The building fabric – roofs and lofts (Eco-Refurbishment)

Eco-renovation of a home is most cost effective when it is linked to necessary refurbishment, such as the renewal of tiles on a roof or external rendering. However, it is important to understand that thermal upgrading of a property might come under building control regulations. The Building Regulations for England and Wales, Part L 2002 include provisions which have a major impact on existing houses by setting insulation standards for any work which constitutes a major alteration. The term ‘major alteration’ includes:

• substantial replacement of any part of a roof including retiling and refelting

• significant changes to a floor including changing joists or re-boarding

• changes to an exposed wall, including renewing external render or internal plaster

• replacement doors, windows and rooflights

• replacement heating systems, including boilers and hot water systems

• heating and hot water controls

• instructions for heating systems must be provided and systems correctly commissioned.

The responsibility for compliance with the Building Regulations rests with the person ordering the work.

The thermal efficiency of a component of a building, such as a roof or wall, is described as its U-value. This is a measure of thermal transmittance, that is, the rate at which a composite element of a structure like a wall or window transmits heat. Technically it denotes the speed with which heat is lost through 1 m2 of the element, when the difference in temperature between the inside and outside face of the element is 1°C. The lower the number, the higher its thermal efficiency. It is denoted by W/m2K. It should not be confused with the conduction value (Lambda) which refers to a specific material like an insulant.


In a home without insulation about 25 per cent of its heat is lost through the roof. To repeat, this is the zone where the most cost-effective insulation investment can be made. The options are either a warm or a cold loft. The former is necessary if activities are to take place in the space or it is used for storage.

As mentioned, if there is a material alteration to the roof, insulation will need to be installed to a maximum U-value (W/m2K) according to the regulations:

pitched roof with insulation between the rafters

(warm loft) or fixed to the face of rafters 0.20

pitched roof with insulation between or over

ceiling joists (cold loft) 0.16

flat roof 0.25

Note: ‘Maximum’ in the context of U-values means the highest figure that is allowed which means the lowest level of permitted thermal efficiency. So, the higher the number, the poorer the thermal performance.

In cold lofts it is essential to ensure that the insulation is wrapped around water tanks with the space below the tank remaining uninsulated (Figure 3.1). All water pipes also must be insulated.

Cold loft and insulated water tank and all pipework.

Figure 3.1 Cold loft and insulated water tank and all pipework.

In the case of inhabited lofts in most situations it is necessary to insert a vapour barrier between the insulation and the plasterboard internal finish. However, some insulants claim to render a vapour barrier unnecessary, for example Foamglas. Insulation board backed by aluminium foil is the most efficient (Figure 3.2).

Insulation for a cold loft.

Figure 3.2 Insulation for a cold loft.

Insulants for lofts

Between and above floor joists

Fibre-based insulants are the most appropriate such as glass wool, rock wool, cellulose and sheep’s wool. Thermafleece sheep’s wool insulation from Second Nature has received an Agreement Certificate which confirms compliance with the Building Regulations requirements for roof and timber-framed insulation. Excel Fibre Technology of Ebbw Vale produces Warmcel-RF from recycled newsprint. The fibre is pumped into the loft space by specialists. The fibre is produced by a low energy mechanical process which returns the newsprint into its original fibrous state (www.house-builder.co.uk).

If there is a risk of moisture infiltration in a loft it is advisable to use cellular glass or one of the organic synthetic insulants.

Warm lofts

Here the cellular insulants should be applied, either mineral (cellular glass, e.g. Foamglas Wallboard) or one of the organic/synthetics (EPS, XPS, phenolic) (Figure 3.3).

If a roof is being totally renewed it may be preferable to place the insulant over the rafters, (such as Foamglas Readyboard) and fixed to the rafters and bonded together with a proprietary adhesive. Battens are fixed to the insulation board. A waterproof membrane is placed over the battens and finally counter-battens are fixed to support tiles/slates.

Insulation for warm lofts.

Figure 3.3 Insulation for warm lofts.

Note: It is important to ensure the ventilation gap of 50 mm between the eaves and the ridge is maintained to avoid condensation.

As a guide, to achieve a U-value of 0.2 W/m2K within the warm loft zone the thickness of insulation required is

Mineral wool, Lambda about 0.037

250 mm

Cellular insulants, Lambda about 0.022


220 mm

For a cold loft (U-value 0.16 W/m2K)

Mineral wool

275 mm

Cellular insulants

250 mm

Spray applied insulation

In some instances there are advantages to employing sprayed insulation. This is usually a two-part polyurethane foam which, when applied to the underside of a roof, bonds to slates or tiles and battens. It not only provides insulation, but also a waterproof barrier which firmly secures the slates/tiles in place. It expands on application to seal gaps preventing penetration by wind-driven rain or snow. The slates/tiles are also less prone to impact damage. The specialist contractor will advise on the requirements to meet the ventilation requirements under British Standard (BS) 5250 Control of Condensation in Buildings.

The insulation is applied to a thickness of 100 mm to satisfy the current Building Regulations to achieve the U-value of 0.16W/m2K for cold lofts. One specialist installer which has received a BBA Certificate for Insulation (93/2939) is ISL Renotherm Ltd (Figure 3.4) (www.islrenotherm.co.uk).

Sprayed insulation by ISL Renotherm.

Figure 3.4 Sprayed insulation by ISL Renotherm.

Flat roofs

Roofs with bituminous felt covering can be enhanced with rigid cellular insulation. It is possible to use felt-backed insulation panels which can then be finished with two further layers of felt or high performance single membrane.

Main points

• Insulating the loft heads the list of cost-effective insulation measures.

• It is first necessary to decide if the loft is to be a cold or warm space. If there it is to be an inhabited or storage space it must be warm.

• It would be prudent to opt for a warm loft to facilitate change of use in the future.

• In a cold loft the water storage tank should be insulated, except on the underside.

• The levels of insulation should conform to Part L of the Building Regulations.

• In most situations it is necessary to maintain at least a 50 mm ventilation path behind the insulation to avoid condensation.

• With specialized treatments, such as spray insulation, it is essential to use a qualified installer, preferably with a BBA Certificate for Insulation.

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