Inside a Copenhagen home

Astrid and Emil moved in during the first cold week of March with a sofa that would not arrive for another month and a single rule they had agreed on in the van: nothing goes up higher than 145 centimetres. Astrid had measured the eye-line of every gallery they had ever liked and it was always the same. "Galleries know something we keep forgetting," she says. "You look at art standing up, but you live with it sitting down."

The flat faces north, which is a problem for plants and a gift for paper. The light arrives flat and even and stays that way until four in the afternoon; nothing fades and nothing glares. The walls were painted the colour of paper left in a drawer, a warm off-white that the previous tenants chose and the new ones decided to keep. "We kept saying we would repaint," Emil says. "Then we hung the first thing and the wall looked finished."

The living room pair came first and took the longest. They had wanted one large piece and kept finding two medium ones. "We leaned them on the bench for a week," Astrid says, "and every morning I would move them six centimetres closer or further apart." The gap that survived is six centimetres, which is what the tape measure said when she stopped moving them.

Both works are by Ida Brandt, whose studio is twenty minutes away by bicycle and who, when told about the 145 rule, said it was the only rule she had ever agreed with. The ochre plane and the green line went up first. The second sheet — a window, or a morning, depending on who is describing it — arrived a fortnight later and made the first one calmer. "They share a palette and disagree about everything else," Emil says, which is a sentence he has clearly said before.

The bedroom broke the rule by ten centimetres, and Astrid would like it noted that this was Emil's idea. The bed has a tall headboard and the one Saga Lindmark print — a metre wide, all sky and sand — needed twenty centimetres of wall above it to breathe. It went up at 155. "It looks right," Emil says. "That's the whole argument." Oak, because the room is the only warm-grey wall in the flat and white looked clinical against it.

It is the room they spend least time looking at and most time in, which is why the work is the quietest in the flat. "You want a bedroom to have nothing to say at eleven at night," Astrid says. "This says almost nothing, beautifully."

The hallway is three metres of wall and no furniture, which is the hardest kind. They tried one large piece alone and it looked like a poster in a corridor. The answer was four: a large blue sheet in oak with a mount, two small expressive ones stacked in walnut, and a green one to finish — four sizes, one centre line, so that the frames do the work and the group reads as a group. "You walk past them thirty times a day," Emil says. "They have to be worth passing."

The rule holds here without argument: 145 through the centre of the group, the small pair stacked either side of it, the whole thing centred on the wall rather than on the door. Astrid has a pencil mark on the skirting board that she refuses to paint over. It is the height of the tape measure's hook.

Six walls, four of them shown here, and two more they will not let anyone photograph yet. "The kitchen is finished," Astrid says. "The study is a floor covered in prints, which is also a kind of finished."