Insulation above fireplace question....

[mtj53]

Hi everyone, Just had a quick question for you guys that have been through this. Over the summer we have had a new woodburning fireplace installed...photo's coming soon...patching up the wall now. I am insulating above the fireplace and I'm a bit paranoid, I want to be sure insulation maintains the clearance from the chimney, and doesn't come loose....so on the back of the studs I fastened 1/16" thick, 1 1/4" wide pieces of strap steel. Just want to make sure, is there any downside to this? Does it matter now if I use faced or unfaced insulation?
The steel pieces might seem overkill, but on the previous fireplace there was faced fiberglass insulation, and when I tore down the old fireplace you could see where the old insulation had come loose from the paper backing and was nearly resting on top the old chimney. In the photo it doesn't appear there is any clearance, but there is 3 inches between steel straps and chimney. Thank you in advance....

 

[jtp10181]

Looks like the outside wall is spray foamed? Why are you insulating that front wall then? All you will do is create an isolated pocket back in there, you want the chase to breathe with the rest of house, its inside the envelope. Insulating that wall is pretty pointless IMO.

 

[cmonSTART]

I don't really see any downside to that as long as you have the proper clearance to the chimney pipe they call for. If you're worried about the insulation contacting the chimney over time maybe try to use a different type such as foam board cut to size.

 

[Slow1]

I don't think you are being paranoid at all. But I'm no expert. I know that you want/need to keep that 2" minimum clearance and I don't know how you can do it without something between the insulation and the chimney. Batt insulation is well known for sagging and such after install and if you don't have anything behind it to hold it in place I can easily see it just slipping down.

If it were my house I think I'd be inclined to put something rigid vertically inside that wall along the chimney line to give just that much more insurance against the insulation being pushed between those horizontal metal strips you added. Again, as long as that 2" clearance is maintained I don't see the harm in putting another rigid layer in there before you insulate and close up the wall.

As to faced vs unfaced insulation. My understanding is that is all a matter of creating a moisture barrier in the right places. What is on the other side there? What is that foam that is sprayed in there? IF that is your 'envelope' and the foam is creating your moisture barrier then I don't think that you need faced insulation. As I type this though I'm betting that the standard advice for placement of moisture barriers may have an exception for a cavity with a chimney in it as it will be open all the way up to the attic and so on so perhaps I'd best punt and see what the real experts have to say.

 

[mtj53]

Thanks for the replies guys...one question of mine always seems to lead to another though...so I might have another here....
jtp10181...In the manual it says I don't have to insulate it, but I was just following the advice from my dealer who installed the fireplace, he told me "it couldn't hurt". Maybe the question I should have asked was should I be insulating it? When my old fireplace was installed the chimney chase wasn't insulated at all, except against the common wall between the house & chase above the fireplace. This time, I did have the entire chase sprayed with foam. The manual said insulate it like your house, but the one tiny disappointment I've had is when the cap was put on, they only put two layers of 2" foam on top which gives only an R value of R20. The galvanized chase top though was caulked and screwed down and to change the insulation up on top they said they'd ruin this one getting it off, so we let that go for now. That's another part of why I thought his advice was good when he said it couldn't hurt". He also said if it still needs to be done, we can do it all from up top later on. I was also wondering if I had times where I wasn't using the fireplace when it was cold, would the cold air intake and the two inch clearance around the pipe at the top make it cold enough to affect the room temp that the fireplace was in?
CmonSTART....I hadn't even thought about putting a rigid foam board insulation in there, that's a great idea and if I do end up insulating it that's what I'll do.
Slow1.....I was thinking of the vertical strap also, although my neighbor was up when I was doing this and he said if that doesn't hold the insulation nothing will! I'm glad I'm not the only one thinking overkill though, far as clearances go when they said two I'd make sure there was three etc....better safe than sorry!

So now I'm wondering, should this be insulated or not? And if I was to insulate it, is my dealer right jtp, would it hurt anything? It'll sort of be dead space anyway no matter what because it will be closed off---drywalled above mantle, and durock cement board below mantle. And if it won't hurt to insulate it, and I use foam do I put a vapor barrier up? Thanks again....

 

[oconnor]

If you are intent on using a batt insulation, get a rockwool based batt, like ROXUL AFB. I wouldn't bother insulating the space in front of the flue - if able, keep the flue inside the envelope of the house and insulate behind it. Make sure that you do have 2 inches around the flue all the way up, with the exception of any firestops you need - they should be metal. Adding the Roxul will limit the airspace that will contain heated air, and help keep any leakage to a minimum, as the volume of bouyant air will be minimized. I would place the roxul right up against the sprayed foam.

As for vapour barrier, the sprayed chase meets that need, just make sure it is tied in with vapour barriers adjacent to it.

 

[daryl]

Never insulate front wall in the living space only outside walls.When you are not using the fireplace it acts like a cooler and stays cold.You want the warm air from the house to keep that area warm.Big temp swings cause condensation.This is stated in most install manuals.

 

[oconnor]

chicken wire stapled atop insulation should work. rule is 2" to nearest COMBUSTIBLE aint it?

Depends on the manufacturer. Most are 2" air space.

 

[daryl]

It needs a ceiling put in at the first fire stop and insulated above it. I always do this within the first 8'.

 

[oconnor]

chicken wire stapled atop insulation should work. rule is 2" to nearest COMBUSTIBLE aint it?

Depends on the manufacturer. Most are 2" air space.

right u are, thanx 4 clarifying but to nitpick 4fun= when it goes thru a metal plate the 2" is gone

Again, manufacturers instructions cover the firebreak requirements. As always, read the manual

 

[jtp10181]

Sounds like your vertical space is only insulated all the way at the top of the chase? Bad idea. You should (by most codes) have a draft / fire stop at each ceiling level. The first one we insulate like an attic and then the rest of the chase is outside of the envelope.

If the outside air does make the space cold that insulation in the forward wall wont do anything anyway. Fireplace have holes in them all over the place and they are made of metal. The cold will just radiate through that even faster then the drywall. Like Daryl and I said, you want that space to breathe with the house and stay warm with the house. As long as the exterior walls are insulated and sealed like the rest of the house will be be doing the best you can. You will always loose some heat though fire-stops and air intakes but that's a trade off of having a fireplace.

 

[mtj53]

Point made guys...saves me some trouble and peace of mind. Makes complete sense the insulation won't do any good. I won't be insulating the wall above the fireplace....sorry I didn't list where I'm from...that would be East Dubuque, IL, extreme northwest corner of IL....1/2 mile shy of the Wisconsin state line.