Effective insulation of gaps and corners – Guide 2025

When discussing thermal or acoustic insulation in buildings, most people think of the usual solutions: polystyrene panels, mineral wool, or insulation mats. These are the dominant materials on the market and are commonly used to insulate walls, roofs, and floors. Yet in real construction and renovation scenarios, there are many situations where conventional insulation materials prove insufficient — not because they lack quality, but because of their inherent physical limitations.

Recesses, narrow corners, gaps, double walls, or the spaces between beams are areas that are difficult to access or simply not suited to rigid or large-format insulation products.

In this guide, we explain why standard insulation doesn’t always perform well and how to select the right material for challenging spaces.

 

Table of Contents
1. Introduction
2. Why is insulating difficult spaces important?
3. What qualities should effective insulation for hard-to-reach areas have?
4. Solution: Expanded natural cork granules
5. Summary
6. FAQ

 

Why is the topic of insulating difficult spaces important?

Standard insulation in the form of boards and sheets — strengths and limitations

Traditional insulation materials such as boards or sheets have many strengths. They are reliable, well-tested, and easy to obtain. Installation on large, flat surfaces — walls, roofs, or floors — is quick and cost-effective. Their thermal and acoustic parameters significantly reduce heat loss and enhance indoor comfort.

However, the same characteristics that make them an excellent choice for straightforward applications become drawbacks in difficult-to-reach locations. Boards are rigid, have a fixed thickness, and are not easily shaped to fit unconventional forms or small cavities. Cutting them creates waste, and any imperfect fit increases the likelihood of thermal bridges and unwanted air leakage.

Where do they work best?

Standard insulation systems are most effective on:

• large, uniform surfaces (walls, roofs, floors),

• buildings with simple geometries,

• areas that are easy to access during installation,

• places where material flexibility is not required.

Why does it fail in tight or irregular areas?

Tight corners and narrow gaps rarely have regular shapes, are often confined, and are generally hard to reach. Boards or mats cannot fill such areas accurately — resulting voids become “weak spots” in the insulation system. In these spaces:

• thermal bridges form,

• water vapour condenses, leading to moisture issues,

• the material may shift or settle over time,

• acoustic performance of the structure deteriorates.

As a result, even well-insulated main surfaces cannot compensate for losses in these neglected areas.

Spaces that tend to cause trouble

Recesses, corners, and gaps

Their dimensions and irregular shapes make them easy to overlook or insulate poorly.

Double walls and interlayer cavities

In older buildings or layered wall systems, the spaces between structural layers are difficult to insulate with rigid materials and often contribute to significant heat loss.

Between floor beams and within ceilings

Cavities between load-bearing beams pose similar challenges. Irregularities and gaps prevent rigid insulation from fitting snugly.

Components of mixes and screeds

Floor insulation and base layers often require reduced overall weight or improved thermal and vapour-permeability properties. Traditional insulation materials are neither loose fillers nor additives for mixes, making them unsuitable for such uses.

 

What features should effective insulation for difficult spaces have?

Not every insulation material works well in irregular or confined spaces. Where standard products fail, different characteristics become crucial — not just thermal conductivity (λ). Effective insulation for gaps, corners, and recesses must fulfil several essential criteria:

Flexibility and adaptability

The key requirement for difficult spaces is the material’s ability to fill irregular shapes. This is why loose, free-flowing, or expandable insulation forms are so effective. Such materials:

• adapt easily to tight, awkward areas,

• remove the risk of leaving empty pockets.

Thermal and acoustic performance

A good fit is not enough — the material must also offer efficient heat and sound insulation. This means:

• a low thermal conductivity value (λ),

• the ability to absorb both airborne and structural noise (e.g. footsteps, impacts, or installation noise),

• dimensional stability and resistance to settling or separation over time.

Moisture resistance and vapour permeability are additional benefits, helping prevent condensation and mould growth.

Low weight

When filling cavities, interlayer spaces, or incorporating insulation into mixes, the material’s weight becomes a critical factor. Insulation that is too heavy:

• can overload the structure — especially in older buildings,

• is more difficult to apply, particularly in confined construction spaces,

• is unsuitable as an additive for screeds because it alters their mechanical properties.

 

Solution: Expanded Natural Cork Granules

What kind of material is it?

Expanded natural cork granules are a sustainable insulation material made by heating cork grains to high temperatures. During this process:

• the natural cork enlarges as it expands,

• a natural resin – suberin – is released, bonding the grains without added adhesives or synthetic substances,

• a porous, ultra-light yet resilient material is created.

The end product comes in various grain sizes and can be easily placed in hard-to-access spaces, blown into cavities, mixed with mortars, or used as a free-flowing insulating layer.

What properties does it have?

Natural cork granules provide all the attributes expected of modern, eco-conscious insulation:

• Excellent heat insulation.

• Very good sound insulation.

• Low density.

• Breathability (vapour permeability).

• Resistance to biological factors: it does not mould, rot, or attract insects or fungi.

• Long-term durability.

Examples of applications for natural cork granules

Filling recesses and gaps

Granules can be poured or blown into narrow and inaccessible areas. Their structure allows them to conform to the shape of the cavity, preventing both thermal and acoustic bridging.

Blown-in insulation between wall and floor layers

This is one of the most efficient applications of cork granules. They can be used as:

• secondary insulation in older buildings (e.g., cavity walls),

• infilling voids between floor beams.

Additive for mortars and screeds

Natural cork granules can act as a lightweight natural aggregate for:

• lime and cement mortars,

• lightweight concrete,

• dry construction mixes.

 

Summary

Insulating recesses, gaps, and awkward spaces is one of the major challenges in today’s construction and renovation work. Although standard materials — such as polystyrene boards, mineral wool, or foams — perform well on large, regular surfaces, their effectiveness drops significantly when dealing with irregular spaces.

A practical answer to this issue is the use of a flexible, lightweight, natural material — expanded natural cork granules. Their structure, thermal and acoustic insulation capabilities, as well as biological durability and breathability, make them ideal for:

• filling narrow spaces and recesses,

• blown-in insulation between structural layers,

• use as an additive in lightweight mortars and screeds.

Cork granules not only address the typical issues found in difficult areas but also respond to the rising demand for sustainable, healthy, and long-lasting building materials. Their versatility allows them to be used both in modern energy-efficient buildings and in the restoration of historic structures, where minimal weight and natural composition are crucial.

 

FAQ – Frequently Asked Questions

1. Are expanded natural cork granules suitable for all types of buildings?

Yes, cork granules can be used in both new builds and renovation projects — including historic buildings. Their low weight and natural origin make them suitable for traditional, energy-efficient, and passive construction.

2. Does installing cork granules require specialised tools?

It depends on the intended application:

• For loose filling — no special tools are necessary; a bucket, shovel, or basic manual pouring will do.

• For blown-in use — pneumatic equipment is advisable (e.g., when insulating cavity walls).

• For mortar and screed mixes — the granules are combined manually or mechanically with an appropriate binder (lime or cement).

3. Is the material resistant to moisture and mould?

Yes. Natural cork is inherently moisture-resistant and does not support mould or fungal growth. It does not retain water permanently, and its breathable structure allows the wall system to dry properly, reducing the risk of condensation.