In cavity wall construction, the main principle behind having a cavity is that the cavity prevents moisture from moving from outside in.
Full-fill cavity wall insulation usage is limited both in terms of external wall construction and exposure conditions. Particular attention should be paid to the requirements with regard to an unrendered masonry outer leaf.
In areas of normal exposure, fairfaced unrendered brickwork is acceptable for full-fill cavity wall insulation up to two storeys in height with a minimum cavity width of 90 mm and up to three storeys in height with a minimum cavity width of 140 mm.
In areas of severe exposure, unrendered brickwork is not suitable for full-fill cavity wall insulation.
Cavity walls with the outer leaf constructed using unrendered fair-faced blockwork are not suitable for full-fill cavity wall insulation.
Full-fill cavity wall insulation must be appropriately certified in relation to the intended use and conditions of use, as per the guidance outlined above, and must be installed in accordance with the requirements of its Agrement certificate.
Building In Insulation
Wall ties should suit the type of insulation being used. Ensure that no mortar falls on top of batts and also that the insulation is held tightly to the inner leaf. Joints between insulation should be tight together.
Diagram C57 - Typical detail for built in insulation
Insulation Around Openings
It is important that thermal insulation does not contain gaps. Thermal continuity must be maintained to eliminate thermal bridging that occurs at breaks in continuity. Where thermal bridging occurs, the inside surface of the wall where the gap occurs is less than the rest of the wall. This leads to a higher rate of heat loss and may increase the chance of local condensation occurring.
Due to thermal bridging being one of a series of factors that affect the overall energy efficiency of the dwelling, it is vital that detailing and installation of insulation around openings is done correctly.
A number of methods to ensure compliance with this aspect of the regulations can be achieved are found in Technical Guidance Document L of the Building Regulations. Using Acceptable Construction Details (ACDs) is one method outlined.
In cases where there are proprietary insulated cavity closers in these locations, they should be appropriately certified and should be installed in accordance with the requirements of the certificate. Extra care should be exercised when using such products along with vertical DPCs.
Some typical details have been detailed below for standard construction details.
Diagram C58 - Typical DPC installation with insulation provided around the opening - blockwork outer leaf
Diagram C59 - Typical DPC installation with insulation provided around the opening - brickwork outer leaf
Diagram C60 - Typical DPC installation with insulation provided around the opening - insulation incorporated within lintel
Diagram C61 - Typical cill detail
Diagram C62 - Typical jamb detail
Diagram C36 - Typical DPC installation detail around window cills
Notes On Insulation
1. Do not install DPC or flashings composite area of the lintel.
2. Unless specified otherwise, insulation around openings is to be in accordance with the acceptable construction details. These details are available on the DoECLG Website https://www.gov.ie/en/organisation/department-of-housing-local-government-and-heritage/ under the building standards section.
3. Where possible ensure that lintels bear on a solid full block.