Semi detached

Heating systems

Gas or oil central heating would be first choice for this type of dwelling, although LPG, solid fuel and wood pellet boilers would also be quite practical if a little expensive to run. All of these systems could be supplemented by solar panels to pre-heat stored hot water.

A ground source heat pump would also be a reasonable choice in terms of running costs if there is a suitable site for the ground collector. However, this form of heating works best with low temperature emitters such as under floor heating, and therefore would be most suitable for dwellings with solid floors. The low delivery temperature also means that stored hot water would need to be brought up to temperature with supplementary electric heating.

Insulation measures

Walls

Semi detached dwellings have been constructed using a wide variety of built forms, from solid or cavity masonry to a large number of 'non-traditional' systems. Deciding the best approach to dealing with the non-traditional systems can be quite complex, and since the best solution is often system-specific it is not practical to attempt general guidance here. That said, internal insulation should be a reasonably safe measure for almost all systems provided there are no moisture penetration problems.

With cavity masonry filling the cavity will be the most economical solution provided the results of the pre-fill inspection are favourable. The best solution technically for solid walled construction is external insulation, but it would be preferable for both of the pair of semis to be treated together. If that is not possible then internal insulation, supplemented by flexible insulated linings where thickness is an issue, should be considered. However, internal insulation deals less well with thermal bridges than does external insulation.

Glazing

Many dwelling of this type will already be fitted with double glazed windows, but some older frames may not have trickle vents. If possible these should be retrofitted. If single glazed windows are not to be replaced consideration should be given to a programme of draught stripping supplemented by retrofitting trickle vents where possible.

Secondary glazing can be considered, but consideration should be given to ventilation requirements, particularly in relatively airtight dwellings (e.g. those with solid floors). In such dwellings it may be preferable to fit new double glazed units with proper provision for background ventilation.

Floors

Most older semis of masonry construction will have suspended timber floors, although solid floors are also possible. In some cases part of the dwelling may have a suspended floor with other parts (for example the kitchen floor) being solid.

Suspended timber floor can be quite draughty, especially if square edged boards have been used. Effective draught sealing of the entire floor (for example by applying hardboard or similar and sealing around skirtings with mastic) would increase comfort levels markedly. If floorboards are replaced insulate between joists.

There may be an assumption that floor insulation/draught proofing is only an issue on the ground floor, but in many older properties air infiltration into the under-floor space at first floor level and above can occur from a number of sources. These include soffits of porches and passageways, the junction between the floor and a bay, and via the eaves box in attic rooms. A proper survey of the dwelling should be carried out if effective draught proofing of floors is to be achieved.

Solid floors can be insulated using an insulation / chipboard composite. These are available in a range of thicknesses, and this approach can be taken using only 5mm of latex foam beneath a chipboard 'floating floor'. Such a thin layer of insulation will not save large amounts of energy but may be sufficient to prevent condensation. If any increase in thickness is unacceptable consideration could be given to applying insulation externally below ground level to reduce cold bridging.

Roof

Lofts should be insulated (or topped up) to a depth of 250mm insulation. Care needs to be taken to ensure that the loft space is ventilated. If for any reason the loft is inaccessible (e.g. due to low pitch) insulating the underside of the first floor ceiling can be quite practical. If slates/tiles need to be replaced insulate roof at the same time, either by conventional loft insulation (breathable sarking can help with the issue of loft ventilation) or by insulating at rafter level thus creating a warm roof construction. Insulation above rafters may be problematic if only one of the pair of semis is being treated, because the roof thickness will increase.

Loft hatches and other points where services penetrate the roof space should be sealed to prevent draughts.

Ventilation

Background ventilation should be provided in habitable rooms. Trickle vents can sometimes be fitted to existing windows, but this may not be practical for some types of frame. If this is the case through the wall ventilators could be considered (although these can easily be sealed up be tenants) or 2m of draught stripping could be omitted per room. If the rest of the structure is airtight, then whole house mechanical ventilation may be appropriate. This would also have the benefit of improving air quality within the dwelling.

Passive stack ventilation in kitchens and bathrooms can be fitted during major refurbishment, although routing ducting may be difficult in ground floor situations. Rooms in upper floors may be more straightforward. Extract ventilation, preferably with heat recovery, should be fitted in situations where passive stack ventilation is not practical.
If dampness and condensation are an issue then positive pressure (mechanical supply) ventilation could be considered.