UKAL aluminium substructure

Why the substructure decides the lifespan

On a deck, everyone looks at the boards. What fails, however, is almost always what lies beneath. A board with a decades-long warranty on spruce battens is a planning error — after eight to twelve years the floor starts to flex, and the whole surface has to come up even though the boards are still perfect.

The problem is structural, not a matter of workmanship. The substructure sits close to the ground, often in splash water, frequently with no way to dry downwards. That makes it the most heavily loaded part of the whole build — and the only one you cannot reach later without dismantling everything.

A deck substructure matters as much as the foundation of a house. Where it is not built properly, problems appear during use that become dangerous and expensive.

The three profiles

UKAL consists of aluminium profiles in three heights, all 45 mm wide and 4 m long. The height follows the build-up, not the surface — all three carry timber and composite boards as well as stone and ceramic slabs.

All three can be used either way up — one face with a screw channel, one smooth. The profiles couple to each other, and the system angles create T-connections for fixed bracing. Profiles are also available in black on request.

The screw channel — the practical difference

A continuous screw channel runs through the profile. Almost any common clip for grooved boards can be fixed to it with an M4 machine screw — without pre-drilling. That is why UKAL does not tie you to one decking system: whatever clips are already in the workshop can be reused.

The 45 mm width also has a practical background: on that bearing surface, HPL boards can be bonded securely.

No system lock-in

UKAL needs no proprietary components such as system pedestals on which the rails must be seated. The frame can be built freely and laid on any commercially available or already existing point foundations. Bracing can be set at any angle and spacing — where you need it, not where the system provides for it.

The adjustable pedestals

The second half of the system is the adjustable pedestal. They carry the profiles, compensate for level differences and create the air space without which no deck stays dry in the long term.

The continuous base plate

This is where pedestals differ. Many makes have a hole in the base or smaller plates. UKAL pedestals have a continuous base of 200 mm diameter and over 300 cm² of bearing area.

In practice that means the pedestal can be placed without an additional pad or base plate directly on consolidated natural ground, grass, gravel, compacted subsoil or on any roofing membrane. Curved soft edges on the base additionally prevent the pedestal from cutting into membranes under load.

The load capacity is not an estimate: in compression tests at the Technical University of Diepholz the pedestal reached between 1 and 1.2 tonnes across eight trials.

Adapters and accessories

• Adapters 50 and 100 mm — to extend or shorten the pedestals individually
• Fall compensation disc — evens out an existing fall or deliberately sets one up to 7 %
• Clever Click adapter — fixes aluminium systems to the pedestals without screws
• Levelling pad 200 × 200 × 5 mm with aluminium facing and integrated slip and tread protection, evening out irregularities such as seams in roofing membranes
• Acoustic pad “Clever Sound” 200 × 200 × 15 mm — impact sound reduction up to 35 dB to DIN ISO 10140
• Slab holder — brings ballast slabs into the system, for instance to secure against uplift on roof terraces; the same holder serves as a ground anchor where the substructure is to be fixed down
• Joint seals in TPE with a woven thread, for timber and composite boards with a groove width of 5 to 7 mm, in dark brown, light brown, light grey and black
• Rubber granulate pads, also aluminium faced — as bedding, levelling and protection; rectangular so that water drains in all directions with point-laid surfaces

Timber protection strip

If the substructure is built in timber after all, it should at least be capped. The flexible PVC protection strip comes off the roll, is 1.25 mm thick and can be cut to length with scissors. Integrated hinges allow it to be folded by hand to the joist width; side lips lead water off the top face down the sides.

Available in 85 mm width for joists from 30 to 50 mm and 115 mm for joists from 50 to 80 mm. The material is lead free and free of plasticisers, UV stable, resistant to frost and moisture, and can be screwed, nailed, bonded or stapled. The effect: moisture content in the timber substructure drops permanently.

Construction profiles for bespoke work

Alongside the substructure profiles there are the UKAL construction profiles with a 45 × 45 mm section. With prefabricated system connectors — angles, couplings and hinges — they build structures that are not available ready-made: stairs, ramps, outdoor furniture, pool surrounds, raised frames and garden substructures such as raised beds.

The hinged connectors are designed specifically for special versions — among them curved boards. Sweeping deck edges can therefore be reproduced cleanly in the substructure as well.

Advantages

• Rot-proof. Aluminium resists every form of moisture — no chance for fungi or mould, no use-class debate.
• Dimensionally stable and torsion free. No swelling, no shrinking, therefore no retightening of screws and no shifting joints in the deck surface.
• Priced at the level of quality timber and composite joists, with all the advantages of aluminium.
• Simple installation without training. Connectors are only screwed, which shortens installation time.
• Few system parts: profiles, bracing, angles, couplings, slab holders, pedestals. Nothing else is needed.
• Light. On roof terraces with weight restrictions that is often the condition, not a side effect.
• Excellent drainage and good under-ventilation from raising the deck — hence no frost damage.
• High walking comfort with reduced slip and impact sound.
• Made in Germany.

Limits and points to watch

• Thermal expansion. Aluminium expands more than timber. Long continuous runs need expansion joints designed in.
• Galvanic corrosion. Aluminium does not sit well with every metal. Fasteners and bearings must suit it.
• Uplift loads on roof terraces are a subject of their own. The slab holder is there for that — but it must be designed, not improvised.
• The number of pedestals is not a fixed figure. Four to five per square metre is a rule of thumb; joist spacing, joist capacity and site conditions govern. Load-bearing build-ups need proper structural design.
• Appearance. Where the substructure remains visible from the side, plan a fascia — or choose the black finish from the outset.
• Data status. The technical figures come from the manufacturer's brochure in its 2019 edition. We will confirm current values before tender.

UKAL and Trex

Both systems come from the same source and are matched to each other. That is why we offer them together rather than separately: a Trex board with up to 50 years of warranty on timber battens would be half a solution.

The combination makes particular sense wherever nobody can get back in later — ground-level builds with no ventilation below, roof terraces above occupied rooms, pool surrounds in permanent splash water. Those are precisely the situations where a timber substructure fails first.

Tell us what you have in mind — area, ground conditions, level difference, fall, decking. We will cost out profiles, pedestals, accessories and decking as one package.