Every demountable flood barrier quote looks similar until you read the spec sheet — and most buyers have never been shown how. This guide walks through the four subsystems of a plank barrier, what each number means, and the questions that separate a serious supplier from a photo with a price. We supply these systems ourselves; the fastest way to check whether we pass our own test is our spec sheet.
Question zero: is the opening actually your problem?
Before any spec sheet matters, answer this: is the door or garage really where the water comes in? Water also rises through slabs, soils and drains, tracks through porous masonry, and falls as rain behind whatever you seal. A perfectly specified barrier on the wrong failure point protects nothing.
And one structural honesty most suppliers skip: in deep, sustained flooding, a fully sealed building starts to behave like a boat — groundwater pushes up on the slab, and slabs aren't designed to be hull bottoms. That's why serious protection above roughly waist depth is an engineering question, not a shopping question. Demountable barriers earn their keep in the metre-and-below range on sound openings — a boundary worth stating before any spec sheet, including ours.
1. Planks: the profile is the product
The extruded aluminum plank is where the engineering lives.
- Profile height — how much protection each plank adds. Common classes run 150–200 mm. Fewer, taller planks deploy faster; more, shorter planks pack tighter.
- Alloy and temper — the category standard is 6063-T6: extrudes cleanly, resists corrosion, holds strength. If a spec sheet says just "aluminum", ask. If the answer doesn't come back with a temper designation, walk.
- Wall thickness — drives stiffness and dent resistance. Ask for the number in millimetres, not "heavy duty".
- Weight per metre — matters twice: deployment (who lifts it) and freight (what shipping costs). A spec sheet without kg/m makes container math impossible — that's usually not an accident.
Ask any supplier: profile height, alloy + temper, wall thickness, kg/m. Four numbers. A factory has them on file; a reseller has to go ask.
2. Seals: where barriers actually fail
Water doesn't break planks; it finds gaps. Sealing is compression-based:
- Horizontal joints — EPDM rubber between planks, compressed by the stack's own weight plus top clamps.
- Base seal — the bottom plank against the ground; the most stressed seal in the system and the reason surface condition surveys matter.
- Vertical ends — plank ends against post channels; compression here comes from the channel design.
What to check: seal material (EPDM is the standard for weathering; cheaper rubbers age fast), whether seals are replaceable (they're consumables over a decade), and whether the supplier sells seals separately. A system whose seals can't be reordered has a built-in expiry date.
3. Posts and fixings: three ways to hold a wall
- Span rule of thumb: single spans run to roughly 3 m in most systems; beyond that, intermediate posts split the load. Suppliers should quote post count from your opening width — if a quote for a 6 m door shows no mid-post, ask why.
- Fixings are site-specific: masonry, concrete, steel and timber each take different anchors. A serious supplier asks what your mounting surface is before quoting. (Ours does — include it in the optional message on our RFQ form.)
4. Height vs span: reading the limits
Water load grows with the square of depth — a 1.2 m barrier carries roughly four times the load of a 0.6 m one, not two. That's why:
- Taller stacks need stiffer profiles, tighter clamp systems, and sometimes narrower spans.
- A supplier quoting the same span limit at every height hasn't done the math — or isn't showing it.
- Deflection data (how much the span bows under load) is the honest way to publish limits. Few suppliers do; ask for it and watch what comes back.
The 10-question supplier checklist
- Plank profile height, alloy, temper, wall thickness, kg/m?
- Seal material — and are replacement seals orderable separately?
- Which post types, what's the span limit *at my protection height* — and what hardware stays visible off-season?
- What fixings for my mounting surface?
- Deflection or test data at height?
- Custom-cut to my opening list, or standard lengths only?
- What exactly is in the box per opening (planks, seals, clamps, labels)?
- Spare parts availability in 3 years?
- Warranty — duration and what voids it?
- Lead time for cut-to-order vs stock?
We answer all ten on one page: Aluminum flood gates — specifications. Or skip ahead — send your opening schedule and get real numbers instead of a brochure: we reply within 12 hours.