Building Construction Handbook, Eighth Edition

Buildings Other Than Dwellings (England and Wales) ~

Notes:

• For display windows separate consideration applies. See
  Section 5 in A.D., L2A.


• The poorest acceptable thermal transmittance values provide
  some flexibility for design, allowing a trade off against other
  thermally beneficial features such as energy recovery systems.


• The minimum U-value standard is set with regard to minimise
  the risk of condensation.


• The concept of area weighted values is explained on page 443.


• Elements will normally be expected to have much better
  insulation than the limiting U-values. Suitable objectives or
  targets could be as shown for domestic buildings.
  Further requirements for the building fabric ~
  Insulation continuity ~ this requirement is for a fully insulated
  external envelope with no air gaps in the fabric. Vulnerable places
  are at junctions between elements of construction, e.g. wall to
  roof, and around openings such as door and window reveals.
  Conformity can be shown by producing evidence in the form of a
  report produced for the local authority building control department
  by an accredited surveyor. The report must indicate that:

• the approved design specification and construction practice
  are to an acceptable standard of conformity, OR


• a thermographic survey shows continuity of insulation over
  the external envelope. This is essential when it is impractical
  to fully inspect the work in progress.
  Air tightness ~ requires that there is no air infiltration through
  gaps in construction and at the intersection of elements.
  Permeability of air is tested by using portable fans of capacity to
  suit the building volume. Smoke capsules in conjunction with air
  pressurisation will provide a visual indication of air leakage paths.

Element of

construction

Limiting area

weighted ave.

U-value (W/m^2 K)

Limiting individual

component

U-value

Roof 0.25 0.35

Wall 0.35 0.70

Floor 0.25 0.70

Windows, doors, roof-lights,

roof windows and curtain walling

2.20 3.30

High use entrances and roof vents 6.00 6.00

Large and vehicle

access doors

1.50 4.00

Thermal Insulation, Buildings Other Than Dwellings---2