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Cathedral ceiling and lack of insulation space


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Hi, we have a second house in NY state. It' a mobile home built in 1983. There is a cathedral ceiling in the dining room and in the family room. The height of the ceiling is 7 ft in its lower point and 10 ft in its higher. I've checked the dept of the space between the ceiling and the roofdeck and it is 7 and half inches. So, I supposed it's 2 x 8 or another design joist. Our energy bills are very expensive. In a winter, not the last cause we winterized it this year, cost $200. a week, without being there, just to protect against frozen! We don't want to add space because we like the ceiling height. So, we expect to remove the actual insulation and

1-) put the Roxul product, 5 and half thick that represent R-24 or

2-) 7 and half thick for R-28 that will let in the first case, 2 inches for the ventilation and in the second case, only a quater of inch for ventilation... Or,

3-) we are wondering if we can put a rigid polystyrene and seal it tight instead of Roxul. Or,

4-) can we mix Roxul and styrofoam?

Another question on that ceiling, is that we want to put thin toungue and groove pine. Is there any restriction to do it?

I join some pictures of the attic in a bedroom that doesn't have a cathedral ceiling. You can see that there is no vapor barrier and not much insulation that caused ice dam. Also, there are no ventilation, blocked by 2 x 8... So many works to do here, so consider the best solution at best price please.

Thank you very much for your precious advice. This is a very nice website! Excuse my english, I'm french canadian.

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Install behind-the-gutter eave vents, a baffled ridge vent and vent chutes from the eaves to the ridge and then spray foam the underside of that roof with a nice this layer of closed-cell foam. Then install an air exchanger on a timer or couple it to a humidistat to activate whenever humidity in the home reaches 45% or better.

Insulate the pipes everywhere in the home, make sure the underside is closed and pipes there are well insulated. Install vents in the toe kicks at under-sink cabinets to allow warm interior air to circulate into those areas. Set the thermostat to keep the place at 55 degrees.

Consider using Dow Wallmate and trim to increase the thickness and insulation in the exterior walls. They are probably only 3 inches thick and are allowing a lot of heat loss. Put a skirt around it to prevent most wind from blowing underneath but still leave it minimally ventilated.

What are you using for heat? Oil? Gas? Electric?

ONE TEAM - ONE FIGHT!!!

Mike

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Don't vent the cathedral ceiling, insulate it. A down and dirty foam insulation for tight spaces that works well and is cheap to apply is:

-cut rigid foam insulation to fit tightly between the rafters. Press it tight to the roof deck. Shoot for R-10.

-install your 5" Roxul to the interior.

-apply your vapor barrier.

You get an R-34 assembly.

If you can afford it, 7" of open cell spray foam will yield R-22 that will out perform R-38 fiberglass. Blow cellulose into the attic areas to at least R-50.

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Excepting cost, why wouldn't one just foam the whole joint?

After doing foam jobs for last couple years, everything else just seems silly.

I'd think doing the skirt would be almost important as anything else, but then again, I have no experience with mobile home stuff.

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That sounds about right.

I think your comment on R22 foam outperforming R34 glass is most interesting. At street level, it seems like an inch of foam is better than an entire wall of fiberglass; density/air sealing characteristics are where it's at.

In something like a mobile home, I'd think a couple inches of ccSPF everywhere and skirt insulation would be much better than dinking around with ventilation, baffling, and fiberglass.

Again, zero experience with mobile home construction, so I'm not sure.

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Judging from photo #3, it isn't a HUD-Code, which is what most folks are referring to when they say 'mobile home'. Might be a modular but I didn't think they were yet conceived in 83'.

Modular would leave Frederic with lots more options than a HUD-Code.

Marc

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That sounds about right.

I think your comment on R22 foam outperforming R34 glass is most interesting. At street level, it seems like an inch of foam is better than an entire wall of fiberglass; density/air sealing characteristics are where it's at.

It's real. This pic is from a new addition. The attic is glass insulated while the cathedral is foam.

Download Attachment: icon_adobe.gif foam v glass.pdf

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Solid Foam: Install solid foam spray-in insulation under the roof ? a ?hot roof? design. This eliminates the entire plan of ventilation, gives maximum R-value for the space, probably costs the most, and risks shorter shingle life (hotter roof) and future hidden damage if leaks occur into the roof cavity ? works, not a solution we like as we prefer to ventilate roofs for longer shingle life and cooler house in summer. See CATHEDRAL CEILING VENTILATION and Roof Venting: Un-Vented Hot Roof Solutions.

This is from what I read on this site: http://inspectapedia.com/interiors/Insu ... ilings.php

What do you think?

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What are you using for heat? Oil? Gas? Electric?

ONE TEAM - ONE FIGHT!!!

Mike

We have get installed a new gaz propane furnace. We also have a little unit of gaz propane heater in the addition room. But, we used two little infrared heathing units to cut the energy cost last year. Not the year that I was talking about for the $200. a week cost. We have a new wood stove but this is for when we are there of course...

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Excepting cost, why wouldn't one just foam the whole joint?

After doing foam jobs for last couple years, everything else just seems silly.

I'd think doing the skirt would be almost important as anything else, but then again, I have no experience with mobile home stuff.

'Cuz you have to ventilate a roof plane in order for the roofing manufacturers to stand behind their warranty. If not for that, I would have said shoot direct. The chutes go in easy. Lap em shingle fashion, top first then the second, etc. so any water thar blows in at the ridge drains all the way to the vents behind the gutter. Foam the hell out of it.

I'm assuming the roof is fine. If not, I'd recommend foaming directly, stripping off the cover, applying a layer of vented foam nail base and then install the new cover with a baffled ridge vent.

ONE TEAM - ONE FIGHT!!!

Mike

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Judging from photo #3, it isn't a HUD-Code, which is what most folks are referring to when they say 'mobile home'. Might be a modular but I didn't think they were yet conceived in 83'.

Modular would leave Frederic with lots more options than a HUD-Code.

Marc

.............mods were around in the late 60's

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What are you using for heat? Oil? Gas? Electric?

ONE TEAM - ONE FIGHT!!!

Mike

We have get installed a new gaz propane furnace. We also have a little unit of gaz propane heater in the addition room. But, we used two little infrared heathing units to cut the energy cost last year. Not the year that I was talking about for the $200. a week cost. We have a new wood stove but this is for when we are there of course...

Unless that small propane heater vents directly outside, get rid of it. Those catalytic propane heaters work well but about 70% of that exhaust is water so it will literally pump moisture into the interior of the home.

Check the flue and damper of that wood stove. When you are not using it, is the damper sealed tight or does it leak air like a sieve? Is air leaking out around that flue where it passes up through the roof plane? Is the propane furnace equipped with a backdraft damper that closes that flue when the furnace shuts down, or does the flue suck interior air out of the house through that furnace as soon as it shuts down and continues to do so until the furnace kicks on again?

ONE TEAM - ONE FIGHT!!!

Mike

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Solid Foam: Install solid foam spray-in insulation under the roof ? a ?hot roof? design. This eliminates the entire plan of ventilation, gives maximum R-value for the space, probably costs the most, and risks shorter shingle life (hotter roof) and future hidden damage if leaks occur into the roof cavity ? works, not a solution we like as we prefer to ventilate roofs for longer shingle life and cooler house in summer. See CATHEDRAL CEILING VENTILATION and Roof Venting: Un-Vented Hot Roof Solutions.

This is from what I read on this site: http://inspectapedia.com/interiors/Insu ... ilings.php

What do you think?

My main thought is I'm surprised Friedman isn't up to date on the whole ventilation = increased shingle life.

Unless I've completely lost track, multiple studies over several years have shown ventilation does nothing to improve shingle life. The single factor that makes the biggest difference is shingle color. White shingles last the longest, black shingles the shortest.

Joe L. has also debunked the whole "ventilation reduces attic temperature" argument. It does nothing to reduce attic temperature. Ventilation is only to reduce or prevent condensation.

The argument against ccSPF of "if there's a roof leak, you won't see it" always struck me as hollow. If one can't put a roof on that doesn't leak, they have no business doing anything else. Modern roof industry principles, materials, and methods guarantees no leaks. If you don't trust your roof, replace it. If you have conventional insulation, do you really think you're going to see a teeny leak? Nope, it's going to keep seeping moisture into the roof structure and insulation and you're going to have the same mess.

If it's in the budget, make sure you have a good roof and foam it. If it isn't in the budget, accept the idea you're going with an inferior material and accompanying performance. If you're time is worth anything, foam is cheaper; dinking around properly fitting baffles, Roxul, insulation, and the other crap is a PITA.

And, like Mike said, ditch the heater; they pump water and contaminants into the house. Get a vented heater.

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Hi Kurt,

I agree with the fact that the ventilation and shingle life issue is bogus. That's not my point. Manufacturer's are belt and suspender types. They'll use whatever they can to insulate themselves from liability. Since they continue to hang onto this ventilation requirement, he needs to accommodate that.

OT - OF!!!

M.

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I know you know.

I'm just a little glazed over at the idea a roofing warranty is worth a dime. If I had to sleep at night knowing the mfg. warranty was good, I'd never sleep.

After using foam, I feel the same way about conventional insulation and venting schemes; for a couple more bucks, you can do away with everything we know now is a PITA and the marginal performance of conventional materials.

I'm spending the OP's money freely, but if an actual accounting is done, where the OP's time is worth a dime an hour, it's a better deal to hire the foam out, then finish the interior and be done.

Or, maybe the guy wants to make lots of trips to the big box, get all scratchy with fiberglass and Roxul, and dink around with outdated technologies.

If he's fine with that, so am I.

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Pic 1 shows a double wide or modular home attic, pic 3 looks more like a typical mobile.

I wouldn't apply spray foam to OSB unless it was bone dry, fresh from the factory. Certainly not the black spotted sheathing in these pics. JMO.

Good point.

Although, wouldn't a treatment with a microbial make it all OK?

Since it's all open, one could tell if it's dry, and a roof leak be readily apparent.

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keep the 2 inch space for ventilation,

make sure the vapor barrier is continuous and covers the entire ceiling without any gaps.

make sure the floor is insulated adequatly

ventilate

Have an expert do the job

Stephen, as I can see, I'm right that in Qubec we still believe in ventilation also for cathedral ceiling but from what Tom and others suggest to forget the ventilation, what do you think?

do you mean the floor or the walls of the skirt?

I'm still confused. There so many positions that all make sens for me... I need learning more. Thank you for your advice.

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Stephen, as I can see, I'm right that in Qubec we still believe in ventilation also for cathedral ceiling but from what Tom and others suggest to forget the ventilation, what do you think?

do you mean the floor or the walls of the skirt?

I'm still confused. There so many positions that all make sens for me... I need learning more. Thank you for your advice.

Ever tried to replace plywood affected by water intrusion that chemical foam has been sprayed underneath?

Keep the air space, that is primordial for a long lasting roof.

Make sure air gets in from the eaves and out through a proper vent such as a ridge vent.

If you want to maximize R value without doing any major transformation, add from the bottom.

A 1 1/2 inch foil-faced polyisocyanurate board will add another 10.8 to the R value (over 11 with air space and drywall).

The floor and all the plumbing and ventilation componants have to be properly insulated and a vapor barrier is also needed (on the warm side).

Make sure you have proper ventilation underneath the home.

Have a professional do the job.

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