Thread: Basement Walls

Anyone know of any code requiring basement walls to be solid, steel reinforced, concrete? I can find no such code or requirement in IRC, Florida Residential Code, or Florida Building Code. Purpose of the question is this-I have a construction progess inspection in the works that is nearing completion and the basement is wet. Owner is under the impression the basement walls should have been solid, cast in place, concrete.

Also, any information regarding basement water/damp proofing would be appreciated. I have little to no experience in this area. After practicing HI in Florida for 20 years now, I have seen only 4 basements. They are a rarity here due to our high ground water table. The particular house though, that is experiencing the problem, is at one of the highest elevations in the state above sea level. It is situate on a steeply sloped site. CMU basement walls were sealed, as required, where below grade with a black roofing cement type sealant product prior to backfill.

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Tom, being that the house is in Florida, there's a very good chance the builder doesn't know how to properly construct or waterproof the foundation walls.

SECTION 1807
DAMPPROOFING AND WATERPROOFING

1807.1 Where required.
Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section, with the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy.

Ventilation for crawl spaces shall comply with Section 1203.3 .


1807.1.1 Story above grade.
Where a basement is considered a story above grade and the finished ground level adjacent to the basement wall is below the basement floor elevation for 25 percent or more of the perimeter, the floor and walls shall be dampproofed in accordance with Section 1807.2 and a foundation drain shall be installed in accordance with Section 1807.4.2 . The foundation drain shall be installed around the portion of the perimeter where the basement floor is below ground level. The provisions of Sections 1802.2.3 , 1807.3 and 1807.4.1 shall not apply in this case.


1807.1.2 Under-floor space.
The finished ground level of an under-floor space such as a crawl space shall not be located below the bottom of the footings. Where there is evidence that the ground-water table rises to within 6 inches (152 mm) of the ground level at the outside building perimeter, or that the surface water does not readily drain from the building site, the ground level of the under-floor space shall be as high as the outside finished ground level, unless an approved drainage system is provided. The provisions of Sections 1802.2.3 , 1807.2 , 1807.3 and 1807.4 shall not apply in this case.


1807.1.2.1 Flood hazard areas.
See Section 3110 .


1807.1.3 Ground-water control.
Where the ground-water table is lowered and maintained at an elevation not less than 6 inches (152 mm) below the bottom of the lowest floor, the floor and walls shall be dampproofed in accordance with Section 1807.2 . The design of the system to lower the ground-water table shall be based on accepted principles of engineering that shall consider, but not necessarily be limited to, permeability of the soil, rate at which water enters the drainage system, rated capacity of pumps, head against which pumps are to operate and the rated capacity of the disposal area of the system.


1807.2 Dampproofing required.
Where hydrostatic pressure will not occur as determined by Section 1802.2.3 , floors and walls for other than wood foundation systems shall be dampproofed in accordance with this section. Wood foundation systems shall be constructed in accordance with AFPA TR7.


1807.2.1 Floors.
Dampproofing materials for floors shall be installed between the floor and the base course required by Section 1807.4.1 , except where a separate floor is provided above a concrete slab.

Where installed beneath the slab, dampproofing shall consist of not less than 6-mil [0.006 inch; (0.152 mm)] polyethylene with joints lapped not less than 6 inches (152 mm), or other approved methods or materials. Where permitted to be installed on top of the slab, dampproofing shall consist of mopped-on bitumen, not less than 4-mil [0.004 inch; (0.102 mm)] polyethylene, or other approved methods or materials. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer’s installation instructions.


1807.2.2 Walls.
Dampproofing materials for walls shall be installed on the exterior surface of the wall, and shall extend from the top of the footing to above ground level.

Dampproofing shall consist of a bituminous material, 3 pounds per square yard (16 N/m 2 ) of acrylic modified cement, 1 / 8 -inch (3.2 mm) coat of surface-bonding mortar complying with ASTM C 887, any of the materials permitted for waterproofing by Section 1807.3.2 or other approved methods or materials.


1807.2.2.1 Surface preparation of walls.
Prior to application of dampproofing materials on concrete walls, holes and recesses resulting from the removal of form ties shall be sealed with a bituminous material or other approved methods or materials. Unit masonry walls shall be parged on the exterior surface below ground level with not less than 3 / 8 inch (9.5 mm) of portland cement mortar. The parging shall be coved at the footing.

Exception: Parging of unit masonry walls is not required where a material is approved for direct application to the masonry.


1807.3 Waterproofing required.
Where the ground-water investigation required by Section 1802.2.3 indicates that a hydrostatic pressure condition exists, and the design does not include a ground-water control system as described in Section 1807.1.3 , walls and floors shall be waterproofed in accordance with this section.


1807.3.1 Floors.
Floors required to be waterproofed shall be of concrete, designed and constructed to withstand the hydrostatic pressures to which the floors will be subjected.

Waterproofing shall be accomplished by placing a membrane of rubberized asphalt, butyl rubber, or not less than 6-mil [0.006 inch; (0.152 mm)] polyvinyl chloride with joints lapped not less than 6 inches (152 mm) or other approved materials under the slab. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer’s installation instructions.


1807.3.2 Walls.
Walls required to be waterproofed shall be of concrete or masonry and shall be designed and constructed to withstand the hydrostatic pressures and other lateral loads to which the walls will be subjected.

Waterproofing shall be applied from the bottom of the wall to not less than 12 inches (305 mm) above the maximum elevation of the ground-water table. The remainder of the wall shall be dampproofed in accordance with Section 1807.2.2 . Waterproofing shall consist of two-ply hot-mopped felts, not less than 6-mil [0.006 inch; (0.152 mm)] polyvinyl chloride, 40-mil [0.040 inch; (1.02 mm)] polymer-modified asphalt, 6-mil [0.006 inch; (0.152 mm)] polyethylene or other approved methods or materials capable of bridging nonstructural cracks. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer’s installation instructions.


1807.3.2.1 Surface preparation of walls.
Prior to the application of waterproofing materials on concrete or masonry walls, the walls shall be prepared in accordance with Section 1807.2.2.1 .


1807.3.3 Joints and penetrations.
Joints in walls and floors, joints between the wall and floor and penetrations of the wall and floor shall be made water-tight utilizing approved methods and materials.


1807.4 Subsoil drainage system.
Where a hydrostatic pressure condition does not exist, dampproofing shall be provided and a base shall be installed under the floor and a drain installed around the foundation perimeter. A subsoil drainage system designed and constructed in accordance with Section 1807.1.3 shall be deemed adequate for lowering the ground-water table.


1807.4.1 Floor base course.
Floors of basements, except as provided for in Section 1807.1.1 , shall be placed over a floor base course not less than 4 inches (102 mm) in thickness that consists of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 (4.75 mm) sieve.

Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a floor base course is not required.


1807.4.2 Foundation drain.
A drain shall be placed around the perimeter of a foundation that consists of gravel or crushed stone containing not more than 10-percent material that passes through a No. 4 (4.75 mm) sieve. The drain shall extend a minimum of 12 inches (305 mm) beyond the outside edge of the footing. The thickness shall be such that the bottom of the drain is not higher than the bottom of the base under the floor, and that the top of the drain is not less than 6 inches (152 mm) above the top of the footing. The top of the drain shall be covered with an approved filter membrane material. Where a drain tile or perforated pipe is used, the invert of the pipe or tile shall not be higher than the floor elevation. The top of joints or the top of perforations shall be protected with an approved filter membrane material. The pipe or tile shall be placed on not less than 2 inches (51 mm) of gravel or crushed stone complying with Section 1807.4.1 , and shall be covered with not less than 6 inches (152 mm) of the same material.


1807.4.3 Drainage discharge.
The floor base and foundation perimeter drain shall discharge by gravity or mechanical means into an approved drainage system that complies with the Florida Building Code, Plumbing .

Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a dedicated drainage system is not required.

Dom.

Originally Posted by Tom McDonnell

After practicing HI in Florida for 20 years now, I have seen only 4 basements. They are a rarity here due to our high ground water table.

Tom,

Dom gave code sections, but, yeah ...

"They are a rarity here due to our high ground water table."

That's the reason you do not find many basements in Florida.

Being on a high elevation means little to nothing, its the depth of the water table below ground that matters. Many high elevations have high water tables, meaning the water table is not all that far down.

In some places, with the underground streams and all running criss cross across Florida, you could actually miss several good water supply sources and have to go 300 feet or more to hit water (I know, some well outside Gainesville were almost 400 deep before hitting water, yet on the next property over the wall may only have been down 50 feet, because they hit an underground stream).

Back in the late 1960s I knew an old man (older then than I am now ) who was a dowser (as in one who uses a dowsing rod, aka divining rod) and he would *always* hit water when he located it with a dowsing rod, he could even tell you (from experience and the feel) about how far down it was, and he would be pretty dang close.

We did an experiment with him one weekend, we buried a many garden hose connected together in a wiggly pattern under a couple of feet of sand (one of my friends had a large pile of sand, a tractor with a plow, and plenty of time). We spread the sand out over an area about 100' square. He walked out over that area and every time he felt the dowsing rod dip, he said 'dig there' and put his foot 'there'. He *never* missed the buried garden hose, and there are areas of 30 feet with nothing in it. Made a believer out of me.

Dom

Wow . . . Thanks. That's a wealth of code information that I'll go study. I assume that since you're located in Florida that those are FBC codes.

Jerry

Thanks for addressing my misconceptions regarding elevation above sea level as it relates to ground water tables. I've never thought of it in that way.

Tom,

Yes, that's the 2004 FBC. Sorry I didn't include that info in the post.

Dom.

Tom,

Maybe the water management district in your area has a table similar to this one?
http://www.srwmd.state.fl.us/DocumentView.asp?DID=43

It would make things easier if you would update your profile to include your city.