Edge insulation strip

What is an edge insulation strip?

An edge insulation strip is a compressible strip fixed around a room's edge that keeps a floating screed apart from walls and other vertical parts. Its Slovak name on manufacturer pages is okrajová dilatačná páska, and Rockwool calls its product okrajový pásik. Baumit describes its strip as a polyethylene tape. Rockwool makes its strip from stone wool. The strip is a component of the floor build-up and not a finish.

How does the strip decouple a floating screed from the walls?

A floating screed rests on a resilient layer and moves as one slab. Baumit's guide says the strip lets the screed layer move as a free plate when its volume changes. The same guide says the strip also stops noise passing from the floor into the vertical structures. Rockwool describes its stone wool strip as minimising acoustic bridges between the floating floor and the wall. Both roles come from one fact: the screed never touches the wall.

Baumit's guide calls an edge joint necessary for all types of screed. The strip is part of the movement system of the whole floor, together with the joints in the screed field.

How thick should an edge strip be?

The thickness depends on the screed system, so the figures below are Baumit's and Ceresit's own. They are not a general rule, and the strip is chosen from the data sheet of the screed system. Rockwool's product page lists no thickness or height.

Condition	Baumit technology guide (2022)	Ceresit guide for levelling compounds
Unheated screed	Strip at least 5 mm thick (types RSS 100/5 and RST 100/5, height 100 mm)	Edge joint at least 5 mm
Screed with underfloor heating	Strip at least 10 mm thick (types RSS 120/10 and RST 120/10, height 120 mm)	Edge joint at least 10 mm
Why	The joint must allow at least 5 mm of movement, and the strip compresses, so it must be at least 10 mm thick	Not stated
Long bays	Over 8 m, a wider joint: 1 mm of joint width for each metre of bay length	Not stated

Baumit's guide gives the same strip rule for cement and for anhydrite (gypsum-based) screed. See anhydrite screed for the material. Ceresit also asks for edge strips under its self-levelling compound when the layer is 5 mm or thicker.

How is an edge strip different from an expansion joint?

Both are compressible gaps, so they are often confused. They sit in different places. The edge strip runs around the perimeter and separates the screed from walls. An expansion joint cuts through the screed field. In Baumit's guide it runs over the full depth of the screed. Baumit makes it with an L profile glued to the base, together with the edge strip.

Feature	Edge insulation strip	Expansion joint in the screed
Location	Perimeter, at walls and other vertical parts	Inside the screed field, between bays
Main role	Free movement of the slab and no sound path into the wall	Dividing the screed into separate bays
Baumit example	Needed for all screed types	Unheated cement screed: bays of at most 40 m2, sides at most 8 m, ratio at most 1:2

In what order is the strip installed and trimmed?

The strip goes in before the screed, so the screed meets it from the start. Baumit's and Ceresit's guides give this order for the edge joint of a levelling compound. Fix the strip to the wall above the planned level of the layer, so no bridge forms between wall and layer. The part that stands above the layer is cut off only after the final floor covering is laid.

Stage	What happens	Why it matters
Fix	Strip fixed upright to the wall before the pour	The screed is placed against it from the start
Pour	Screed placed with the strip standing above the finished level	The strip reaches above the surface, so no bridge forms
Trim	Excess cut off after the final floor covering is laid	The final level is known before the strip is cut

What goes wrong when the strip is short, missing or bridged?

Any rigid contact between the screed and a wall removes the free movement that the strip gives. It also gives sound a direct path into the wall. In Baumit's guide, separation from the vertical structures lets the screed move as a free plate. The impact sound insulation article explains how to judge the performance of the whole floor.

Check the strip before the pour and again before the floor covering goes down. Look for places where it is cut short, pressed flat, or interrupted at a door frame or a pipe.

Which mistakes come up most often with edge strips?

The first mistake is treating the strip as a substitute for the resilient layer. The strip handles the perimeter, while the insulation layer under the screed covers the whole floor area. The second is choosing any foam strip. Thickness depends on the screed system and on heating, as the table above shows, so the choice comes from the data sheet. The third is leaving the strip out of a small room. Baumit asks for an edge joint for all screed types, and a small room still has walls. Before the covering goes on, the screed also has to be dry enough, which the screed moisture test article covers.