Thread: Wood Foundation

I inspected a home today with a wood foundation (Crawl space) for the first time. Everything appeared to check out, although it was hard to see the wood foundation with it being insulated as such, but Ive never seen truss like supports like this (2X6 floor joists).

Any opinions?

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I'm confused about the foundation reference. The foundation looks to be concete to me. Pretty sure your trusses are field built. They may be field built as engineered, but just a typical floor with some field installed bracing. Factory building, shipping and installing assemblies like that would not probably be practical.

Garry,

I believe you are referring to the concrete footing. The foundation walls may well be wood as wood foundation walls are allowed if constructed within the requirements of that code section.

The trusses look like truss plant built trusses to me.

Originally Posted by Jerry Peck

Garry,

I believe you are referring to the concrete footing. The foundation walls may well be wood as wood foundation walls are allowed if constructed within the requirements of that code section.

The trusses look like truss plant built trusses to me.

Copy that J.P. I was referring to the footings. When looking at both sides, ( photos ), the trusses looked to long and awkward to me for shipment and setting. They have a straight back; no triangulation to maintain independent structural integrity. How would they boom in a truss like that w/o it's buckling in the center ?

I'm going to agree with Garry. Site-built.

The truss plates are installed at slightly different angles, see pic 1, and a couple are wider than the others, see pic 2.

Wooden perimeter walls would just fall over without those braces. I don't see the logic in giving up the strength and durability of concrete, and then having to add all that extra framing to compensate for the flimsy wood walls.

Thank you gentlemen.

This has been uncharted territory for me. Quite a few houses in this area were built this way (wood crawlspace foundations), but Im not sure if the supporting method is similar. A HUD approved guy OK'd this homes foundation awhile ago and stated: "is in satisfactory condition and meets or exceeds HUD requirements for foundations."

Not sure if it covers these supporting structures........I think a phone call is in order.

Deflection problems?

Thanks.

Originally Posted by John Kogel

I'm going to agree with Garry. Site-built.

The truss plates are installed at slightly different angles, see pic 1, and a couple are wider than the others, see pic 2.

Wooden perimeter walls would just fall over without those braces. I don't see the logic in giving up the strength and durability of concrete, and then having to add all that extra framing to compensate for the flimsy wood walls.

..........pressure treated wood foundations, known as AWWF, (all weather wood foundations) are readily adaptable to standard building plans calling for masonry walls. Typically the wall sections rest on a 2X which is placed directly on well-drained stone/gravel. The concrete basement floor is placed against the base of the wall, the flooring sytstem is added and the system performs as any other. There are advantages for interior wall finishing etc. I believe that the increasing popularity of pre-cast light weight concrete foundations has lessened the use of AWWF. My guess is, in this situation the system was modified to use those rather odd floor trusses to permit the AWWF wall to be used in crawl space applications without the concrete floor...........Greg

I don't see or hear you saying anything to worry me structurally about the design, but below-grade wood components automatically put me in 'moisture hunting' mode. I don't generally like to move insulation, but I would in at least a couple of spots and assess using infrared and moisture meter.

Originally Posted by Mark Fisher

I don't see or hear you saying anything to worry me structurally about the design, but below-grade wood components automatically put me in 'moisture hunting' mode. I don't generally like to move insulation, but I would in at least a couple of spots and assess using infrared and moisture meter.

I did, and did that too. No moisture detected, but we have had a hot dry summer, and the color of the wood preservative would mask water stains.

Thanks

Originally Posted by Garry Blankenship

They have a straight back; no triangulation to maintain independent structural integrity. How would they boom in a truss like that w/o it's buckling in the center ?

The same way they set long rectangular floor trusses - with a strongback carrying the trusses.

Scroll down to page 29: http://medfordtruss.com/builders%20g...%20trusses.pdf

Thomas, I am one of those HUD guys. HUD regs call for engineered plans ans specs to be available on site in order for the HUD guy to do the inspection. (Gotta know what you are inspecting). The pictures indicate that the floor truss was manufactured and not site built. (Not many contractors have the proper presses to install metal plates shown). The braces indicate to me that they were installed to prevent racking of the floor system. If you can get a hold of a copy of the orginal foundation plans and specs, it will help you to get rid of your concerns. Sometimes, I disagree with the engineer and may voice my concerns to him, I can not over ride his specs nor require the contractor to do so. It must at least meet the specs called for by the engineer as a minimum anthing over that is a plus in my mind. You bet you need to check for moisture intrusion and call out any thing you find. But if the foundation system is built to spec there shouldn't be any. If there is my bet would be that the drainage has not been maintained. Just remember you can't over ride the engineer.

I had to inspect a wood foundation last year, first and only. These links came in handy:

Wood Building Foundations: Inspection, Diagnosis, Repair

CBD-234. Wood Frame Foundations - IRC - NRC-CNRC

I've inspected maybe 100 or so in the Indianapolis area. They were built with young first time homeowners in mind that didn't have a lot of money and they were priced somewhat lower than conventionally built homes.

Although they may have been built to manufacturer's specs, I have seen a lot of settlement issues and moisture issues. I've also seen delaminated, treated plywood on the exterior of the foundations and on some wood foundation basements, foundation deflection due to hydrostatic pressure. Our local university has certified that these foundations should have a fifty year life expectancy. They started building them in the 70's. I would not feel good about buying one that is 45 years old. The builder went bankrupt about five years ago.

Most of these homes use the crawl space as the furnace plenum. Since they are wrapped on the sides and bottom with poly sheeting, they appear to stay fairly dry but I think about radon. Clearance is tight!

I have run into these in one local neighborhood where they were building low cost homes about 15 years ago. There have been no unusual problems, just the same issues that all homes seem to have. The one thing I caution to all clients who are looking at these homes is to doubly ensure that the exterior base of the home is kept clear of debris, vegetation and well maintained. Also to ensure any grading changes over time are addressed to ensure that unwanted pests cannot enter unseen.

My concern with this system is the lack of any lateral bracing in the direction of the footing for the first photograph. Conventional construction would have a 2x4 stud wall with mud sill and double top plate and plywood, or at least let-in bracing, applied to the face of the studs to provide braced wall panels per IRC R602. The IRC also would require bridging of the joists per section R502. I can't tell from the pictures, but if it were a "wood" foundation it would need to comply with IRC R403.

Very interesting. Never seen this before. The first picture doesn't look like treated wood and it's embedded in concrete. What is that drain with shut off valve for in the second picture?

Thomas Jones,

Due to your location (NW US) and the details of what I see in your pictures, I believe this to be similar to, if not an actual, "(Al) Bowen 12-day schedule house" or "in the style of Bowen", at least regarding the engineered wood floor truss system that also serves as the crawl space foundation, IOW the wood foundation system combined with floor structure adapted truss system on footings.

I disagree with those posters who contend the trusses pictured were site built.

I recognized the design pictured, just took a while to find a still-functioning and freely available site on the web. Since I don't expect what still remains to last long.

Here goes, this was originally from an article in Builder Magazine in November 1, 1982, Pg. 42:

Al Bowen knows about scheduling construction. He builds houses so fast that he doesn't even get a construction loan. His houses are pre-sold. Construction starts the day after the buyer receives approval for permanent financing. Twelve days later the house is completed and the buyer goes to settlement before the construction bills come due.

Bowen built and sold 30 homes in Spokane, Wash., in two months after he introduced his 12-day schedule, and he has orders for 15 more. Because he pays no interest on construction loans and builds tile 960 square-foot ranches on inexpensive land. Bowen can sell the homes for $37,900 - $6,000 less than the FHA-appraised loan value of $43,900 and about $10,000 less than the market value.Bowen observed that many builders allot an entire day to a subcontractor when his job can be finished in hours. To save time, Bowen schedules subcontractors by the hour and has several trades working in succession on the same day. Now that's scheduling construction!




But the key to the 12-day construction schedule is a patented engineered wood floor truss system that also serves as a foundation.

"In this part of the country, wood is the least expensive building material in the house and concrete is the most expensive," said Bowen, head of Bowen Construction Co., Post Falls, Idaho. "I knew that if I could find a way to build a foundation of wood, I could save in materials and labor and simplify my schedule as well."Before he began using the truss system, Bowen worked with a 45-day construction schedule. He paid as much as $2,700 in interim financing interest. He developed the system after months of research.


Among the systems he investigated was the All-Weather-Wood Foundation (AWWF) developed by the NAHB Research Laboratory in conjunction with the National Forest Products Association and the U.S. Forest Service. He obtained information about the AWWF from the American Plywood Association.

Bowen ended up modifying the crawl space AWWF, and using trusses instead of floor joists. The trusses have integral legs and leg supports that are stamped together with the truss by metal plates in a factory.The legs extend down to concrete footings below the frost line and support the floor system. An assembled 24-foot truss weighs about 47 pounds, so one man can handle it. Bowen begins construction by excavating the crawl space and forming and pouring footings. The crawl space is covered with a 4-mil polyethylene sheet that serves as a vapor barrier.

The two end trusses are set with the bottom plate already attached. After measuring the distance between the two trusses, framers anchor the bottom plate to the footing with bolts or strapping.

Intermittent trusses are similarly set 24 inches on center and floors are decked as the trusses are erected. The two outside legs of the trusses are pressure-treated lumber. These are covered by pressure treated plywood cut lengthwise into 2x8 foot sheets to enclose the crawl space.

The inside of the crawl space wall is insulated with R-11 batts and the outside is caulked and painted with asphalt. Then the foundation is backfilled. Above the floor decking, Bowen builds a conventionally framed house following HUD's OVE design and construction principles. These include studs 24 inches on center, single top plates, two-stud corners with drywall clips and elimination of headers and cripples at doors and windows. Roof trusses are lined up 24 inches on center above the wall studs.

Bowen uses pressure treated wood studs to frame the garage, starting from the footing. Studs run from a bottom plate bolted to the footing to a single top plate. Half-inch pressure treated plywood is applied a minimum of 16 inches below grade and 8 inches above grade. A 2x6-inch wood border is applied around the inside of the garage to act as a form for the concrete.

Bowen saves further time in his schedule with the extensive use of jigs.

"Although my system and building methods let me build a small, low-cost house a lot faster, they will work with any type of house at any price," he said. "With the high cost of construction money, every builder is going to have to look for ways to build faster."

I'm still searching through pages of old links to hopefully find some that work regarding old design and construction program standards and an older AWWF version file from the contemporaneous time period of the original article.

HTH.

Originally Posted by Garry Blankenship

Copy that J.P. I was referring to the footings. When looking at both sides, ( photos ), the trusses looked to long and awkward to me for shipment and setting. They have a straight back; no triangulation to maintain independent structural integrity. How would they boom in a truss like that w/o it's buckling in the center ?

Garry,

Take a look at the article I quoted in the post above (and the diagram).
You'll see the answers to some of your questions are underlined, bolded & highlighted. You might also want to expand your knowledge base on truss construction.

Since there are homes in your area so built (and some larger) - you might find it worth keeping a copy of the article for your records, should you ever have the opportunity to inspect one.

HTH.

Thanks gents. I now agree / aquiesce to the pre-built trusses. Probably more, but there is a local plant that pre-manufactures the entire structure including sheathing. They have a modicum of floor plans to use ~ you are responsible for the requisite foundations and they can have your house up, ( w/o roof ), in one to two days. Amazing stuff.