Annexe questions, answered straight.

Almost certainly, yes. A garden room or home office can often go up under permitted development, but an annexe that someone lives in — with its own bedroom, kitchen and bathroom — is self-contained living accommodation, and that needs full planning permission plus building control sign-off. We supply the drawings and the technical pack your application needs.

Building control does — either your local authority or an approved inspector — and deliberately not us. We supply the kit, the drawings and the technical pack; the inspections and the final certificate sit with an independent qualified body, exactly as they do on any house extension. The wall system is specified to be Building Regulations compliant, and your inspector is the one who confirms the finished building is.

Both are correct in the UK. "Annexe" is the more common British spelling for a building attached to or beside a house; "annex" is the American spelling and is also widely used here, particularly as a verb. They mean the same thing in this context, and we use them interchangeably.

Yes, and it is the most common reason people come to us. This is often called a granny annexe or granny flat. It still requires full planning permission as self-contained accommodation, and some councils attach conditions tying occupancy to a family member or to the main house. Your planning officer will tell you which conditions apply locally.

It can. A self-contained annexe may be banded separately for council tax. There is a statutory annexe discount in England for annexes used by a relative of the people living in the main house, and an exemption where the occupant is a dependent relative. Check the specifics with your local billing authority before you commit.

Ground screws are steel piles wound into the ground with a hydraulic drive head. They take load immediately, so there is no excavation, no muck away and no waiting for a slab to cure before you can start building. They also sit lightly on the site, which matters if there are tree roots, services or a garden you would rather not dig up.

Most gardens are straightforward. Clay soil with mature trees close by, made ground, or anything unusual underfoot means more assessment before the screws go in — it does not mean an automatic no. The plot is surveyed and the screw specification set for what is actually there before any work starts, which is the advantage of a foundation designed per site rather than poured to a standard detail.

ICF stands for insulated concrete formwork. Insulated blocks are dry-stacked to form the shape of the wall, reinforced with steel, and then filled with concrete in a single pour. What you end up with is a solid reinforced concrete wall with insulation permanently on both faces. Doors and windows are hung in a poured wall rather than fixed to a panel, which is why it reads and behaves like a small house rather than a garden building.

The build-up does the work. Insulation sits permanently on both faces of the wall with the concrete core between them, so the insulation is continuous and there is very little left to bridge it, and the floor and roof are insulated to match. In practice that means a small building that holds its temperature and costs little to heat. We are not publishing U-values or a predicted heat demand until the formal calculations for each size are complete — the same rule we apply to build times, for the same reason.

For a self-build kit, that is largely down to you, and we are not quoting a completed-build time of our own until we have real build data to quote — we would rather say that than invent a number. If Solvere manages the build for you, the target programme is 28 days, and that is a target we work to rather than an average we have measured. What we can say either way is where the time goes: there is no excavation and no slab cure before you start, and the wall system goes up dry and is poured once, so the wet trades are few and short. The fit-out moves at whatever pace you set.

Our self-build kits are £54,000 for 28 m², £72,000 for 35 m² and £90,000 for 45 m², all including VAT. That covers the ground screw foundation and steel ring beam, the floor, the full ICF wall system, windows and doors, the roof and weatherproofing, and internal partitions ready for your finish. If you would rather not build it, our sister company Solvere will manage the whole job — a 45 m² managed build is £129,995 including VAT, and the two smaller sizes are priced on application. Cladding, electrics, plumbing, heating, kitchen, bathroom and decoration are yours to specify, and drainage and utility connections are quoted separately once the site has been assessed.

We set out the site, drive the ground screws and level the steel ring beam — the engineering that is difficult to get right and expensive to get wrong. You take it from there: the block walls, the pour, the roof frame and deck, the membrane, and the windows and doors. Cladding, electrics, plumbing, heating, kitchen, bathroom and decoration are all specified by you.

Then you do not have to. Solvere, our sister company, takes the whole job — built and project managed start to finish. A 45 m² managed build is £129,995 including VAT and the two smaller sizes are priced on application, and the target programme is 28 days, which is a target we work to rather than an average we have measured. It costs more than the kit, and it is a real alternative rather than an upsell: if you already have a builder you trust, use them.

Yes, entirely. We do not supply or specify either, so there is no fixed allowance to spend and no factory range to choose from. Partitions arrive plasterboarded and ready for your own finish, and everything after that — kitchen, bathroom, cladding, decoration — is yours. Spend where you want to spend and save where you do not.

These are quoted separately, and deliberately so. What they cost depends on how far the annexe sits from the house, the fall across your garden and what you are connecting into, and a single headline figure would be wrong for most plots. Depending on the site it ranges from a straightforward gravity connection to a macerator pump, or a treatment plant where there is no main drain within reach. Which one applies to you comes out of the site assessment.

The ground screw foundation carries a 10-year warranty from the installer who drives it, and that is the part installed by us rather than by you. Above the foundation this is a self-build kit, so what cover the finished building carries depends on how it is built and who signs it off. If you need a structural warranty for a mortgage or a future sale, say so early and we will go through the options before you start.