Building a new house in Palo Alto

Building a new house in Palo Alto

Sunday, September 23, 2012

Subfloor construction & tricks to avoid a haunted house

Ruh roh, spooky house!
It's that time of year...the days are getting shorter, the supermarkets are stock piling Halloween candy and Fall is creeping up on us. Our construction is in full force and we're aiming to have the walls and roof in place before the rains come. The highlights of this next stage are some simple tricks our general contractor Jeff uses to avoid creaky floors and the horrors of poor plumbing. It's tempting to shave costs in the areas of the house you don't see, but cutting corners in the subfloor will come back to haunt you.
The Mudsill: When wood comes in contact with concrete it must be pressure treated to prevent rotting.
After the foundation comes the subfloor construction. The subfloor is the base for framing the walls and roof. It begins with the mudsill, which is treated lumber that is bolted down to the foundation.  Pressure treated posts get mounted vertically in the concrete piers and horizontal beams which extend across the length of the foundation are placed on top of them. Next, 2x6" floor joists get framed in creating a structure that looks like a platform bed.
Astro supervising the layout of floor joists.
Tip #1: Avoiding a bouncy floor
One trick to creating a more sturdy floor is to double the floor joists in high traffic areas and rooms that will bear a lot of weight. This prevents the feeling of bouncy or shaky floors when people are moving around. Because we plan to have a large island and super sized appliances, we doubled up on the floor joists in the kitchen. Since people tend to congregate in the kitchen, this makes a lot of sense for most homes.

See if you can spot our kitchen (hint, it's the area with double floor joists)
Once the floor joists are in, the plumber sets up all the underfloor plumbing lines. Our plumber Antonio installed a combination of copper, cast iron and black PVC pipes--copper for the water supply, cast iron for the vertical drops and black PVC pipes everywhere else. One side note, some cities (like San Francisco) require all cast iron pipes by code.

Don't be haunted by poor plumbing. 
Tip #2: Quiet your plumbing
While cast iron pipes are significantly more expensive and harder to install, they are quieter and better for sound control. Jeff has our plumber using cast iron pipes for the all the drops and pipes that run through our walls.

Tip #3: Beware of the PEX (aka rat bait) shortcut 
This tip is courtesy of my builder pal, James Witt.  PEX tubing is a popular way to save money. It's a flexible waterline that is increasingly used to replace copper pipes. Unless embedded in a slab, James says PEX is a shortcut you don't want to take because rats treat it like a chew toy.  PVC should also not be used for water supply pipes because they can leach chemicals. James says  if you have exposed piping, copper is well worth paying for in order to avoid pesky leaks and ensure safe drinking water.

Once the plumbing is set up, insulation goes in and we are now finally ready to cover it all up with the plywood subfloor.

Subfloor insulation keeps the winter chills out.
Tip #4: Avoiding creaky floors
Creaky floors are often caused by a loose connection between the floor joist and the subfloor. To combat this, Jeff made two small upgrades to ensure that our subfloor stays put for the long haul. First off, he opted for a premium grade glue to be applied between the subfloor and floor joists and secondly he used screw nails which are threaded and have more holding power than standard nails.

Premium glue and screw nails will keep this puppy down.
And voilĂ ! The subfloor is finis!
Scooby approved subfloor. No spooky creaks, squeaks or leaks.


  1. Cool to see the actual footprint of the house, Kay! And who knew all that was underfoot...

    And now I have a good idea of what's happening that causes me to hop from one spot to another as I approach Maya's room when she's sleeping to avoid those pesky squeaks! Do stairs get the same glue/screw nails treatment as the subfloor?

  2. We just started on the second floor and the stairs come later, so I'll keep you posted. I sure hope so. As for your creaks, if you're willing to go under your house, you can fix them!

  3. Basement Subfloor insulation are usually created of concrete. To set up subfloors, an option used by many is to build a wood made shape first. Then plyboard sections covered with insulating content and a steam hurdle are placed between the tangible and the new subflooring. This results in a hotter base for most flooring surfaces completes. The width of the plyboard or wood subflooring must be considered in regards to the weight of the flooring surfaces content as it must be powerful enough to hold all the furniture placed on the ground.