Truss foundation system?? - InspectionNews

Chris Weekly · #1 (**permalink**) 11-04-2009, 12:08 AM

SFD 1000sf: Wondering if any of you have ever come across this - a truss system that supports the house from the ground (actually below ground) up. Concrete was placed at the perimeter and an interior center beam of the house so that there are three points of contact/support for the trusses - but the concrete is about 24" below grade. Wait it gets better. So the three points of contact (and the trusses)) are below grade. A plywood skirting (?) retains the soil at the perimeter. The trusses have the three points of contact on a treated sill plate at the perimeter and center bond beams. This whole affair is in a wet environment. Gusset plates are showing signs of rusting (along with foundation bolts, the toe nails holding the 2x4 points of contact to the sill plate). Treated truss members against the skirting, I suppose the plywood skirting was also treated - but for how long will this last in a damp environment? What might truss manufacturers say about their gusset plates in a wet environment? If you know what to call this system and what its' longevity might be would appreciate any info.

Thanks, Chris in nocal

Bruce Breedlove · #2 (**permalink**) 11-04-2009, 12:52 AM

Welcome, Chris. Where are you located?

I have seen a handful of wood foundations here in Colorado, mainly up in the mountains. They are made of treated plywood and wood. But I have not seen anything like the design in your photos. That's an oddball for sure.

The "trusses" in your photos appear to be field fabricated. It looks like the framers slapped gusset plates on some lumber and created "trusses". I wonder if an engineer designed that system. (I doubt it.)

Are permits required in your area? If so, you should be able to get a copy of the foundation plans and see if they were followed.

It is obvious -- based on the rusting gusset plates and the crap growing on the surface of the lumber -- that there is a moisture problem in that crawlspace. Were you able to identify the source of the moisture? (Drainage, plumbing leak, clothes dryer discharging in crawlspace, etc.)

Even if the foundation and floor "trusses" were built per an approved and permitted set of plans and specs they should be inspected by someone familiar with this type of construction. I would pass the ball off by recommending further review by others.

Let us know what you find out.

Chris Weekly · #3 (**permalink**) 11-04-2009, 07:51 AM

Hi, Bruce. Thanks for your reply. The property is located in Sacramento, Ca (I'm in the bay area where we have bridge problems). 25 year old house. I've been doing inspections over 20 years and this is a first for me. This may have been an early attempt at trying a wood truss design for a supporting system for a house. Everything relies upon the three 2x4 support points of each truss (about 20 trusses). Trusses are 24" oc, and a 2x8 joist for floor support.

Everything in the house suggests that the system is working - level floors, no cracks, square door frames, etc. It's just all that hardware in a damp environment doesn't look right. Not to mention the treated (hopefully) plywood skirting retaining 18" of dirt at the exterior. Certainly this skirting can't be too successful at keeping out the ground water - thus the damp environment. Sacramento typically is hot and dry, but there is a rainy season during the winter months and there was a recent heavy rain prior to my inspection.

I'm wondering if a truss manufacturer would suggest how to prevent rusting of gussets in damp environments. Wouldn't they have taken that into consideration in the first place? Would they even have approved this knowing the high probability of moisture here?

Just wonderning
Chris in nocal

I believe I'm ready to learn Its a process

Gunnar Alquist · #4 (**permalink**) 11-04-2009, 08:06 AM

Quote:

Originally Posted by Chris Weekly

SFD 1000sf: Wondering if any of you have ever come across this - a truss system that supports the house from the ground (actually below ground) up. Concrete was placed at the perimeter and an interior center beam of the house so that there are three points of contact/support for the trusses - but the concrete is about 24" below grade. Wait it gets better. So the three points of contact (and the trusses)) are below grade. A plywood skirting (?) retains the soil at the perimeter. The trusses have the three points of contact on a treated sill plate at the perimeter and center bond beams. This whole affair is in a wet environment. Gusset plates are showing signs of rusting (along with foundation bolts, the toe nails holding the 2x4 points of contact to the sill plate). Treated truss members against the skirting, I suppose the plywood skirting was also treated - but for how long will this last in a damp environment? What might truss manufacturers say about their gusset plates in a wet environment? If you know what to call this system and what its' longevity might be would appreciate any info.

Thanks, Chris in nocal

Hey Chris,

Aren't you local?

Looks like a manufactured home support system. I have seen metal supports in similar configurations in Petaluma, but not wood. I have similar concerns about the metal. I think you stated it perfectly in you post and would use most of that in the report. State your concerns about the earth/wood, the condition of the metal gussets, areas below grade, etc. Just like you did in your post. How old was the house? The primary problem that I see is who to defer to. I would guess a structural engineer and a pest inspector.

Chris Weekly · #5 (**permalink**) 11-04-2009, 08:58 AM

Hello, Gunnar

Sure, we've met at a few meetings back in the day.
Thanks for your reply. It's an odd duck this house, but I know its not a common system - I'm calling it a truss foundation system. Yeah, lots of metal at the underfloor area.

All things being equal it has lasted now for 25 years, and if they could keep the area dry, it might last another 25 (or more). Problem is moisture, and a plywood skirting for retaining system (and for now poor grade situations - photo of house - yes, thats a gravel driveway up against the front of the house) add up to wet conditions under the house. Just saw it yesterday, today I'll try my luck at a few truss manufacturers to see what their take on it is.

Another thought about this is shear factor - minimal bracing was installed under there between the trusses - must be that the plywood perimeter skirting is also a shear wall. Shear wall, retaining wall. Ok, but what if the plywood deteriorates? or the nails rust? would they leave that to chance when they designed this?

again, just wondering

Chris

Jim Luttrall · #6 (**permalink**) 11-04-2009, 09:25 AM

I betting that house was built off site and trucked in ala' modular home of sorts. I would also go so far as to theorize that the "truss" system was intended as a temporary system for transit. Were there any other clues that might support the theory like electrical panel, water, etc.

Chris Weekly · #7 (**permalink**) 11-04-2009, 09:46 AM

Hello, Jim
It appears that the whole thing is put together on site. They would have had to excavate the entire footprint, trench for footings/bond beam (or whatever the concrete is - I could only see the top of the concrete under the sill plate - don't know about depth, footings, steel or whatever), install the truss framing, attach the 2x6 rim band, and then the plywood skirting/shear panels. Then backfill. At what point would they have wondered whether this would actually work? Is this a test house?

Gunnar Alquist · #8 (**permalink**) 11-04-2009, 01:37 PM

Chris,

Obviously, I was not there, but it sure smells like a manufactured home. What I can't figure out is - if it is, how did they place it on the trusses? Ok, you may well be correct, because I cannot see how the system would go together on-site. In any case, I think you are correct in your concerns about moisture. If you are going to recommend a fix, it seems to me that regrading and use of a different sheathing (Hardie, for instance) might be prudent. When I see something like this, my primary recommendation is to install a concrete perimeter foundation. Did the other homes in the neighborhood have a similar look?

What about aluminum wiring? When I see weird stuff like this, they have had aluminum wiring for the branch circuits. Once again, an indication of a manufactured home.

Were you able to get in the attic? Manufactured homes have a distinctive truss system that is attached/bolted on-site.

On another note:
I thought it might be you. We have moved our monthly CREIA meetings. They are now the first Wednesday of the month at Star Restaurant in Cotati. That would be this evening. Hwy. 116 offramp on the west side of the freeway at Redwood Dr. It would be great to have you come back to the meetings again. If you give me your email, I will send you the specific information. You can use the "private message" feature of this site at the upper/right hand corner of the page.

Chris Weekly · #9 (**permalink**) 11-09-2009, 06:24 PM

Hello, Gunnar
Sorry for the delay getting back to the board - sometimes it gets busy out there.
Thanks to you and the others who gave suggestions on this white elephant. It is surely one of the strangest foundations I have seen - almost surely built on site with the prefab trusses brought in and placed on the concrete footings.
Anyway, I have moved on and have issued the report with appropriate recommendations for specialists, including my concerns with moisture that is eventually going to be the undoing of it all.

Thanks for the invite to the meeting - couldn't work that one in the schedule. How about next time.

I'll send you my email
Chris

Gunnar Alquist · #10 (**permalink**) 11-09-2009, 08:15 PM

Quote:

Originally Posted by Chris Weekly

Thanks for the invite to the meeting - couldn't work that one in the schedule. How about next time. I'll send you my email

Chris,

I will hold you to that. We have some really good guest/educational speakers coming up in January and February. And, a new member (new to the North Bay Chapter, not the association) that I am really excited about.