Does cork render insulate a house?

It provides a small thermal contribution and it raises internal surface temperatures slightly, which can help with condensation. It does not deliver the level of heat-loss reduction that an insulation system of 90mm or more provides.

Can cork be applied over existing render?

Yes, provided the render is well-bonded, stable and prepared correctly. Hollow or actively cracking render needs cutting out and repairing first.

Is external wall insulation suitable for a cavity wall?

It can be, but if the cavity is unfilled it is usually more cost-effective to insulate the cavity first. EWI makes most sense on solid walls, non-traditional construction and properties where a re-render is happening anyway.

Do either of these need planning permission?

Cladding or insulating the exterior can require permission depending on the property and its location, and it is restricted in conservation areas and on listed buildings. Check with the local authority before ordering materials.

Materials & Comparisons

Cork Render vs External Wall Insulation

Name: Mighty Oak Construction
Address: Tunbridge Wells, Kent, TN1, GB
Telephone: 07850 357962
Price range: ££

Both products are applied to the outside face of a wall and both are sold on thermal performance, but they are not alternatives in the way marketing often implies. External wall insulation is an insulation system with a finish on it; sprayed cork is a thick, flexible, breathable coating that adds a modest thermal benefit. Choosing between them starts with what problem the wall has.

What each product actually is

External wall insulation fixes insulation boards — typically mineral wool or EPS — to the wall, then covers them with a mesh-reinforced base coat and a thin-coat render finish. Total thickness is usually 90–150mm depending on the board.

Sprayed cork is a granulated cork and resin coating applied in layers a few millimetres thick. It is elastic, so it bridges hairline movement, highly vapour permeable, and it resists rain penetration while letting the wall dry outwards.

Where the thickness matters

EWI's thickness has consequences at every detail of the building, and those details are where systems fail if rushed.

Window and door reveals become deeper and need insulated reveal boards
Sills, verges and eaves usually need extending
Downpipes, meter boxes, vents and external lights all have to be re-fixed forward
Boundary walls and passageways may not have the physical space
The base of the system needs a starter track and a correct DPC relationship

Where cork suits better

Cork earns its place on walls that are already suffering from crazed or slightly cracked render, on properties where thickness cannot be added, and on solid walls that need to stay breathable. It is also easier to apply over awkward, detailed elevations because it is sprayed rather than boarded.

It is not a substitute for insulation. If the objective is a measurable reduction in heat loss through a solid wall, EWI or internal insulation is the honest answer and cork is not.

Preparation is the same either way

Whichever route you take, the substrate has to be sound, dry and free of organic growth, and the cause of any existing damp has to be removed first. Both systems are unforgiving of being applied over hollow render, and both need a proper base detail so the coating is not carried down into the ground.