Building a new house: foundation question

[Anonymous]

Does anyone have any idea about what specs the foundation cement needs to be. I have no clue as to whether what the builder is providing is sub-standard, standard or above standard for this area's soil strength and topography. I'm most concerned about water leaks in the basement. Building in N. Arlington.

[Anonymous]

There are code requirements for foundations, and all local areas require inspections to ensure compliance. But your question is probably a little more complex, so apologies in advance for the lengthy answer, but here it is.

There are three major components to a foundation - the footings, the walls, and the floor slab. The footings sit below the foundation walls and support those walls. These are almost always poured concrete, reinforced with steel, and are anywhere from 8 to 24 inches thick depending on local codes and load requirements. They also sit below the frost line and must be on undisturbed or tested, compacted soil.

The walls may be poured concrete or concrete masonry units (CMUs), both of which will be reinforced with steel rebar, and grouted if CMU. There is not a huge difference structurally between poured concrete and CMU, nor is the cost that different generally. The foundation slab is generally 4 inches thick, and carries little load.

The basement walls are waterproofed on the outside using an integrated system, comprised of a painted on rubber membrane and mesh. A hard plastic waterboard is then applied. At the bottom of the footing, a weeping pipe is installed, and excess water is collected and routed via gravity away from the house. Depending on local site conditions, an interior weeping system may also be installed, and may be connected to a sump pit (or multiple sump pits depending on the size of the basement). Usually, interior sumps are avoided in new construction unless the site sits within a bowl and no other drainage option is possible.

Your engineer is primarily responsible for drawing the foundation to comply with local codes, and your inspector will enforce those codes very strictly for foundations. But a new, modern foundation system *should* prevent any water infiltration into your basement.

[Anonymous]

I should add that proper sloping away from the house and proper gutter/downspout placement (all downspouts should empty a minimum of 3 feet from the foundation wall) will also greatly enhance the likelihood of never getting water penetration into a basement.

[Anonymous]

for leaks the concrete isnt the main concern, its the drainage system. AS a minimum get a rubber membrane (not just tar paint), get an interior AND exterior weeping system with sump.

[Anonymous]

Anonymous wrote:for leaks the concrete isnt the main concern, its the drainage system. AS a minimum get a rubber membrane (not just tar paint), get an interior AND exterior weeping system with sump.

This is what I'm concerned about. So, the tar paint is worthless? Are rubber membranes AND weeping systems common in new homes? (I think I remember someone telling me that they had water issues in their new home and the builder came back and drilled [extra?] holes).

[Anonymous]

Yes tar minimum code is worthless

[Anonymous]

Most waterproofing systems include 2 or 3 different layers...the "tar" paint is actually a rubber membrane product applied like a paint. There are different manufacturers and specs, this is an example:
http://ca.henry.com/waterproofing/coldfluidapplied/bluesealconcrete

The rubber never fully cures, creating a resilient, expandable barrier. Far from worthless, it is a key piece of a waterproofing system. A rigid barrier is also important.

All new homes should have at minimum an exterior weeping system. If water is going to be a likely concern given grading and drainage, an interior system can also be used, tied into a sump pump. For new construction, I would do both, unless the basement was fully at grade level on one side and the entire site sloped away from the house (i.e. you live on the top of a hill). Otherwise, the additional cost of adding an interior system is insignificant compared to the potential cost of water intrusion.