12.1 Initial period at commencement of re-use
It is important to remember that, if the building has been unoccupied for a number of years in a state of disrepair, a great deal of water may be present in the fabric and one or two years can elapse before it has all dried out. During this period, moisture may continue to appear on the walls, some of it as a result of evaporation from the fabric and some of it as condensation forming on the surfaces of parts of the envelope that have their insulating properties impaired due to absorbed water. It is essential to recognize the risk of entrapping stored water behind new work such as dry lining to walls.
12.2 Thermal insulating materials
The insulation values of open cell or fibrous materials will be adversely affected if wetted. Remedial work should include drying materials that are to be re-used. Precautions should be taken to prevent wetting of all new materials introduced into the structure.
The provision of protection against mechanical damage to insulating materials should also be taken into account.
12.3 Furniture
Consideration should be given to removing built-in furniture from an outside wall to allow heat to reach the wall from the room, otherwise water vapour could penetrate to the wall and condense, resulting in mould growth, not only on the wall but also on the contents of the furniture.
12.4 Larders and unheated stores
Particular attention should be paid to the ventilation of larders, unheated storage spaces and enclosed porches. Water vapour migrates to these areas from adjacent heated spaces where the vapour pressure is higher. Consideration should be given to the heating and insulation of such storage spaces.
12.5 Redecoration
The materials used for decoration during a period when the building is drying out should be capable of allowing moisture to evaporate through them without incurring damage. Neither wallpaper nor impervious paints should be used till the structure has achieved a near equilibrium condition with the prevailing internal conditions. Occupants should be warned that the drying out period will be protracted and be advised not to commence the decoration of walls until an equilibrium condition is attained.
12.6 Heating
12.7 Ventilation
In existing buildings, problems often arise because higher levels of comfort expectations, combined with rising costs of heating, have led to a reduction of unwanted air movement, which have become apparent as draughts, for example by:
a) removal of fireplaces;
b) draught-proofing as a cost effective method of energy saving.
Fortuitous means of natural ventilation have often, therefore, been eliminated.
While the removal of moisture at source by mechanical extraction or PSV for example, in kitchens, bathrooms and general moisture generating areas is an obvious remedy, it should be remembered that the air extracted has to be replaced by incoming air, which in turn needs to be heated.
In dealing with ventilation rates and methods in existing buildings, all the technical and economic considerations and methods of assessments given previously should be employed.
12.8 Drying clothes
Where possible, the drying of clothes inside should be avoided. If a heated cupboard is not provided or not used, occupants should be advised to restrict clothes drying within a dwelling to a room fitted with an extractor fan. When extraction is not continuous, controls should be provided to enable the extractor fan to be switched on for clothes drying.
It is particularly important not to dry clothes in unventilated rooms, especially those kept at low temperatures.
It is essential that tumble driers are vented outside or be of the condensing type.
13 Precautionary measures during construction
13.1 Construction information
The precautions to control condensation taken by the designer can be negated by lack of site supervision. Having followed the advice in the preceding sections, the designer should ensure that his design
precautions are clearly shown in the specification, drawings and other construction information. All supervisory staff should ensure that the design is strictly complied with and the work monitored. It is essential therefore that easily understood information is given to the tradesmen executing the work. The construction information should be given to the contractor and all precautions designed to prevent harmful condensation should be brought to the attention of the supervisory staff on site.
13.2 Site checks
13.2.1 Materials and storage
All materials should be checked to ensure that they meet the specification and should be stored so that they do not suffer damage.
13.2.2 Vapour control layers
It should be ensured that any vapour control layers are in the correct position, cover the whole area to be protected and are fully lapped and/or sealed in accordance with the design. Special attention should be paid to ensure that following trades do not damage the vapour control layers without repair. Where gaps are cut through, e.g. for services, the hole should be sealed.
13.2.3 Dry construction
Where dry forms of thermal insulation are used, a check should be made to ensure that they cover all specified positions, e.g. that lightweight sheet or slab insulation has close fitting joints and is free from gaps caused by broken corners, etc.
In application, dry insulation should be protected from rain or other wetting. This is especially necessary in positions such as roof insulation laid above a vapour barrier and beneath an impermeable roof finish, and also in uncompleted insulated walls.
Insulation materials liable to mechanical damage should be fixed as late as other requirements allow. A check for possible damage should be made immediately before the insulation is covered by other materials.
13.2.4 Wet construction
Due to the presence of residual construction water, in situ concrete or masonry structures take a
considerable time to reach their ultimate “in-use” insulation values. Because it is normally impracticable to allow sufficient time for complete drying out before buildings are occupied, it is important to prevent unnecessary wetting of the materials during building.
The tops of walls should be protected from rain penetration at all times during construction. This is especially important where walling materials would readily absorb water.
For floors and flat roofs full protection from rain might be impracticable but precautions should be taken to avoid unnecessary wetting, e.g. by avoiding standing water. This is particularly necessary where, for any reason, the construction is likely to be exposed for a long time.
When using wet roof screeds, where they have to dry inwards after the roof finish is complete or where they would be dried outwards only by limited ventilation to the exterior, care should be taken to prevent the ingress of excess water.
Adequate ventilation should be provided during both the construction and the drying out period.
13.2.5 Services
Gaps around services through walls and ceilings should be sealed to prevent moisture laden air getting into cold voids.
13.2.6 Draught proofing
Where draught proofing is required it should be continuous with corners and junctions joined as specified.
13.2.7 Ventilation
Most forms of ventilation would be checked during normal building supervision. Aspects which may need particular attention include ensuring that small ventilation openings, such as those to roof spaces, are provided as specified and have not been made ineffective by unintentional obstructions or by late changes in the design details, e.g. by roof insulation blocking the ventilation openings or by any interruption to intended cross ventilation.
13.2.8 Final checks and maintenance
These should include the following.
a) Replacing any insulation which has moved out of position. b) Checking that pipework and water tanks are fully lagged. c) Checking that nothing has blocked ventilation airways.
d) Checking that the performance of dry insulation is not impaired by moisture.
e) Checking that seals on hatches, mechanical and electrical services, penetrating a ceiling under a roof are intact.