Existing buildings

Reducing heat losses

Advice given here is based on a typical house but the principles apply to any heated building.

The above illustration shows the heat loss from a typical house. This illustrates that air leaks normally account for the greatest heat losses. The good news is that the sealing of draughts is cheap and relatively easy to DIY.

To tackle heat loss from a building it is a matter of imagining every possible way in which heat may escape and systematically tackling the building elements, joints, cracks, thermal bridges etc. Having your building highly insulated and airtight is the best energy saving measure (it is hardly possible to have too much insulation) There are a number of things that a householder may easily do, including:

Seal draughts around doors, floors, windows, letter boxes, etc.
Use energy efficient lamps, boilers and other appliances
Insulate hot water tanks and pipes
Building an extension (main building or garage) on your home
Carrying out a loft conversion
Making certain alterations within your home
Installing new - or changing the positioning of old - heating appliances
Fitting hot water storage
Inserting cavity wall insulation
Replacing windows or doors
Fitting glazing in existing and/or new conservatory
Upgrading existing or fitting new air conditioning / mechanical ventilation to offices over 200 m2

When the Building Regulations Apply

The Building Regulations generally apply when building work is carried out and matters regarding energy conservation. The circumstances, under which the Building Regulations apply, include

More information on Energy and the Building Regulations

Even if not required to do so under the Building Regulations, you may choose to upgrade your house or place of work to the current standards (or better) so as to be energy efficient and minimise CO2 emissions.

Improving Insulation

There follows guidance on:

Roofs
Floors
Walls
Doors and Windows

Roof insulation

Pitched roofed buildings offer the opportunity to increase the insulation in the roof space. Check the thickness of insulation. To comply with the new Building Regulations, which came into force April 2006, the loft insulation thickness required is approximately 270 mm, depending on roof construction and insulation type. The insulation needs to be laid both between the ceiling joists and over them. Simply placing insulation between the rafters very greatly reduces its effectiveness and the required insulation is not achieved. Ensure that the insulation is well fitting without air gaps and is complete and continuous right to the perimeter. Recommended insulation types include cellulose fibre (from recycled newspapers), mineral wool fibre and glass fibre.

Remember to take the insulation over water storage tanks to prevent them from freezing during the winter. Ensure that the loft space is adequately ventilated or that water vapour can escape through a suitable breathable roof membrane.

Loft insulation over as well as between rafters

Loft insulation laid over rafters, as well as between rafters, achieving high levels of insulation

Ground floors

Suspended timber and concrete floors can be insulated on their undersides. Access to underside can be via a basement or while the floorboards are raised. Suspended floors insulated in this way will require ventilation to the void below, to prevent the formation and build up of condensation. Professional advice should be sought on how to minimise the risk of condensation.

The construction shown below illustrates one of several constructions that may be applicable. The points to watch are

Airtighness
Full fill insulation between joists
Avoid the use of netting that may allow insulation to sag
The underside layer must be vapour permeable, i.e. not plywood
A vapour control layer (e.g. polythene) is not normally used as it would retain split liquids

Insulated floor construction detail
Insulating under a suspended timber floor

T&G boards or floor panels glued for airtightness
Insulation filling void
Fibreboard panels fixed to battens on joist sides
Services in insulation

Wall insulation

These are three possible ways of upgrading the insulation of an existing wall:

Cavity wall insulation
Internal insulation
External insulation

Cavity Wall Insulation

Filling an existing wall cavity with insulation is generally the cheapest and least disruptive way of insulating a wall. The thickness of insulation is limited by the width of the cavity and the cavity needs to be at least 50mm for the process to be successful. Approach a reputable company for advice on whether the walls have a cavity and that the cavity is suitable for filling with insulation. Location, exposure of the wall and its condition are all factors which may affect a decision to fill.

Cavity wall insulation
Wall Cavity being filled by mineral fibre

The cost will typically be a few hundred pounds for a semi-detached house but could be significantly cheaper with a grant and there are various schemes run by the energy supply companies and energy advice centres.

Grants may be available check the Energy Efficiency database or phone/e-mail the Warwickshire Energy Efficiency Advice Centre (tel: 0800 512012 or 01789 842898)

Internal Insulation

If cavity wall insulation is not possible or extra insulation is required, this can be installed by drylining the walls internally. This results in a reduction of space within the building adjacent to external walls, which could be a problem in certain locations like stairways. The wall construction has to be considered as a whole and a vapour barrier is likely to be required on the warm side of the insulation. The effectiveness of such an installation is partly dependent, on the attention to details, such as the continuity of the vapour control layer, the continuity of the insulation and the control of air leaks.

External Insulation

Insulating a stone or brick building externally will change its appearance significantly. Render, timber boarding, tile hanging and other forms of cladding are more easily reproduced in the new finish and buildings with these finishes are not likely to undergo quite such a dramatic visual change. Insulating a building on the outside is thermally the most advantageous in that the masonry mass of the original construction may be used for thermal storage. Also thermal bridging around doors and windows may be minimised.

The success of the wall upgrading will depend on the design, the weatherproofing afforded by the external cladding and the details of the junctions at the eaves and verges. These junctions are not only critical with regard to weatherproofing but also visually important.

Eaves detail - external insulation retrofitted

Window and Door Replacement

The windows and doors are the 'weakest link' in the external envelope of a building. Improving the thermal resistance of these areas will have a significant effect on the overall performance of the building as well as reducing cold spots. The reduction of cold spots and induced draughts will make more of the internal space comfortable and habitable.

If the windows and/or doors are due for replacement, this is a good opportunity to upgrade the thermal performance of the building. In fact, it is a requirement of the current building regulations that replacement windows met new tougher standards, typically having a maximum overall U-value of 1.8 W/m2K for extensions and 2.0 for existing dwellings, exact details including permitted areas are given in the regulations. U-values for new / replacement glazed doors is 2.2 and for other doors is 3.0

The following table lists the U-values of different window constructions and gives an approximate U-value if covered with heavy curtains or insulated shutters.

Window U-value [W/m²K]
	Window only (daytime / nighttime)	with heavy curtains (nighttime)	with insulated shutters(nighttime)
Single glazed	4.5	3.3-3.6	2.6-3.1
Double glazed, 12mm cavity	2.8	1.9-2.3	1.3-1.7
Double glazed, 16mm cavity, low-E	2.0	1.2-1.6	0.7-1.1
Triple glazed	2.5	1.7-2.1	1.0-1.4
Triple glazed, 2 low-E, Argon filled	1.7	0.8-1.3	0.4-0.8

This table is based on information contained in European Passive Solar Handbook, CIC

Metal doors and windows are generally more conductive around the frames and hence are less energy efficient. Timber and uPVC are similar in performance and choice is a matter of personal preference. However, please note that uPVC is a plastic based on chlorine chemistry, which has a high environmental impact and is toxic in its production and disposal and has a high-embodied energy. uPVC windows normally look uncomfortable in traditional buildings and cannot be repaired like timber.

Information on window materials can found on the Green Building Store site under "Windows, doors and the environment"

uPVC window

Information on PVC by Greenpeace

Link to an environmentally friendly source of high thermal performance timber windows

The products shown here are simply illustrative of a type of product. Action 21 does not endorse any particular product or any particular manufacturer.