Foundation drainage and exterior insulation
Hi,
I am located in Massachusetts. My house sat on a stone foundation with zero to eighteen inches clearance between the floor joists and soil. I decided to have a new foundation installed–full basement. The work is underway and they are getting ready to set the forms to pour the walls. The contractor insists that no drainage system is needed. The lot is relatively level, though the street is somewhat elevated relative to surrounding area, My gutters work fine and the finished grade should slope away from the house on all sides. Should I take their word for it and not install a drainage system, or should I insist on having it done while it is still possible to do it? Is a foundation drain system required by code in MA? I haven’t been able to find out through the internets.
Also, I plan on installing a product such as roxul drainboard on exterior of foundation and will probably go with sub-slab insulation (though the contractor doesn’t see the point of that). Besides the exterior insulation, are there any other things I should take into consideration before walls get poured and back-filled? I just want to make sure I think of everything while it’s easy to do it, considering we will use this space as living space sometime in the future.
Thank you,
Steve
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Replies
Absolutely. Do install a perimeter drain system. It's the cheapest and easiest time to do it. There are three steps to a dry basement.1) Remove the water. This is impossible, but it can be reduced with proper gutters, drip strips, and grading. 2) Seal out the water. Possible but imperfect. No matter how good the membranes are applied (or fastened) time and pressure will eventually create a flaw. 3) Remove the driving force from the water. Let it hit a porous material (crushed stone, dimple mat or roxul) where a drainage plane is created where the force of gravity is stronger than driving force of the water. It falls and you collect it with a drainage system.
Now where to put it? It sounds like you can't drain to daylight, can you tie into a storm sewer in the street? If not you may want to lead the water to a dry well (cistern filled with crushed stone) so that your house can take a storm surge, then the dry well can purcolate the water out slowly.
Chris Briley, Architect
Steve,
I'm surprised that your contractor told you that "no drainage system is needed." Your contractor is wrong.
Q. "Is a foundation drain system required by code in Massachusetts?"
A. Yes. Here is the GBA article that discusses the issue: Code Tip: Footing Drains and Foundation Waterproofing.
And here is the reference in the 2009 International Residential Code: Section R405: Foundation Drainage.
Thank you Chris and Martin for your replies. Correct, it would not be possible to drain to daylight. Also, there is not a sewer system to tie into so we would have to build a dry well.
I will have the drainage system installed--it makes sense to do it now of course, and I also want to have some pretty deep window wells for egress as well as daylighting, which should be tied into a drainage system. I think the contractor was probably thinking of the exception to the code:
"Exception: A drainage system is not required when the foundation is installed on well-drained ground or sand-gravel mixture soils according to the Unified Soil Classification System, Group I Soils, as detailed in Table R405.1. "
The contractor apparently feels that there is "well-drained ground or sand-gravel mixture", but of course, I'm the one who has to deal with it later if that turns out not to be the case.