.

More importantly for this conversion, the class is switched off entirely on what the legislation calls article 2(3) land. That includes conservation areas and National Landscapes, the designation formerly known as areas of outstanding natural beauty. It is not a restriction or a tightening. Any addition to the roof in those areas is a full planning application.

That matters here more than for almost any other conversion, because a hip to gable is visible. A rear dormer can hide behind a roof and be invisible from the street. A gable changes the outline of the building against the sky from the pavement opposite, permanently. Officers know this and so does everybody who lives on the road.

Locally that puts parts of Lexden inside a conservation area, along with the historic core of the city and village centres including Dedham and Wivenhoe. Coggeshall is designated too, but it is Braintree District that decides there. Dedham Vale is a National Landscape, which catches property well outside the village itself. An Article 4 direction can remove permitted development rights over a defined area for defined types of work, and where one is in place it does exactly what it says.

None of this makes the conversion impossible in those areas. It makes it an application, on merits, with design that has to answer for itself.

Semi-detached symmetry, and why officers weigh it

A pair of hipped semis was designed as one building. Squaring off one half changes the whole thing.

This is the design question that comes up more than any other on this conversion, and it is a legitimate planning consideration rather than a neighbour’s opinion.

A 1930s semi-detached pair is symmetrical about the party wall: two bays, two porches, two hips, one composition. Build a gable on one end and the building is no longer balanced. From directly in front it can read as a slightly lopsided single house, and from an angle it reads as two houses that no longer match.

Officers do weigh this, and they weigh it differently depending on the street. On a road where several pairs have already been squared off, the harm is limited because the character of the street already includes gables. On an intact terrace of pairs where none has been altered, the same application is a harder argument. Neither outcome is predictable from a distance and we would not pretend otherwise.

Where the design can respond, it usually does so in one of three ways. Matching materials honestly, so the gable reads as part of the original building rather than an addition: the right brick, the right bond, a mortar mix matched to what has weathered on the house rather than to whatever the merchant has in stock. Setting the gable back slightly from the front elevation, or keeping a small return of hip at the front corner, which softens the change from the street while still gaining the internal space. And occasionally both halves converting, either together or with one designed so the other can follow, which restores the symmetry completely.

The last of those is not always possible and it is never something you can rely on your neighbour to do. It is worth a conversation though, because a pair converted as a pair is the strongest version of this scheme by a distance.

Foundations and when to dig a trial hole

You are adding load to a footing nobody has looked at since it was poured.

A 1930s strip footing is typically shallow by modern standards, often 450 to 600mm deep, sometimes a stepped brick footing rather than concrete, and it was designed for the house that sits on it. A hip to gable adds load to the wall above it, so the question of whether the footing can take that load is a real one rather than a formality.

In many cases the added load is modest relative to what is already there and no work is needed. The engineer will say so on the basis of what is found, not on the basis of hope.

A trial hole is how you find out. It is a hand dug hole against the outside of the flank wall, taken down past the bottom of the footing, exposing its width, its depth and the soil beneath it. It takes half a day and it settles the argument. Where the footing is shallow, narrow or sitting on made ground, the options are underpinning a length of it, casting a new pad beneath a beam bearing point, or redesigning the gable to reduce weight.

Ground around Colchester is varied. The higher ground to the west and north sits on clay, and clay is shrinkable, which makes nearby trees and their species a genuine input. Closer to the Colne valley you find sands and gravels, which behave differently again. This is why the answer is a trial hole rather than a rule of thumb.

Reducing the weight is an option worth knowing about. A gable can be built as a timber framed panel above first floor ceiling level, clad in tile hanging or render board, rather than in masonry. It is dramatically lighter, it goes up faster, and whether it looks right depends entirely on the street. On a road of plain brick gables it will not. On a road with tile hung gables already, it will.

The new floor

Ceiling joists hold a ceiling up. A floor is a different order of load entirely.

The timbers currently spanning your loft were sized to carry plasterboard and a few boxes. They are not a floor and boarding over them does not make them one.

A conversion introduces new floor joists, deeper than the existing ceiling joists, usually carried at each end on steel beams. Those steels typically run across the house and bear into the party wall on one side and the flank wall on the other, which on this conversion is the wall you have just built a gable on top of. The two things interact, and they should be designed together rather than by two people on different days. A chimney breast standing in the loft is part of the same design.

Steel bearings are concentrated point loads landing on walls that were carrying distributed ones, so each end sits on a padstone. The pocket is cut, the padstone bedded, the beam craned or manhandled in and packed, and the masonry made good above it. On a semi, cutting that pocket into the party wall is the trigger for a formal notice, which is the next section.

The new joists sit above the existing ceiling joists rather than replacing them, so the old ceiling below stays intact and undisturbed. That is why head height gets eaten from both directions at once, roughly 150mm at the floor and around 300mm at the ceiling once insulation, structure and plasterboard are in.

It is also why the 2.4 metre figure matters so much. Take 450mm off 2.4 and you have just under 2 metres of finished height at the ridge, which is the working minimum for a room that feels like a room.

What the gable actually gains you

Width and floor area at full height. Not height, and not more roof.

It is worth being precise about this, because the gable is often oversold and occasionally undersold.

What you gain is the wedge of space the hip was taking: on a typical semi, roughly the last 2.5 to 3.5 metres of the room at the hip end, restored to the full width of the roof. In floor terms, on a house where the usable zone was around 3 metres by 3.5, the gable can take it to something nearer 3 by 6. That is the difference between a study and a bedroom.

Just as importantly, it gives you a full height wall at one end of the room. Every piece of furniture that needs a vertical surface behind it, which is most furniture, now has somewhere to go. It also gives the staircase somewhere sensible to arrive, because you can land at the gable end with head height above you.

What you do not gain is any additional height at the ridge. If your loft measures 2.2 metres from ceiling joist to ridge, it will still measure 2.2 metres afterwards, and squaring the hip off will not fix a head height problem. That needs a dormer, a raised ridge or a lowered ceiling below, all of which are different projects with different costs.

You also do not gain much on the plan area under two metres. The eaves are where the eaves were, and the low margins at the front and rear stay low. Those become storage, which is genuinely useful, but they are not floor area you stand up in.

The staircase, and where it lands on a 1930s semi

Part K decides the geometry. The existing landing decides the position.

Part K sets a maximum pitch of 42 degrees, a minimum going and maximum rise, handrail requirements, and 2 metres of headroom measured vertically above the pitch line. That headroom requirement is what usually decides where the stairs can go, because they have to rise through the existing roof structure and there has to be height above them at the top.

On a standard 1930s semi the answer is nearly always over the existing staircase, running in the same direction, so the circulation stacks and the new flight arrives on the landing above the old one. The landings on that house type generally have the length for it, which is one of the reasons the house type converts so well.

The hip to gable helps here in a way that is easy to miss. Because the gable end now has full height, the top of the stairs can arrive against or near it with 2 metres above, instead of arriving into a sloping ceiling. On an unaltered hipped roof the only place with height is the middle, which is also the only place the room wants to be.

The cost of the stairs is space on the first floor landing. A new flight and the trimmed opening take floor area from somewhere, and on a small semi that sometimes clips the corner of the smallest bedroom or the airing cupboard. It is better to see that on a drawing early than to discover it later.

Alternating tread space saver stairs are permitted in defined circumstances for a loft conversion. They are a genuine last resort rather than a way to save space, they are unpleasant with laundry, and Building Control will want to be satisfied about what the room they serve is used for.

The en suite: soil route and extract

Getting a 110mm pipe from the top of the house to the drain is a route that has to be found, not assumed.

Almost every hip to gable with a dormer includes an en suite, and the soil connection is the detail that decides where it goes.

The options are a new internal stack, which usually boxes into the corner of a bedroom below and then into a cupboard or the corner of the hall, connecting to the existing drainage at ground level. Or a new external stack on the rear elevation, which is simpler to build and harder to look at, and which on a side elevation raises the same visual questions the gable does. Or connecting into the existing soil stack, which is neat where the geometry allows it and the existing pipe has capacity.

A macerator is the fallback. It works, it is quiet enough now, and it cannot serve as the only WC in the dwelling. It is a compromise rather than a first choice and it should be described as one.

The waste and vent arrangement needs designing rather than improvising: the stack needs venting, either to open air above the roof or through an air admittance valve in an accessible position, and branch connections have length and fall limits.

Extract ventilation from a loft bathroom must reach outside air, which usually means a tile vent or a duct through the dormer cheek. The duct itself has to be insulated where it crosses cold space, or the warm wet air condenses inside it on the way out and the water runs back down into the room. That is a five minute detail at first fix and a recurring complaint if it is missed.

How long it takes, and living through it

Eight to twelve weeks on site, plus whatever the front end takes.

Front end first. Where the scheme is permitted development we would apply for a Lawful Development Certificate, which is a determination rather than a decision on merits. Where a full application is needed it is the statutory eight weeks from validation. Building Regulations full plans approval runs alongside. Party wall notices run one or two months depending on the section, and they are shortened only by the adjoining owner consenting in writing, not by everybody being reasonable about it.

On site, a hip to gable with a rear dormer is commonly eight to twelve weeks. Roughly: a week for scaffold and strip out, two to three weeks for the gable, roof structure and steels, two weeks getting it watertight and the dormer formed, a week or so for the staircase, then first fix, plastering, second fix and finishing.

The character of the disruption is different from an extension. Most of it happens above you, which sounds better than it is, because for a period the end of your roof is open under temporary sheeting and that is loud in rain and alarming in wind even when it is entirely secure. Plan for that fortnight rather than being surprised by it.

The genuinely intrusive phase is the staircase, because it happens inside the house. The first floor landing becomes a building site for a week or so, fire doors go onto rooms you are living in, and dust from the stairwell works travels further than anyone expects. Protection is our job rather than yours.

Most families stay throughout. The bathroom keeps working, the kitchen keeps working, and the noise is concentrated in the structural weeks rather than spread across the whole programme.

Questions we get asked

Will a hip to gable give me more head height?

No. The ridge stays exactly where it is, so the maximum height in the room does not change. What changes is how much of the floor has that height above it. If your loft measures under about 2.2 metres from ceiling joist to ridge, squaring the hip off will not solve that on its own and you are looking at a dormer as well, or a different project entirely.

Do I need planning permission for a hip to gable?

Frequently not, if it is within the volume allowance and the house is not in a conservation area, is not listed, is not a flat, has no Article 4 direction over it and had no estate condition removing the rights. Combining it with a rear dormer is what most often takes a scheme over the allowance. We check the position on your address before quoting and we tell you which route we think you are on.

Does my neighbour have to agree?

Not for planning purposes. They can comment on an application and the council will consider what they say, but a neighbour has no veto. Under the Party Wall etc. Act it is different: they have a right to notice, a right to dissent, and a right to appoint a surveyor at your cost. Neither of those is a reason to avoid talking to them early, which remains the most useful thing you can do.

Can I do the gable and add the dormer later?

You can, and occasionally there is a good reason to. Mostly it costs more overall, because you pay twice for scaffold, twice for the roof being opened and twice for living through it. It also means the volume already spent on the gable counts against the dormer later, which can push the second phase into an application when the pair together might have been designed differently.

What happens to my neighbour’s roof where the pair meets?

Nothing, in the sense that the shared roof structure over the party wall is not being altered by squaring off your outer hip. What does touch their property is the floor steel bearing into the party wall, which is section 2 work and needs notice, and any scaffold that has to stand on or oversail their side.

Is a timber framed gable acceptable?

Structurally yes, and it is genuinely lighter, which sometimes solves a foundation question. Visually it depends entirely on the street, because it will normally be finished in tile hanging or render rather than matching brick. On a road of plain brick gables it looks like what it is. Where the original houses already use tile hanging, it can be the better answer.

How much value does it add?

We are builders rather than valuers, so the honest answer is to ask a local agent. What we will say is that a hip to gable with a dormer usually produces a genuine double bedroom with an en suite, and that is a different proposition from a room described as a study. There is also a ceiling price for every street, and on a road of three bedroom houses a fourth bedroom has a limit to what it returns.