Perimeter detailing
Missing Perimeter Insulation Around a Screed
A perimeter isolation strip is a small detail with a big job — missing it causes cracking, cold bridging and, on UFH floors, real heat loss.
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The strip of foam that runs around the edge of a screed, between the pour and every wall, column and threshold, does more work than its size suggests. It allows the screed to expand and contract with temperature changes, and on insulated floors it stops the perimeter becoming a cold bridge.
When it's missing, incomplete, or gets compressed and buried during the pour, the consequences show up later: cracking at the perimeter, heat loss through the wall junction on UFH floors, or the acoustic flanking issues covered elsewhere on this site.
This page explains what the isolation strip actually does, what happens when it's absent, and how the situation is corrected if it's found after the fact.
What perimeter isolation actually does
- Allows the screed slab to expand and contract with temperature change without cracking against a rigid wall
- Breaks the thermal bridge between a heated floor and the surrounding wall or column
- Contributes to acoustic isolation on floating floor build-ups
- Prevents the screed transferring load or movement into the wall structure
- Provides a clean edge detail for skirting to sit over without touching the screed itself
Consequences of missing perimeter isolation
| Missing detail | Typical consequence |
|---|---|
| No isolation strip at all | Perimeter cracking as the screed expands against a rigid wall |
| Strip present but not full height | Localised cracking or cold bridging above the strip line |
| Strip compressed or torn during pour | Reduced acoustic and thermal isolation at that point |
| Strip omitted at internal columns/thresholds | Isolated cracking radiating from that specific point |
How we fix it if it's found after the fact
- 1
Identify the extent
We check the full perimeter to see where isolation is missing, damaged or undersized.
- 2
Cut and clear
A perimeter channel is cut back to the wall along affected sections, removing screed that's bridging the gap.
- 3
Retrofit isolation
Compressible foam strip is fitted into the cut channel to restore the movement gap.
- 4
Reseal and finish
The channel is finished with a flexible sealant or covered by skirting, restoring the intended detail.
Get your perimeter detailing checked
If you suspect the isolation strip is missing or damaged, send us photos or book a site visit and we'll assess the fix.
The isolation strip is cheap and easy to get right before the pour, and genuinely disruptive to retrofit afterwards. It's one of the first things we check on site.
— Exeter Liquid Screeders
Missing Edge Insulation — questions we get asked
Keep reading across the site
Get your perimeter detailing checked
If you suspect the isolation strip is missing or damaged, send us photos or book a site visit and we'll assess the fix.