We have a strong odor in our house every time we get a hard rain - any ideas what it could be? WE had an addition bulit onto our house about 1 1/2 years ago and ever since then we have had this strong odor every time it rains. We have had a plumber come out and they could find nothing... any ideas.. Our Septic tank is set in front of our house. The odor is not specific to bathrooms.

I'm assuming the addition has a crawlspace. If so, I'd suspect the soil underneath is getting damp. After a rain, inspect underneath the addition and if you see any standing water, you have a real problem. You need to divert the water away from the house from the outside BEFORE it gets into the crawlspace. This would require professional attention on the outside of your house, along the foundation.

If the soil looks dry, but there is no plastic sheet covering it, I'd cover the entire area with a 6 mil or so plastic sheet. Tape the seams if you can (best) or overlap the joints by a couple of feet at least if you can't. Make sure to get the appropriate tape for the plastic.

This is not professional advice, simply long-time homeowner advice.

Best of luck,
WallyH

Guess, I should have mentioned it was a two story addition. The original house (11 years old) does have a crawl space. We did have to do a french drain along side of the house to divert the water, as well as a drainage system (pump) from ALL Dry- after the addition because the water was standing. Thank you for your advice..

It can be number of things:

1. Anytime it is raining, or day or so before the rain, there is low pressure outside. Vent fumes do not raise straight up but have tendency to hang around the house bit longer. That's what you smell. ( I grew up in a big city and we used to predict rain by smelling sewer in the streets )
2. Make sure all vents are above roof line and clean outs are properly sealed.
3. Make sure there are traps installed on each plumbing fixtures, including floor drains
4. As mentioned in previous response, standing water will smell. That includes water standing in improperly sloped garden drains
5. If you have septic tank, make sure the lid is sealed
6. If you have septic tank / leach field pipes than ground does not percolate as good as during dry season. Waste water then stays close to the top