What Is Platform Framing (It’s Not A Podium)?

by Erik North on October 22, 2011

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What is platform framing home construction?

Everyone has a mental image of different types of home construction. From Amish barn raisings to frontier log cabins, you can summon a picture of folks building their homes. The indelible picture of modern home construction, likely from a blue collar tinged movie or TV show starring D.B. Sweeney or Matthew Fox, involves plywood, 2x4s and unfinished walls.

As an aside, my favorite part of movies and TV scenes like these are the star hammering nails with an actual hammer. Very blue collar but my dad and I were building garages and additions back in 85-86 and even then used a nail gun.

What Is Platform Framing?

This image depicts modern platform framing. Platform framing is the most common method used in modern residential buildings. The name is derived from how the building is assembled. Each subsequent floor is built on top of the platform ceiling of the previous floor.


 
A platform framed building starts with setting the foundation (OK, not many start with the roof). The 1st floor platform is built on the foundation sill and band joist. Once the sub-flooring is installed, the first floor walls are constructed.

What is Platform Framing – Construction

Newer homes use 2×6 studs space at either 16 or 24 inches on center for the walls. Once the walls are framed, the floor joists and 2nd floor sub-floor are installed. Wash, rinse and repeat for each subsequent floor.

The exteriors of the wall assemblies are usually sheathed with plywood or OSB, adding rigidity and sheer strength. Adding a weather resistant barrier allows construction to move indoors, installing the heating system, other house systems, cavity insulation and finishing (love how I condensed a six month process to one paragraph).

What is Platform Framing – Advantages

Platform framing supplanted balloon framing and post and beam construction for several reasons. It is less expensive because it doesn’t require the 18 or 27 foot timbers of balloon frames (think about how long a tree takes to grow 27 feet…then multiply by 600,000 homes a year).


 
Platform frames produce a very sturdy building frame, being continually reinforced by the exterior sheathing. Unlike balloon frames which are open through their entire length, platform framed buildings don’t require fire blocks. Finally the walls are much lighter so are easier and safer to assemble.

What is Platform Framing – Disadvantages

The disadvantages of platform framing contrast more with modern construction than historic ones. The more complicated housing frames get, the tougher it is to tighten the building envelope. The sheer, huge number of framing joists in modern houses make it challenging to tightly seal the air barrier.

Thermal bridging (see this article for details on thermal bridging) is a big Achilles heel of platform framing (or any wall assembly with heavy wood timbers). Modern code is moving toward mandating techniques, like external insulated sheathing, which stops thermal bridging. Construction with advanced framing techniques minimize thermal bridging or with structural insulated panels (SIPs) eliminate both issues entirely.

What is platform framing? It is the most widely spread modern residential construction technique. The low expense and advantages helped platform framing overtake older techniques. As energy efficiency becomes more prominent, platform framing will adapt and be supplemented by other techniques.

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