Design recommendations

The entry door is a weak point in highly insulated houses and, as such, either a highly insulating door or a vestibule should be specified.

Table 9.3.7 Requirements for a high-performance entry

Property

Requirement

U-value

A value of 0.8 W/m2K or better should be achieved (conventional doors typically have

U = 1.1 to 2.0 w/m2K).

Air tightness

The leakage should not exceed 2.25 m3 per m perimeter and hour by a pressure difference of 100 Pa.

The tightness of the door is reported by its 'A-value' (hourly perimeter air leakage rate).

Form stability

This is essential because warping will increase air leakage.

Sound insulation

Since the ambient noise levels are lower in highly insulated houses, occupants are more sensitive to

outside noise.

Cost

Better insulation, more precise hinging, compression locking and tighter weather stripping increase

costs; but expensive doors are also tolerated in conventional houses for prestige.

Materials

Avoid foam insulation where FCKW (hydrofluorocarbons) is an output in the manufacturing.

The following advice is offered regarding location and construction:

• Incorporate an external vestibule, if possible, and include substantial glass with a normal U-value of 1.3 W/m2K to provide daylight in the vestibule (that is, 40 per cent to 60 per cent of the wall areas).

• The plane of the door should be towards the outside of the wall opening to minimize thermal bridging.

• The wall insulation could extend over the door jambs and head to further reduce heat loss, as is often done in window details.

• If the threshold is metal (aluminium), it should have a thermal break. The problem of thermal bridging at the hinges has not been solved.

• In no case should the door or entry have a mail slot!

• If there is a home automation system, the status of the door should be registered to provide a warning if the door is left ajar by accident or held open for an excessive time. A warning can also occur if it is left unlocked.

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