Windows and doors include draft proofing as part of their construction. Trickle vents that make up part of the frames should be inspected and not overly leaky. Particular attention should be paid to door thresholds where provision had been made for drainage. These drainage holes can be a common place for air to escape from or to cause drafts.
Where a letterbox is located on the front external door, it must be fitted with a draft excluder; this might not be necessary on porches but it is advisable to install regardless. Gaps at sills, heads and jambs can all allow air to leak into the cavity or directly to the outside.
