Category Archives: Foundation

Starting the Pier and Grade Beam Foundation.

In our earthquake prone region of Northern California, building codes are incredibly strict and complex. This particular site has a high content of sand and the building codes require that we take the foundation piers to a depth of 11′.

The piers support the load of the building and prevent the foundation from settling.

Rebar structure for the piers.

Ready to pour the piers.

Foundation Grade Beams

The beams trasfer the vertical load imposed on the span (or middle) of the beams to the concrete piers.

Cardboard forms placed at the bottom of the trench decompose and create a void which prevents unwanted uplift on the grade beams.

A conditioned crawl space will be constructed above and allow us to insulate the structure from moisture and cold ground temperatures from the sub-soil.

High Performance Foundation Technology: Insulating Concrete Forms (ICF).

High Performance Foundation Technology: Insulating Concrete Forms (ICF).

We are building our foundation walls using Insulating Concrete Forms (ICF) which are rigid plastic foam (EPS – Expanded Polystryrene) forms that hold concrete in place during curing. The ICFs remain in place to serve as thermal insulation for the concrete foundation walls.  These ICFs are made by Greenblock and have an R-value of about 22.

The ICFs have plastic webs every six inches for strength and for tying the two walls of EPS foam together. Rebar is placed and tied to the webs as we place layers of ICF blocks together… kind of like Legos!

Once the concrete has cured, ICFs form an incredibly strong structure that is permanent and durable. Since the protective insulation provides an ideal curing environment, tests conducted by the Portland Cement Association have shown that concrete is up to 50% stronger than concrete cured in traditional wood form systems.

We brace as we stack anticipating the pressure from the concrete pour. The ICF’s will be pumped full with a soupy concrete mixture held to a 5″-6″ slump.

Pre-manufactured 45- and 90-degree corners and a precision alignment system helps to adjust the walls to ensure a perfectly square and plumb structure.

The same system is used for the attached garage.

Our crew has laid rebar horizontally and vertically inside the ICF’s to create a structurally sound unit designed for the expected vertical and lateral loading conditions according to the structural engineer’s specs. This is earthquake country so there is lots of steel!

It’s time to call for the concrete.

Energy Efficient Foundation: Concrete Pour into ICFs

By using Insulating Concrete Forms (ICF’s), reinforced concrete is sandwiched between two layers of lightweight insulating EPS foam. The wall that is created provides a combination of air tightness, strength, sound attenuation, insulation and mass.

This is a LEED Platinum construction project using sustainable materials. We are using a special concrete mix which replaces half of the Portland Cement content with flyash. Flyash is a waste by-product of coal-fired power plants. We save embodied energy contained in the concrete at no loss of strength while keeping the flyash out of a landfill (…and this sustainable concrete mix doesn’t cost any more than standard concrete!)

No wood forms to strip!! …saving wood and labor.

We just have to remove a few wood stakes used for bracing and recycle them.

Next up: waterproofing the exposed foundation walls.

Moisture Management of the Foundation: Liquid Rubber and Stucco Coatings

The crew is applying a special blend of adhesive, high strength, elastomeric liquid rubber to the exterior ICF walls which will create a water-proof membrane around the foundation. This coating is waterbased and contains no petroleum. It is non-toxic and VOC-free.

On the protected, interior side of the crawlspace we spray on a thin hard-coat stucco product and back trowel it over the relatively soft EPS foam walls of the ICF’s. No water proof membrane is required on the interior side. It’s easy to apply the stucco with an air compressor, hose and sprayer and provides a uniform protective barrier.

On the exterior side we spray on the same hard coat stucco over the water-proof membrane and then embed a fiber glass mesh material into the base coat for added strength. We finish with a second coat over the fiber glass mesh and trowel the finish.

It’s time to install the perimeter drains and backfill.

Moisture Management of Foundations: Perimeter Sub-Surface Drainage

The finished soil grade will be sloped away from the building so that surface water will naturally drain away from the structure. As an additional best practice for managing site and foundation drainage, we have installed a sub-surface “French drain” system at the base of the foundation walls to insure that sub-surface water can never accumulate and seep into the crawlspace. Storm of the century or flood?? …bring it on. This house will stay high and dry.

The building pad is graded so that sub-surface water will naturally flow to the sides and then the rear of the lot. Gravity put to good use.

A French drain or sub-surface perimeter drain is a trench filled with gravel encapsulating a perforated pipe at the bottom. The pipe and gravel are wrapped in a protective “geotextile” fabric to prevent fine soil from entering and clogging the pipe holes. Moisture accumulating in the trench percolates down and enters the pipe which transports the moisture to a point of discharge away from the building.

Here is where it all comes together at the rear (lower grade) of the foundation. The drain pipe coming from under the crawlspace floor from the 4″ gravel drainage plane joins the exterior perimeter drain pipes and runs down and away 20 feet to a gravel pit. There is a backflow preventer as well so that neither air nor water can enter the building through the drain pipe.

The perforated pipe used for French drains is typically manufactured with two parallel rows of perforations (round holes) which are positioned on the under side of the pipe. This guy must be praying to the gravel gods or something?

The perforated drain pipe has been fully encapsulated with at least 6 inches of 3/4″ drain rock on all sides.

The landscape fabric is carefully folded over the top of the gravel to form a barrier against soil intrusion into the drain trench. This foundation drain system is complete and ready for backfill.

The French drain system properly designed and installed below grade at the base of the foundation walls relieves hydrostatic pressure and is a very valuable component of our site and foundation moisture management. This is a best practice required by the EPA Indoor Air Plus certification we are following on this project.

Mudsills – Where the Framing Meets the Foundation

The framing meets the foundation at the mudsill and the space between them can be the cause of serious air leaks which transport moisture and waste heating/cooling energy. In order to insure an airtight crawl space we made a tight seal between the mudsill and the top of the foundation by placing polyethylene sheeting between the mud sill and the top of the foundation.

The mud sill assembly starts with a 1/4″ closed-cell polyethylene foam gasket directly over the rough surface of foundation wall concrete. The gasket fills gaps and protects the 10mil poly sheeting strips which are placed on top of the gasket. The pressure treated mud sill is then placed over the poly sheeting.

The tough poly sheeting over the top of the foundation acts as a capillary break and vapor barrier preventing moisture in the concrete foundation walls from wicking into the interior wooden structure or evaporating into the interior crawlspace area.

Photos showing the inside foundation wall edge flashing sealed with foam and roof edge flashing screwed to the plastic ICF web. This cap acts as the interior side air seal

Inspection is a constant activity at our job site …but this guy looks confused.

The exposed flap of poly sheeting will be sealed to the exterior sheathing to create a durable air seal at this critical foundation to framing intersection. Next, we begin the crawl space girders and joists.