Thermal Insulating Boards and Internal Cladding


Older properties, in particular, can suffer from being cold even with gas central heating. From this, condensation and mould growth can become a problem which is often exasperated by the living habits of the occupiers. When visiting properties, landlords often find that particular issues can seem to occur on north-facing walls as these walls never get direct sunshine, and often the wind and rain affect these walls more than most. If the property is pre-1920, it will likely not have a cavity, too, which can worsen problems. 

One thing that you can do is to insulate the wall itself using what are officially called thermal laminate boards (but I've always called them styro-boards). 

These plasterboards with polystyrene stuck to the back are available in varying shapes and sizes. You can fasten them to a wall with what is officially called thermal insulation fixings (but I have always known them as mushroom plugs because that's what they look like). 

This method's primary advantage is that boards cover the offending wall, so it doesn't matter how rough the wall looks before installation. Also, because you can fasten the boards directly to the wall, installation is quick and easy (assuming you have an empty property, though).

Cavity wall insulation

The first thing to consider when advising landlords on appropriate damp or cold issues is whether internal insulation is suitable. Where the property has a cavity, cavity wall insulation usually will be the most cost-effective solution because it's a less labour-intensive method of insulating buildings. 

Cavity wall insulation seems to be more available under energy improvement schemes because of its initial lower cost and good savings ratio. 

However, internally cladding a wall or walls is suitable in addition to cavity wall insulation if the property requires extra thermal efficiency (particularly useful in basement conversions, we find).

What are thermal laminate boards?

Thermal laminate boards are plasterboards with polystyrene attached to the reverse side. Generally, the boards are 2.4 meters high by 1.2 meters wide (around 8ft x 4ft), and the face is regular plasterboard. On the rear is attached polystyrene of varying thicknesses and grades. 

Commonly, the thickness of the whole board (including insulation) ranges from 22mm to 60mm, depending on the insulation needs of the building. In addition, the insulation can be made up of varying degrees of thickness and compression, ranging from expanded polystyrene to high thermal performance phenolic foam which also acts as a fire barrier.

Fixing thermal laminate boards

The marvellous thing about thermal laminate boards is the ease of installation.

We should say from the outset that this retrofitting board can only realistically be done in an empty property when undergoing major refurbishment because, generally, full access to all external walls is necessary. 

You can fix thermal laminate boards directly to a wall or by first fastening studs or battens to the wall/s and attaching the boards to the studs.

Fixing directly to the wall

The most common approach in traditional buildings would be to attach the boards directly to the wall. Where the board is being fastened, they are secured with large plugs called thermal insulation fixings, which hold the board up against the wall. A hole is drilled through the board and into the wall. Then, the thermal insulation fixings (mushroom plugs) are hammered into the hole. Because the head of the fixing is so large, this pulls the board into the wall. You stop beating the plug as it rests just below the surface of the plasterboard so that when the board is skimmed with plaster, the fixing doesn't stick out.

Fixing with battens

Alternatively, studs or battens can be fastened throughout the wall/s. You could fill the gaps with rock wool and the thermal laminate board attached to the battens. This would be appropriate where a wall is very uneven, for example, so with battens, the wall could be flattened and smoothed over more gradually. The boards are slightly flexible, allowing for a bit of roughness without the need for battens. 

Battens are also helpful if more thermal integrity is required in a particular room because the gaps are filled with rock wool, adding to the thermal property of the wall. (Although, it is, of course, possible to buy thicker or more compressed boards.)

Where battens have been used, screws specially designed for plasterboard (which doesn't rust) should be used to fasten the boards to the battens. You will need longer than regular screws to accommodate the insulation part of the board.

Thermal insulation fixings

The thermal insulation fixings, as described above, are large plugs long enough to penetrate the board and the wall itself. They are available in varying shapes and sizes, and you should seek advice depending on the type of wall the boards are being fastened.

Building regulations

Regulation 23 of the Building Regulations 2010 provides that where a person intends to renovate a thermal element in an existing dwelling, such work shall be carried out as is necessary so that reasonable provision has been made for the conservation of fuel and power by limiting heat gains and losses through thermal elements and other parts of the fabric of the building.

Renovation in relation to a thermal element means:

the provision of a new layer in the thermal element (other than where that new layer is provided solely as a means of repair to a flat roof) or the replacement of an existing layer but excludes decorative finishes, and 'renovate' shall be construed accordingly.

Notification to building control body

To comply with the building regulations before works are started, notification will need to be made to a building control body, either the local authority or an approved inspector. 

Approved Inspectors are companies or individuals authorised to carry out building control work in England and Wales. 

Where a local authority has been chosen, and any work relates to the common parts of a block of flats, the notification must be made with the deposit of complete plans. Complete plans or a building notice may only be necessary for other works. There is no set procedure where an approved inspector has been notified as long as the notification was at least five days before work starts

Suppose the works are being carried out as an emergency, and it is not practicable to notify before commencing the work. In that case, you must notify the building control body at the earliest opportunity.


A U-value is the standard measurement of the flow of heat through an insulating material or building material (such as bricks, windows, doors etc.) The lower the U-value, the less heat passes through the material or assembly of materials, and therefore the materials have better insulating properties. U-value is expressed in units of W/m2, which relates to the loss of heat in watts (W) per square meter (m2) of material. For example, if a material has a U-value of 1 w/m2-K, 1 watt of heat is lost through each square meter of the material's surface for every degree of the temperature difference between inside and outside. For example, a 225mm solid brick wall with 10mm mortar joints has a U-value of 2.0 W/m2 and a typical cavity wall with no insulation has a U-value of 1.6 W/m2.

The installation of cavity wall insulation or thermal laminate boards can dramatically improve (reduce) the U-value of the wall and considerably improve the wall's thermal efficiency.

Provision of thermal elements

Where a thermal element is being renovated through the provision of a new layer, i.e.:

  • Cladding or rendering the external surface of the thermal element; or
  • Dry-lining the internal surface of a thermal element.

Or, an existing layer is replaced by stripping down the element to expose the basic structural components (brick/ blockwork, timber/metal frame, joists, rafters, etc.) and then rebuilding to achieve all the necessary performance requirements then, the performance of the whole element should be improved to gain a better U-value than 0.30 W/m·K, provided the area to be renovated is greater than 50 per cent of the surface of the individual element or 25 per cent of the total building envelope. 

When assessing this area proportion, the area of the element should be taken as that of the individual element, not all the elements of that type in the building. This means that if the plaster is being removed from a bedroom wall, the relevant area is the area of the external wall in the room, not the area of the exterior elevation, which contains that wall section. This is because the marginal cost of dry-lining with insulated plasterboard rather than plain plasterboard is small. 

Suppose the achievement of the relevant U-value is not technically or functionally feasible or would not achieve a simple payback of 15 years or less. In that case, you should upgrade the element to the best standard that is technically and functionally feasible and which can be achieved within a simple payback of no greater than 15 years.

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