When you want water to drain out of a house

Wendy Tsao May 7, 2018, 12:46 p.m.

How would a “passive” or airtight house fare in a flood incident, either from inside (burst water tank) or from outside (like New Brunswick’s spring floods)?


Responses (1)

Ecohome May 8, 2018, 10:51 a.m.

Hi Wendy, 

That’s more of a durability issue than wall performance. Some Passive Houses may do fine, others may be severely damaged. You could get a home Passive House certified (PH) with a basement that has poor drainage and no sump pump and find your basement ruined by a minor flood, but if you built a slab on grade house a foot above the surrounding ground you could canoe away from your front door in a flood with no damage whatsoever. 

If you are in the design phase and concerned about durability, I would look into building a slab instead of a basement as it virtually eliminates your risk of flooding, but if you’re building a basement I would install a sump pump with a battery backup, a drain around the exterior, eaves troughs that take water far from the house and  slope the land away from the foundation. And be sure to raise any wood flooring above the surface of the concrete. 

As for appliance leaks, there are a couple of easy steps you can take to prevent drainage – place washing machines and water heaters on a tray with a drain and have easy shut off valves installed, or include a 
 floor drain in your laundry or mechanical room. (see photos below)

And air tightness isn’t an issue at all in regards to flooding, after a major basement flood you may have a fairly lengthy drying out period where you would need a lot ventilation and dehumidification, way more than a house that leaks air could manage. 
The LEED rating system is more about durability measures than PH, so if you’re looking to have a house built and want a performance certification, that may be the better choice. The design and construction could still meet PH efficiency levels if you like but it would also ensure that it is inspected by an independent third party for its durability measures. 
Hope that helps, here are a few reference pages that you may want to check out: 

Stormwater management
Slab on grade
LEED durability
Sewage backup prevention