Ceilings in the south

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nikotromus
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Ceilings in the south

Post by nikotromus » Sun Nov 05, 2017 7:42 pm

I see a lot of houses like the one in this photo where the ceiling has exposed rafters and wood. It looks pretty, but it's gotta be really cold in the winter. Would a solution be as simple as adding insulation between the rafters and dry-walling over it? Has anyone ever retrofitted a house in Chile with insulation?

Thanks in advance for any advice.
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ghibli
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Re: Ceilings in the south

Post by ghibli » Sun Nov 05, 2017 7:59 pm

You can remove the shingles or what have you (techo exterior) put down some 2x3 sleepers w/ insulation in between, add a layer of OSB board and a layer of Tyvek, then replace your shingles or what have you roofing. That way you could keep the cool looking viga and wood ceiling. Not too difficult.

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Re: Ceilings in the south

Post by David_Bro » Sun Nov 05, 2017 8:07 pm

Probably most homes I have seen with open ceilings contain no insulation------its just what it is----I have built several with and without insulation-----you can purchase various quality rigid foam insulation, in different thicknessesses, to apply above the finish cieliing material and below the roof----your choice-----

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nikotromus
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Re: Ceilings in the south

Post by nikotromus » Sun Nov 05, 2017 8:26 pm

David_Bro wrote:
Sun Nov 05, 2017 8:07 pm
Probably most homes I have seen with open ceilings contain no insulation------its just what it is----I have built several with and without insulation-----you can purchase various quality rigid foam insulation, in different thicknessesses, to apply above the finish cieliing material and below the roof----your choice-----

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Are you talking about removing the roof, putting down insulation and then putting the roof back on? That sounds like a new roof job. If that is not what you are suggesting please elaborate.

I guess the drawback to insulating and sheet rocking is that it won't look as good?

Thanks again.

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Re: Ceilings in the south

Post by David_Bro » Sun Nov 05, 2017 8:44 pm

Roof has to be off-----i'd sheet it with 3/4 ply over the cosmetic t and g that is the visual part from below---apply the sleepers----the insulation in between and then the roof----depends on the roof you have and what part of Chile you are in but i'd sheet over the sleepers and insulation with felt paper over that and then the roof-----your call on insulating from below with sheetrock or other material-----you can purchase US style fiberglass insulation in any sodimac in Chile



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Re: Ceilings in the south

Post by Julito » Sun Nov 05, 2017 10:38 pm

There're paintable cement board insulation panels of various thicknesses available at Sodimac and elsewhere which can be cut to fit between the internal ceiling joists. We did it to a small living area extension and it works a treat. We've considered doing it to the rest of the house but it'd be a hell of a job, scaffolding and bloody messy with styrofoam beads over everything.

Looking at the photos it's a similar house to ours ceiling wise. Our large kitchen stove happily heats the open plan living area to 23C at head level over winter but when I push a thermometer up into the ceiling apex it's 33C, wasted heat being lost through the poorly insulated original roofing.

So the plan is to fit a strategically placed ceiling fan or two to run very slowly, pushing that heat down and disperse it further throughout the house. Given the early stove heat goes straight up to the ceiling apex, my figuring is the house will warm faster and by a very rough estimate probably cut the annual wood bill by a third to a half.

I'd attach photos if I knew how :)

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Re: Ceilings in the south

Post by admin » Mon Nov 06, 2017 7:16 am

The problem with insulating vaulted ceilings is humidity control. all the humidity from inside the house rises and creates condensation on the ceiling. So, to stop rot from forming inside the ceiling, you need to insulate, then put something that is semi-impervious like sheet rock and paint (OSB would probably work too, if you wanted to then run boards for cosmetic appeal over them); either that, or you have to vent the ceiling above the insulation.

Ideally, yea doing insulation on the outside is the best way to go, due to there not being sufficient depth in the rafters for both insulation and vents. Should be something like 6 inches of rigid insulation, plus about 1-2 inches of full length venting from the eve of the house to the peak, with a ridge vent running the full length. So, basically you need a 2x8 beam, which the chilean maestros love to do everything they should not do with just 2x6 (e.g. span 6+ meters, with several splices, with a 2x6 green pine, and have it be load bearing) The point being, you need the roof sheathing to be able to dry out from at least one side.

Now, in a small wood structure, with wood heating or whatever, how big a deal the condensation on the ceiling is I am not sure. Probably a very big deal somewhere with snow loads on it, but most of central chile not that big of deal. Further, depending on what you have on the top of the roof, a metal roof may have sufficient venting on the top side to keep whatever is there dry (e.g. the little ridges commonly found on metal roofs).

However you do it, you don't want to create a warm dark place, where humidity builds up, with no way to vent the humidity inside the ceiling.

I just looked at a house, where that was my first thought regarding the ceiling (looks almost exactly like the photo). Luckily, or unluckily, the maestros had failed to put anything down under the metal roofing (no tar paper or similar). There is just osb. So, I figure it would be pretty safe to insulate and enclose the ceiling, as the wood can breath from the other side.
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Re: Ceilings in the south

Post by nikotromus » Mon Nov 06, 2017 8:52 am

admin wrote:
Mon Nov 06, 2017 7:16 am
So, to stop rot from forming inside the ceiling, you need to insulate, then put something that is semi-impervious like sheet rock and paint. either that, or you have to vent the ceiling above the insulation.
From this line of thought, it sounds like insulating and enclosing the ceiling would be the super easy way to go. If the ceiling is dry walled and painted, I would think it would keep the moisture off of the wood that is enclosed above it.
admin wrote:
Mon Nov 06, 2017 7:16 am
I just looked at a house, where that was my first thought regarding the ceiling (looks almost exactly like the photo). Luckily, or unluckily, the maestros had failed to put anything down under the metal roofing (no tar paper or similar). There is just osb. So, I figure it would be pretty safe to insulate and enclose the ceiling, as the wood can breath from the other side.
From this line of thought, it sounds like I still need to make sure the other side of the roof is breathable. Is this still a concern after the interior ceiling has been sheet rocked and painted, or am I reading this wrong?

The last thing I want to do is take off and reconstruct a roof.

Thanks a bunch - this is great info.

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Re: Ceilings in the south

Post by Rhodolite » Mon Nov 06, 2017 9:38 am

I have a different idea about this. No matter how well insulated the top of your home, all of the hot air is going to be hanging - for lack of a better word - just below the ceiling. So while the lovely warm air may not escape the house as quickly it will still be above your body-height and not doing much to enhance your comfort.

Would ceiling fans rotating to push the warm air down be effective?

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Re: Ceilings in the south

Post by admin » Mon Nov 06, 2017 11:42 am

Well it is like putting a hat on, most your heat escapes out your head; but yea fans or just circulating the air helps move it off the cieling.


I think the rule is dont sandwich or trap something with moisture, between two layers that are water proof. Bad things happen.

By insulating the roof decking, you are also avoiding heat loss being transfmited through the beam. With sheat rock it is known to cause visible ghosting. Rigid exterior insulation is all the rage in the states and other places now. No more fiber glass.
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Re: Ceilings in the south

Post by nikotromus » Mon Nov 06, 2017 12:27 pm

I think I understand that the short answer is there is no easy fix for this. ;-)

My take away is that trying to insulate this type of ceiling from the inside would be a bad idea because of moisture problems. I finally found a youtube video where they talk about insulating cathedral ceilings. They say to add a 1 inch gap between the roof decking and insulation to allow heat to escape through the roof vent (and moisture I suppose). That was a roof with just plywood that led straight to a ridge vent.

In the situation of these wooden cathedral ceilings, even if the roof was built with a ridge vent, how would you get the air to escape to it? I guess I would have to drill holes (what could possibly go wrong there?). Everything is all closed in as you can see in the image.

I suppose another solution might be to build a drop ceiling and have a proper attic. With the lower ceiling, it would be also easier to heat and cool.
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Re: Ceilings in the south

Post by Julito » Mon Nov 06, 2017 8:23 pm

We also fitted skylights which have a "vent only" setting. So without the skylights actually open they vent while remaining weather proof. Though we never had humidity problems before they were fitted anyway.

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