Before you start: what almost nobody checks
Most problems with a double trundle bed don’t show up when you assemble it, but on the third or fourth use, when the mechanism starts to rub. Before taking the parts out of the box, it’s worth checking three things: the thickness of the mattress you’re going to use (trundle beds usually accept between 18 and 22 cm; above 22 cm the upper bed won’t close), the clearance under the bed base, and the type of wall anchoring if the manufacturer requires it.
A common mistake: assembling the trundle on newly installed floating laminate flooring and then discovering that the wheels mark the joint. According to documentation from hardware manufacturers, nylon wheels leave the least mark; soft rubber ones deform under weight and drag dirt.
Step 1: prepare the area and sort the hardware
Spread out a blanket and separate the hardware into bags. In double trundle beds it’s common to find screws of two nearly identical lengths (for example, 16 and 18 mm). Swapping them weakens the headboard joint and causes creaking. Count the pieces before you start: if a locking nut is missing, don’t improvise with a regular one.
You’ll need a Phillips screwdriver, an Allen key of the indicated size (usually 4 or 5 mm), a rubber mallet and, if the model allows it, a drill for wall fixing.
Step 2: assemble the lower frame and the pull-out system
Here’s the key to the setup. The trundle frame goes first, without the bed base. Place the runners or wheels according to the diagram: on models with wheels, two are fixed and two have brakes. The braked ones should be on the headboard side, not the foot, so the bed doesn’t slide when you sit down.
If the system uses metal runners, lubricate lightly with silicone grease (never cooking oil, which attracts dust and becomes sticky). This detail extends the life of the mechanism and prevents the typical squeak of the second year.
Step 3: join upper and lower and adjust clearances
Screw the upper frame to the lower one only when both are square. Check the diagonal with a tape measure: if the two diagonals don’t match, the structure will end up twisted and the trundle bed won’t slide in straight. Tighten the screws to 70 % first and finish once everything is aligned.
A real case: in trundle beds with beech slat bases, the slats must be placed with the curve facing up. Placing them the other way makes the mattress sag in the middle within a few weeks, and it’s not a warranty defect.
Step 4: mattresses, stops and use test
Use a 90×190 or 135×190 mattress depending on the model (check the spec sheet; many double trundle beds use two 90 mattresses joined together). Leave a clearance of 1-2 cm on each side so the trundle slides in and out without rubbing.
Install the safety stops if they’re included and try pulling the bed out and pushing it in five times in a row. If you feel resistance in the last third, check that the rear wheels aren’t hitting the skirting board. In rooms with skirting boards thicker than 8 mm, some models need a spacer that isn’t always included in the box.
What doesn’t work and when not to choose this system
A double trundle bed isn’t suitable if you need two adults to sleep on the extra bed every night: the lower mattress is usually thinner and the mechanism isn’t designed for intensive daily use. It also doesn’t perform well in rooms with less than 2.60 m of free length, because pulling it out blocks the passage.
I can’t guarantee that a specific model will fit your space without measuring; commercial spec sheets sometimes round figures. Always measure the actual gap with the extra bed pulled out, not just closed.
Minimal maintenance so it lasts
Re-tighten screws every six months, clean the runners with a dry cloth and check the wheels. According to furniture maintenance guides, relative humidity above 65 % accelerates swelling of the board, so avoid placing the bed against a damp wall.