Cost and Time Study for Constructing Raised

Wood Floor Systems

This study was undertaken to further knowledge about wood utilization and performance in wood-framed housing, specifically raised wood floor foundation design. The study focused on several foundation and elevated first floor systems common to the Gulf Coast region, including two raised concrete slab systems: raised concrete slab on fill within stem wall,structural plastic materials highly filled composite and raised concrete slab on fill pad. These were compared with a raised wood floor system on stem wall with a crawl space. While not the most cost-effective raised wood floor foundation system, we chose the stem wall system because the builders participating in the study preferred them. Cost and time considerations involved in constructing each of these foundations were reported for nine builder case studies, including four raised wood floors on stem wall foundations, two raised concrete slabs on compacted fill pads, and three raised concrete slabs on stem wall foundations and compacted fill. Table A covers the average costs of the three foundation and floor assembly construction types.
As anticipated at the outset, a raised concrete slab on a compacted fill pad had the least total cost and the shortest time to construct. However, the average wall height of the two slabs on fill pads was less than 2 ft, which is the prescriptive building code’s height limit for this design and a lower average elevation than was required for the topography of the other seven house designs on the lots in this study. A slab on a fill pad does not require a footing or perimeter walls because a turned down, thickened, and reinforced haunch shaped by a trench and slab form serves the two functions at the slab edge. It also takes up more lot space because of the sloped fill pad extensions on all sides of the foundation.
The three raised concrete slabs on compacted fill retained within perimeter stem wall foundations averaged 3 ft in height with first floors sized similarly to the slabs on fill pads. There was an average cost of $7,400 more for the additional 1 ft, 3 in. of foundation wall height, compared with slabs on compacted fill. The raised wood systems cost an average of 27% more than the raised concrete on fill with stem wall (as measured by average total cost). The difference in average elevation of the foundation walls supporting the two floor types was approximately 4 in. (wood measures 3 ft, 5 in., whereas concrete measures 3 ft, 1 in.).
Wall height was a cost driver in the foundations,[url=http://www.woodplasticcompositepanel.com/project-case/wood-plastic-composite-siding-and-roofing]Wood plastic composite Siding and Roofing[/url] and the study reflects that by reporting in cost per square foot of foundation wall. However, the cost per square foot of stem wall foundation declined as the wall got higher because the cost of the footing was spread over more area. Footings and foundations of the two raised floor systems with stem walls could be constructed with equal cost, but interior piers and crawl space foundation accessories (vents and access panels) will add cost to the raised wood floor system. Given a defined base flood elevation floor height requirement, there should be no difference in cladding volumes between the two systems, provided finished floor heights are designed to be at the same elevation.

Floor joist and girder costs of the raised wood were on par with the cost of the concrete slab, as were sheathing and insulation costs compared with the fill dirt and compaction, but there was a disparity between the cost of carpentry labor and that of slab labor. This contributed to the cost difference between the two systems. An optimized cost approach is presented to normalize the variance in wood floor labor and material costs borne by the builders in the study. The optimized approach results in an average cost difference of $2.53 per square foot of foundation wall between wood and concrete on stem walls at the given average foundation heights.
The study relied on project homes volunteered by builders,raw material for composite boards and the cost comparison is based on regional costs of key components such as concrete, lumber, concrete masonry units, and the associated trade’s labor rates, as reported in this study. Potentially less costly foundations, such as pierand-beam raised wood floor foundations, were not investigated.

The resources come from:http://compositedeckingfloor.com