Airtightness FAQs

[David OLIVIER]

I think it's nearer 100-200 kWh/m2yr. Still not huge though and vastly outweighed by air infiltration losses around the edge of the door leaf or between door and wall.

A third alternative to reduce it is a cheap North American-type insulated steel-faced.PU foam door. DIY sheds there sell them for about £100. I think the whole door U-value including frame is usually 0.8-1.2 W/m2K, suggesting PH doors with a U-value of nearer 0.6 may be just a little over-priced. 

David.

[Mark Siddall]

David
What does the 100/200 kwh/m2.yr refer to? Not having a porch? Refer to 'Sustainable Solar Housing' by Hastings and Wall for more details about the porch vs PH door study.

The uk doors situation seems to be largely misleading. I did some fairly deep interogation of this the other year. Most uk door u-value calcs failed to live up to the hype. Most u-values did comply with the EN standard partially this was because few included thermal bridge calcs. Basically UK door u-values seem to rely up centre of panel values rather than the real deal.

Mark

[David OLIVIER]

This is the annual heat loss in kWh per m2 door leaf, not per m2 floor area.

Modelling in USA and Canada about 1992 found that a (solid wood) frame increased the whole-door U-value. Possibly manufacturers there now quote whole door U-values. They generally do for windows.

Steel doors are popular there because they're (1) much cheaper (2) less prone to warp than poor-quality timber. They're cheaper no doubt because bent and painted steel profiles are the technology of car manufacture, not of craftsmen machining wood laboriously by hand. The airtightness of these doors is especially worth having, given that the UK has such a windy climate compared to other countries.

One drawback of thick PH-type doors (65-75 mm foam contained in a wooden structure = a very bulky door leaf) is that the rough opening needs to become wider to be navigable, say 1050 instead of 900 mm. The implications for disabled access are also a possible issue to consider. Not sure if those have been considered yet in the UK though.

I got a joiner to build a highly-insulated door for my house - I thought the asking prices for such doors were ridiculous, and still do - but the extra 110 mm taken up by the door is quite obstructive, given the fact that in a thick wall with the door in the plane of the insulation they do not open more than 90 degrees.

To return to Frances's question, yes in an airtight building an open door only causes a brief heat loss while it's open, due to air turbulence in that region of the house. An airlock entrance might be a good thing, but might not be right at the top of the list of priorities if it costs say an extra £3k.

But so few UK buildings are "airtight" (1-3 ac/h @ 50 Pa) that this question is a bit academic today. Old stone buildings aren't this tight. In windy climates these buildings suffer constant air movement from one side to the other and a periodically open door makes conditions even more miserable.

[Andy Simmonds]

a slight aside:
top 15 airtightness results from the AECB/TSB databse: http://www.retrofitforthefuture.org/projectbrowser.php?sort=airtightasc
click the 'view all as figures' tab, to scan down 15 airtight projects.

[Dave Howorth]

I recently reread the ATTMA spec and discovered that it had changed. It used to say:

"Trickle vents, smoke vents and all passive ventilation systems should be closed but not artificially sealed. Permanently open uncontrolled natural ventilation openings should be temporarily sealed"

while now it says:

"Background trickle ventilators, passive ventilation systems and permanently open uncontrolled natural ventilation openings should be temporarily sealed"

My emphasis added. Does anybody know why the about face?

[Nick Grant]

My guess would be that it is the building envelope that is being tested not the seal on the vents which would never need to completely shut. Similarly with mech' vent that would obviously be sealed off as in operation it is meant to allow air to pass.

[Patrick Osborne]

I was just wondering if we've got any closer to a FAQ on airtightness?  I'm struggling to convince our contractor about the benefits and would like some ammunition!
Patrick