Cornice

A cornice (in Slovak rímsa) is a projecting horizontal moulding that crowns a wall or divides its surface. Slovak heritage guidance lists it among the plastic parts of a plastered facade. The others are rustication and window surrounds. It is also one of the first details lost in renovation, so the decision about it belongs before the work starts.

What is a cornice and where does it sit?

The Pamiatkový úrad SR (Slovak Monuments Board) methodology on plasters shows a profiled crown cornice (korunná rímsa) under the roof. It is one level of plastic facade articulation. It also shows cornices, plaster rustication and window surrounds formed on site in plaster. The methodology notes that forming the relief on site copes more easily with the dimensional deviations of a building.

Type	What it is	What to check in a renovation
Crown cornice	A profiled moulding under the roof, at the top of the facade	The roof overhang, the drainage of roof water and the flashing of the cornice
Plaster cornice formed on site	A profile built in plaster together with other facade relief	The plaster type and any earlier repairs
Timber cornice in roof carpentry	A profiled timber member fixed on the projecting ends of horizontal roof members	The condition of the timber, and the heritage office if the building is protected

How is a plaster cornice different from the timber cornice of a roof?

The Slovak roof-carpentry glossary of the Pamiatkový úrad SR defines rímsa (or rímsička) as a decoratively profiled timber member. Carpenters tenon it onto the ends of projecting horizontal roof members. These members are mostly tie beams or collar beams (hambálky). The plaster methodology uses the same word for a profiled facade moulding. A drawing or survey should say which one it means.

How does a cornice shed rainwater?

A conservation guide on decorative masonry repairs lists drips among the protective details that shed rainwater. It places them on the lower leading edges of cornices and other projecting mouldings. The guide covers stone masonry.

The Slovak plaster methodology adds that the damage a facade plaster suffers depends on its position on the facade. It lists the flashing of parapets and cornices, the roof overhang and the drainage of roof water among the factors. A cornice with a worn edge or missing flashing therefore puts the plaster below it at risk.

Why does a cornice matter on a protected building?

Act 49/2002 Z. z. on the protection of the heritage fund defines restoration of a cultural monument (§ 32 ods. 1). Restoration includes maintenance, conservation, repair, adaptation or reconstruction of the monument or of a part of it. Repair of a cornice on a monument is therefore restoration. The act then sets these steps:

• Before work starts, the owner asks the regional heritage office (krajský pamiatkový úrad) for a decision on the restoration intent (§ 32 ods. 2).
• If the owner starts without a valid decision, the office opens proceedings and calls on the owner to stop work (§ 32 ods. 2).
• The decision says whether the intent is admissible and sets the conditions. It also says whether the work needs research and other preparatory and project documentation first (§ 32 ods. 4).

The same article covers a house that is not a monument but stands in a heritage territory. A heritage territory is a heritage reserve or a heritage zone (§ 2 ods. 4). Before a new building or an alteration, the owner needs a decision of the regional heritage office on the alteration intent. The office can set conditions for the architectural solution of the exterior (§ 32 ods. 5 and 7). It also issues a binding opinion on the preparatory and project documentation (§ 32 ods. 10). A heritage authority decision is the document that settles whether the proposal can go ahead. A house in a protection zone needs a binding opinion of the office before an alteration (§ 32 ods. 11).

The Pamiatkový úrad SR methodology on chimneys says that profiled cornices were the most common architectural feature of chimney heads. It adds that renovation often replaces the heads with simplified new forms that ignore the original profiled cornices. The decision should therefore come before the work, not after it.

What happens to a cornice when you add external insulation?

The Pamiatkový úrad SR methodology on the energy efficiency of historic buildings calls external insulation the least risky option in building physics. It is also the most common option. It adds that external insulation is in most cases in conflict with the architectural values of the building. The office allows contact insulation of a facade only in exceptional cases. One example is an unarticulated side facade of a building that is not a national cultural monument.

Thickness matters as well. The methodology states that any larger insulation thickness changes the proportions of the building. It also changes the depth at which windows sit in their openings. Where the heritage office agrees, it suggests moving the windows toward the outer face of the new plaster. This keeps the proportions and the original window depth. The methodology gives no cornice detail. A designer must therefore draw the junction of the new insulation and the cornice and agree it with the office.

Approach	Position in the methodology
External contact insulation of the facade	Least risky in building physics but in most cases in conflict with architectural values
Contact insulation on an unarticulated side facade of a building that is not a national cultural monument	Allowed only in exceptional cases on a decision of the heritage office
Insulation on the inside of the walls	Must be calculated by a building physicist because of the risk of condensation in the structure

How can you repair a plaster cornice without losing it?

Start with a survey. Measure the profile, its projection and its height, photograph it and draw it before any work starts. For a protected building the heritage office may require research and preparatory documentation before it allows the work (§ 32 ods. 4 and 7 of Act 49/2002 Z. z.). A drawing of the existing profile also stops a contractor from replacing it with a generic one.

Choose the repair material with care. The Pamiatkový úrad SR plaster methodology says that earlier repairs with incompatible materials cause damage. These materials are harder and have lower porosity and vapour openness. It names cement-containing plasters as harmful to lime plasters. It says that later cement fillings of lime plasters that harm their surroundings are to be removed. Where the original profile is lime plaster, repair it in lime-based plaster.

A cornice is a small element with a large share of the character of an old facade. Survey it first, agree the approach with the heritage office where one applies, and detail the junctions before the insulation contractor arrives.