Why do some public buildings have two layers of doors?

editing_for_authors
Editing for authors: because every writer needs a good editor.

Lunatique

Fluffy Wolf
Super Member
Registered
Joined
Aug 18, 2011
Messages
327
Reaction score
23
Location
Lincoln, CA
Website
www.ethereality.info
Does anyone know why some public buildings such as shopping malls, Target stores, airports, or hospitals have double layers of doors? You open one door and there's another door just a few steps away, forming this small room between the two layers of doors.

Is it for the sake of security? If so, why?

Maybe it's to create an air cushion so the air conditioning doesn't escape as easily?

Anyone know? I tried searching the web and found nothing. I also tried calling the local Target but the store manager won't tell me. I told him I was writing a novel and he said it's not the kind of information he could give out.
 

alleycat

Behaving
Kind Benefactor
Super Member
Registered
Joined
Apr 18, 2005
Messages
72,848
Reaction score
12,194
Location
Tennessee
Primarily for energy efficiency.

It's also called an air lock.

In industrial buildings it will often be a curtain of plastic strips. Tow motors and personnel could easily go in an out but it keeps the building from losing so much of the heat or cooling.
 

Literateparakeet

Nerdy Budgie
Super Member
Registered
Joined
Dec 31, 2011
Messages
1,386
Reaction score
225
Location
Seattle
Website
lesliesillusions.blogspot.com
I believe it is for air conditioning and heating purposes. Remember when you were a kid and you mom was always yellling at you to close the door so you don't let the heat out, or in? (surely that wasn't just at my house).

In Alaska most of the homes have this too...two doors, with a small space inbetween. They call it an "arctic entry". The purpose to protect those inside from a blast of cold air every time the door opens.

Imagine a mall where there are people coming and going all day long...it does make an arctic entry seem like a good idea to keep down heating and air conditioning expenses.

I also tried calling the local Target but the store manager won't tell me. I told him I was writing a novel and he said it's not the kind of information he could give out.

LOL, he couldn't give out that information because he has no idea and won't admit it! That's my guess. :)
 

Lunatique

Fluffy Wolf
Super Member
Registered
Joined
Aug 18, 2011
Messages
327
Reaction score
23
Location
Lincoln, CA
Website
www.ethereality.info
Heh, so my guess was right. The security aspect didn't make sense, that's why I guessed it probably had to do with the air conditioning.

Thanks!
 

Chris P

Likes metaphors mixed, not stirred
Kind Benefactor
Super Member
Registered
Joined
Nov 4, 2009
Messages
20,222
Reaction score
3,898
Location
Wash., D.C. area
I worked at a Walgreen's back in high school, and we only had one layer of doors. I hated working Register 4 in the winter, getting blasted with cold air every 90 seconds when people came in.
 

WriteKnight

Arranger Of Disorder
Super Member
Registered
Joined
Mar 16, 2008
Messages
1,746
Reaction score
247
Location
30,000 light years from Galactic Central Point.
In malls, its primarily an air conditioning issue. In Banks, and jewelry stores, it's called a 'man trap'. Yes, you can lock someone between the doors as they exit, if the silent alarm has been tripped.
 

LJD

Super Member
Registered
Joined
Sep 12, 2010
Messages
4,226
Reaction score
523
Location
Toronto
When I go to restaurants in the winter, which usually only have one door, I try to sit as far from the entrance as I can to avoid the cold air that accompanies everyone who enters.

So I always assumed it was for heating/cooling.

I believe this is also one of the advantages of revolving doors.
 

patskywriter

Super Member
Registered
Joined
Aug 27, 2011
Messages
326
Reaction score
54
Location
Durham, NC, USA
Website
www.durhamskywriter.com
My local K&W Restaurant has the same set-up and it's fun to watch the people pulling with all their might to open the outside door as the inside door is closing. They don't realize that if you wait a couple of seconds for the first door to close behind you, you can open the outside door quite easily.
 

Literateparakeet

Nerdy Budgie
Super Member
Registered
Joined
Dec 31, 2011
Messages
1,386
Reaction score
225
Location
Seattle
Website
lesliesillusions.blogspot.com
In malls, its primarily an air conditioning issue. In Banks, and jewelry stores, it's called a 'man trap'. Yes, you can lock someone between the doors as they exit, if the silent alarm has been tripped.

Cool, I didn't know that.

In prison they have something like that, but it's called a "sally port" spelling???. Only with the sally port everyone knows that as you enter one door it locks behind you and you are trapped in that space unless the person in the control booth lets you out. It's easy to understand the purpose for that. They have it for vehicles too...at least where I worked we did.
 

Sarpedon

Banned
Joined
Jan 20, 2008
Messages
2,702
Reaction score
436
Location
Minnesota, USA
It is called a sally port. It is so called because Old castles had the same thing: A controlled exit where the outer doors could be opened while the inner doors remained closed, with a space big enough for a number of knights in between. When the castle was under siege, the people inside would sometimes send a bunch of knights out to raid the besiegers. This was called 'Sallying Forth."

In modern buildings, the double sets of doors are called 'vestibules,' and limit the amount of air that goes out or comes in when people leave or enter. Revolving doors are basically just tiny vestibules. Modern energy codes require them in all but single family residential buildings.
 

shaldna

The cake is a lie. But still cake.
Super Member
Registered
Joined
May 12, 2009
Messages
7,485
Reaction score
896
Location
Belfast
Does anyone know why some public buildings such as shopping malls, Target stores, airports, or hospitals have double layers of doors? You open one door and there's another door just a few steps away, forming this small room between the two layers of doors.

To stop drafts etc. Many air condition systems are designed to stop working if windows or doors are left open.
 

Elizabeth George's book Write Away