How the trundle works
A trundle is a second, lower bed that stores under the murphy bed and pulls out when you need it. On a wall bed, the trundle lives in the dead space beneath the raised cabinet, that 10-to-12-inch gap between the cabinet bottom and the floor. Pull it out on casters, and you've got a twin sleeping spot next to the main bed.
The trundle is dead simple: a shallow frame, four locking casters, and a thin mattress. No mechanism, no pivot, no math. It's the easiest part of the whole project, which is why it's such good value: one extra sleeper for a couple hundred dollars.
Who it's actually for
Kids' sleepovers, grandkids, and vacation rentals where the headcount varies. A queen murphy plus a twin trundle sleeps three in the footprint of one bed. That's the whole pitch.
It's not for nightly use by adults. Trundle mattresses are thin by necessity, and crawling into a bed 10 inches off the floor gets old. This is a sometimes bed, and it's perfect at that job.
Dimensions and footprint
The trundle frame runs about 38 by 72 inches with a 10-inch profile, on 3-inch casters. It needs the floor under the cabinet completely clear: no baseboard heaters, no floor vents, no thick carpet that swallows the casters.
The trundle mattress should be 6 to 8 inches thick, max. Thicker and it won't clear the cabinet bottom. When pulled out, the trundle needs 40 inches of floor beside the open murphy bed. Plan the room layout with both deployed: measure twice.
DIY vs buying: the real cost
Retail murphy-plus-trundle setups run $1,800 to $4,500. The trundle itself is a small fraction of that; you're mostly paying for the bed.
DIY: build the standard bed ($600 to $1,000), then the trundle is a weekend side project: $80 to $150 in plywood and lumber, $40 to $80 for four locking casters rated for 150 pounds each, and $100 to $200 for a 6-inch twin mattress. Total addition: $250 to $450. Our $100 plans include the trundle as an optional add-on with the clearance dimensions worked out.
What to watch out for
- Lock the casters when the trundle is out. An unlocked trundle drifts, and a drifting bed at 2 a.m. is a rude awakening.
- Keep the under-cabinet floor clear permanently. If that space becomes shoe storage, the trundle stops being usable.
- Carpet vs. casters: low-pile works, thick pile doesn't. If you've got plush carpet, use larger 4-inch casters or rethink the trundle.
- Don't exceed 8 inches of mattress. Measure the actual clearance under your cabinet (not the plan dimension, the real one) before buying the mattress.
- Dust it. The under-cabinet zone collects everything. Pull the trundle quarterly and vacuum.
Frequently asked questions
Can an adult sleep on the trundle?
For a night or two, yes, a 6-to-8-inch mattress on a solid frame supports an adult fine. For a week, they'll want the main bed. It's a comfort question, not a strength question.
Where does the trundle go when not in use?
Under the raised murphy bed cabinet, in the gap between the cabinet bottom and the floor. Out of sight, zero footprint.
Does the trundle work with the bed open or closed?
Either, but it's designed to pull out when the murphy bed is open. That's when you need the extra sleeper. It stores under the closed cabinet.
Can I add a trundle to my existing murphy bed?
If you've got 10-plus inches of clearance under the cabinet and clear floor, yes. Build the trundle frame to fit your actual clearance. Measure, don't assume.