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walkereng, Consultant
Category: Structural Engineering
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Residential Building Advice. I'm in the process of designing

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Residential Building Advice.
I'm in the process of designing my own home. I intend on having a certified engineer look over my plans prior to construction but to try and save cost I’m attempting to ensure my plans are structurally sound to prevent the engineer from starting from square one. However, I need some clarification for a few structural items. The house will be single story with basement ICF construction with a 12:12 primary roof pitch. The local authorities abide by the IRC.Floor Trusses and Span
1. The largest span of my house is 32', I plan on going above code with 60 psf live load/ 15 psf dead load as well as deflection of 480. Adding extra psf to account for hydronic radiant heating and simply because bear minimum rarely works well. I'll be placing them 16" OC. I intend on using the least amount of supporting walls as possible (open floor plan). Floor truss span charts indicate that a 2x4 truss capable of my loads/deflection requirement that is 14" deep has a max span of approx 19' (dependent on wood species).-Can I have a 2x4x14 truss built that's 32' long if I support it mid span with a beam to simplify construction? Or will I have to have two 16' trusses instead? If I can't do a single truss could you explain why?Attic roof truss combined with floor truss?
2. Since I plan on a 12:12 roof pitch with a few dormers I’d like to make use out of the large space above the main floor. However standard deflection and loads are fine for this space (L360, 40psf). There is a 20psf snow load requirement.- Is there a feasible attic truss that can accommodate this span? Can the bottom cord be a truss as well?ICF
3. Most of the older homes in the area that I’ve visited are stick built on 8-10” pour concreate basements. The area is clay and water-table over 100’ deep. If I’ve read IRC correctly I can use 6” ICF forms for the basement as well as the main floor(using #4 rebar). The total wall height will be 20’ from slab to top of Wall, 9’ of which will be below grade. Roof will be trusses. Ground is level (>10% slope) There is also Wind speed 90 mph seismic design category.- Will 6” forms be sufficient to carry this load? I know vertically it will be more than sufficient but uncertain how to calculate horizontal strains.4. Again to save cost I’m attempting to hire the pump truck only once. I’ll set up the ICF forms braced from the outside, set my WWM w/ hydronic radiant tubs ready for the slab. Possibly set up form for suspended slab for attached garage (haven’t compared yet compared if material cost >= sqft/house value increase).
- Can a 20’ wall and footing be pour monolithically(using FastFoot)? Would it be safer to only set up half the wall and have it poured and continue building the wall between lifts? Not fond of this idea simply because the chances of the 2nd half of the wall not being plum is relatively high in my unprofessional opinion. On the other hand, I’m not familiar with ICF and not sure it can handle concreate dropping from 20’ up without a blowout.I apologize for this being so lengthy and thank you in advance for any advice you may provide.

I can help.

I am leaving my office right now, can I get back with you when I get home this evening?

Customer: replied 2 months ago.
No rush. I'm just in the beginning of my research/design phase. Actual engineer stamped plans are still five years away when I retire from the service.

1. Here is a link to a very good Floor Truss span table sheet: As you can see, if you go with a Live Load of 60 psf and a Dead Load of 15 psf, a 14" deep floor truss spaced at 16" o.c. will only span 19.75'. If you use the IRC Code required Live Load of 40 psf and Dead Load of 15 psf, a 14" deep floor truss spaced at 16" o.c. will span 22.58'.

2. You can have a local truss manufacturer design a truss system that will have an opening in the middle for storage or occupancy along with a roof snow load. The bottom chords do not need to be trusses, see attachment below:

I am working on question #3 and #4 right now

3. If you are planning on using ICF construction for your basement and 1st story walls, you will need to get with your local ICF product supplier and they should be able to size the wall properly for their specific system. They will most likely have an approved ICC Evaluation Report for their product.

4. In my opinion, a 20' high wall form being poured all at once will not work. You are correct about the possibility of blowout and of lateral instability until the concrete cures. Again, once you choose a supplier for the ICF system you will be using, they will have technical staff that will help you with these type of details.

I hope this helps.

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Let me know if you have any questions

Customer: replied 2 months ago.
Just to clarify. The roof truss would or wouldn't require a supporting wall? Or is that dependent on the manufacturer?

Roof trusses can be designed to clear span 32'.

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Good Luck with your project planning!