NW Seismic

Brick and Crumbling Foundation Repair

Tue, 23 Jan 2024 23:22:28 GMT

While Portland does occasionally have houses with brick, unreinforced concrete block or terra cotta block foundation, it is most common to have a poured-concrete foundation. Unfortunately, older poured foundations mixed with sand scooped unwashed out of the river create a crumbly foundation that not only won’t be able to resist the lateral loads unleashed in an earthquake, but are also prone to collapsing into the basement from external soil pressure. Years of overfilling gutters and downspouts only accelerate the speed of degradation, especially below soil levels.

We often see concrete walls that have been skim-coated on both sides in an effort to hide the poor quality of the concrete. We once repaired the concrete walls in a house where a previous owner had constructed a block wall against the concrete so that it appeared the house had a block foundation (at least it looked better).

On the outside, the previous homeowners had installed sheet metal from the bottom of the siding to a foot below soil level, making it impossible to see the actual foundation holding the house up without destroying the finishes that had been put in place. The owner had lived there for 13 years without realizing how flimsy the construction was.

Whether you have brick, block, or crumbling concrete, all are candidates for full or partial replacement.

A typical foundation replacement goes as follows: completely replace the foundation. Lift the house, tear out the existing foundation, pour a new foundation and slab, lower and anchor house to the new foundation. Time Required: ~3 months.

Do you have a finished basement? We remove walls, finishes and fixtures as necessary, and replace them when we’re finished with the structural work. Do you have a partial crawlspace or low ceiling? We can dig it out at the same time to increases your usable square footage.

Construct a SR wall, which involves cutting the floor around the perimeter walls, digging out for a new footing, constructing sections of 2×6 or 2×8 stud wall with plywood on the outside and fitting them together around the perimeter, all within 2 inches inside the existing foundation. That 2 inch gap is then filled with a high-density foam. The plywood-reinforced stud walls, or shear walls, resist lateral loads, and the foam resists inward pressure from soil loads. Time Required: ~4 weeks.

Cut the floor around the perimeter walls, dig out for a new footing, pour a new 6 inch concrete footing and wall to the level of the outside soil to resist soil pressure, then construct a new plywood-reinforced stud wall from the top of the new concrete to the floor joists above. Time Required: ~4 weeks.

While we can do any of the above options, the most popular is the last one because of the cost and time required. Do you have a finished basement? We remove walls, finishes and fixtures as necessary, and replace them when we’re finished with the structural work. Do you have a partial crawlspace or low ceiling? We can dig out at the same time to increases your usable square footage.

Does Your Retrofit Need A Retrofit?

Tue, 23 Jan 2024 23:22:27 GMT

Buyer beware, Pt. 1

A handyman’s work cleared the low bar for an earthquake insurance policy. See how we addressed the issues found here and how the homeowners can rely on tour retrofit to work, instead of relying only on earthquake insurance.

Buyer Beware, Pt. 2

Michael covers incorrect hardware usage, improper installations of the correct hardware, and techniques to address special circumstances. This work was performed by another seismic specific retrofit contractor, not just a handyman.

Buyer Beware, Pt. 3

While attempting to perform a seismic retrofit, this foundation repair contractor (not a seismic retrofit contractor) came across insulation that seemed to prevent a necessary connection from being made. Instead of maneuvering around this minor complication with simple engineering, the company left the project partially finished. This retrofit was ineffective without all connections made.

Buyer Beware, Pt. 4

This retrofit was installed by a waterproofing company hired to waterproof a crawlspace. Michael discusses how these homeowners paid too much money for a retrofit which after an earthquake, may disqualify homeowners from compensation from their insurance company.

Buyer Beware, Pt. 5

Another example of hardware installed by a general contractor that doesn’t quite qualify as an effective retrofit. Michael describes the math that goes into designing a retrofit and how NW Seismic will supplement the existing hardware.

"Retrofits" Gone Wrong

Don’t pay for your retrofit twice. Click on the images below to learn why these photos are concerning for both homeowners and seismic contractors.

Automatic Gas Shutoff Valves

Tue, 23 Jan 2024 23:22:26 GMT

Historically, post-earthquake fires have been responsible for more damage than from the earthquake itself. The Northridge 2000 device is designed to automatically shut off your gas after a seismic event. Installed on the gas meter, it shuts off the gas before it enters your house. It’s designed to know the different between passing trucks and busses, or being bumped, and an actual earthquake. The valve is set to trigger for an earthquake that is stronger than a 5.2.

Earthquake-activated gas shutoff valves are now mandatory in most of California, and will likely be here in Portland too.

We exclusively install the Northridge 2000 valve, mainly due to its simple design. In the rare case of a nuisance trip, the valve is very easy to reset – just turn the dial to the left a full turn.

Other models require that the gas be shut off to the meter prior to resetting the device, the reset pin is difficult to locate, and the warning sticker with directions usually wears off in the weather.

Nuisance trips are very rare, but resetting the Northridge 2000 is as easy as it gets. Slowly turn the faceplate in the direction of the reset arrow one full turn.