JoeKeresztury's blog
Drainage Slope away from Foundation needed
Submitted by JoeKeresztury on Sun, 10/01/2017 - 05:27.Your San Antonio Area Foundation
The illustration above shows proper drainage slope and clearances around the foundation that is needed as per modern standards and minimal IRC requirements. Proper drainage slope based on the International Residential Code is a minimum fall (slope) of 6" away from the foundation for the 1st 10'. Proper clearance above grade to the top of foundation / bottom of exterior cladding is a minimum 4" for masonry areas with a minimum 6" clearance above grade at siding areas.
Proper drainage slope away from a foundation is not just required but needed to help prevent unneeded settling issues to the foundation of a building that can affect the entire structure over time.
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Please excuse the quality of some of the images shown below- some of them were photos taken of the engineers requirements on their foundation plans for the builder at the time of an inspection.
One builders Superintendent (Construction Manager) actually pevented me (Joe Keresztury) from taking photos of the engineers foundation plan. Another Builder at a New Home Pre Move In Inspection refused to let us (JWK Inspections) and the client to see the engineers foundation plans after we called out how inadequate the drainage slope around the foundation was.
from our foundation pre-pour construction phase inspections in the San Antonio or surrounding areas. 5 of the engineers are calling for more drainage slope then the minimum called for by the IRC. The IRC calls for a
minimum 6" fall for the first 10' (5% slope) away from the foundation. 5 of these engineers above are calling for a minimum 6" fall in the first 5', which is 10% slope. Also, 5 of the engineers also call for more
than the minimum IRC requiremnt for foundation clearnce above finished grade. The IRC requires a minimum
4" clearance above grade at masonry areas and 6" clearance above grade at siding areas. Some of the engineers
call for a minimum 8" clearnce above grade to top of foundation (bottom of cladding) and one engineer shows
a minimum 10" clearance above grade areas. The bottom left illustration above shows that engineer calling out &
emphasing no less than 2 times the requirement for proper drainage slope away from the foundation and that it
also needs to be established right away, within days after the concrete is poured and forms are removed.
Above left- A drainage slope survey showing inadequate drainage slope away from the foundation in areas shown. Center- The Zip Level Equipment shown at that San Antonio Home Inspection that included the Grading / Drainage Level Survey by JWK Inspections (shown at left). Readings were taken at 10' away from the foundation to evaluate needed drainage slope as as per requirements. The natural grade as seen at above center slopes from front to back. Even though it has that slope, it should first slope away from the foundation (which it doesn't) than drain down the natural slope See sample above right, of the grading slope first falling away from foundation than draining down the natural slope. Otherwise drainage runs down along the edge of the foundation and softens the soil and / or washes it away, which can lead to settling issues of the foundation & entire structure.
Above- This San Antonio area home had settling issues which most likely were contributed to by inadequate drainage
away from the foundation in numerous areas as shown in this illlustration of a Drainage Level Survey.
Below- A Drainage Slope Survey was performed at the driveway of that inspection. Zip Level Elevation readings showed inadequate draiange slope away from the foundation. At right below, our drone view photo shows the area of the readings shown in the layout illustration at the left.
that did not have adequate drainage slope as needed away from the foundation.
Proper Drainage Slope is needed around a foundation whether it is a slab type
foundation or other type foundation including pier & beam types (below). Pier & Beam
foundations are common on homes in older neighborhoods around the San Antonio areas.
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Home Inspector, Consultant & New Home Construction Specialist
Illustrations & photos by JWK Inspections, Grading / Drainage Slope Surveys by JWK Inspections
Engineers requirement images were from construction phase inspections (foundation pre pour) performed by JWK Inspections, including by GE Reaves, Galbraeth, Law, Westbrook Engineering & others in the San Antonio and South Texas areas.