intermittent darkening of stone tiles and strong mildew smell in house extension

[tbubah]

Hi, we have an extension to our house built on a slab, and the ground floor room has developed a strong mildew smell for the first time since we moved here in 2006. It started last weekend, after a few days of heavy rain, and by Monday was overwhelming. There are no water pipes under or in the extension part of the house. The gutter is above the 2nd floor room (above the mildew smell room) and there is no smell or moisture in that room. My first guess was that groundwater was not draining under the slab room and coming up into the foundation, since I have occasionally seen dark areas of the stone-tiled floor (which my wife recalls being listed as granite), and the smell seems the strongest at the front of the room where those tiles are. Also the drainage on our block is terrible, the water stays curb high for hours after a heavy rain. It would have to be a lot of water to reach the tiles though, as the flooring is raised up above the foundation. I ran a dehumidifier for the day but it didn't collect much water or reduce the smell. Tuesday the weather was cooler and drier so I opened all the windows; the odor dissipated, but didn't disappear completely. Yesterday (Saturday) the weather was back to hot and humid, the odor was strong again, and there were dark areas in the floor tiles (pictured), even though it hadn't rained in days. The outside foundation is visible from 2 sides but doesn't look wet. I removed a board from the deck right outside the front of the room, I did smell the mildew but the ground was dry. Since hot temps and humidity seem to aggravate the problem, is it possible that room air moisture is being absorbed by the tiles and activating mildew (or mold) that has grown under them? OR if it is groundwater, could it take days for it to flow from surrounding areas to under my slab room?

 

[inspectorD]

Next question is do you have a chimney cap on the brick chimney, and where does that water go.

 

[nealtw]

The smell will be coming from something that will feed mold like wood, finding the soarce of water is one thing but drying it out is also important. I would remove the molding from the wall at the floor and maybe you can see wet sills there.

 

[tbubah]

Next question is do you have a chimney cap on the brick chimney, and where does that water go.

Yes the chimney is located along the right side of the extension halfway back and it has a cap. The roof of extension is pitched down from center to front & back, with a gutter on each side. It was redone a couple years ago.

The photo shows the extension -- that front wall is where the mildew smell is the strongest, and at the wall to the right of the slider is where we see the tiles with darkened areas, as well as a little by the brick chimney, but to a lesser degree.

 

[nealtw]

We don't see a drip flashing over the door, is the floor inside higher than the side walk, how much?

 

[joecaption]

I'd be removing the siding at the bottom of the wall to take a look under it.
Red flag seeing siding that close to grade.

 

[tbubah]

I'd be removing the siding at the bottom of the wall to take a look under it.
Red flag seeing siding that close to grade.

You mean the siding on the outside of the house, correct? Can you explain what "grade" means and why being close to it is a red flag? The bottom of the siding ends behind the first deck board (see photo) and the deck is maybe a foot or a bit less above ground.

 

[slownsteady]

Has the brick in the chimney been waterproofed?

 

[nealtw]

In the other picture it looked like sidewalk. Is there wood behind where the deck is attached to the wall or is that concrete.
Take this piece of molding off.

 

[tbubah]

Has the brick in the chimney been waterproofed?

I don't know if it's waterproofed, but we had chimney people here a year or so ago, I know they checked it out and replaced the liner.

 

[tbubah]

The smell will be coming from something that will feed mold like wood, finding the soarce of water is one thing but drying it out is also important. I would remove the molding from the wall at the floor and maybe you can see wet sills there.

I will do that this week and report back, thanks.

 

[tbubah]

We don't see a drip flashing over the door, is the floor inside higher than the side walk, how much?

You are probably right about the drip flashing (see photo) however the 2nd floor roof extends about 1.5 feet past the wall, so is a drip flashing necessary?
Yes, the deck is almost a foot above ground, and the extension floor is maybe an inch higher than the deck. The driveway in front of the deck then slopes downwards to the apron & street.

 

[nealtw]

Strange that the siding was left on when the deck was built?
We do want to see what you find behind the molding. This could be anything, from brick absorbing water or a flashing leak or other damage on the roof.
That looks like vinyl siding, which is in no way waterproof, so then the house wrap behind it could come into question or the fact that there is no drip cap over the door or the trim above the door, and we could question the door installation itself.
Then it is true that water can travel great distance almost level from just about anywhere above.

Was all the siding replaced when the addition was built or was the inside corner just made to work?

 

[tbubah]

In the other picture it looked like sidewalk. Is there wood behind where the deck is attached to the wall or is that concrete.

Not exactly sure what you mean but here are photos I took after removing the first deck board. The first photo is aimed at the slab right under the slider door; the lower piece of wood is the first deck frame piece, the upper piece of wood is the extension floor support. The second photo I held the phone down under deck level, pointed at the slab.

Take this piece of molding off.

I will do that this week and report back, thanks.

 

[nealtw]

the lower piece of wood is the first deck frame piece, the upper piece of wood is the extension floor support.

Can you explain this a little more, extension floor support. Is the addition not a concrete slab floor.

 

[tbubah]

Can you explain this a little more, extension floor support. Is the addition not a concrete slab floor.

The addition is built on a concrete slab but the flooring is raised up above the slab by 2x2's or 2x4's (which I called floor support, sorry I don't know correct terminology).

 

[nealtw]

Sleepers might be the term.
So the deck is level or just above the concrete slab. And what is the floor in the rest of the house and is there wood below the level of the deck.
So part of the floor framing, sleeper or what ever is exposed below the deck?
Your photo under the deck the wood looks dry but wet and maybe deteriorated in the corner. Poke around that stuff with a screw driver and look for soft wood.