Bunk bed mattress depth and guard rails
A thick mattress lifts the child up the guard rail. The frame is marked with a maximum mattress thickness. A trade summary of BS EN 747-1:2024 says the mattress top should stay at least 160 mm below the top of the barrier.
The rule to follow is the mark
SATRA says every such bed must be permanently marked with the maximum thickness of the mattress to be used. Flair’s summary of BS EN 747-1:2024 says the top of the barrier is at least 260 mm above the bed base, and the top of the mattress at least 160 mm below the top of the barrier. Flair also says the maximum thickness is permanently marked. If those two ideas ever seem to disagree on a particular frame, the mark and the instructions win.
The Julian Bowen Jupiter listing states both ideas in product language: the top of the mattress at least 16 cm below the lowest part of the guardrail, and a maximum mattress height of 18 cm. That 18 cm is that listing’s figure, not a universal cap.
A 15 cm mattress is not automatically right
The OYT listing is a 90 × 190 × 15 cm foam single. Fifteen centimetres is inside an 18 cm mark such as the Jupiter’s, and it is over the mark if your frame says 12 cm or 13 cm. Which? notes that plenty of ordinary mattresses are 20 cm or deeper. Those are the ones that quietly disable a guard rail.
Do not “fix” a short rail by screwing on a toddler bed rail. The Safety 1st 90 cm bed rail listing is sold for the move from cot to bed, for ages 18 months to 5 years. That is the wrong product and the wrong age for a top bunk. The barrier has to be the one the bunk was built with.
Published examples
Julian Bowen Jupiter midsleeper
A mid sleeper with a pull-out desk, shelves and drawers, lower than a full bunk. A room that needs a desk underneath and has less ceiling height than a standard bunk.
- The listing’s dimensions bullet says H 138 × W 196 × D 135 cm, net weight 126.5 kg, mattress 90 × 190 cm.
- The same listing says the top of the mattress must be at least 16 cm below the lowest part of the guardrail, and that the maximum mattress height is 18 cm.
- A product-dimensions row on the listing shows 53.1 × 77.2 × 54.3 cm, which is not a bed. Ignore that row and use the maker’s sheet.
We haven’t tested this product. Dimensions and limits are as the maker’s listing states them (checked 13 November 2026).
OYT single mattress, 90 × 190 × 15 cm
A rolled foam single mattress listed at 15 cm thick. A top bunk whose marked maximum mattress thickness is at least 15 cm. If the mark is lower, do not use it on top.
- The listing’s size is 90 × 190 × 15 cm (3 ft × 6 ft 3 in).
- The construction line says 2 cm memory foam over 13 cm of support foam.
- Depth on a listing is not the maximum your frame allows. The mark on the bed wins.
We haven’t tested this product. Dimensions and limits are as the maker’s listing states them (checked 13 November 2026).
Questions people ask
Can the bottom bunk take a deeper mattress?
Often yes, because it is not behind the upper barrier. Use the mark for each sleeping surface. Do not swap them later.
What if the bed has no thickness mark?
Do not guess. SATRA says the maximum thickness is part of the permanent marking. Ask the seller for the marked figure, or do not use it as an upper bed.
Sources
Opened 13 November 2026. The maker’s sheet and the mark on the bed take precedence.