6.7.7 Timber doors and windows
Timber and wood-based materials shall be of suitable quality and be naturally durable or suitably treated. Issues to be considered include:
- quality assurance
- classification and use
- drying shrinkage
- preparation and finish.
Quality assurance#
Manufacturers of timber doors and windows should hold appropriate third-party certification to assure the fitness for purpose and quality of their products.
Classification and use#
Timber windows should:
- conform to BS 644
- have a minimum 15mm rebate where double glazed units are to be installed.
Timber and wood-based materials should conform with the relevant requirements of BS EN 942 as shown in Table 3.
Table 3: Relevant requirements of BS EN 942
| Component | Requirement |
|---|---|
| Glazing beads | European Redwood |
| Casements and sash windows | J classes |
| All other elements | Table 1 of BS EN 942 |
In England, Wales, Northern Ireland, and the Isle of Man, planted stops are not permitted on frames to external doors.
External doors should be 42.5mm minimum (44mm nominal) in thickness.
Drying shrinkage#
To minimise drying shrinkage, the moisture content of joinery, when fixed, should not exceed the value given in Table 4.
Table 4: Moisture content of joinery
| Joinery items | Moisture content (%) |
|---|---|
| Windows and frames | 17 |
| Internal joinery: Intermittent heating Continuous heating Near to a heat source | 15 12 9 |
Notes
On delivery, the moisture content should be within +/-2% of the values specified.
Preparation and finish#
The following elements of timber doors and windows should be of naturally durable timber or timber pre-treated against fungal decay:
- external door frames
- windows
- timber surrounds to metal windows
- external doors, other than flush doors.
Where material is:
- to be painted, it should be primed before fixing
- to be stained, it should have the first coat applied before delivery to site.
Compatibility between preservative treatment or primer, with glazing compounds, sealants, and finishes, should be checked with the relevant manufacturers.
Prefabricated items should conform with the relevant parts of BS 1186: Part 2, including:
- the fit and construction of joints and moving parts
- the construction of finger joints
- gluing and laminating
- surface finishes.
Last updated: 2nd January 2024