Potential subfloor problem

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Old 03-11-05, 08:50 AM
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Potential subfloor problem

I had this poste don the Framing and subflooring forume and a member suggested I post it here also!
My husband and I have been building a weekend house for some time. It is a Polysteel concrete/foam house built over a crawlspace. We built the main support beams ourselves and have been concerned about it being undersized. The main beam is a ‘sandwich’ beam built from 3 - 2x8 boards and 2 - 8” wide strips of plywood all nailed and glued together, staggering all seams (all green-treat). The footprint of the house is 44x26 (inside dimensions) and the main beam spans the entire 44 feet with each end resting fully in a concrete pocket. Approximately every 8 feet there is a similar beam running perpendicularly underneath the main beam for support. These secondary beams are resting on large concrete footings (5 ft deep). We then have the floor joists resting on the main beam. I have called several structural engineers but because of the remote location have been unable to get someone willing to come and take a look at it. Normally my husband over-engineers everything but in this case we just don’t know. We have continued on with construction and the house/floor is very solid – of course we put a double layer of OSB down to eliminate any squeaking. We noticed right away the center sagged about one inch but were unsure if it was because we may have installed the joists about an inch high on the outer walls. Fortunately, we have only one interior wall so the main concern is the weight of the main floor. Our plan of attack is to dig out under the main beam and try to pour 5 individual concrete posts as additional support. There is hardly any room in which to work so we are trying to brain storm other ideas. Any help would be greatly appreciated!!
 
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Old 03-11-05, 09:04 AM
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suebar,

The footings that you mentioned are 5 feet deep but what are the dimensions of them? Were they dug into virgin soil or was this excavated then backfilled?
 
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Old 03-11-05, 09:19 AM
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The footings are quite big; I would say about 3 feet. The soil was not excavated prior to them being dug – the ground feels like concrete!
 
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Old 03-11-05, 09:24 AM
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suebar,

How many footings are there now along this 44 foot run? How far apart are they? Is this a single story home?

Why would the beam be 1 inch lower? or is it 1 1/2" lower?

The exterior walls of main floor consist of what?

What size are the floor joists?

Are we looking at a problem of installation being at fault - just too low as you said the soils are very hard?

Sorry for the many questions
 
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Old 03-11-05, 09:40 AM
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suebar,

Pardon the additional question but you said,

We noticed right away the center sagged about one inch but were unsure if it was because we may have installed the joists about an inch high on the outer walls.
I am assuming that there is a missing sill plate under the beam that would match that of the main perimeter. When the ICF's were installed and then the floor joists, I am assuming that a 1 1/2" Wood Treated plate was laid over a sill sealer. The beam I am assuming might had been placed flush with the top of ICF and thus the difference you mention, with the sag being in the middle, would have me thinking a W/T plate was omitted.

Is this possible?
 
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Old 03-11-05, 09:47 AM
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Appreciate the questions!

This is kind of hard to explain but I will try.
1. The footings are beneath the secondary support beams which support and run perpendicular to the main beam. There are 2 concrete footings underneath each of the secondary beams for a total of 10 (5 secondary beams).
2. I think the beam may be an inch lower purely by our having installed it slightly lower. We were using a line-level when we installed the main beam but since it had to first fit into the pocket in the concrete wall, I don’t think it is out of the question that it was an inch or so lower. I really doubt the ground compressed. The other possibility is that the main beam sagged immediately upon having the joists and double-layered floor installed. The beam has not appeared to have sagged any more since installation.
3. The exterior walls are 12” thick poured concrete in foam forms (Polysteel). The joists are then sitting (and attached) to a concrete ledge along the 44’ walls. This is part of the Polysteel design system.
4. The floor joists are 2x8 green treat – 14’ lengths. Because the span is 26’ the joists actually meet and cross at the center beam .They are screwed together where they meet. They were installed 16” on center.
5. We installed a double subfloor to prevent any squeaking or movement thinking this would make installing a wood floor easier. Bad choice…?

Thanks again.
 
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Old 03-11-05, 09:53 AM
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I forgot to mention the 2nd floor. There is a large loft but it is supported by beams that do not rest no the main floor. The 2nd floor joists rest on large support beams that have their own concrete footings completely bypassing the main beam we are discussing.
 
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Old 03-11-05, 10:34 AM
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suebar,

Great job at answering my questions!

Personally, 2x8's are stretching it for a 14' span. I know that would not fly here. Adding the extra subfloor is good but doesn't provide much for overall support. As long as these were glued and screwed, then it will be quiet for sure.
 
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Old 03-11-05, 12:43 PM
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I confirmed with spousal-unit and the joists are 2x10 green-treat
 
 

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