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Brandi Johnson:


Renovation & Design

Loose pipe on sump pump likely cause of noise

Question: We live on the river and have a 2,000-square-foot home that is approximately 25 years old, with steel beam construction and wood floor joists. We also have an HRV system with our furnace, which is about five years old.

Our sump pump is located in the crawl space below our structural wood floor. It was making a loud banging noise after the water was pumped out. The sump is working fine, but this banging noise is a nuisance. I had inspected the sump and pit and everything looks fine. 

While in the crawl space I had noticed a couple of things. The banging noise was perhaps the ABS pipe shaking and banging against the wood floor when turning off. I am going to try and stabilize the pipe from shaking with a couple more metal strappings to the wood floor joists. I will also try and replace the horizontal check valve in case it is faulty.

The second issue I had noticed when in the crawl space was that it seemed humid, even though there is a vapour barrier underneath the pea gravel. I am concerned that over the years the wood floor joists might start to deteriorate because of higher humidity in the crawl space. Is there a way to measure the humidity of the crawl space and what is an acceptable humidity level reading? 

Thanks, Alf.

Answer: Problems with moisture and humidity are common in crawlspaces and are often related to poorly installed or functioning sump pumps. Fixing your noisy pump system is a good idea, but may not have much to do with your moisture issue. Improving grading and more crawl space ventilation may be a better idea to prevent high relative humidity in the space below your structural floor.

There are many homes now built in our area with large crawl spaces underneath a structural wood floor, replacing a typical concrete basement floor slab. The benefit of this type of construction is the ability to heat the crawl space, making the basement area of the home much warmer and more comfortable for living space. The potential downside to this style of home is the potential for moisture buildup, which may occur in any crawl space, especially well below grade, like in your home.

You are likely right in the ballpark with your assessment of the noisy sump pump issue. Often, check valves make a noise right after the sump pump stops, which can also cause significant vibration in the ABS discharge pipe. Sometimes this is the function of a defective or poorly installed valve, but more often it is due to a sudden change in water pressure within the piping. If the solid pipe is well secured this usually makes a small noise, which may not be noticeable in the house above. 

As far as high humidity within the crawl space, checking it may be easily done by leaving a small electronic hygrometer in the area and checking it, regularly. Relative humidity at normal room temperature exceeding 40 per cent can cause moisture-related issues and damage. To reduce this, two main areas should be addressed. First, most of the moisture that often seeps into the crawl space comes from the area adjacent to the foundation, or the soil within the void. Since you should have a good 6MIL Polyethylene air/vapour barrier covering the dirt floor, the moisture may be coming in from soil around your home. Ensuring that the grading around the home is sloping away from the home and foundation, and that eavestrough runoff is directed well away from the building may help, considerably. Secondly, ensuring the crawl space has good air circulation and ventilation should help prevent too much moisture. That can be accomplished by ensuring adequate heat and return air ducting to the HVAC system, and proper connections to the HRV as well. Getting an experienced HVAC technician to assess and rectify any deficiencies in those two systems should minimize the moisture issue.

Stopping the noisy sump pump discharge issue may only require proper securing of the piping and check valve attached to the unit. Preventing excess humidity in the crawl space may be more complex and improvements to water management outside the home and better air and heat circulation inside the area should eliminate that concern.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba ( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at


Ari Marantz 
June 13

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