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Author Topic: Advice on vapor barrier  (Read 4273 times)

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Offline bugmeist

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Advice on vapor barrier
« on: February 27, 2012, 04:47:27 PM »
We live in an old round log house that is just too cool in winter (I live in Central Ontario).  The logs average about 6" in diameter and there are fewer air leaks than there used to be as I've rechinked with Perma-Chink.  But when it gets to -20C it usually means wearing a warm sweater.  I'd like to have the inside temp be in the 68-70F range.

I am thinking that I might build a frame wall outside the logs and insulate that wall.  What I'd like to get advice on is whether I should have a vapor barrier between the logs and the insulated frame wall.

Any advice would be greatly appreciated.

bugmeist
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Offline beenthere

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Re: Advice on vapor barrier
« Reply #1 on: February 27, 2012, 05:17:08 PM »
Put the vapor barrier on the warm side of the insulation.
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Offline Thehardway

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Re: Advice on vapor barrier
« Reply #2 on: February 27, 2012, 07:31:09 PM »
6" log walls that have been well chinked should perform adequately.  It makes me think you might want to take a look at the floors, roof and windows.  Can you give us a description of these parts of your building envelope?  See if there is a company that does infrared thermal imaging in your area.  They can tell you exactly where your heat loss and air leaks are.  It would be much cheaper than building new walls and then finding your roof is the culprit etc.

As for the vapor barrier, I would hesitate to put a VB between wall systems.  As stated it should be on the warm side of the wall,  in cold climates, typically between wall insulation and interior finish.
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Offline Brucer

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Re: Advice on vapor barrier
« Reply #3 on: February 29, 2012, 11:57:06 PM »
6" log walls that have been well chinked should perform adequately. ...

Probably they would in Virgina. I don't think so in Ontario :).
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Offline frwinks

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Re: Advice on vapor barrier
« Reply #4 on: March 01, 2012, 09:57:09 AM »
I'd leave it out, and put your efforts into air sealing the two systems.  I mean get really INTO it...OCD like ;)
as per Thehardway's post, you don't want to trap any moisture inbetween wall systems.  With super tight air barriers and a mechanical ventilation system, you can control much of the indoor/outdoor vapour drive. 

Offline bugmeist

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Re: Advice on vapor barrier
« Reply #5 on: March 01, 2012, 03:10:52 PM »
Thanks for the replys guys.

The roof is reasonably well insulated with no room for more.  Some windows need to be upgraded,  doors are great.

The logs are about 50-55' F when its -10F or colder outside.  This is most noticeable in the kitchen cabinets as all the plates, cups, etc are around that temp too.

I am just thinking that adding some insulation, stopping a few air leaks, etc would raise the ambient temp inside.  Then again so does burning a bit of fire in the small stove we have in the kitchen.

I'll probably opt for the latter option as I cut firewood anyway.

bugmeist
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Offline Thehardway

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Re: Advice on vapor barrier
« Reply #6 on: March 01, 2012, 03:52:16 PM »
Bugmeist,

When it comes to insulation, quantity is no equal for quality.  If you aren't concerned about the log exterior of the home being visible, and are willing to cover it up,  have it spray foamed with 1" of spray polyurethane foam.  This will seal all cracks and airleaks as well as form a leak proof vapor barrier.  Since it will adhere directly to the logs there is no place for moist air to gather and condense.  It will stop the logs from acting as a thermal bridge and make the house more comfortable all year long.  You can apply siding of your choice over it.   It is likely you could do this on the walls facing north and east only and achieve significant benefit. 

This is probably the quickest, cheapest and best way to seal it up, much better and cheaper than building and insulating second envelope. 

A 6" log wall has a measured R-value of roughly 7.2 depending on log specie and moisture content.  The thermal mas of the log allows it to perform 30-40% beyond this.  Your log wall system should perform equal to or slightly better than a standard 2X4 frame constructed house.  I know in the colder climate areas of Canada 2X6 construction is standard with more insulation however you have thermal mas working to your benefit.  Your southern walls should actually gain some heat during the day even in the winter, especially if they are dark colored.  Northern walls  or walls with no solar exposure will be your main nemesis.





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Offline clif

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Re: Advice on vapor barrier
« Reply #7 on: March 01, 2012, 05:30:27 PM »
The Cooperative Extension Service here in Alaska has some great info on retrofitting log homes I have taken several classes from Richard Seifert up/ over here .  PM me and I will get you in touch with him.  Well worth the effort.  Clif
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Offline krusty

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Re: Advice on vapor barrier
« Reply #8 on: March 07, 2012, 09:31:15 PM »
I am in Ont as well with 6" log walls and find no issues. I would spend the time figuring out where your air leakage is and spray foam in a can is your friend.

This concept of an air tight home though is a load of donkey dung! All you need is a few really bad air leak points and the drafts coming in in winter will make it that cold.

Pick a really windy day and you will have no doubt finding where the leaks are. Many of  mine were in the corner dovetails. They were tight but shrinkage cannot be stopped.


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