A: The U-value of a wooden frame depends on the thermal resistance (R-value) of the wood and its thickness.
Different species and types of timber have different insulating properties:

  • Accoya® tends to have higher natural insulation

  • Softwood generally performs better than hardwood

  • Hardwood will usually have a slightly higher U-value

In practice, thicker sections of timber with higher R-values give lower overall U-values. The exact performance depends on the frame design and glazing details.