Architecture, Engineering & Planning EVstudio | Denver & Evergreen Architect | Colorado & Central Texas | Blog » Foundation

Don’t Forget to Check your Sump Pit and Pump

Jim Houlette — Thu, 19 Jan 2012 21:00:51 +0000

Your home may or may not have a sump pit. If you have one be sure to check it every few months, especially when you may have heavy rain. Most people forget about the sump pit leaving them open to a good chance of major problems.

When checking your sump pit check for the following items:

Standing water more than 4"
Properly working sump pump, it should turn on when the float is raised
Discharge pipe properly attached with no leaks
Discharge pipe exists the dwelling and extends at least 5ft away from the foundation
Water entering sump pit, is it dripping or pouring in?

Around the Denver area many houses are built with an elevated structural floor. When you are checking the sump pit be sure to check the conditions in the crawlspace. Feel the soil to see if it feels soft below the vapor barrier. Soft or muddy soil is a sign of high water content. Also, check the floor joists for signs of rotation or buckling. If the foundation wall is exposed look for cracks larger than 1/8" wide.

If you allow water to collect in the sump pit it will eventually rise to a level where the water then collects in the perimeter drain. Once water collects in the perimeter drain the foundation is at great risk to move if swelling soil is present. Also, you are exposing your house to potentially flooding during a heavy rain.

Originally posted 2009-12-20 22:44:14.

Resistance Piers for Economical Foundation Repair

Adam Denton — Thu, 19 Jan 2012 21:00:37 +0000

EVstudio is asked quite frequently to perform structural evaluations of cracked foundation walls. These cracks are often due to settlement. Modern design philosophy (and most geotechnical reports) calls for the original structural engineer to design foundation walls to clear span ten to fifteen feet to account for soft patches of bearing soil or soils that may be become saturated and hydro-consolidate (shrink in volume when wet). Older homes are more susceptible to damage because they were typically not designed with this in mind. This is not to say they were designed poorly, there were just different design philosophies and industry standards at the time they were constructed.

Installed Resistance Pier Bracket

How a resistance pier works is quite simple. First, a steel bracket is fastened to your foundation, typically at the footing. Then a hydraulic ram is installed on the bracket which drives a steel pier into the ground. Using the hydraulic forces in combination with the weight of the structure above, the steel pier is driven down through the softer soils (which are causing the settlement problem) until bedrock or suitably firm soils are reached. Once the pier reaches competent bearing, the foundation is stabilized and in some instances can even be raised back into a level position.

EVstudio works closely with Pinnacle Structural Services in the evaluation of foundation repairs utilizing the resistance piers as one of many considered solutions.

For more information on resistance piers please watch this informative video.

Originally posted 2011-09-24 00:49:33.

Steel Screw Pile Foundation

Jim Houlette — Thu, 19 Jan 2012 21:00:31 +0000

A deep foundation system that is gaining popularity in areas with difficult soil, contaminated soil and due to its speed of construction is steel screw piles.

At first glance screw piles look like the typical helical pier. However, there are significant differences that make a dramatic change in capacity. First, the screw piles are installed as a single continuous piece in lieu of sections bolted together. Second, the machinery used to install screw piles is larger and capable of producing a higher torque.

The components of a screw pile are simple; a steel shaft, steel helix at bottom of shaft, and a connection plate at the top of the shaft. Screw piles can vary in size to accommodate different design loads. The steel shaft size is a function of axial load, torsion during installation and thickness due to corrosion. The helix is a plate that is shaped just like the threads of a wood screw and engages the soil to distribute the axial load and it locks into place to provide tensile loads as well.

One of the first questions people have is, “How long will it last until failure from corrosion?” There are several factors that go into corrosion of steel; oxygen, moisture, dissolved salts and other corrosive chemicals. Since there is very little oxygen in the soil, corrosion is limited and can be controlled by using thicker material to allow for expected corrosion. The life of steel screw piles can be 50 years to an indefinite period depending on the type of structure and life span needed.

I designed foundations in Stapleton where the site was located over the old terminal and contaminated soil was discovered. If typical straight shaft drilled piers were used the spoils from drilling the hole would have had to been bagged and disposed of properly. To avoid bringing contaminated soil up to the surface steel screw piles were used.

I list a lot of PROS below and for good reason. I have been very impressed with screw piles and the wide range of uses of them. EVstudio was recently visited by Alpine Site Services for a lunch and learn. Mike Oliveira discussed how screw piles are installed and the many advantages to their system over other typical foundation types. What really impressed me was the speed of placement of screw piles. Alpine can place 30 to 50 screw piles in one day!

Another great advantage to screw piles is that they can be placed at an angle to provide bracing and tension resistance that is aligned with the force of the tension. An example is a typical counterfort that braces a foundation wall. You can see the angled screw pile above.

PROS
Fast Installation
Can be Proof Tested
Negligible Uplift Pressure from Swelling Soil
High Capacity up to 500kips
High Tensile Resistance
Made from a reusable material (LEED point)

CONS
Specialized System
Large Equipment
Concerns with Corrosion

Learn more about different foundation types.

Originally posted 2009-10-10 00:21:43.

Straight Shaft Drilled Concrete Pier Foundation

Jim Houlette — Thu, 19 Jan 2012 20:59:49 +0000

When the soil is unstable and does not allow for a typical spread footing foundation a deep foundation that bears on stable soil below is needed. A deep foundation supports the structure by bearing on stable soil below the unstable soil. It may be helpful to think of a house above water supported by columns. The water represents the unstable soil and the columns bypass the water and bear on the stable soil below the water. Some of the earliest deep foundations were built the same way. The Aztecs built walkways over water by hammering logs into the bottom of the lake bed. This is a typical driven pile foundation, but the same principal applies.

There are many different types of deep foundations. In this post I will focus on Straight Shaft Drilled Concrete Piers. But other deep foundation systems include, wood or steel piles, helical piers, caissons and screw piles.

Straight Shaft Drilled Concrete Piers are constructed by drilling a hole into the ground and filling it with concrete and reinforcing. The diameter of the pier varies depending on the load the pier must support. A 10” to 12” diameter is typical for light loads in residential. Typically, a pump truck with a long tube is used to place the concrete directly at the bottom of the hole to displace any water.

The reinforcing is needed to provide a tensile strength for the pier to resist uplift and moment forces. For small residential piers three to four vertical bars are placed the entire length of the pier. As the loads become larger, a cage of steel may be needed in addition to the full length vertical bars.

Drilled concrete piers must be designed to support the applied loads from the structure and the forces from the unstable soil. First, the applied load from the structure is transferred into the pier and the load is distributed into the bearing soil through skin friction and end bearing. With unstable swelling soil an uplift force may be applied to the pier as the soil swells pushing in on the pier. I like to describe this action similar to the water snake or water tube toys. When you squeeze the toy it slips out of your hand. Obviously, concrete doesn’t behave like water, but when the soil pushes in on the concrete pier the soil pushes to concrete pier up and out of the ground. So the pier must extend deep enough into stable soil to resist this force, therefore, creating a tensile force between the stable and unstable soil layers.

The design of deep foundations can get very complex and the design allows for very little forgiveness if done incorrectly. Unfortunately, this has caused many geotechnical and structural engineers to over-engineer drilled piers.

PROS
Minimal labor
Bypasses unstable soil

CONS
Expensive
Subject to failure if incorrectly designed
Does not address basement floor, so an elevated structural floor is typically needed

Learn more about different types of foundations

Originally posted 2009-10-03 00:01:44.

Helical Pier Foundations

Jim Houlette — Thu, 19 Jan 2012 20:59:45 +0000

Helical piers are typically used when repairing failed shallow foundations. The helical piers are a deep foundation system that can be placed alongside existing foundations with very little interference.

However, helical piers are also used for new construction as an alternative to typical straight shaft drilled piers. EVstudio recently designed a new foundation using helical piers due to high water table and swelling soil. With a small surface area on the steel shaft the helical pier is very stable is highly expansive soil. We have also recently used helical piers for an addition to a home. There was no soils report, but the house was on drilled piers. A drill rig for new drilled piers could not gain access to the backyard, so helical piers installed using smaller machinery was recommended.

The real advantage helical piers have is their use for repairing moving foundations. The entire existing structure can be underpinned using helical piers that are bolted to the bottom of the foundation. Once the structure is underpinned the moving soil below the footing can be removed, establishing a void space separating the structure from any future movement.

PROS
Fast Installation
Can be Proof Tested
Negligible Uplift Pressure from Swelling Soil
High Tensile Resistance
Moderate to Small Equipment Needed

CONS
Specialized System
Concerns with Corrosion

Learn more about different types of foundations

Originally posted 2009-12-11 00:54:22.

Quickly Construct Concrete Pad Footings with FASTBAG

Adam Denton — Thu, 19 Jan 2012 20:59:39 +0000

At a recent seminar I attended I was introduced to the Fab-Form product called FASTBAG. This product is brilliantly simple….a textile bag you can fill with concrete and reinforcing bars to take the place of the wood formwork traditionally utilized to construct pad footings.

FASTBAG in the field.

The bags come in multiple sizes designed to replace standard pad footing sizes. While the shape of the filled bag does not look like the traditional footing the contact patch and load path are designed to be identical to a square footing as illustrated below.

I admit I have not seen these bags used in practice and unless I come across a project that requires the use of multiple pad footings I am not certain they would pay off over traditional wood forms for new construction. However, I do a lot of retrofit structural design for residential repairs and remodels and I see that the FASTBAG would have a wonderful application in this arena. I have had many projects that require new concrete pad footings to be constructed in very close quarters such as crawlspaces. I can see this product being a considerable help to a contractor who needs to construct a footing deep inside a crawlspace with only 20” of clear space to maneuver in. Stay tuned to this blog for a follow up report on the real world application of this product.

Originally posted 2011-03-31 00:21:24.

Insulfoam R-Tech Under-Slab Insulation

Beth Concha — Thu, 19 Jan 2012 20:59:27 +0000

The builder for the Haley Residence we designed in Evergreen is using Insulfoam R-Tech for the under-slab insulation. Insulfoam R-Tech is a high-performance, block-molded expanded polystyrene (EPS) rigid insulation product for under-slab applications. It is an ideal solution for projects that incorporate radiant-heat flooring systems, as the picture above shows. The material is extremely lightweight, has a high moisture resistance and is 100% recyclable. It contains no ozone-depleting HCFCs or formaldehyde and can be used toward LEED credit requirements.

Insulfoam’s compressive strengths range from 1,140 to 8,460 pounds per square foot, and is currently the industry’s leading product in geofoam applications to construct highways, interstate on-ramps, and airport runways. It also offers an extremely stable R-value and is very versatile. Insulfoam products are available in a wide variety of sizes, shapes and densities which helps minimize unwanted labor and material costs. It typically comes in 4’x8’ sheets with thicknesses from 3/8” to 5” in 1/8” increments. It also has an optional InsulSnap feature which allows the user to cleanly break the sheet into any desired width.

Insulfoam R-Tech has also been used successfully for numerous commercial and industrial applications as well and is not only used for under-slab insulation, but also basement walls, crawl spaces, interior walls, wall sheathing, and siding & stucco underlayment.

Originally posted 2010-11-17 00:54:23.

Foundation Engineering for Home Plans Purchased Online

Jim Houlette — Sat, 31 Dec 2011 21:21:10 +0000

Many people are searching the internet and purchasing home plans online. While these plans won't be custom tailored to fit your exact needs, many people find they are close enough.

However, there is one very important thing to keep in mind when purchasing these plans, the foundation and possibly framing must be designed by a structural engineer licensed in that state.

I've worked with many clients that have purchased plans online and then unfortunately find out they can't get a permit. For many building departments you must have a soils report stamped by a geotechnical engineer and a set of foundation and framing plans stamped by a structural engineer. Without these plans the building department will not release a permit to build. Of course, all building departments vary on their requirements, so contact yours BEFORE you purchase plans online. I highly recommend speaking with an architect as well before purchasing the online plans. You may find out that you will get more for your money when working with someone that understands your needs.

But if you have already purchased plans off the internet and in need of an engineer to design your foundation and possibly verify or design the framing plans EVstudio will be happy to help. We are experts in residential design and have designed all types of foundation systems. We also work with many builders that are familiar with many of the plan providers found online.

Originally posted 2011-03-19 00:19:01.

Repairs to Concrete Foundations Made Simple Using Carbon-Fiber Kevlar Grid Straps

Jim Houlette — Sat, 31 Dec 2011 21:20:52 +0000

From Fortress Stabilization Systems

EVstudio recently met with Pinnacle Construction where they introduced us to Carbon-Fiber and Kevlar Grids used to repair foundation walls. Carbon-fiber has recently been introduced into the construction industry due to its very high tensile strength, lightweight and workability. Sections of the grid can be adhered to the concrete surface using a high strength epoxy bonding agent.

Fortress Stabilization Systems appears to be the leader in introducing this new technology to the construction industry, applying it to many different situations from bridges to basements. The most useful application for residential would be the Carbon Staples, Kevlar Neckties, and various shapes of Carbon-Fiber/Kevlar grids used to control cracks and provide additional strength to an otherwise failing foundation wall.

EVstudio's structural department is very excited to research more about Carbon-fiber and other applications it can be used in. Carbon-fiber is a great alternative to commonly used steel repairs.

From Fortress Stabilization Systems

Originally posted 2010-03-02 00:01:01.

Foundation Wall Height Design Considerations for Residential Garages

Kacy Landsittel — Sat, 31 Dec 2011 21:20:46 +0000

There are many ways that openings like doors and windows come into consideration with respect to how we, at EVstudio, design foundation walls. More specifically, there are special criteria that go into a foundation wall design for residential garages because the threshold of door openings are at grade elevation. It is firstly critical that the wall maintain a minimum height of 6 inches above grade to prohibit moisture penetration to the typical wood framed structure it supports and of course the interior too. The foundation wall has to also maintain proper frost depth, which is a specific distance below grade, determined by local building codes and varies by location and state. Typically in our plans, the heights of a foundation wall are all relative to the finished floor elevation. However, when it comes to incorporating a swing door or an overhead door, the distance that a portion of the foundation wall we specify to be dropped is relative to the wall at that particular location.

There are some general rules we go by and different circumstances can result in a variety of solutions. For a typical above grade garage accommodating one car length in depth, we normally set the top of foundation wall height a minimum of 6-12 inches above the lowest point of the top of the garage floor slab. There are a variety of reasons the top of foundation wall is set to where it is and some architects and builders take that into consideration on a case by case basis, others just conform to standard practices. Also, we specify to slope the garage floor, and is usually 4-6 inches of fall from back to front depending on the depth of the garage and the presense of any floor drains. The result then at the rear of the garage is that the foundation wall ends up at 2-8 inches above the rear of the garage floor. For the allowance of a swing door or an overhead garage door, whether it is at the rear of the garage or the front, not only does the foundation wall need to be lowered for the purpose of the door threshold, but it also needs to be dropped further to allow for the floor slab to be thickened for structural support of the slab itself, stabilization of the adjoining foundation walls, and also the load of vehicles above. This thickened slab is formed and poured after the foundation walls have cured, which is why specifying the distance of the drop itself is important for the workers in the field who set up the form work for the concrete that is to be poured. We set the vertical depth of the thickened slab at a minimum of 8 inches below the 4 inches of actual floor slab, or 12 inches below the lowest top of slab height .

Once we have determined what height the foundation wall needs to be above the lowest top of slab height and take into account the 12 inches of thickened slab, the drop in the wall for an overhead garage door is pretty easy to calculate. For the graphic example above, I have set the foundation wall height at 8 inches above the lowest point of my top of slab height, so the net distance for dropping the foundation wall is 8 inches plus 12 inches, or 20 inches. While an above grade garage will usually have a continuous foundation wall height, we specify the necessary drops in it so doors can be incorporated. All in all, each project requires its own analysis to determine foundation wall heights and these design considerations are critical for every project.

Originally posted 2009-11-01 02:00:36.