General Requirements and Specifications for a Concrete House

1. Background

We have been working through `figuring out' a bunch of stuff for our (example) concrete house ... the wall reinforcement, foundation and footing details, attachment of roof and floor, reinforcement for openings, and so on. We're about ready to put this information all together in our Construction Documents. The focus of our example has been structural design, specifically prescriptive structural design. I leave it up to you to come up with the floor plans in terms of what rooms go where, the stairs, lighting, finishes, electrical plan, and all the non-structural items. I will call what we are going to assemble now the `Structural Sheets' for the project. The sheets need to show `what is to be built' (not necessarily how), and `what materials are to be used'. So, we will have plans, details, specifics (specifications and other requirements) the Contractor needs to follow. And to a great extend, how the Contractor accomplishes the construction is up to Contractor.

2. General

The first Structural sheet should contain the design criteria for the project. So, we list (for everyone to see) what we have used as input for our design. Table R301.2(1) provides a `fill-in-the-blank' table for this information. This information itself is (mostly) obtained from the Building Department. For our example we obtained it from Moscow; for your projects it will be obtained from the Building Department for your project area.

Pertinent to our project we list: ...

CODE AND GENERAL

Governing Building Code

... 2006 International Residential Code as Adopted and Amended by the City of Moscow.

Ground Snow Load ... 64 psf

Sloped Roof Snow Load ... 40 psf

(Note: if applicable I could include the increased Snow loads for lower roof surfaces and / or balconies or decks.)

Basic Wind Speed ... 90 mph

Exposure Category ... `C'

(Here I could include `Topographic Effects' ... such as wind speed up if the structure is located on a hill or ridge.)

Seismic Design Category ... B

Weathering Potential ... Severe

Frost Depth ... 30 in.

Allowable Soil Bearing Pressure (Presumed, ML-CL) ... 1500 psf

Design Lateral Soil Pressure (Presumed, ML-CL) ... 60 psf /ft

Generally the Exposure Category must be determined by the designer based on how exposed the planned structure will be on the site. In our example we chose a site that is exposed, and so will be the structure ... so, `C'. (I will not get into the specifics of wind design, categories, etc. here.)

The soil pressure information is `presumptive' in our case based on observation of site soils and values taken from the `Code'. If site-specific information for the soils is available, say, from a Soils Investigation, we would use those values instead, and make reference to the Soils Report.

3. Specifications and Requirements

Here we list things like the required strength of the concrete, grade of rebar, etc. Since our house is concrete, Section R402 is a great help. From Table R402.2 we see that we need to specify concrete strength of at least 2500 psi. If our concrete is to be exposed to weather, then 3000 psi. (But, remember, we chose ICF construction; so the concrete will not be exposed.) We have also decided to use Gr. 60 reinforcement. Table R402.2 also provides minimum concrete strength for slabs; and we'll repeat the information in our `Docs'. And we'll collect other specifics that we used as we went along in our design, such as Gr. No. 2 ledger, A307 bolts, and so on. Let's do it.

SPECIFICATIONS AND REQUIREMENTS

Concrete Compressive Strength ... @ 28 days
... 2500 psi for ICF walls and Basement slab on grade
... 3500 psi for sidewalk exterior slabs on grade
... 3500 psi for garage slab on grade

Air Entrainment ... 5 - 7 %

Reinforcement ... Grade 60 ksi, deformed bars

Lap Splices (contact or non-contact) ... 40 diameters.

Dimension Lumber ... DF-L No. 2

Anchor Bolts ... ASTM A307

We could include specifics about the nails, the roof and floor sheathing, etc. I have chose not to and instead provide (hopefully) enough information on the plans and details themselves.

Some designers include references to the standards for various materials, e.g., ASTM A307 for the anchor bolts, where ASTM refers to the American Society for Testing and Materials, and A307 is the document specific for anchor bolts. Unless I possess copies of those standards, I generally do not cite them.

In plans that have a lot of fasteners I sometimes include ...

Alternate code-approved fasteners may be used provided they are rated at equal or greater capacity as the ones shown.

4. Engineered Systems

In our example we found that 2 x 10 DF-L No. 2 framing would work for our main floor system. And we would show this on a Floor Framing Plan. Since you have already taken a course in `wood design' - I'll leave that up to you. You will need to deal with the stairs, the framing of the (wood) interior bearing wall, and headers, etc. in the bearing wall. We designed the footing for the interior bearing wall. If openings in that wall end up being particularly large, we may also need to design spread footings for the posts supporting the beams/headers for those openings. Overall, the main floor system is Rx (prescriptive).

The roof, however, was a different matter. We chose to have a truss roof system that will be manufactured and designed by someone else (the Manufacturer). To make sure it `meets code' I generally include the following:

ENGINEERED SYSTEMS

Manufactured Truss Roof System (Trusses 24 in. o.c.)

Manufacturer of Truss Roof System shall provide all plans, details, and construction requirements necessary for roof construction and such documents shall be sealed by a professional engineer licensed in the State of Idaho. Documentation shall include truss reactions and other necessary information for connection hardware selection.

Or something like that ...

Our structure did not have lower roofs or valleys. Where we have valleys, lower roofs, or other situations where snow may accumulate, it may be prudent to include ...

Truss design shall take into consideration snow accumulations in valleys and ...

But, this may get overlooked, so I also generally show the design Snow load(s) on the ROOF FRAMING PLAN.

Sometimes I will include language that leaves no ambiguity that I want the roof information to include details of the roof rakes and any outrigger construction.

If we had selected a Manufactured Floor System, a similar paragraph would be appropriate for that system as well.

Note that I have not included a stairs design. I leave stairs designs up to Architects, or Contractors ... If I leave it up to the Contractor ...

Contractor shall provide an approved stairs framing plan and details. Foundation shall be modified as required to provide stairs support.

Scary, perhaps.

Obviously you (the Architect) will show location and what the finished product is to look like in your architectural details.

Note the word `approved' above. The building code defines the word `approved'. It means "Acceptable to the Building Official." If you want it to mean more than that, you could put in language such as ...

Contractor shall provide ... approved by the Owner, Architect, and Building Official.

Note also that I included the truss spacing. My selection of roof sheathing is based on truss spacing.

5. Structural Sheets

Now let's list the structural sheets we anticipate in our Construction Documents.

1. GENERAL STRUCTURAL REQUIREMENTS AND SPECIFICATIONS
2. FOUNDATION PLAN
3. FLOOR FRAMING PLAN(S)
4. ROOF FRAMING PLAN
5. BRACING PLAN
6. DETAILS
   A. FOOTINGS
   B. WALL / BUILDING SECTIONS
   C. FLOOR TO WALL CONNECTIONS
   D. ROOF TO WALL CONNECTIONS
   E. STAIRS (Ha!)
7. DECK (if applicable)
8. GARAGE (if applicable)

Obviously Decks and Garages may themselves require several sheets ... as they also have need of bracing, foundation, etc.

6. Conclusion ... for Now

Construction Documents vary from project to project. I prefer to show only what is necessary and hope (or require, where possible) that a competent Contractor figure out the rest. In my own practice and my advice to others I strongly recommend against `cutting and pasting' information from one project onto another. What may be very appropriate for one project may be flat out wrong for another. As the `Architect' you are the `Master Builder' ... you need to know what is going on with the structure/project ... and I maintain that you will hardly know if you simply take a detail for some other project and paste it into another.

Note (under Concrete): with ICF construction you might want to add something along the lines of ... "mix design (aggregate size and consistency/slump per ICF manufacturer recommendations."

7. References

2006 International Residential Code, International Code Council, 4051 West Flossmoor Road, Country Club Hills, IL 60478.

Climate and Geographic Design Criteria, Design Standards, Community Development, City of Moscow, 221 East 2^nd Street, Moscow, Idaho 83843.

Residential Construction Requirements, Community Development, City of Moscow, 221 East 2^nd Street, Moscow, Idaho 83843.