Heaving Concrete and Asphalt – Subgrade

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In Minnesota, there are some excellent references that can be used as a guide for the design and construction of residential driveways. However, what is needed is a code that addresses the key elements of a driveway structure. I find it fascinating that there is nothing in the code that addresses the design or the construction of a residential driveway.

In my professional opinion, the key elements to a properly designed residential driveway are as follows: the proper subgrade with the required compaction, a solid base upon which the driveway material will rest (this blog is based on an asphalt driveway), the right asphalt thickness, and once the driveway is constructed, preventing water from entering the subgrade (water management system).

Proper Subgrade

What is a proper subgrade? The answer – one that is NOT prone to frost heaving.  Damage from frost heaving can result in the buckling of garage door trim which can cause the misalignment of your garage door. This misalignment can make it difficult to open and close the door.

Buckling of garage door tripm. Clay soils push concrete soils upward in winter.

Buckling of garage door apron. Clay soils pushes concrete soils upward in winter.

The subgrade should either be granular or con-bit.  Most subgrades today consist of clays and silts, soils that are considered expansive – these materials are not the proper subgrade.  If you have subgrade consisting of clays and silts, it should be removed and replaced with granular material or con–bit (this is normally referred to as a soil correction). Here at CBS we recommend using con-bit rather than granular material. Whether it is con-bit or granular it must be compacted and it should be compacted in lifts. Each lift should be about 8-10 inches. Once the subgrade is prepared then the base is constructed.

Concrete and asphalt can move as much as 8 inches when the soil beneath it freezes.

Concrete and asphalt can move as much as 8 inches when the soil beneath it freezes.

Many driveway problems occur right in front of the garage door. This is an area where the native soils are used for backfilling and they are seldom compacted properly and are often placed wet. This area is prone to becoming “wetter” over time because other elements feed moisture into it (poor water management systems). Disregarding this compaction and allowing the subgrade to become saturated are the key reasons why driveways settle and are subjected to frost heaving.

 

Moisture Intrusion Solutions: Solid Base & Asphalt Thickness

The next element of importance in a pavement structure is the base. The base is the layer directly below the driveway surface (either asphalt or concrete). AS previously stated, this article is based on a hot mixed asphalt driveway. The base material, in my opinion should be a class V material or con-bit (recycled concrete and asphalt). The thickness of the base will depend upon the thickness of the asphalt.

Let me explain – the design of the pavement structure should be based upon a term called “Granular Equivalent” (GE). The granular equivalent concept defines a pavement section by equating the thickness of the base and asphalt layer to an equivalent thickness of granular base material. Note: this is not my term, but a term used by the Minnesota Department of Transportation (MN/DOT) for designing pavement sections.

As an example, a class 5 aggregate base has a granular equivalent of 1 per inch of thickness and an asphalt course has a granular equivalent of 2.25 per inch of material.  So, if I have an asphalt thickness of 3 inches, and a class 5 course of five inches, my granular equivalent would be 11.75 inches. If I had an asphalt thickness of 2 inches and a class 5 base of seven inches, my granular equivalent would be 11.50 inches.

So, you see the granular equivalent can be any combination of asphalt and base. It goes without saying that the higher the GE number, the better the pavement structure (I have personally seen this to be true).  Low GE’s might not show pavement distress in the first few years but within 3-7 years, signs of distress will begin showing up.

The next element in the pavement structure and the ones everyone sees, is the surface course. To be frank, I am not sure what specification most residential paving contractors use for their design mix. I have seen HMA thicknesses from 2” up to 3” used for driveways. I think most paving contractors will use 2”-2 ½”. Especially in large residential developments. If you are an individual homeowner the contractor will probably use 2 ½” – 3”. In my professional opinion, I would recommend 3” – 4”.

Now getting back to the GE. I would recommend a GE between 10.5”-12” for residential driveways. Similarly, for reference – the Minnesota Asphalt Pavement Association (MAPA) recommends a GE of 11.5” for driveways also.

Conclusion:

The building codes govern the applications of these materials and practices. Neither the IBC, nor the IRC include information for residential driveway designs. Nor is there a recognized national standard. Maybe it is far “fetched” of me to think that one could be established, but at the very least, I believe the Minnesota State Building Code should address the issue.

Incidentally, I have over 30 years of experience with the Hennepin County Department of Transportation dealing with bridge and roadway designs.

 

 

 

Remodeling dilemma’s

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home remodel

 

So you want to remodel, but you have questions!  So many times homeowners want to remodel their homes but don’t know if they can.  They ask themselves; 1) can I remove that wall to open up more space? 2) will the deck be able to be converted into a three season porch?  3) can I put in a header to support a load bearing wall? 4) can the attic be converted into living space? 5) how big of a footing do I need in order to support the remodeling I want to accomplish?

Complete Building Solutions, a structural engineering consultancy & engineering firm based out of Minnesota, can help with your dilemma!  We have assisted many customers with answering these type of questions. Our staff and engineers can help determine the proper construction detail you will need. We will work with you to develop a potential budget for your specific remodeling plan, and can recommend several contractors to bid your work.

Keep in mind that many cities in the Minneapolis metro are calling for engineered plans before they will issue a permit.  We can provide you with the consultation and plans required for project advancement. CBS will also explain if your plans just won’t work or are not cost beneficial. So when you are ready to remodel and you have your very own dilemma, please consider CBS to assist you in answering your questions.

The Vices of Ices: How to get Rid of Ice at your Home

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Ice Dam Prevention MN

Minnesota winters produce harsh winds, dark skies, and snow. But, the most precarious weather consequence affecting, not only the elderly population, but all generations, is ice.  Ice is a rigid structure maintained by hydrogen bonds and forms when water is cooled below 32°F (0°C). It hosts many of our states favorite pastimes (shout out to the Minnesota Wild), but also poses danger to drivers, pedestrians, and homeowners who are simply trying to maneuver through the labyrinthine byways of a once secure driveway. Needless to say, this challenge is not always a success.

Incidentally, the leading cause of brain injuries in the state of Minnesota is from falls. The Minnesota Brain Injury Alliance and the Minnesota Department of Health say, falls are responsible for 38% of all brain injuries annually (https://www.braininjurymn.org/aboutBrain/falls.php). That is a huge number! Ideally, we would like to completely eradicate ice in order to decrease the injuries that coincide, but this is not realistic. However, individually, we can take measures to drastically decrease the problem within our own home.

First, one must be aware of the drainage system on their roof. A functioning roof system will shed moisture off the roof and into gutters where it can be properly filtered away from your foundation and walkways. If you have noticed ice dams, your roof is unable to perform because an issue exists within in your attic. It is important to note that a permanent solution, which does not require continual snow removal of the roof, exists and will increase the life of your roof and structural components of the attic. Check out our blog on attics & energy loss to learn more about the attic system http://cbsmn.com/blog/?p=121. At CBS, we specialize in these exact issues and offer lasting solutions to ensure peak energy efficiency, life span, and performance of your roof and attic.

Roof Ice Dams Solution

*This ice dam is preventing the roof’s drainage system from functioning properly.

A second factor to consider is the foundation of your home. It is paramount that water be directed away from the foundation to avoid ice build-up, but to also prevent basement leakage.

Charles Glossop, owner of Minnesota’s most highly esteemed commercial snow, landscaping, and consulting company, Hantho Farms, LLC, provided us with some of his methods (which CBS highly supports) for the best ways to prepare for this phenomena pre-winter: 1) Downspouts and gutters must be efficiently draining water away from entrances and walkways and 2) A positive slope must exist around the foundation, walkways, and driveways with at least a  6” drop in elevation within the first 10 feet of the foundation (International Residential Code). This positive slope encourages water to move away from your home and 3) Consult a professional before planting trees near your home. If trees are too close, their roots can actually grow into the foundation, causing cracks, and will retain water near the base of the home. If you combine a negative grade and trees in close proximity to a foundation, the tree roots will actually follow the water (which is trapped near foundation from negative grade) and may cause serious damage to the home’s foundation (International Residential Code).

Bad-grading

*The above photo demonstrates a gutter that is not draining water away from the foundation and a negative grade that is holding water near the foundation.

Now, we know it is mid-winter and your negative grade issues cannot be addressed until spring. However, there are some measures you can take NOW to prevent ice build-up. Charles Glossop suggests using a liquid brine BEFORE it snows to “prevent the bonding of snow to the pavement.” Check out Hantho Farms website http://www.hanthofarms.com to learn more about the liquid brine they make and use for commercial snow removal.

To recap, the two main sources that propagate ice are 1) an insufficient roof drainage system and 2) Improper drainage system of your foundation. After the recent snows, and upcoming freeze/thaw cycle, you will quickly know if there are problems within these drainage systems. If you have ice dams, slippery sidewalks, ice build-up on driveways, or around other areas of your home, you may need to start planning for next year. Call CBS to come inspect your property and start working towards a plan to create an efficient and safe environment at your home.

Foundation Urination

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As you can see in the video above, the title is very fitting.

Earlier this week, CBS was called to investigate a property which had sidewalks tipping towards the front door and block failure. Watch what happened when the soil is excavated away from the foundation! Four to five feet of soaked organic clay mixed with an alluvial layer surrounded the foundation wall. This soil had been holding water for over 20 years as clay will never dry out. After time, the ground water will permeate the foundation and has nowhere to go! The building owner had no indication that their foundation was slowly degrading due to the retained water. CBS is known for drying out properties around the state of Minnesota and this property had the same issues we find in buildings on a regular basis.

Unfortunately, builders/developers are not paid to do correct soil conditions on the property when they do the original dig and build. Inadequate soils should be removed and replaced with compactable aggregates that will retain their shape and shed water at the same time. In this case, the clay surrounding the home was holding water instead of shedding it away from the foundation. Concrete sidewalks and driveways are also susceptible to issues because of soil conditions. The holding of water below the concrete freezes and expands during winter months. In the spring the thawing moisture makes the concrete drop back down creating large cracks.

If you suspect that your building is suffering these issues or showing signs of stress or water, give us a call to help your building perform the way it should!

Why not Building Codes for residential driveways?

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Our company, Complete Building Solutions, investigates construction defects – including but not limited to the building envelope, water management issues, soil issues, settlement problems, concrete issues, and driveways. We also can provide engineering services and construction oversight.

As we conduct our investigations we have found that many of the defects observed do not comply with the building codes.  And, as most people know, the building industry is governed by codes. We rely on the International Building Code (IBC), the International Residential Code (IRC), and the Minnesota State Building Code as our references when conducting our investigations as we look for construction defects. They all do a good job of addressing all facets of a building. But, there is nothing in the code that addresses the design or the construction of a residential driveway.

In Minnesota, there are some excellent references that can be used as a guide for the design and construction. However, what is needed is a code that addresses the key elements of a driveway structure. In my opinion the key elements are having the proper subgrade with the required compaction, a solid base upon which the driveway material will rest (incidentally this blog is based on an asphalt driveway), the right asphalt thickness, and once the driveway is constructed keep the water from entering the subgrade (another words – a good water management system).

What is the proper subgrade? The answer – one that is not prone to frost heaving.  Damage from frost heaving can result in buckling your garage door trim to causing the misalignment of your garage door making it difficult to open and close.

Complete Building Inspections In MN

The subgrade should be either granular or should be con-bit.  I can tell you that most subgrades under driveways consist of clays and silts, soils that are considered expansive – those are not the proper subgrade.  So if you have subgrade consisting of clays and silts, it should be removed and replaced with granular material or con–bit (this is normally referred to as a soil correction). Here at CBS we recommend using con-bit rather than granular material. Whether it is con-bit or granular it must be compacted and it should be compacted in lifts. Each lift should be about 8-10 inches. Once the subgrade is prepared then the base is constructed.

The area where we see most of the driveway problems is right in front of the garage door. This is an area where the native soils are used for backfilling and they are seldom compacted properly and are placed wet. It is the area where the contractor has to excavate in order to install the footing and construct the foundation. Typically the excavation extends out from the building’s foundation several feet and extends down to the footing.

That is also the area that is most prone to become wetter over time because other elements feed moisture into it (poor water management for one). Disregarding compaction and allowing the subgrade to become saturated are the key reasons why driveways settle and are subjected to frost heaving.

Moisture Intrusion Solutions

As previously noted, poor water management can affect driveway behavior. Since the presence of water reduces the strength of the pavement structure, it is important to not let water enter it. I can’t tell you how many times I have seen downspouts dump huge amounts of water right next to the driveway.

The next element of importance in a pavement structure is the base. The base is the layer directly below the driveway surface (either asphalt or concrete). AS previously stated, this article is based on a hot mixed asphalt driveway. The base material, in my opinion should be a class V material or con-bit (recycled concrete and asphalt). The thickness of the base will depend upon the thickness of the asphalt.

Let me explain – the design of the pavement structure should be based upon a term called “Granular Equivalent” (GE). The granular equivalent concept defines a pavement section by equating the thickness of the base and asphalt layer to an equivalent thickness of granular base material. Note: this is not my term, but a term used by the Minnesota Department of Transportation (MN/DOT) for designing pavement sections.

As an example, a class 5 aggregate base has a granular equivalent of 1 per inch of thickness and an asphalt course has a granular equivalent of 2.25 per inch of material.  So, if I have an asphalt thickness of 3 inches, and a class 5 course of five inches, my granular equivalent would be 11.75 inches. If I had an asphalt thickness of 2 inches and a class 5 base of seven inches, my granular equivalent would be 11.50 inches.

So you see the granular equivalent can be any combination of asphalt and base. It goes without saying that the higher the GE number, the better the pavement structure (I have personally seen this to be true).  Low GE’s might not show pavement distress in the first few years but within 3-7years, signs of distress will begin showing up.

The next element in the pavement structure and the ones everyone sees, is the surface course. To be frank, I am not sure what specification most residential paving contractors use for their design mix. I have seen HMA thicknesses from 2” up to 3” used for driveways. I think most paving contractors will use 2”-2 ½”. Especially in large residential developments. If you are an individual homeowner the contractor will probably use 2 ½” – 3”.

In my professional opinion, I would recommend 3” – 4”.

Now getting back to the GE. I would recommend a GE between 10.5”-12” for residential driveways. Similarly, for reference – the Minnesota Asphalt Pavement Association (MAPA) recommends a GE of 11.5” for driveways also.

Conclusion:

Neither the IBC, nor the IRC include information for residential driveway designs. Nor is there a recognized national standard. Maybe it is far “fetched” of me to think that one could be established, but at the very least, I believe the Minnesota State Building Code should address the issue.

Incidentally, I have over 30 years of experience with the Hennepin County Department of Transportation dealing with bridge and roadway designs.

Bruce Polaczyk, P.E.

Negative Grade

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This week’s blog is on a topic that has been fresh on my mind as of late, that being negative grade around building foundations.

Many people don’t acknowledge that this plays a crucial role in the longevity of your buildings foundation and the way water moves around your property.  Grade can be defined as slope, and you’ll want to ensure that the soils around your home are sloped in a positive fashion so as to direct water away.  All too often when we get to a property experiencing moisture related problems we find that the soils are pitched back towards the buildings foundation, allowing water to flow back in the same direction.

You may be asking yourself what happened to the soils around my home?  Why did they settle?  Soils around a building will settle over time.  When your home was new, the soils were probably placed in a positive fashion by the builder.  However, most builders will not take the time to compact the soils used to backfill your home because that takes time and resources, and let’s face it, time is money.  You may also want to consider the type of soil your builder may have used to backfill your home.  Sure, you may have some black top soil underneath your landscaping but what’s underneath that?  We typically see a lot of natural clay used for backfill purposes during our investigations.  This is likely because it’s essentially free to use for the builder and it’s already located onsite.  The time of year the soil was placed back in against your foundation will also play a crucial role in things.  Had the soil experienced a month of solid rain, or maybe it was frozen in chunks during the winter months?

Like any building product, soils contain certain properties in the way they move and how well they accept moisture.  Clay for example is a very cohesive soil, meaning it can get very hard when dry but will expand and become something you can throw on a potter’s wheel in art class when saturated.  Throw the seasonal freeze and thaw cycles experienced in a year’s time in Minnesota into the mix and you now understand why this becomes so crucial to the longevity of your homes foundation, surrounding driveways/sidewalks, patios, deck footings, etc.  When correcting the grade around your home we often recommend a soil correction before achieving the final, positive grade away from the foundation.  This entails removing the saturated, cohesive, unsuitable soils used by the builder and replacing them with a compactable, more permeable soil such as recycled asphalt and concrete (con-bit), red rock gravel, or equivalent.  Compaction of this soil in layers is a must to ensure your newly achieved positive grade does not settle leaving you in the same boat you may currently be in.

I briefly touched on moisture in the soils in the last paragraph.  One other item to consider as you look at the settled landscaping around your property is whether or not you have rain gutters along the eaves of your roof and where the rain gutter downspouts drain to.  Rain gutters are a must to direct your roof water where you want it to go and this includes the downspouts.  CBS recommends placing extensions on your downspouts that take the rain water away from all landscaping along your foundation, sidewalks/driveways, deck footings, etc.  Did you know a 1” rainfall will produce .6 gallons of water per square foot of roof area??  That’s a lot of rain water allowed to access your building foundation should you not have rain gutters and downspouts directing this away!

I’m going to leave you with a couple of photos of the damages to building foundations we’ve witnessed due to prolonged exposure to water and negative grade.  The first images are of deck joists that are pulling away from the ledger board due to vertical movement in the outer deck post footings.  Not only may this cause costly damage but may also present a safety factor to its users.

deck joists that are pulling away from the ledger board due to vertical movement in the outer deck post footings

deck joists that are pulling away from the ledger board due to vertical movement in the outer deck post footings

deck joists that are pulling away from the ledger board due to vertical movement in the outer deck post footings

deck joists that are pulling away from the ledger board due to vertical movement in the outer deck post footings

The last image is of a deteriorated concrete block foundation that has been exposed to water in the soils for the last 25+ years.  We actually see this quite commonly, believe it or not.  This moisture in the soils, when combined with the movement in the freeze and thaw cycles experienced in Minnesota, has broken down the concrete blocks to mere sand if you will and can be broken just by kicking them with your shoe.  Concrete products are not designed to take on such moisture and movement in the surrounding soils.

deteriorated concrete block foundation that has been exposed to water in the soils for the last 25+ years

deteriorated concrete block foundation that has been exposed to water in the soils for the last 25+ years

Hopefully after viewing this blog you have taken away something about the importance of having a proper grade around your building that you may want to apply to your own projects this coming spring.  Until next time, stay warm and keep an eye on your buildings!