Guide
Under-eaves storage: how to plan a unit that actually fits a sloping ceiling
The space under a sloping roof is usually the last storage in a house to get used, because nothing standard fits it. A shelf unit built for a flat wall will not go in, and the awkward low corner tends to become a place things disappear into. Planning a unit for this space is not difficult, but it depends on a handful of measurements and two safety points that most guides skip. Here is what to check before you cut anything.
Measure the slope, do not assume it
Roof pitches are rarely the round number people expect, and a ceiling that was plastered or lined may not match the roof above it. Measure the one you have.
The simplest reliable method is rise over run. Hold a spirit level horizontally against the sloping surface, mark a run of exactly 50 cm along the level, then measure straight down from the far end of the level to the slope. That vertical drop is your rise. The two numbers together define the angle, and they are what a plan needs.
A cardboard template is worth the five minutes it takes: cut a piece of card to the corner you are filling, offer it up, and trim until it sits flush. It catches things a measurement misses, such as a ceiling that changes angle partway or a lining that bulges.
Do not take an angle from a protractor held against the slope by hand. The reading is easy to get wrong by several degrees, and on a two metre panel a few degrees is a few centimetres of gap.
How deep and how tall the unit can be
Depth is limited by the slope itself, not by preference. The deeper the unit, the further forward its front edge sits, and the front edge is where the ceiling is highest. Under eaves, useful depth is usually somewhere between 40 and 60 cm.
Kamba accepts any depth from 20 to 80 cm for an under-eaves unit, deeper than the 60 cm a normal shelving unit stops at, because a low unit under a pitch is often a plinth for bins and cases rather than a bookcase. Whether the boards sold where you live come that wide is a separate question, and the plan tells you when they do not. For comparison, a standard bookshelf is only 25 to 30 cm deep, so an under-eaves unit is generally deeper than a normal shelf and shallower than a wardrobe.
Height is set by where the sloping surface crosses the front of the unit. This is why an under-eaves unit is almost never a rectangle: the usable height at the back and at the front are different numbers, and the difference is what the slope gives you.
For shelf spacing, 25 to 30 cm suits most stored items, which sits inside the 20 to 30 cm our shelf reference gives for general shelving. That reference puts paperbacks at about 20 cm, hardbacks and larger books at about 28 to 30 cm, and display or baskets at 35 cm and up. Add 2.5 to 5 cm above whatever you plan to store so you can get it in and out.
The low corner is the part that goes wrong
The lowest part of the space is the hardest to use and the easiest to waste. A shelf there is reached by kneeling and looking sideways into a dark triangle, so it fills with things nobody sees again.
Three approaches work better than shelves:
- Drawers that pull out. You reach the contents from above rather than from the front, so the depth of the space stops mattering. Because they sit low, drawers can also be made deeper than shelves you would have to reach into.
- Doors on the front face rather than lids on the top. A lid needs headroom to open, and headroom is the one thing this corner does not have.
- Push-to-open catches or slim handles. A conventional handle at eaves height is something you knock your head on while reaching for it.
Nothing in the room is square
Floors slope, walls lean, and ceilings wave. A unit built perfectly square will still look wrong if it is fitted to surfaces that are not.
Work from a level reference line rather than from the floor. Draw a horizontal pencil line on the wall with a spirit level, and set the unit out from that line. Fronts and shelves that line up with each other read as correct even in a room that is not, whereas fronts aligned to a sloping floor look crooked.
Where a panel meets the ceiling, scribe it rather than measuring it. Scribing traces the actual surface onto the panel so the cut follows every bump.
Before you cut into a knee wall or drill into a sloping ceiling, drill a small inspection hole first and look. Cables and pipes are routinely run in exactly these voids. If the knee wall is carrying the rafters, cutting an opening in it is a structural job that needs a header and posts, not a DIY afternoon.
Ventilation, the point most guides miss
This one matters more than it sounds. The pocket behind an under-eaves unit sits against a cold roof surface. Warm moist room air reaching a cold underside is how condensation and then mould start, and a cupboard front that seals the pocket makes it worse rather than better.
Keep the roof ventilation path clear. Most pitched roofs rely on air moving from the eaves up to the ridge, and that path needs roughly 50 mm of clear space above the insulation at the eaves. Do not push insulation, boards, or stored boxes into that gap.
If the space behind the unit is outside the insulated envelope, insulate and air seal the back of the knee wall rather than relying on the unit to do it. Do not compress insulation to make room, because compressed insulation loses most of its value.
What the floor can carry
Attic and loft floor joists are often sized for a ceiling and insulation below, not for storage above, and you cannot see yours. So Kamba does not rate your floor: it weighs the unit. A free-standing under-eaves unit whose total loaded mass (the unit itself plus every shelf at its rated load) passes 150 kg asks you to confirm the floor can take it before it will produce a plan. A built-in or hybrid unit is not asked, because its load goes into the slope and the wall rather than into the joists.
Two practical consequences. Spread the load across several joists rather than concentrating it, which a unit with a continuous base does naturally and a unit on four feet does not. And keep the heavy items low and near the supported edge rather than out in the middle of a span.
If you are storing something genuinely heavy, or the loft was never converted, have the floor checked before you load it. This is not a case where being cautious costs you anything.
Anchoring, and why a slope changes it
Anchor a freestanding unit. Kamba treats anchoring as required from 120 cm tall, and at any height in a child’s room; below that it still ships the anti-tip hardware and tells you to fit it. So no height takes anchoring off the table: the threshold is where the plan stops recommending it and starts requiring it, and nothing else about the job changes.
Fix into something solid. A screw into a timber stud or rafter holds; a screw into plasterboard alone does not, whatever the packet claims. Studs are usually 40 cm apart, sometimes 60, and loft joists and rafters are commonly 60 cm apart.
The point specific to slopes: when you fix a unit to a sloping surface, gravity no longer pulls it down along the face, it pulls it away from the face. The fixing works in withdrawal, which is the weakest direction for a screw. Fix into the vertical knee wall where you can, use longer framing screws into rafters where you cannot, and support the low front edge from below rather than hanging everything from the slope.
See when wall anchoring is required
The trick that halves the offcuts
An under-eaves unit has two sloping side panels, and they are mirror images of each other. Set out on a single board, the offcut from the first side is the second side. Cutting them as a pair rather than one at a time is the single biggest saving on a job like this.
The related idea is to build square boxes inside a sloping surround rather than making every box follow the slope. Square boxes are stronger, drawers run better in them, and only the outer skin has to deal with the angle.
In Kamba
Kamba works from the two numbers in the first section. Give it the rise and run you measured, the space you are filling, and the material you plan to buy, and the plan works out which shelves actually fit under the slope, cuts the side panels to the angle, and drops the levels that would end up too low to use. The cut list gives the two edge lengths of every angled piece, so you mark and cut from real numbers rather than transferring an angle by eye.
See standard shelf dimensions and safe spans
Have a question about building with Kamba? Read the FAQ