What is Pumped Cavity Insulation?
There are three main choices for insulating walls: cavity, internal, and external wall insulation. Influencing factors include the wall type, insulated (if dry-lining), suitability of the walls, whether the outside of the house needs to be, or can be, given a facelift and the typical occupancy patterns of the home.
Cavity Walls: A cavity wall consists of two rows of brick or concrete block with a continuous cavity or space between them. Injection of insulation from the outside is the best method for retrofitting insulation in this type of wall. It may also be used in a new-build. The installation of this insulation should be carried out by an contractor that is registered with NSAI Agrément and the insulation material used should be certified for use cavity walls. The contractor should assess the walls and cavities in order to determine their suitability for blown insulation before carrying out any work. The work is done from the outside so there is minimal disturbance. Holes with a diameter of 17-26 mm are drilled in the wall, usually between 0.6 m and 1.0 m apart and generally not more than 300 mm from the top of the wall, then the insulation is blown in through these holes. The holes are then filled to match the wall appearance as closely as possible, as prescribed by the NSAI Irish Agrément certificate. The job should take less than a day to complete. Fully filling the cavity with a certified insulation will not lead to dampness on the inside of your walls, if the cavities and walls are free from defects that the contractor will assess before carrying out any work.
Internal Insulation: If the wall is of solid masonry or constructed from 9 inch (225 mm) hollow blocks, your options are to insulate internally or externally. Internal insulation involves insulating the inner surfaces of external walls, i.e. dry-lining. The standard method for insulating internally is to fix insulated dry-lining panels to the walls. These panels consist of plasterboard with insulation bonded to it and with an integral vapour barrier. (Alternatively, insulation may be fixed to the wall, covered with a vapour barrier, e.g. polythene, and then plasterboard.)
The U-value achieved will depend on the thickness of insulation installed and the properties of the insulation material. By using better insulation materials, i.e. those with lower thermal conductivities, a good level of insulation can be achieved using a thinner layer of insulation. The main drawbacks to insulating internally are the disruption due to installation works, a small loss of room space due to the insulation, possible reinstallation of services (such as electrical wiring, sockets and heating radiators) and the redecoration required after the installation works. For this reason, any time you are considering major redecoration of a room or rooms in your house, or fitting say a new kitchen, bathroom or built in wardrobes, should be viewed as an important opportunity to carry out such internal lining insulation works in a way which causes little or no additional internal disruption.
Careful attention needs to be paid to the sealing of joints between boards and around service penetrations (sockets etc.). It is also important to seal around the perimeter of the insulation, i.e. at the floor, ceiling, at adjoining walls and windows. If the insulation is not sealed around its perimeter, warm air will leak into the space behind the insulation and condensation is at risk of forming on the cold wall surfaces outside the insulation.
External Insulation is relatively new to Ireland but it has been widely used in northern Europe for several years. It involves fixing insulation materials to the outer surfaces of walls so that the house is effectively 'wrapped' in insulation. Typical insulation materials used are mineral fibre slabs, expanded polystyrene, extruded polystyrene, polyurethane and phenolic foam. The insulation is covered with a render known as a basecoat, a reinforcing mesh providing strength and resistance to damage from impact, and a render finish. It should not be used with unfilled cavity walls due to the possibility of thermal bypass and thermal looping within the cavity. The cavity should be filled where external insulation is to be applied. Window sills and eaves may need to be extended and downpipes and cables relocated. A thin layer of insulation is applied at the edges of windows and doors to minimise thermal bridging.
It is important to get an external insulation system that is certified by NSAI Agrément. A certified system means the system as a whole has been independently tested, assessed and approved (subject to specified conditions) by a competent body for appropriate climatic conditions. External insulation installed as a piecemeal solution may use 'guaranteed' materials but the system as a whole may not be guaranteed. The work should be carried out by an approved contractor who is registered with NSAI Agrément.
An architect should be able to talk you through all the different construction methods available, and recommend the solution, which is best suited to your situation.