Melting Frosty Chimney chase into house

[RCR 3 EVER]

Contractor built our chimney chase for the metal chimney vent to be installed whenever the installers decide to install the rest of our fireplace, hopefully within the next year. Anyway, our empty chase basically a hollow wooden structure developed a major problem with the warm temperatures (above freezing) yesterday. There was a thick layer of frost and ice on the inside walls of the chase and it melted, thus sending streams of water into attic, soaking thru 16" of insulation, and dripping into the house.
Numerous buckets later and hoisting a heater up into attic to melt the frost and dry the wood we sealed the hole to the chase at the roof boards with insulation and visqueen.

We have never had a frost problem on trusses or roof boards at any time in the attic prior to this, why now?

Does the chase need to be insulated, if so can it be done on the inside, and with what? The chimney vent pipe is 8" diameter and the chase is 24" sq. Insulation can not be added to outside as allowances were not made to allow for this plus the siding to be installed.

Builder says the chase does not need insulating and the problem of frost will not occur with the chimney vent inside. My parents have a sheet metal brick chase and it is not insulated and they have not had frosty chases.

This project is a TRUE test of patience and we are nearly ready to rip the thing out and demand our money back from dealer!:angry2:

Here are 2 photos of the chase, 1st during build (2 months ago)

2nd waiting waiting & waiting for the chimney.

 

[LarryTheCableGuy]

Is the attic ventilated?

.

 

[RCR 3 EVER]

Soffitt vets on front and back of house, not blocked by insulation. 1 gable vent on side.
There are 4 roof vents and a roof peak vent (forgot what it is called) but these get covered with snow.

The only place the frost appeared is INSIDE the chase. We have never had frost in the attic before. We do not get ice dams either.

 

[Geez]

Is the chimney chase open into the house at all yet? That is, is there any openings through the ceiling? If the vapor barrier at the ceiling has been compromised at all then the moist air inside the house will sneak out and condense on the first cold surface it finds, That may be why it never happened before (no hole in the ceiling).

 

[RCR 3 EVER]

Contractor cut a plywood board in place of the drywall ceiling for where the chimney vent will eventually pass thru. That 24" sq. board did not have vapor barrier, but I did have insulation on the board prior to dripping frost. After flooding I installed new dry insulation with a vapor barrier on the board. There are no other opening made from house to attic. My concern is the board will not be sealed entirely once the chimney is in. Therefore the chase will get frost again.
Or will the insulated attic radiation shield around the chimney allow me to have insulation with a vapor barrier installed next to the shield?

I could ask Lennox but they have not been helpful on other matters and the dealer does NOT know anything.

 

[Haywire Haywood]

That chase construction doesn't look like it would take any wind at all. The 2x4s laid flat on just 2 sides for a frame doesn't look very stout for as tall as that is with no support. We're going to have ours built like a standard 2x4 wall (I think) so we can put R13 all around the pipe. Ours is going to be on an outside wall though, so insulation might not be that big of a deal for yours. I still think it looks like it will blow off your house in a storm though.

Ian

 

[volks-man]

$.02

perhaps a small vent at the top rear of the chase would prevent this from occuring again. any warm moist air escaping from the insulated envelope below will leave through the vent. just as it would through the gable vents if there were no chase.

i agree with the clown..... that thing looks like it is just nailed on top of the roof. looks like you could grab the top and push it over.

 

[Haywire Haywood]

Do those flat 2x4s go all the way down into the attic and fasten to the ceiling joists? That would stabilize the whole contraption greatly...

Went back and looked at your pics again, nope. I see the ends of the verticals just below roof level. I'd have that looked at by a different carpenter before it's totally finished.

Ian

 

[Marklambert61]

Vent

Moisture from the attic is causing your problem....

vent vent vent

Mark

 

[ericjeeper]

You need to totally 100% block off the opening from your living space to the chase.. You have warm moist air rising up the chimney..
My ac is in the attic.. I have to every year cover every register in my ceiling 100% or the duct work condensates and drips like a banshee..
Has nothing to do with attic conditions. as I have ridge vents, gable vents and a cupola.
It is simple physics/.

 

[November Wolf]

I had a similar problem when I had my house built back in 95. I was getting frost build up on my fireplace insert ( when I didn't have a fire in it). It was just like a freezer, you could put a six pack in the fire place and it would get cold. The problem turned out to be the chimney chase was not insulated. I had to take off the siding and install insulation about 10ft up. The other 20 ft I left as it was and problem solved.

 

[chowdozer]

Where does your bathroom fan vent? Somewhere where it can be drawn back into the attic, like a soffit?

 

[mga]

just an FYI.....ridge vents should only be used in conjunction with soffit vents....not gable vents.

the theory behind ridge vents is to allow warm air to rise up and out, while drawing cooler air thru the soffit vents...like convection.

the theory behind gable vents is to allow the attic to breathe....like lungs...as the wind blows in different directions.

like ericjeeper said, you obviously have warm air rising up into the chase. it's also a sign of heat loss.

 

[dingeryote]

RCR,

Get on the horn to your insurance guy and let him know, and let your contractor know he's caused the problem. Take lots of photo's, and get it all inspected.

The chase should be closed off to the living space untill the fireplace is installed. Nothing elaborate, just some tape and plastic will do.
Lemme guess... the genious sealed it off at the top?
If so get in the attic and eyeball everything else, there might be other problems that wont show up for a while.

And yes, Insulation is a good thing. R-11 stapled to the sheathing.

I swear... If ya don't draw and quarter that contractor of yours, someone else will shortly.

Stay safe!!
Dingeryote

 

[Mike Van]

I gotta agree with Haywire on the construction - It looks weak. A 50 mph gust of wind will either rip it off or knock it out of plumb. The height of it gives it a lot of leverage against the little thats holding/bearing on the 2 rafters it's on. At the least, it needs some long studs run up inside it at least halfway, and down into the attic where they can tie into something? besides where they sit. I'd 3" screw them too, nails tend to get sucked out/worked lose over time.

 

[RCR 3 EVER]

Looking at it again today and it does look weak and there is a hole at the base where the flashing is not covering corner. I need to talk to contractor and get him to fix the hole and strengthen the mounting. They used strips of 3/4" OSB nailed to the top chord of the trusses.

Vent at rear of the chase sounds like a good idea. Would that be on leeward side or the windward side?. Leeward side would put on the front.

Regarding attic ventilation we have a whole house fan vented into attic, in the winter we cover the fan with batts of insulation. Previous to the chase we did not have frost on inside of attic even with this huge opening just covered with insulation and no vapor barrier. The only change done now was cutting hole in ceiling replacing that with wood and adding the chase.

Our bathroom fan is vented top the outside as well as the kitchen fan. I also added 4 roof vents above the fan and larger soffit vents.

The fireplace is in middle of house with the chimney going up through the ceiling ,6' of attic space then 6' chase.

 

[Mike Van]

I do the same with our attic fan, but throw a sheet of clear poly on first, then 4 batts of R30.

 

[RCR 3 EVER]

Contractor says that is the way he does all the chase he builds and in combination with the chimney it will stand up to a wind no problem, he has had no complaints.
Still, I have my doubts, so I am adding additional braces with screws. At least a quarter of the nails that were used are bent over instead of pounded in all the way also. I have never seen so many bent nails on a small project in my life as this project.