What does the garden room designer do?

Peel the walls back a layer at a time — cladding, battens, breather membrane, sheathing, insulation, vapour control layer, and the frame underneath — and you're looking at what you'll actually build. Every layer is drawn where it goes, at the thickness it is.

That’s the difference between this and a garden room you can spin round on a company’s website. Nothing here is drawn by hand or filled in from a table of typical values, and nothing is a picture standing in for a decision somebody else will make later. If you can see it, it’s on the list, and you can point at the member and read its line.

You’re going to build it yourself. You can see how a garden room goes together before you commit to anything — where the studs land, what carries the door, how thick the wall ends up — and then take a cut list to a supplier and order once. To see each stage done, there are build videos, stage by stage.

You’re having it built. The output is a cut list and, on Pro, a dimensioned drawing, so any carpenter can price from it without redrawing your building first. You turn up to the conversation knowing what you’re asking for.

You’re the expert. You don’t need showing how a garden room goes together. What you get is the take-off done the moment the design is, a link that agrees the garden room with a client, and an order you can send without redrawing anything.

Every stud, plate, noggin, joist, header, cripple, sill, batten, board and sheet, as a real member at a real size. Joist depth comes from the span and the centres together, read off a published span table.

The framing around each opening: king studs, jack studs, a doubled header scaled to the span it carries, cripples, and a sill for a window. Corners are California corners, so there is somewhere for the insulation to go.

The roof fall, which is 1:60 to the back. The roof is flat, and flat isn’t level — but the joists, the plates and every stud stay level, so the garden room has one head height. It tells you what that height is once the floor and the ceiling are finished.

Where two things you have both chosen can’t both be true, it says so against the control that caused it and changes nothing else. It won’t quietly deepen a joist or lower a door head to make a problem go away.

For a worked example rather than a description, see what timber a garden room takes — every piece in a 4 × 3 m and a 5 × 3 m garden room, with its section and how many.

You choose permitted development in England or a full application. Under permitted development the overall height is capped at 2500 mm within 2 m of a boundary, and 3000 mm beyond it. Tell it how far the nearest boundary is and it measures the highest point on the building — the outer edge of the front overhang, which is what the cap is measured to — against the cap that applies.

Going over is reported as an error, not as advice, because the planning route is something you chose. Switch to a full application and the cap and the error both disappear. The building was never unbuildable; it stopped satisfying a constraint you set.

Size. Width, depth and wall height, from 1.5 m to 12 m on a side.

Floor. Joist spacing and depth, cassette width, whether interior rims are doubled, and what stands underneath: ground screw, concrete pad and concrete block. You set how far apart the supports stand in each direction.

Walls. Stud spacing, and the cladding wall by wall: timber horizontal, timber vertical and metal sheet, each with its own board size, colour and counter-battens. A wall against a fence can be cheaper than the wall you look at.

Doors and windows. Put them where you want on any wall, at the size and sill height you want. Windows: fixed, casement, double casement and top opener. Doors: single door, french doors and bifold doors. One system for the building, aluminium or uPVC, with a colour, and heritage bars on aluminium.

Roof. Warm or cold construction, insulation from 25 to 150 mm, an EPDM, GRP, felt or TPO covering, the fall made by raked walls or by firrings, an OSB or tongue-and-groove deck, joist spacing, and the overhang on each side. Fascia in uPVC or timber, soffit in composite or timber.

Loads. A normal or a high roof load, and whether free weights, cardio machines or machinery go in the garden room. This changes the joists, not the picture.

Your supplier. Stock lengths and sheet sizes per material, and one spare figure for the whole build. Change what your supplier stocks and the order re-folds without regenerating the building.

The sun. Give it a postcode and which way the plan faces, and it puts the sun and the shadows where they will be on a given day.

Designing a garden room costs nothing and needs no account. Signing in opens what you take to a supplier. Pro is for building it yourself off the drawing; Studio is for building it for someone else.

It doesn’t give you a price. Oakward Studio holds no supplier and no price for anything. What it produces is the quantified list and the email that gets that list priced, which is one step short of a cost and the honest place to stop.

Rectangular plans only. No L-shapes, no bays, no internal walls. The shorter side may not exceed 5 m, because no joist on the span tables spans a building that is long in both directions — an 8 m × 3 m garden room is fine, a 6 m × 6 m one isn’t. The limit is why the numbers hold.

Flat roofs only, and one way of building: timber frame, studs at centres, a suspended floor, a warm or cold flat roof. It isn’t a configurator over framing styles. Every extra convention multiplies the junctions somebody has to detail.

The planning check is England only. The permitted development rules differ in Scotland, Wales and Northern Ireland, and it doesn’t pretend to know them.

No sliding doors. A slider is panels that overlap, which is a different geometry from panels that fold, and adding it because it sounds similar is how the wrong thing gets built.

It isn’t an engineer. The sections come from published span tables and trade practice. For anything that needs sign-off, take the drawing to somebody who can give it.