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Furring out cathedral ceiling help

sandking's picture

Hello all.  I am in the process of pretty much redoing our whole house since we found lots of rot after removing an extension.  My den has a cathedral ceiling constructed of 2x6's and i want to put in recessed lights but  they don't seem to fit since the beams have shrunk some.  My plan was to fur the ceiling with 2x4's running perpenticular to the 2x6 rafters.  This will give me an extra 1.5" of headroom for the recessed lights and I'll reinsulate with R19.

Is this the best way or sould I rip a 2x4 and attach them to the bottom of the 2x6?

Just to clarify, there are no soffits in this roof as it's attached to the back wall of the upstairs and the facia is attached to the sheathing.  I don't understand why they didn't build my style house with soffits.

 

Thanks in advance.

depends (post #206878, reply #1 of 12)

How you want to hang the sheetrock.

You can strap across or add to each.

Is your roof vented?

 

Remember to get cans rated for insulation and air sealed. 

If in a cold temp zone in winter-expect condensation on ordinary IC rated cans as well as most probably, the air sealed ones.

The heat of the bulb as well as the moist air of the room goes up into the can and condenses on the tin.  Water marks usually appear at the low end of the can in a vaulted ceiling.

With the right depth of rafter you might be able to successfully conquer this problem.

But a 2x6 and another inch and a half might not do it.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


reply (post #206878, reply #3 of 12)

calvin wrote:

How you want to hang the sheetrock.

You can strap across or add to each.

Is your roof vented?

 

Remember to get cans rated for insulation and air sealed. 

If in a cold temp zone in winter-expect condensation on ordinary IC rated cans as well as most probably, the air sealed ones.

The heat of the bulb as well as the moist air of the room goes up into the can and condenses on the tin.  Water marks usually appear at the low end of the can in a vaulted ceiling.

With the right depth of rafter you might be able to successfully conquer this problem.

But a 2x6 and another inch and a half might not do it.

 

Sorry for the delay, I've been away.  Thanks for the response.  I live in NY so we do get the winter temps.  The roof is NOT vented my guess is because the high side attaches to the middle of the upstairs outside wall so there would be nowhere for air to go.

I did get an estimate on reinsulating the room.  This person recommended putting the baffles in the full length and then adding R15, saying that the air space would be enough to keep the roof from rotting on the inside?  Is this true?   I was just going to add R19 to the 2x6, attach the 2x4's flat accross the rafters and then purchase 12ft drywall to run accross the 2x4's.  This should leave me with no butt joints to spackle.

What do you think about that plan????  Am I doing it correctly?

Piffin's plan above would give you more R (post #206878, reply #4 of 12)

Why not direct your question to him to see if he recommends an airspace above the insulation.

Best of luck.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Note that there are some (post #206878, reply #5 of 12)

Note that there are some reasonably effective vents available for shed roofs.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

rot (post #206878, reply #6 of 12)

There are a number of things to do to prevent the problems.

 

The rot is caused by wood that is damp and warm enough to support the growth of the micro-organisms that eat wood.
 Deprive them of moisture and warmth and there is no rot.

 

More R-value is better

and condensation happens where you allow a dew point temperature. You have to prevent warm moist air from contacting cool surfaces.

So you  want to prevent moisture from getting into the rafter spaces and you have to insulate wwell enough to keep the roof sheathing from contact with warm air.

FG insulation allows air movement through it, so if you are going to use it, you need a VB that is nearly 100% impregnable in adition to doing good insulation work. R15 is nothing close to good enough. Aim for R30.

If you seal the inner surface well so no moisture gets in, then no venting to carry it out is needed.

 

So install the 1-1/2" Foil faced Thermax foam after placing the FG batts. can foam any gaps, then seal seams with tape.

Do the furring over it carefully and hang the SR.

 

 

Oh Well,

We did the best we could...

R30? (post #206878, reply #7 of 12)

Piffin wrote:

There are a number of things to do to prevent the problems.

 

The rot is caused by wood that is damp and warm enough to support the growth of the micro-organisms that eat wood.
 Deprive them of moisture and warmth and there is no rot.

 

More R-value is better

and condensation happens where you allow a dew point temperature. You have to prevent warm moist air from contacting cool surfaces.

So you  want to prevent moisture from getting into the rafter spaces and you have to insulate wwell enough to keep the roof sheathing from contact with warm air.

FG insulation allows air movement through it, so if you are going to use it, you need a VB that is nearly 100% impregnable in adition to doing good insulation work. R15 is nothing close to good enough. Aim for R30.

If you seal the inner surface well so no moisture gets in, then no venting to carry it out is needed.

 

So install the 1-1/2" Foil faced Thermax foam after placing the FG batts. can foam any gaps, then seal seams with tape.

Do the furring over it carefully and hang the SR.

 

Thank you for the response.  A couple of follow ups:

1. R 30 is 9.25" thick, that won't fit in my 2x6 cavity (even if I rip 2x4's and attach them to the bottom of the 2x6)

2. If I did do R30, wouldn't compressing it 3 inches make it useless?

3. Shouldn't the foil faced foam be incontact with the roof sheating and then the FG batts and then SR?

PolyIso foam board is R6.5... (post #206878, reply #8 of 12)

PolyIso foam board is R6.5... so that leaves you with R23.5 to make up.  At R3.5, that gives you 6.7".  Lets round that up to 8" total (1"+6.7"= 7.7")

A 2x6 is between 5.25" and 5.5" deep, and a 2x4 is 3.5" deep, giving you nearly 9" of space to fill.

Span the 2x4 across the rafters and glue insulweb under them, then fill them with cellulose.  Should be cheaper than FG, and more insulation total to boot!

YAY!  I love WYSISYG editing!  And Spellcheck!

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Ok but (post #206878, reply #9 of 12)

If I understand you correctly, you are recommending to nail the 2x4 on edge across the 2x6, correct?  If that's the case then i would 2 cavities to fill (the 2x6 and the 2x4) but since they are running in opposite directions, I don't have 9" of clear space, I have one pocket 5.25" deep and one 3.5" deep??

 

In addition, how do I attach the 2x4 on edge in a way that will support the SR, seems like a lot of weight ?

 

Thanks

whachoo saying Maynard? (post #206878, reply #11 of 12)

That is 6.5 per inch.

Two inches is 13 in th efoam and 19 in the FG for R32, plus  minimal effect of the radiant.

 

7" of cellulose is only R25 +/-

 

 

Oh Well,

We did the best we could...

7" of cellulose is only R25 (post #206878, reply #12 of 12)

7" of cellulose is only R25 +/- - I wasn't clear earlier, there would be an inch of foam there as well that would bring it up to over R30.

YAY!  I love WYSISYG editing!  And Spellcheck!

____________________________________________________

"1. R 30 is 9.25" thick, that (post #206878, reply #10 of 12)

"1. R 30 is 9.25" thick, that won't fit in my 2x6 cavity (even if I rip 2x4's and attach them to the bottom of the 2x6)"

That is why I sugested the foil faced foam. Easy to get R27 or R30 with 2" plus the FG

 

"2. If I did do R30, wouldn't compressing it 3 inches make it useless?"

Yes.

 

"3. Shouldn't the foil faced foam be incontact with the roof sheating and then the FG batts and then SR?"

No. Foam across inside of studs or rafters prevents thermal bridging, and gives a better seal against infiltration

 

 

Oh Well,

We did the best we could...

better yet (post #206878, reply #2 of 12)

What I have often done is to add 1" Thermax foam insulation bd, then 3/4" strapping . This would add to your dimension as well as your insulation value. R19  FG plus R5 foam = R24.

You could even use 1-1/2" to get up to R27 more or less!

 

 

Oh Well,

We did the best we could...