DIY’s & House Flippers! How to Know When You Need to Consult with a Licensed Engineer

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This blog is for all the handy husbands and professional home flippers out there. We frequently hear you asking when you need to pull the trigger and book an engineering inspection on a working project. Too frequently inspections are put off in the hopes of saving money on an expensive engineering bill.  As engineers, it is not only an ethical obligation, but the law to uphold individual and societal safety. Truthfully, monumental damage can occur if certain structural elements are altered during a project. So, how you do know when an inspection is essential?

The the answer is not so simple . However, it is safe to say when the homes skeletal structure is being altered, a  licensed engineer’s opinion should be sought out. Skeletal structures can include foundation framework, floors, walls, and ceilings. These elements are responsible for keeping the structure together & standing.

So, if you are modifying your home or building’s skeletal structure you should call an engineer. Great. But, you might also be wondering what specifically is considered a structural modification. A modification is when a load bearing element is repaired, changed, removed or when a new load bearing element is added. One example is the removal of a wall in your home. Certain walls are responsible for bearing weight and would be detrimental to your home if removed. However, there are also non load bearing walls that would present zero damage to your home if knocked out. Telling the difference between them is why you need an engineer.

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Another example is the removal of a metal post responsible for supporting beams in your basement. These posts are present to help disperse forces throughout different areas of the home. If one of those posts were to be moved, it could severely alter the structure of the home. An engineer knows how to diagnose this.

If you are a seasoned home flipper you probably have worked with an engineer on some of the examples discussed above. On top of this, it is likely you have hired a structural engineer to inspect a home before deciding if it was a worthy investment. Professional home flippers highly value engineer inspections. Our firm works regularly with clients who base their purchasing decisions on our findings. They want to know what they are getting themselves into before they make a significant investment in a project. Engineers are able to spot hidden problems, such as a faulty foundation, that could end up costing a home flipper or homeowner large amounts of money that was not budgeted for during the purchasing decision.

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To conclude, preventative inspections are always advised to attain a return on investment or save money long term. If you are working on a project that incorporates an alternation to a skeletal structure such as removing a wall, altering joists, or removing a beam, get a professionals advice. If you have a contractor aiding in your project, heed their guidance. A reputable contractor will let you know if they are uncomfortable working on your project without an engineer’s inspection. Sometimes the city might even require an engineers inspection before a contractor is allowed to pull a permit. We will be talking about this further in an upcoming blog post.

Remember, it the engineer’s job to make sure your dwelling is safe. It is best to consult and engineer and discuss a plan that will allow you to achieve your goals in an affordable manner. If you have any questions about your project, be sure to contact Complete Building Solutions today to speak with an expert (612) 868-2922.

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.

 

 

 

Has your Home Inspection Left you Requiring an Engineer?

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Home sales today often require the issuance of a Home Inspection. A home inspector’s report may cite issues and problems within homes that sometimes need an engineer/consultant to review. These may include foundation issues such as cracks in basement walls, moisture intrusion, bowed walls, alterations to foundations, ice dams, etc. Sometimes they include structural questions regarding load bearing capacity, structural changes made to existing walls, trusses or other structural members. These questions and issues are included in the inspector’s report in order to determine that the home is safe,  structurally sound, and that any modifications have been made appropriately.

Complete Building Solutions has been called on to provide both Sellers and Buyers with solutions to these Home Inspection questions.  If you find yourself needing a resolution to an issue discovered during a Home Inspection, please call Complete Building Solutions, LLC.  We will promptly assist you in resolving your question.

(612) 868-2922

www.cbsmn.com