Crawl space - sump pump 2

[grnmon97]

Good Day.. Recently converted a seasonal Cape Cod cottage to a year round home and mechanicals (forced hot air furnace/ac and hot water heater) were installed in a newly insulated and encapsulated crawl space with a newly added sump pump.. The crawl space has one section (1/4 of crawl space) where you enter from a bulkhead that is roughly 5' below the floor joists. The other areas of the crawl space are roughly 2' below the joists. The crawl space had a history of flooding with a high water line approximately 8" up on the cinder block retaining wall that outlines this lowest section. The sump pump was installed approximately 12-18" below the existing floor (low point of crawl space) and with the high water table, the pump runs every 60-75 seconds. I recently had the installer back to discuss options as the pump discharge is directly under bedrooms and extremely noisy with a series of elbows to exit the crawl space. We discussed a larger basin for the pump and/or perhaps a secondary switch to allow for more water into the pit before pumping. There were no guarantees that this would work, but they are options to try. I have no manufacturing background but my way of thinking tells me if the highest level of water in the crawl space was 8" above the current floor level (based on water mark on the cinders), if I was to raise the floor and essentially the sump pump up 1 foot with a crushed stone/sand mix (don't need 5' height for any function I can think of), wouldn't this essentially reduce the amount of pumping significantly and reduce it to only occur during extreme high water table situations? Are there other factors to consider in doing this beyond the amount of available head space? Interested to hear thoughts on this. Thanks in advance!!

 

[phamENG]

Yes. There are code minimums for clearance between joists and girders. There are a few reasons for this. One is access - I've had to crawl through some old crawl spaces with only 8" between the girders and the floor. It hurts. Not easy to inspect and maintain anything down there and it leads to big problems down the road. The other is moisture. Proximity to damp soil in the crawl space means higher humidity and higher moisture content in the joists. This reduces their capacity, increases long term deflection, and makes them less dimensionally stable and prone to seasonal shrink and swell which can play havoc with your wall finishes.

Your best bet is to keep the water from entering in the first place. Take a look at your gutters. Where do the downspouts lead? Does grade slope away from house? You may need to look at getting french drains in to help force seasonally high ground water down below the level of your crawl.

 

[bimr]

Many areas require concrete over the dirt when a crawl space is used. It is extremely important to use a plastic vapor barrier under the concrete. There is a tremendous amount of water vapor that moves through the concrete without the vapor barrier.

Moving the sump upward so that you aren't pumping the water table is a good idea. This can also be done by allowing the water level in the sump pump pit to be increased as long at it doesn't overflow.

On my crawl space, there is a foundation drain that is outside the foundation wall and it drains into the sump inside the wall.

Most sump pumps come equipped with cheap level switches that only last 5-7 years. The sump pumps last much longer that the switches, but people throw them away when the switches go bad. There is a product called Levelguard which is an electronic level switch that is a permanent switch. Levelguard

It is surprising that the piping is making so much noise. The piping is relatively cheap PVC and you may consider upsizing the piping to reduce the noise.

Not clear from reading your post how much headroom that you will sacrifice. Having said that, it is a good idea to raise the level of your sump pump to reduce the pumping of the ground water table. It's probably a good idea to increase the piping size as well. Be sure that a vapor barrier is used as well. Invest in something like the Levelguard.

 

[dik]

Excellent replies pham and bimr... another caution is the possibility of brown rot (aka dryrot) due to the high humidity and making sure the space is well vented.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[grnmon97]

Thank you all for your feedback. The crawlspace is currently insulated and encapsulated with heavy poly plastic liner with taped seams. There is also a dehumidifier running in this area as well to remove any residual moisture. The clearance is currently nearly 5’ of head room in this one section. I can’t imagine raising the floor by 8-10” or even a foot and then reinstalling the plastic encapsulation will cause issue with maintaining the mechanicals or plumbing that is located down there. I think this covers the major hurdles mentioned in your replies. I never thought to increase the piping diameter to reduce the noise. It is 1 1/2 pvc coming out of the pump. How much larger would I be able to get away with?? 4”?
Thanks for your replies and let me know if you have any more pointers!

 

[phamENG]

larger diameter means lower flow velocity for the same volumetric flow rate. Reducing the bends or at least swapping them for strategically placed 45s should reduce turbulence and noise.

I thought this was happening in the 2' area. If you have 5', then raising it some shouldn't hurt. I wouldn't raise it more than a few inches above exterior grade, though.

 

[FacEngrPE]

If the water level rises above the encapsulation liner, it will attempt to float unless the sump makes a hole in the encapsulation, in which case you get standing water.
So to increase slow the pump cycle time you have some choices, in all cases leave the pump as low in the sump as practical:
Increase max level to a bit below the liner level. Just adjust the on and off trip points of the level switch.
Install a larger sump.
Increase the floor level, suggest getting the outfit that installed the encapsulation involved to avoid warranty problems; Cut the liner, add fill, reinstall the liner over the newly compacted floor.

 

[grnmon97]

Thanks FacEngrPE... Your last sentence is the direction I plan to go. I'm intrigued by adjusting the upper trip point of the float and have read a little about add on switches that are adjustable, opposed to my float that has no adjustment. I may look into this and if the expense is such that it's worth a trial, I'm going to give that a go before sacrificing the foot of headroom in the crawlspace that I'd lose by raising the floor up 12".
Any opinions on the best material to fill the floor with? I was thinking a 7-9" layer of crushed stone topped off with a 3-5" layer of pea stone. Concerned with doing the whole thing with crushed because I don't want to puncture the poly barrier. Also considered setting a bunch of cinder blocks leveled to just below the height I want and then fill them with crushed stone and top off with pea stone. Any thoughts?
Thanks again for your response.

 

[bimr]

You can upsize the piping to 2-Inch. That would reduce the velocity from 7 ft/sec to 3 ft/sec and reduce the noise.

On my crawl space (retrofit on older house), the contractor installed a foundation drain on the inside of the wall and put a new sump pump. That and the plastic under the concrete eliminated the moisture and keep the humidity below 40%. No longer need the dehumidifier.

Would have to disagree with the "in all cases leave the pump as low in the sump as practical". As long as the sump pump is below the concrete level, it is futile to try to pump down the level of the groundwater.