Sealing and insulating chimney in attic

[gwmiller]

hello, i've had my jotul 550 for one and a half seasons now and have been having issues with heat escaping into the attic, melting snow and creating ice dams.
my house is a rancher and the fireplace is in the middle of the house. There is a 6-8' section of the chimney running up through the attic that is constructed of 8" masonry block. there are several gaps and spaces in the masonry wall where i believe heat is escaping to the attic.
when my insert was installed, they had to chip out the clay liner in the chimney in order to fit the insulated liner.

can i just fill these gaps with sprayfoam and wrap the whole thing in insulation? its my understanding that an insulated liner will contain any flue fires that may occur but...what do you think?

pics are attached.

 

[pen]

You could wrap the whole chimney in un-face fiberglass as it won't burn.

Are the ice dams happening all over the roof at the edges? How deep is the attic's insulation? Even with adequate insulation, a lot of ice dam problems on roofs are because of lack of ventilation.

I see you have rafters instead of trusses. Is there a ridge cap vent or are there gable vents? Is it a ventilated soffit? Are there baffles to keep the insulation from plugging the soffit?

Welcome to the forum!

pen

 

[jimbom]

Take a look at this document, A Crash Course in Roof Venting:

http://www.buildingscience.com/index_html

for some ideas.

 

[northernontario]

Instead of fiberglass, I would recommend using Roxul (rock wool). If you ever were to have a chimney fire that escaped the liner, and the blocks got hot enough, it *could* melt the fiberglass. Roxul is essentially the same price, so might as well go that route for the small area you'll need to cover. (Of course, there's blown insulation right up against the chimney... so using fiberglass can't be that bad of an idea).

I would also second the thoughts about attic venting; Do you have proper soffit venting and peak venting? Has the insulation been blown/installed right upto the eaves, preventing air from coming in the soffit to keep the edge of the roof cool?

 

[My Oslo heats my home]

I would suspect more than the chimney is to blame for the ice dams. Has the ice dam problems only existed since you used the chimney for the insert? How much insulation is in the attic now? What kind of ventilation does your attic have, gable vents or ridge and soffit vents?

 

[gwmiller]

hi thanks everyone for the replies.
as of now there is no ridge vent, nor are my soffits vented. i do have small vents on either gable end but i'm sure they don't perform as i need them to.
the insulation is at least 8" deep loose vermiculite for most of the ceiling, although there is a section that has batt fiberglass from a recent kitchen renovation.

i was going to have either a fan installed on the one gable end (drawing air out), or a ridge vent cut out. since my soffits are not vented, im not sure the ridge vent is the best idea.
not sure which would be better.

the reason why i thought that insulating the chimney was a good idea was because the snow melts on the roof surrounding the chimney and the water re-freezes towards the edge of the roof.

 

[Swedishchef]

Just install a couple of Maximum vents, they don't get better than that.

I agree on the roxul, I think it's a bit better than fiberglass and the same price.

Wrap it with something though!

A

 

[pen]

It's an external problem why water melts around the chimney, not an internal one necessarily. The blocks absorb energy from the sun since they stick up above the snow, then melt the snow which exposes the roof, which warms up and melts more snow, and the cycle begins.

8 inches of vermiculite is roughly R-16- to R-17. Code for a new home in Pa is R-49 for a roof like this, R-38 if there are 1 foot risers to bring the trusses up so that baffles are needed and insulation isn't squished out at the edges over the walls.

The chimney is the least of your worries here. You are getting far more heat into that attic because of the lack of insulation than that chimney is providing. But even if you add insulation, w/out ventilation there is always heat loss and it will warm the attic and cause ice problems.

You need more insulation and more ventilation. The icing on the cake would be to insulate that chimney but if everything else is appropriate, you won't need to as the ventilation would take care of any heat that it is putting in there.

pen

 

[Swedishchef]

It's an external problem why water melts around the chimney, not an internal one necessarily. The blocks absorb energy from the sun since they stick up above the snow, then melt the snow which exposes the roof, which warms up and melts more snow, and the cycle begins.

8 inches of vermiculite is roughly R-16- to R-17. Code for a new home in Pa is R-49 for a roof like this, R-38 if there are 1 foot risers to bring the trusses up so that baffles are needed and insulation isn't squished out at the edges over the walls.

The chimney is the least of your worries here. You are getting far more heat into that attic because of the lack of insulation than that chimney is providing. But even if you add insulation, w/out ventilation there is always heat loss and it will warm the attic and cause ice problems.

You need more insulation and more ventilation. The icing on the cake would be to insulate that chimney but if everything else is appropriate, you won't need to as the ventilation would take care of any heat that it is putting in there.

pen

Yeah, what Pen said (are you a building technician or inspector?)

 

[PLAYS WITH FIRE]

I would use a power vent to help some up there! It may not work so well in the far reaches but it will help. When you go to Lowes to get the Roxul also get a fan for like 30-50 bux and wire that sucker up!

 

[pen]

author="Swedishchef" date="1315891026"] Yeah, what Pen said (are you a building technician or inspector?)

Certainly not a pro but I've learned a lot over the years which has saved me a lot of money and helped me to make some good decisions.

We just went through this insulation scenario with a home we built this summer. I thought R-49 was the code for all new construction, but so long as the outer walls can get R-38 over it w/out being smashed, then R-38 is all the home needs. I guess they figure the r-49 in the center of the structure will make up for the losses at the edges. Unfortunately, these losses over the outer walls cause this ice damming which is why so many roofs fail prematurely around here on older homes.

pen

 

[gwmiller]

update with some more questions.
I assumed that my joists were 8" tall but they turned out to be 6", so I have even less insulation than I thought.
I've hired a contractor to install baffles and blow in fiberglass to R49.

I had another roofing contractor come out to give me a price to install a ridge vent and swap out my solid soffits with vented (and drill holes in whatever is underneath the existing soffits). He wants $5500. A bit more than I want to spend right now. Not sure if that is a fair price but I was expecting lower than that.
Anyone think that's a decent price for 60 lin.ft of ridge and 120 lin.ft of soffit?

After reading various web info, not sure what to believe. Some sites say that ridge vents dont work unless there is a breeze, and if there is more than 2" of snow they become useless. I am thinking that a fan on one gable end will exchange the air enough but not sure which one to buy.

 

[pgmr]

I did this late last year - see https://www.hearth.com/econtent/index.php/forums/viewthread/66640/ for details.

Those AC powered attic fans use a lot of electricity. Unless you have one running constantly, you'll need a humidistat to turn one on in the winter. You might check out the solar powered versions. I've seen them at Costco recently for ~ $200 (IIRC).

You'll need to ensure you have enough inlet vent area when using a fan, otherwise, you can depressurize the house a bit (air will be sucked through all the little penetrations in the ceiling and walls), causing more heat loss.

 

[jharkin]

Lots of good advice. First get air sealing done, then venting, and finally upgrade insulation last (since you have some already). Without the air sealing the drafts reduce the insulation's value by something like 50%.


I have my stove venting in a liner that runs through an interior chimney in the attic and we have ice dams. But the reason really is that we had NO ceiling insulation and MASSIVE air leaks from the inside. The chimney chase was open enough I could climb through it.

The contractors sealed all the penetrations (wiring, vent pipes, etc) with foam, sealed the chimney chase with metal flashing and firecaulk. Then they dammed around the chimney with roxul and blew in cellulose. My existing venting is good. I think that will fix it but if not I'll wrap the chimney in roxul.