A. Introduction

The building envelope should be designed to naturally shed water without relying directly on seals to prevent water ingress. This aim is usually well achieved where temperate weather conditions prevail, however extreme weather conditions conspire in their attempts to force wind driven rainwater past the seals which have been provided. In addition to the task of keeping the weather out, the building envelope is also charged with assisting in the task of maintaining the internal environment in the required state. Preventing the air contained within the building from escaping through gaps in the envelope, taking any heat with it and allowing the ingress of outside air which will have to be processed to the required condition, is a task which can be performed by correctly positioned and installed seals and profile fillers. It may be appreciated from this that the selection of the correct grades and types of seal, and their correct application to the building envelope, is critical to the performance of the finished article.

B. Seal Types

The following descriptions give an overview of the types of seal specified by Ward:

Type 1 - Silicone Sealant
The silicone sealant specified is a translucent low modulus neutral cure multi-purpose sealant. It adheres well to all common building surfaces including glass and PVC. It is a very flexible sealant when dry, accommodating up to 35% joint movement in all directions.

Type 2 - Gun Grade Butyl Sealant
Gun grade butyl is a durable, permanently flexible butyl rubber sealant which is dispensed from a tube. It remains soft in the joint and has good self healing properties and can accommodate joint movement. The vapour permeability and water resistance of these sealants is good.

Type 3 - Impregnated Expanding Foam Tape
This seal is self adhesive on one side and is supplied on rolls in a compressed state. It has the property of expanding to several times its compressed thickness if the space is available. It is weatherproof when compressed to 20% of its expanded thickness so should be used only as a draught seal or as a backing to a true seal.

Type 4 - Pre-Formed Butyl Strips
Cross linked and non-cross linked butyl rubber seals are available in a multitude of extruded sizes and shapes in release paper backed lengths on the roll. The vapour permeability and water resistance of these sealants is excellent.

Butyl strips can be classified:
i) Class A: Higher Performance
ii) Class B: Normal Performance
iii) Non Recommended

For side and end lap joints a seal material complying to Class A should be used.

Only butyl seals which conform to Class A or Class B shall be used to seal the building envelope.

Type 5 - Form Cored Butyl Strips
The properties of this product are similar to these of pre-formed butyl strips, the foam core gives better compressibility and recovery from compression.

Type 6 - PVC Foam Tape
PVC foam tape is a compressible self adhesive tape requiring 30% compression to effect a waterproof seal. In certain cases it is supplied with a polyester film surface to aid assembly. It is an effective air seal and a moderate vapour seal, depending on the level of compression.

Type 7 - EPDM Foam Tape
EPDM seals are supplied as a self adhesive foam strip requiring minimal compression to effect a watertight seal. The resistance of black EPDM seals to UV light is excellent. They provide an air tight seal and their vapour permeability is better than that of PVC.

Type 8 - Expanding Canister Polyurethane Foam
Normally supplied as a 750ml aerosol can - a self-expanding polyurethane foam with propellants. Moisture sure, fill cavities to 50% foam expansion for air seal and 30% for water seal. Cured foam must be protected from UV radiation either by painting or applying a top layer of sealant.

Type 9 - Vapour Seal
This is a dual purpose air seal and moisture barrier tape. It provides sealing whilst allowing movement at the joints.

Type 10 - EPBM Bubble Gasket
Supplied as a 25m roll with adhesive strips on the back. Sealing is achieved by application of pressure from the panels.

Other seals and tapes are available for more specialist applications, e.g. intumescent seals, electrical isolator tapes, expanding polyurethane seals and vapour control tapes. Where these types of materials are required, consult Ward technical services or the sealant manufacturer.

Application of Tape Sealants

Tape sealants must be applied to the full profile without stretching, any backing paper must be removed only after the tape is in position. Seals stretched during fitting are responsible for a large proportion of roof leaks, so correct fitting can save a lot of trouble after the building is complete. Care is necessary when placing the overlapping element on all seal types to avoid damaging or displacing the seal, butyl strips require particular care as they tend to stick on contact. Gun grade silicone performs best in butt joints and fillets when there is clearance between the elements to be sealed. To avoid a ‘three sided joint’, it may be necessary to include a flexible backing tape. Never attempt to apply silicone sealant in conditions where the temperature is below 5°C. With all seals it is important to ensure that surfaces to be joined are clean, dry and grease free.

Correct Application of Seals and Tapes


Incorrect Application


Incorrect Application