Internal Wall Insulation

ABOVE: This old Victorian house has been transformed into an eco home due in no small part to new insulation. (Read more about this renovation...).

The simplest solution is to apply insulation-backed plasterboard, directly onto the original walls, using dabs of adhesive bonding and a suitable form of mechanical fixing (such as Fischer Fixings fischer.co.uk). As well as covering at least 20% of the board area, it is recommended that a continuous strip of plaster adhesive is used at floor and ceiling level, and around window and door openings, to stop the spread of fire.

Many internal insulation finishes use a plaster board finish, either lamin ated to insulation board, or fixed directly to stud - work, and depending on the type of board used, they can then be finished with a skim coat of gypsum plaster or taped and filled.

The current Best Practice standard issued by the EST is a maximum U-value of 0.45W/m²K. This can be met using several different insulation options and manufacturers can provide technical solutions for their products showing suggested build-ups.

Where space is a priority, it makes sense to use high-performance insulation materials such as polyurethane (PU), polyisocyanurate (PIR) and phenolic foam (PF), which have a lower conductivity than air-based insulants such as mineral fibre or cellulose, and therefore achieve a better U-value for a given thickness.

An alternative solution is to fix insulation board to the walls and then plaster directly onto the boards with a bonding plaster and finishing coat. The insulation board can be shaped, for instance, to create curved arises around window and door reveals, and then plastered to create a more characterful traditional finish.

Other alternative solutions include fixing timber battens to the walls and infilling the space with insulation, followed by timber battens and then plasterboard. This is a common option where non-rigid board insulation products are to be used. Even timber studs act as a cold bridge between external wall and plasterboard, however, and so the EST recommend that this solution is combined with the use of some sheet insulation material laid over the studs to create a thermal break.

A consideration that will affect your choice of specification is the need for an air/vapour barrier to ensure that any interstitial conden - sation, forming at the coldest point in the wall, can dry naturally. Allowing some movement of air is important and of particular issue for solid walls that contain timber elements, such timber lintels. This can be achieved either behind the insulation, or behind the board, by using counter-battens.

Where the external walls are below ground level, for instance because the house is partially built into a hillside, or has a cellar, it is possible to introduce a damp-proof membrane behind the new layer of internal insulation. This could be a traditional tanking membrane, providing it is continuous across the floor and dressed partially up the internal walls. A good solution is to use a textured waterproof membrane behind the new insulated internal wall lining and continued across the floor. Any damp is caught by this lining and channelled down into a drain or sump, from where it either flows, or is pumped, harmlessly away. This is an ideal solution for cellar conversions.

An Internal Wall Solution

This solid-brick-walled Victorian house in Camden, North London, is situated in a Conservation Area, which meant that an external insulation solution was out of the question. As part of a package of insulation measures, Kingspan’s Kooltherm phenolic urethane insulation was specified. For most walls on the ground floor and above, 102.5mm-thick Kooltherm K18 Insulated Plasterboard was fixed on battens, protected from the wall by a strip of DPC. The U-value of the walls is now 0.19W/m²K. 62.5mm of the same plasterboard was fixed for the basement walls. All plasterboard joints were taped to get the best possible airtightness. Junctions between the insulation and other materials were sealed with flexible mastic or foam to further improve airtightness. At the edges of floors and walls, the floorboards were cut away and the insulation drawn up to meet the neighbouring layer. Making the insulation continuous in this way prevents a thermal bridge (or heat loss) around the floor junctions.

How it works

For those unable to fix insulation externally, an insulated dry-lining board might be an option, fixed to timber battens

Solutions for Insulating Walls:

• Insulating Walls
• External Wall Insulation
• Insualting Walls: Traditional Construction