CASE STUDY – from the files of Integral…………
Water ingress through foundation/basement walls is a common occurrence which has resulted in an average of one hundred and fifty million dollars per year in insurance claims. The average claim is $5,000 for resulting damage. This does not include the cost of rectifying the cause which is not covered by insurance.
A single family 1,500 square foot home with a completely finished basement was built in the early thirties and remodeled several times over the years. Located on the Lower Mainland, nestled on a private acreage with a mountain stream running within 15 feet of the back door, it is a homeowners retreat. Or is it?
On the surface, the east and north lawns sloped towards the residence and unfortunately not away, toward the creek or drainage ditch at the road. The original footings were exposed to the north and the east acting as window wells. This raised the question – Why was the residence not built on the original footings when the home suffered a major fire in 1935?
There was a surface drain in the new front entry which was located at a higher elevation. Once the door to the basement opened nothing but the odour of moisture, dampness, and mold was evident.
Water had entered the basement all along the north foundation wall from corner to corner in different places. Entering the northwest corner beside the fireplace in the basement, it had run across the hearth, into the middle of the room. Some water had accumulated in the south west corner of the fireplace alcove in the family room. The water had traveled through the doorway into the hall and foyer.
This source of moisture had wicked through the east wall of the family room under the north bedroom sub floor. Once the basement was stripped out of all finishes, the bare foundation wall along the north side revealed additional points of entry into the family room and the east bedroom.
The other major point of entry was in the North West corner of the laundry room. The moisture had covered the floor in the small laundry area, running out into the hall in front of the furnace and hot water tank. It also had wicked under the sub floor of the east bedroom and its walk in closet.
Over the years, rumours had developed with the supposition at the time of the remediation being:
- There were springs all over the mountain where this property was located.
- There was a spring under the residence.
- In the rainy seasons, the water table was at ground level because of these springs.
- A corner of the mountain was under the corner of the house and as a consequence there were lots of boulders in the way around the perimeter of the house.
A week of dry weather would allow the hydrostatic pressure against the foundation walls to withdraw and the water table as a result would drop.
RUMOUR # 1
Investigation revealed that there were no immediate springs surrounding or near the residence.
It was determined that the source of the surface water was rain, snow, or run off. There was nowhere for this surface water to go other than to pool in the north and east lawns. The reason was that under the sod there were approximately two inches of sand then hard pan clay which would not allow the surface water to drain.
The east lawn did not play a role in the water ingress into the basement because it was on the other bank of the stream. It was determined that at some point it should be re-sloped, so that the runoff would head towards the stream rather than pooling in the middle of the meadow.
RUMOUR # 2
Investigation revealed that there was no spring under the residence.
The source of the water was actually an old abandoned clay drain tile run that had not been capped, rather was allowed to drain under the basement slab.
RUMOUR # 3
Investigation revealed that the water was at ground level simply because the soil in the area would not allow surface water to drain into it. It was hard pan clay.
RUMOUR # 4
Investigation revealed that the residence was not sitting on a mountain shelf.
There were simply boulders surrounding the perimeter of the residence. All of these boulders were removed when the remedial work to the weeping system was completed. It was discovered that the weeping tile had been diverted around or over these boulders.
RUMOUR # 5
Investigation revealed that the hydrostatic pressure against the residence was normal.
The reason for water penetration was determined to be that the water had breached in through the north foundation walls. Old corners of old foundations were broken away and the foundation extended beyond that corner. These breaks were patched with tar.
The north and west foundation walls were not the original walls but had been moved approximately 5 feet inside the old foundation wall and built on top of the old basement slab floor. There were no footings under them.
A Foundation Repair Specialist along with a Geo Technical Engineer and a Structural Engineer determined the most cost effective method to rectify the foundation failure.
To obtain full or partial recovery of the settlement of the foundation was determined to not be doable. The resolution selected was to stabilize the conditions. First by running 3 separate weeping tile systems around the perimeter of the foundation (1 on the inside and 2 on the outside). Then by blending the new façade with the old by incorporating the old façade finishes. Because the existing foundation and pad could not be removed and replaced, any type of recovery would have been considered a bonus. At this point, 7 years later, there has not been any further water ingress.
Foundation repair is never pretty, nor is it ever cheap. We must dig into the unknown – an underground world of dirt, mud and trouble. Foundation Repair Solutions can cost as low as $10,000 and go as high as $250,000 or more for a residential home.
The real cure for the case study situation would have been to raise the basement pad above the stream and water table. However constraints existed that prohibited this occurring. The remedy chosen at the end of the day was not to minimum code requirements – it far exceeded these requirements.
LESSONS LEARNED FROM THIS REMEDIATION
GO DEEP ENOUGH – Excavate slightly below footings, fill with ¾ inch drain rock up to footing level, lay solid perforated drain tile with holes facing down along perimeter of footings, and place ¾ drain rocks around and over drain pipe.
USE EXISTING SITE CONDITIONS – The exterior retaining wall was actually on one of the original foundation walls. The remediation process developed it into a large window well for this area, helping with hydrostatic water pressure against the foundation wall of the residence.
SEPARATE WATER LEADERS FROM ROOF – The solid pipe (not perforated) at the extreme right is drainage for the down pipes from the roof; they were not tied into the perforated weeping drains next to the footings.
WATERPROOFING EXTERIOR FOUNDATION WALLS – The first application was a waterproofing membrane applied to part of the foundation walls over the old inadequate tar waterproofing. The second and totally new application was applied before rubberized sheets were installed.
RUBBERIZED MEMBRANE ON FOUNDATION WALL – Rubberized membrane was applied to foundation wall repelling water from entering the foundation walls into the basement. The rubberized membrane forces the water to run down the pucks that are embedded on this sheet and end up in the drain tiles at footing level. Three quarter inch gravel is spread out from the foundation approximately 4 – 6 feet.
GRAVEL BEDS – Gravel was backfilled over the new drainage piping out from the foundation 4 to 6 feet up to ground level. This resulted in a natural drainage bed for surface water. This bed was developed around the perimeter of the home all the way out to the field.
OTHER EXISTING CONSTRUCTION DEFECTS EVIDENT – The original foundation wall was buried and the new foundation wall was constructed on the existing basement slab. Effectively, this did create a buried water reservoir for the ground water to pool in and penetrate the new foundation at the slab level. The basement slab should have been broken out and new footings poured.
INTERIOR PERIMETER DRAIN PIPE – The basement slab was cut out approximately 18 inches around the perimeter of the interior foundation wall where the new foundation wall was constructed on the existing basement slab. The void was dug out about 2 feet down, ¾ crushed gravel was added as a base; solid perforated drain pipe was installed and covered over with more crushed gravel. The slab was repaired and the new drain pipe was routed out into the field as well.
These repairs that cost $50,000 were only a fraction of the total cost because the completely finished basement had to be gutted and restored in order to eliminate mold, mildew, rodent infiltration. This will be the subject of a future issue. All too often we find that a band aid repair or the cutting of corners to reduce costs has been applied. The work that was performed for this remediation was well beyond minimum code requirements. This work would not have been necessary if, for an additional $5,000, the basement slab and the footings had at the time of original construction been raised above the water table due to the location being next to a creek. The remediation work was required because the basement was below the normal water table as well as being below the creek bed level.
WATER INGRESS EXPLAINED
Foundation cracks and/or inoperative weeping tile systems are the most common causes of basement leakage. Water which seeps into the basement at the base of the walls, at floor level, or through cracks in the floor, will usually indicate the weeping tile system is not working. Many homes constructed in the 1950’s-1960’s, have terracotta clay weeping tile, which over a period of years, can become plugged with clay or sand or crumble and as a result collapse, preventing the water from being carried away from the house. Homes built prior to 1950 almost never have any weeping tile system at all.
Clay soil conditions are a hazard. Clay allows water saturation of soil, rather than drainage which is required in order for water to flow to a weeping tile system. Saturated clay will freeze and often, with the thaw in the spring, will cause foundation cracks and poor drainage in window wells, resulting in back-ups and flooded basements.
Foundation construction materials have changed over the years. Materials include rubble stone, boulder stone, cinder block, concrete block and the current standard – poured concrete. Poured concrete walls, especially those in newer homes, are the most resistant to leakage; however, they too, often develop cracks that allow water to enter.
Concrete blocks and stones are quite porous, which can result in water seepage directly through foundation walls when the ground is saturated or the water table rises. Water can also seep through the porous mortar joints between bricks, stones or concrete blocks. In addition, the hollow cores of concrete blocks may eventually hold water, thus, when the water level within the blocks is higher than the basement floor, water seepage occurs.
Other common culprits include poorly positioned downspouts and missing, leaky or plugged gutters. Downspouts should direct water runoff from the roof to a discharge point several feet away from the house. A downspout that is improperly positioned to drain against the side of the house allows water to build up along the foundation wall, until the backed-up “reservoir” finds a weak spot to enter the basement. Gutters should be cleared of leaves and debris at least once a year. Basement leakage from either of these causes is usually restricted to one spot and disappears when the external problem is fixed.
Improper surface drainage is another common cause of basement leakage. In many cases, this can be alleviated simply by re-grading the yard to slope slightly away for the home’s foundation.