A tension rod is the best thing to buy for a rental and the most frequently fitted wrong. It goes inside the window recess, presses against both sides, and holds a curtain with no screws anywhere. Most of the problems people have with them come from fitting the wrong type in the wrong place.

Tension rod against cafe pole

A cafe pole is a decorative pole that clamps between two windows, or a pole that sits in a socket on the sill. It has no tension mechanism at all and it will not hold a proper curtain. Buy one for a net curtain over a small window, not for anything heavier.

A tension rod has a spring inside, or a screw thread that expands the ends. That spring is what presses the rod against the walls of the recess, and it is what determines whether the rod holds. Check that the closed length is smaller than the recess before you buy, because this is the only measurement that matters and it is the one people skip.

Inside the recess, not across the glass

The rod goes inside the reveal, between the window frame and the outer wall, pressed against the sides. Fitted there, the curtains sit back in the recess and open flat against the wall, showing the full width of the glass.

Fitted across the front of the glass instead, the rod cuts the window in half, blocks the middle, and loses a good deal of light. It also makes the curtains look short, because the recess is no longer behind them.

Measure before you buy

Three measurements, in this order.

• The width of the recess, measured at the top, the middle and the bottom. Recesses are often not square and the narrowest point is the one that matters.
• The depth of the recess, from the front face of the window frame to the wall. Most rods need at least half an inch of clearance each side before they will seat properly.
• The closed length of the rod compared with the narrowest width above.

If the recess is too shallow for a spring rod, the fix is a smaller diameter rod, not force. Forcing a rod into a shallow recess tilts it, and a tilted rod leaks curtain weight through one end and slowly walks out of the recess.

Getting it level and high

Fit the rod six inches above the window frame, which usually means it sits above the top of the recess and onto the wall. A rod at that height cannot be a pure tension rod, because there is no recess up there to press against, so the practical version is a no-drill bracket clipped to the top of the window frame.

Either way, mount it as high as it will go. A tension rod fitted level with the window frame wastes the single advantage it has, which is that it makes curtains look longer without any floor space being used up.

The curtain height guide has the measurements in full. In short: measure the recess, fit inside it, push the rod high, and expect to change the curtains more often than the rod. Nothing about a tension rod touches the wall, so it comes down with the flatpack and takes nothing with it.