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Information on the Do's and Don'ts concerning Foundation Drainage

By Warren Goodrich
Information on the Do's and Don'ts concerning Foundation Drainage

Information on the Do's and Don'ts concerning Foundation Drainage.

Concrete or Masonry Foundations (NEC R405.1)

Drains shall be provided around all concrete or masonry foundations that retain earth and enclose habitable or usable spaces located below grade. Drainage tiles, gravel or crushed stone drains, perforated pipe or other approved systems or materials shall be installed at or below the area to be protected and shall discharge by gravity or mechanical means into an approved drainage system.

Gravel or crushed stone drains shall extend at least 1 foot (305mm) beyond the outside edge of the footing and 6 inches (153 mm) above the top of the footing and be covered with an approved filter membrane material. The top of open joints of drain tiles shall be protected with strips of building paper, and the drainage tiles or perforated pipe shall be placed on a minimum of 2 inches (51 mm) of washed gravel or crushed rock at least one sieve size larger than the tile joint opening or perforation and covered with not less than 6 inches (153 mm) of the same material. (From 2000 INTERNATIONAL RESIDENTIAL CODE, SECTION R405, FOUNDATION DRAINAGE)

Concerning basement footings and foundation drainage and water sealing

SPECIAL NOTE BY AUTHOR: The perimeter drain hose may be placed below the top of the footer if you have a thicker footer,but that hosemust not be place so that the top of the drain hose is placed above the top of the footer in any manner.

Make note and spread the word in your company that the mud, muck, and debris that often appears during the time the walls are constructed must be removed from around the footing and basement wall areas at least out one foot from the basement walls or footing whether you use a UL listed forma drain product or a perforated plastic drain line or even a clay tile drain system. This mud and muck that often is around the bottom of the basement wall during the construction of the basement wall and footing appears commonly due to rainsetc. while you are trying to build the basement. This mud and muck will ruin any proper drainage of your basement perimeter. It must be removed to a point at least 6 to 8 inches below the top of the basement footing.

Plastic Perforated Drain Line

If you are planning on using a form a drain product to form the basement footing and also intended to let the form a drain product remain in place after that footing is poured with intent for it to serve as the perimeter drain, then that area that is 1 foot out and 3 inches below the slots of that forma drain product must be crumbed out [dug back out] removing any mud, muck, and debris to that point below the slots of that forma drain product and at least 3'below the slots in that forma drain product. The slots of that forma drain also must be cleaned from any debris or mud caked in or plugging of those slots during the wall or footing construction process.

If a plastic perforated drain line hose style product is used this drain line should not be installed along the footing until after the basement wall shave been poured and after all the mud and muck and debris has been removed to a point 6' below the top of the newly poured footing just before back filling with the required 6 inches of rock or stone, cheese clothe and dirt above perimeter drain hose or form a drain during the basement back fill process. The perforated drain line must be installed on top of 2' of stone or washed rock installed between the 4 inch and 6 inch level below the top of that footing. The rock must be sized at least one sieve size [aka rock size] larger than either dimension of the holes or slots in that drain line or form a drain product. The plastic perforated drain line must be placed so that the top of that plastic perforated drain hose is laid even with the top of the footing. This plastic perforated drain hose must be installed level the entire length of the drain system around the basement footing and installed out to the approved outlet away from the house with no up and down sloping of that hose while laying that drain line on that required 2' of washed rock or crushed stone. The no dips or raises is so those dips or raises does not hamper or stop the natural drain action of that perimeter drain line.

A flat and level laying plastic drain hose or horizontally slotted on the vertical laying manufactured, UL listed plastic foundation perimeter forma drain system must be a clean installation with no mud and muck or debris within 1 foot horizontal or anywhere above either of those type drain systems to a point at least 6' above that drain pipe or form a drain. However, only 2 inches of WASHED GRAVEL OR CRUSHED STONE is required or allowed below the perforations of that drain tile or form. The footing must be on solid ground forbidding going any deeper than that 2' and the International Residential Code requires at least a minimum of 2 inches of this rock or stone.

The perforated drain line or form a drain product must then be installed so that the top of that drain is level with the top of the footing with the 2 inches of crushed stone or washed rock installed under that installed perimeter drain. Then 6" of crushed stone or washed rock must be installed over the top of that drain tile or form and at least 1 foot out horizontal from that drain system. The forma drain would just have washed rock or crushed stone filled 8 inches thick and one foot out starting at least the 2 inches below the slots of that forma drain. The hose would have the 2 inches of stone or washed rock, then the slotted rain hose then6 inches of stone or washed rock above the drain hose totaling again 8 inches thick of stone or washed rock. This is a total a 12 inch layer of rock and hose. This layer of rock is counting the 2 inches of crushed stone and then the rock around the hose of 4 inches of crushed stone or washed rock around the drain hose then 6 more inches of stone or washed rock above the drain hose. Then a porous cheese cloth [used as a dirt fines filter must be placed over the top of that washed rock or crushed stone. Remember, the washed rock or crushed stone must be sized at least one sieve size [rock size] larger in diameter than any dimension of that hole or slot found in that form a drain or perforated drain hose.

A Walkout Basement

If you have a walk out basement then 2 feet of crushed stone in a French design drain method is accepted by the International Residential Code, without the drain hose or form a drain product being used. This French drain system is are cognized drainage system used predominantly for walkout basements allowing the subsurface water to drain along the perimeter of the basement footing and basement wall horizontally until it leaches out the end of that walkout basement' s walls onto the surface of the finished grade and filtered through the grass of that lowest area that would be outside and below the floor of the basement. This allows the water to drain from the basement wall' s perimeter without the need for mechanical pumping or drain piping product,but will drain by gravity away from the basement walls, limiting the basement walls from subsurface wall exposure to the subsurface water that will be present from time to time or constantly. This French drain design requires at least 2 feet of stone vertically and at least 1 foot out horizontally from the outside of that basement wall, the entire circumference of that basement footing and basement wall area. Still a cheese clothe filter sheet is required by the International Residential Code to be installed at the 6' level above and out at least 1 foot horizontally from the top of that basement footing in order for that cheese clothe can filter dirt fines of the surrounding dirt preventing the dirt fines from clogging that rock French drainage system.

In some areas a basement may be approved on flat land with a forced pumped drainage system. Some areas will allow this mechanical drain system to be pump out the side of the house onto the grass to dissipate across the grass unnoticed using the required 5' of fall in 10' from the house on the finished grade as required by the International Residential Code. Check with local rules for possible rules requiring this drain instead of pumping out the side of the house to be pumped subsurface to an approved drainage outlet with an animal guard remote from the house. This rule is often found in local ordinances or laws.

Sump Pump

While a sump pump inside the concrete basement is not required by the International Residential Code, there is no rule against you installing an inside sump pump pit. Personally I would rather see that inside sump pump pit drainage system to be installed remote from the outside perimeter drain system with the inside sump pit pumped to daylight separate from the gravity perimeter drain system. There has been a common practice among many to tie the inside sump hole and outside perimeter drain together. This is not a violation of the International Residential Code.

However this is not a recommended installation method in my opinion, to tie the two drainage systems [inside sump hole and outside perimeter drain system] together. This inside sump pump if you wish to install it should, my opinion should not be connected to the outside drain to a combined drain outlet. This separate inside and separate outside drain system outlet in my opinion should be installed to eliminate the possibility of a backflow from a flooded gravity drain area into the basement thus flooding the basement by back flow during flooding or heavy rains causing high water, where the outside perimeter drain hits approved daylight outlet if so connected inside to outside, or during heavy rain the subsurface water draining into the sump pit faster than the sump pump can pump the water out of the basement.

Flat Land and Basements

Few areas of flat land should be areas inviting a basement to be installed. If you have a building site that is flat land and you desire abasement then pay a soil scientist to perform borings in the ground to find the consistency of the earth. If well drained sand or gravel then you may be fine. If sand and gravel with clay trapping sub surface water from readily being drained then the horizontal perk of the sand and gravel containing the high amount of trapped subsurface water trapped by the slow perk clay below would bean indication that this land should not have a basement. This sand and / or gravel would promote fast drainage of water horizontally to the basement and basement wall most likely running in so fast a brush pump could not keep up. Watch for a soil consistency of sand or gravel with clay or other slow perk soil below it. Rain water will rapidly enter the sand or gravel and perk rapidly horizontally to the basement walls while being trapped from perking on down due to the slow perk soil below it. This is often the case of the horror stories you hear of high water inside basements or more than one brush pump to keep the water out of the basement during wet seasons. Know your soil content. This will help you to know if a basement is desirable or best to omit a basement and also help you design your perimeter drain capacity and type system.

Outside Only Perimeter Drain System

However if you end up with a house with a basement on flat land, then you will be best served to use an outside onlyconnected outside perimeter drain system to drain into an outside sump hole or cistern. This sump hole on a house with flat land and nowhere to drain by gravity will have to be pumped away from the house. Then you must tie the outside system to a sump hole. I recommend creating an outside sump pit separate from the inside sump pit. The intent of a subsurface perimeter drain is to keep the water out of the basement.

While it is not a violation of the International Residential Code to drain outside drain to inside sump pit, it does seem to be kind of ludicrous to drain the outside subsurface water into the inside sump pit inside the basement to pump it back out of the same basement that you are trying to keep the water out of. If this outside to inside drainage and sump pump system is designed and the inside sump pump fails, then you will have a flooded basement, and a lot of heart ache. If you were to create an outside sump pit or cistern such as buying a 24' plastic drive way drain line and while digging your basement dig an offset allowing that 24' drain line to be installed vertically into the earth with about 2 inches deeper of a larger stone layer in the bottom of that 24' drain pipe you have created a cistern outside where you are even with the top of the basement footing at the bottom of that cistern you created allowing a solid cistern type hole down to that level even with the top of the basement footing. Then you can install a weatherproof receptacle in that cistern to plug in a subsurface sump pump sitting on the bottom of that cistern stone you installed. Then connecting a line large enough to handle the pumped water and dig it subsurface to a low spot in your land where you can bring it today light remote from the house to pump the water through an animal guard at that day lighted mechanical drainage pipe. Then you connect the outside perimeter basement drain perforated pipe to that cistern at the bottom so the subsurface water can drain into that outside sump pump cistern, then pumped by the sump pump in that cistern to daylight that has an outlet installed remote from that house. This will keep that subsurface water out of the basement as originally intended, thus limiting the basement from a chance of flooding during heavy rains. Then you can install a hand hold cover flat with the grass that you can mow over yet have access into the subsurface cistern in order that you can replace that subsurface cistern sump pump if it fails.

If you so desire to install an inside sump pit and sump pump inside your basement to pump out the side of the house separate from the outside perimeter drainage system you can have a back up sump pump system inside not exposing the basement to possible flooding from the perimeter drain installed outside to the subsurface cistern sump pump. This allows your basement not to be exposed to subsurface water hazard of flooding your basement and still have both type drain systems if you so desire.

If you have an outside perimeter drainage system that has enough fall ina hilly construction site that can be drained by gravity drainage method to allow part of your land you can again keep it separate from the inside sump pump system to avoid the back feeding flooding that can occur if the low area outlet happens to flood due to high water that can happen during an extreme heavy rainstorm. The purging [waterproofing] of water as required by the International Residential code to be installed on the outside of the basement walls should repel subsurface water flooding for a couple of days during flooding conditions allowing that low area where your subsurface drain outlet is located to have receded the flood water thus allowing the drains to again drain subsurface water from your basement wall area again ensuring a dry basement. If this flooding occurs on your gravity drain system back feeding and flooding your basement due to the flooded low land outlet of your drain system can not occur if you did not tie the outside perimeter drain to the inside sump pit. Again you may install a separated inside sump pit pumping out the side of the house in case any water does get into the basement during flooding that may occur though this inside sump pit is not required in a properly installed basement.

If you purged [water proofed] the basement walls correctly making them damp proof or waterproof, and if you create your perimeter drain system correctly whether outside cistern mechanically pumped on flat land or gravity drained on hilly outlet to daylight in a low area of your property, then your basement should remain dry, and the added separated inside sump pump hopefully will not even need to run. Yet if you install the inside sump pump pumped out of the house by a separate drain outlet from the perimeter drain then, you have this sump pump as a back up if all else failed.

Thoughts on Soil Types and Lay of Land

Remember there are areas and certain soil types that do not work well due to high water trying to flood your basement. The advised soil scientist boring test and report of soil types and seasonal high water table will go a long way to tell you compatibility of a basement installed at your building site. Don't guess, check before you leap on a basement design ! Know what you have to deal with concerning lay of land and types of soil and scientifically reported seasonal high water report, then make an informed decision using a good drainage design that meets the International Building Code rules. See International Residential Building Code reference number R405 for perimeter drain design for concrete basements. See International Residential Building Code reference numberR406 for water and damp proofing of your basement.

Final Thoughts

Don't forget to refer to the International Residential Code concerning insulation installation and R values required found in reference number N1101 concerning insulation requirements on outside of basement walls in your area.

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