Interstitial Spaces Part 1 [Design]

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NOTE: THIS WILL BE A TWO PART POSTING DUE TO ITS LENGTHIER TOPIC. One of the things that is a challenge with all design and architecture, is how to produce something that achieves what you want, perhaps better than you expected, for the same or even less cost. One of the strategies that we like to use here at The 4Corners is something called an interstitial spaceFirst developed in the 1960's, the architect Louis Kahn brilliantly used them in his Salk Institute in La Jolla, CA. Interstitial spaces provide:

  1. Smoother framing inspections for city inspectors
  2. Quicker and simpler install of all utilities / services
  3. Labor cost savings due to quicker install times.
  4. Better sound separation between occupied floors
  5. Easier repair access

What is an interstitial space?

Basically an interstitial space is a space between spaces. In architecture it used as a space for mechanical and electrical services. By locating these services within this horizontal cavity, its easier to adapt the rooms above and below to evolving needs. For this reason, the most common buildings that use interstitial spaces are hospitals and laboratories.

In residential construction you rarely if ever see it. We however, love it. Consider the fact that one of the biggest costs to a any project is labor; usually amounting to 50% of total hard costs. Changing out fancy tile for example won't go anywhere near as far as reducing 1 day of labor cost to your project, give or take. So let's explain why we like it and why we use it.

Traditional Construction Method

Image - Traditional Construction

Image - Traditional Construction

Fig 1. Traditional residential construction showing all services embedded within floor joist and floor assembly.

In the typical construction method, shown above, all utilities are run through the floor joists. This is always a challenge for all the subcontractors. As you can see in Fig 2 below, you get a lot of conflicts; pipes running into each other. More importantly, every service needs a hole bored through the joist in order to fit; this takes much time and effort. After all of these utilities are in, you usually end up with a swiss cheese effect and the building inspectors hate that. So guess what. You have fix that, and that takes much time and effort. Other issues include, drywall screws and or nails puncturing critical piping, soffits becoming necessary when two services just can't pass each other (such as the drain pipe and HVAC duct below, and wood blocking (which prevents joist twisting) being insanely hard to deal with.

Image - Traditional Construction - Close Up

Image - Traditional Construction - Close Up

Fig 2. Close up of floor assembly in traditional construction method.

All of these issues are easily handled with an interstitial space. I would be remiss if I didn't note than one other solution to this has been the use of open-web joists, or engineered joists with pre-punched cut out areas. We have not used these to date, but the additional material cost may be overshadowed by what we consider the advantages of using an interstitial space.

In the next post, we will explain how we create our interstitial spaces and how we used them in our most recent project, Beethoven Four. Check back soon!

Update: Check out the 2nd part of this post here.