Summary

This guide picks up where the comparison article spc vs lvt flooring comparison leaves off. That article covers why a customer or specifier might choose SPC over standard LVT — subfloor tolerance, dimensional stability, water resistance, cost. This one assumes SPC has already been chosen and is written for the fitter standing in the room with boxes of planks, asking "what do I actually need to check and do to get this right first time." SPC has become one of the most commonly specified resilient floor coverings in UK domestic and light commercial refurbishment over the last several years, largely because its rigid core forgives subfloor imperfections that would telegraph straight through a thinner, more flexible LVT product — but "more forgiving" is not the same as "no prep required," and most SPC callbacks trace back to skipped subfloor prep, insufficient expansion gaps, or underlay mismatched to the installation type.

The core of an SPC plank is a dense composite of natural limestone powder and PVC/stabiliser compound, extruded into a rigid board typically 4–7mm thick, topped with a printed decorative layer, a clear wear layer (commonly rated in the 0.3mm–0.7mm range depending on product grade), and often a factory-applied underlay or acoustic backing bonded to the underside. Unlike flexible LVT, which needs a near-perfectly flat, smooth substrate because any dip or ridge telegraphs through the thin, pliable material, SPC's rigid core bridges minor subfloor irregularities in a way that reduces (but does not eliminate) the risk of visible imperfections and click-joint stress. That rigidity is also why SPC almost always goes down as a floating floor using a click-lock (drop-lock or angle-tap) mechanical joint rather than being glued — the planks lock to each other, not to the subfloor, which is what allows the floor to expand and contract as one connected sheet with the thermal/humidity movement of the room.

Key Facts

Quick Reference Table

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Check/Requirement Typical Figure Notes
Subfloor flatness tolerance ~3mm over 2m straightedge Rigid core more forgiving than LVT but not unlimited; confirm against product TDS
Perimeter expansion gap 8–10mm minimum Larger for bigger continuous areas
Max continuous run before transition strip ~10–15m Manufacturer-specific — confirm before laying large open-plan areas
Core thickness 4–7mm typical Excludes wear layer and integrated underlay
Wear layer 0.3–0.7mm typical Higher for commercial-grade/high-traffic products
Max UFH surface temperature ~27°C Manufacturer-specific — exceeding risks joint/core distortion
Acclimatisation period 24–48 hours typical Flat, unopened boxes, room temperature
Subfloor moisture testing Per BS 8203 guidance Even though SPC itself is largely water-resistant
Adhesive required? Generally no (floating) Some commercial/warranty cases specify full-spread
Underlay Integrated (most products) or separate acoustic Check before adding a second layer

Detailed Guidance

Subfloor preparation and tolerance checking

Before ordering material, check the subfloor against the manufacturer's stated flatness tolerance using a straightedge across the room in multiple directions, not just a single check — SPC's rigid core bridges small local dips and high spots better than flexible LVT, but a floor with a genuine slope, a ridge at a screed pour joint, or a significant low spot will still cause click-joint stress, visible movement underfoot, or in extreme cases joint separation over time. Where deviations exceed the manufacturer's tolerance, a self-levelling compound is the standard fix on concrete/screed subfloors; on timber subfloors, sanding high spots and packing or overlaying low areas with ply is the equivalent approach. Skipping this step because "SPC doesn't need it" is one of the most common causes of SPC callbacks — the rigidity reduces the problem, it doesn't remove the need for a reasonably flat, sound, clean, dry substrate.

Moisture testing before laying

Even though the finished SPC plank is largely impervious to water at the surface, moisture trapped beneath a floating floor on a concrete or screed subfloor is still a problem — it can degrade underlay, encourage mould growth in the void, and cause issues if the floor is later lifted or if moisture migrates to adjoining materials like skirting or door frames. New screeds in particular need to be tested for residual moisture content before covering, using a calcium carbide (Speedy) moisture meter test or in-situ relative humidity probes, broadly consistent with the guidance in BS 8203 for resilient floor coverings — don't rely on a surface moisture meter alone or on "it feels dry," and don't assume SPC's water resistance means moisture testing can be skipped.

Click-lock installation method

SPC planks use a mechanical locking joint — either a drop-lock system (plank lowered at an angle and pressed down to engage the joint) or an angle-tap/fold-down system depending on the manufacturer — installed working from a squared, chalk-lined starting wall with spacers maintaining the perimeter expansion gap throughout. Rows should be staggered (commonly a minimum stagger such as 300mm between end joints in adjacent rows, though this varies by plank length — check the specific product guidance) to distribute joint stress and for visual appearance. Because the floor is floating and not fixed to the subfloor, it must be free to move as a connected sheet — nothing should be screwed, nailed or glued through the SPC into the subfloor anywhere in the field of the floor, including under kitchen units or fitted furniture footprints unless the manufacturer specifically permits a glue-down fix in that scenario.

Expansion gaps and transition points

Every floating floor needs room to expand and contract with temperature and humidity changes, and SPC is no exception despite its dimensional stability being generally better than standard LVT. A perimeter gap — commonly 8–10mm but always checked against the specific manufacturer's installation guide — must run around the entire room including at door frames (undercut rather than butted tight), pipework penetrations, and any fixed vertical surface. This gap is then covered by skirting (lifted and refitted, not fixed through the floor) or by scotia/quadrant beading fixed to the skirting or wall, never to the floor. Where a continuous open-plan area exceeds the manufacturer's stated maximum run length or width, a expansion/transition profile must break the area into separate floating sections — skipping this on a large open-plan kitchen-diner is a common cause of "buckling" callbacks months after installation, particularly where the room gets significant seasonal temperature swings (e.g. large glazed areas, conservatories).

Underlay selection — integrated vs separate

Many SPC products now ship with an integrated underlay or acoustic backing pre-bonded to the underside of the plank at manufacture — where this is the case, adding a further separate underlay is usually unnecessary, can create an unstable "double cushion" effect that stresses the click joints, and may void the product warranty. For SPC products without an integrated backing, a separate underlay compatible with rigid-core floating floors should be selected based on the acoustic and subfloor performance required for the job — see acoustic underlay selection for underlay selection criteria against Part E impact sound targets where the installation is a flat, conversion, or any situation with a separating floor to another dwelling. Always check the specific SPC product's technical data sheet before adding underlay — "always use underlay" is not a safe default assumption with integrated-backing products.

Underfloor heating compatibility

SPC is broadly compatible with underfloor heating, water-based and electric, which is one of its practical advantages over some timber floor coverings — but every product has a maximum rated surface temperature, commonly in the region of 27°C, above which the core can distort, the click joints can be stressed by expansion, and the wear layer can be damaged. Confirm the specific product's rated limit rather than assuming 27°C applies universally. Before installation over UFH, the system should be commissioned and run through a heat-up/cool-down cycle per the heating manufacturer's commissioning schedule, then brought to a stable, moderate temperature (not switched off, not at full output) during the SPC acclimatisation and installation period, then eased back up gradually after installation rather than switched straight to full output.

Frequently Asked Questions

Can I lay SPC straight over old tiles or vinyl without lifting them?

Often yes, provided the existing floor is sound, securely fixed, flat within tolerance, and not itself the source of a damp or structural issue — but always check the specific manufacturer's guidance on overlay-eligible substrates, and note that overlaying will raise the finished floor level, which affects door clearances and transition heights to adjoining rooms. Loose, damaged, or cushioned/spongy existing vinyl should generally be lifted rather than overlaid.

Does SPC need an expansion gap even though it's so rigid?

Yes. Rigidity affects how well the floor resists local deflection and telegraphing from a slightly uneven subfloor — it does not stop the material expanding and contracting with temperature and humidity as a connected floating sheet. Skipping the perimeter gap is one of the most common causes of buckling callbacks, particularly in rooms with large glazed areas or significant seasonal temperature swings.

My customer wants underlay added under an SPC product that already has integrated backing — should I do it?

Generally no, and you should explain why: doubling up underlay under a product with a factory-bonded backing can create excess cushioning that overstresses the click joints over time and will likely void the manufacturer's warranty. Check the specific product's technical data sheet — if it explicitly permits an additional underlay for acoustic upgrade purposes, follow that guidance exactly rather than a generic assumption either way.

Is SPC suitable for a flat where Part E sound insulation applies?

SPC alone is not a sound insulation solution — the acoustic performance depends on the full floor buildup including any separating floor construction and the underlay (integrated or separate) used beneath the SPC. Where Part E applies (typically flats, conversions, or any separating floor to another dwelling), the underlay needs to be selected and verified against the required impact sound reduction (ΔLw) figures — see acoustic underlay selection rather than assuming any SPC/underlay combination will pass.

What's the biggest cause of SPC installation failures in practice?

In order of frequency: inadequate subfloor prep (flatness or moisture) despite the rigid core's forgiveness being overestimated; insufficient or missing expansion gaps, especially at large open-plan runs and doorways; and fixing furniture, kitchen units or trims through the floating floor into the subfloor, which locks the floor in place and prevents the natural movement the click-lock system is designed to accommodate.

Regulations & Standards