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How to insulate cabin floor?


mchristo's Avatar
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NH

10-15-07, 05:42 PM   #1  
How to insulate cabin floor?

I have a cabin in NH that sits on piers with very shallow clearance to bare ground underneath. (8" at its lowest clearance to 30" at the largest clearance.) I could insulate the floor from the bottom where I have clearance, but for the majority, there is no clearance to get at it from the bottom.
The floor is 2 x 8 joists 16" oc. the subfloor is 1x6 boards on diagonal, then covered with plywood and vinyl tiles.
I'd like to replace the flooring with wood flooring, so now is the time to insulate it. I was also thinking of heating the floor with radiant. The footprint of the building is 32'x24'.

Can I insulate on top of the subfloor and under the radiant floor heat/wood flooring? Or do I need to rip up the diagonal and plywood subfloor to insulate the joist cavity from top?
Or do I just $uck it up and rely on the heated floor?
I anticipate the cabin will get used 2 weekends per month over the winter months.
The last option seems wastefull and shortsighted.

 
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sgtgerryf's Avatar
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10-16-07, 10:34 AM   #2  
Cost vs. Usage

You have to look at the cost of whatever you chose vs. the potential useage during the winter months.

If you use it two weekends a month that is four nights per month. If you say five months for winter (cold weather) in NH that is 20 nights you will be in the cabin, so base you plan on this. Might be cheaper to get a good pair of thick socks and slippers!!!

One thing you have to take into consideration is that any insulation, either added from the top after ripping up the floor or from below, provided you can get to it, would be a haven for rodents of all sorts unless you can attach some type of sheathing to the underside of the joists after the insulation is installed. Highly unlikely that you can get sheets of plywood nailed/screwed to the undersides of the joist if you only have 8" of clearance for the majority of the cabins footprint.

Doesn't L.L. Bean have an outlet store in N.H. where you can get those socks and slippers?!!!

 
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10-16-07, 07:41 PM   #3  
If you have room for more build up, you could put 1" foil faced styrofoam down and add radiant and wood over that. You would have to judge if it is too costly or too difficult to install but it would help the heatloss quite a bit. The radiant would perform better too.

Ken

 
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10-16-07, 09:17 PM   #4  
I've had some people tell me to add an airtight insulated skirt around the base of the cottage. (presently there is a non airtight, uninsulated skirt around the cabin.
Do you think that would make much difference? or would the heat just get absorbed into the ground? Also would that not create a problem with moisture and rot of the joists?

 
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10-17-07, 04:54 AM   #5  
The airtight skirt if insulated would be a good idea. As would about 4 feet of perimeter insulation on the ground inside the skirt. The idea is that the ground never gets below about 55 degrees and that is way closer to indoor temp than whatever the outside air temp is in the winter. The ground will conduct some cold under the skirt but if you have 4 feet it will not be nearly as bad. Keep thinking and you will reach a good decision using modern info and common sense.

Ken

 
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10-17-07, 06:26 AM   #6  
My only concern with sealing the skirt is moisture problems and rotting the floor joists. would that not be a problem?

 
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10-17-07, 08:11 AM   #7  
Moisture would be a problem and although it sounds difficult, you should have a 6 mil groundcover under there.
Tape it at the seams.

Ken

 
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10-17-07, 08:13 AM   #8  
Posted By: KField Moisture would be a problem and although it sounds difficult, you should have a 6 mil groundcover under there.
Tape it at the seams.

Ken
would the ground cover solve the moisture problem or only reduce it?
thanks again for your thoughts.

 
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10-17-07, 08:55 AM   #9  
If the ground cover is installed properly and sealed at all seams and penetrations, the problem is solved. It is being taught as the best place to isolate the building envelope today as opposed to past advice to ventilate. You should make it dry and not ventilate it. Check for more info at www.comfort-institute.org I'm not sure if they have it online but they are a wealth of knowledge.

Ken

 
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06-30-09, 06:20 AM   #10  
I have insulated my cabin floor with 3 in no paperback insulation & 1inch foan insulation(taped at seams with 30ins ground clearence.Skirting has vents on
all sides.In summer with a/c on the sheeting has mositure beads all over it.Do I need to install electric fans for air movement?I live here full time.Thank yoe -Me Bob

 
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07-07-09, 12:11 PM   #11  
You have two issue here, the chance of wood rot and the idea of fitting UFH.

As wood is a mixture of cellulose and water it is subject to rot and mould if it gets wet.
The first thing to do is pull up the floor and paint all the joists with waterproof paint. Taking great care to paint and seal the bottoms where the rot tends to set in.
As joists rely to a great extent on heat from the rooms above to keep them dry and you are not there very much the possibility of wood rot is high.

The next thing is fitting UFH, radiant heating has a problem, it radiates heat over 360 degrees and you only want the heat to rise.

The best way to stop the heat going downwards is to lay six inches of polystyrene on the sub floor and staple the plastic pipe to the polystyrene, then lay 3 inches of concrete over. As there is a very real possibility of the concrete curling up when it gets hot the concrete needs to have quarter inch thick reinforcing mesh laid in it.

If you then connect your heating controls to a telephone, you can phone the cabin on your way up and it will be nice and warm when you arrive.

 
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07-07-09, 12:13 PM   #12  
Posted By: mebob1503 I have insulated my cabin floor with 3 in no paperback insulation & 1inch foan insulation(taped at seams with 30ins ground clearence.Skirting has vents on
all sides.In summer with a/c on the sheeting has mositure beads all over it.Do I need to install electric fans for air movement?I live here full time.Thank yoe -Me Bob
=================
The beads of water show it is doing its job - provided there are no holes for the damp to get in this is OK

 
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